In this study, micro-scratch tests were conducted on a diamond-coated tungsten-carbide substrate to investigate the coating adhesion. High intensity Acoustic Emission (AE) signals were detected once the coating delamination initiated during the scratch test. It has also been found that the tangential force increased gradually with the normal force, but varied significantly
when the critical load of coating delamination was reached. A finite element (FE) model with a cohesive-zone interface was developed to simulate the scratch process and the coating delamination phenomena. The preliminary results indicate that it is feasible to use the FE combined with scratch tests to evaluate the coating interface characteristics.
MSEC2013- Interface delamination of diamond-coated carbide tools considering ...The University of Alabama
Interface delamination is the major failure mode of diamond-coated carbide tools in machining. On the other hand, coating cracking is possibly accompanied during a tribological process that induces the delamination phenomenon. However, such an influence between the two failure behaviors has not been investigated in a quantitative way to better understand and design diamond coating tools.
In this study, a three-dimensional (3D) indentation model combining cohesive interactions and extended finite element method (XFEM) was developed to investigate the diamond-coating, carbide-substrate interface behavior with the incorporation of coating cracking. The cohesive interaction was based on a cohesive zone model (CZM) with a bilinear traction-separation law. XFEM was applied to the coating domain to model cracking in the diamond coating with a damage criterion of the maximum principal stress. Deposition stresses were also included to investigate their effect on the coating delamination and fractures. The model was implemented in finite element (FE) codes to analyze the cone crack in brittle coatings, as well as the interface delamination of diamond coated carbide tools. The XFEM model was validated by the indentation testing data from literature in crack initiation and propagation in brittle materials. FE results from the indentation on diamond-coated tools show that the interface delamination size and loading force become smaller when coating fractures are incorporated in the model, and the deposition stresses will increase the initial crack radius and the critical load for delamination in diamond coatings.
MSEC2013- Interface delamination of diamond-coated carbide tools considering ...The University of Alabama
Interface delamination is the major failure mode of diamond-coated carbide tools in machining. On the other hand, coating cracking is possibly accompanied during a tribological process that induces the delamination phenomenon. However, such an influence between the two failure behaviors has not been investigated in a quantitative way to better understand and design diamond coating tools.
In this study, a three-dimensional (3D) indentation model combining cohesive interactions and extended finite element method (XFEM) was developed to investigate the diamond-coating, carbide-substrate interface behavior with the incorporation of coating cracking. The cohesive interaction was based on a cohesive zone model (CZM) with a bilinear traction-separation law. XFEM was applied to the coating domain to model cracking in the diamond coating with a damage criterion of the maximum principal stress. Deposition stresses were also included to investigate their effect on the coating delamination and fractures. The model was implemented in finite element (FE) codes to analyze the cone crack in brittle coatings, as well as the interface delamination of diamond coated carbide tools. The XFEM model was validated by the indentation testing data from literature in crack initiation and propagation in brittle materials. FE results from the indentation on diamond-coated tools show that the interface delamination size and loading force become smaller when coating fractures are incorporated in the model, and the deposition stresses will increase the initial crack radius and the critical load for delamination in diamond coatings.
Presentation at icotom17 dresden 20140826Xiaodong Guo
ICOTOM stands for International Conference on Textures of Materials. it is the biggest conference in the field of texture and microstructure of materials in the world.
Structural Changes in the Surface Layer of Deep Rolled Samples Due to Thermal...IJERA Editor
Deep rolling processes initiate plastic deformations in the surface layer. The local characteristics of deformation are dependent on the induced stress expressed by the local stress tensor. Equivalent stresses above yield strength cause plastic deformation. Additionally the intrinsic energy, e. g. the dislocation density, is enhanced and the residual stress state is changed. The effects to a deep rolled surface from an increase in temperature are mainly dependent on the material, the microstructure, the initial residual stress state, the inclusion density, the distribution of soluted alloying elements and the plastic deformation. In the described experiments the interactions between deformation and temperature of the steel grade AISI 4140 (42 CrMo 4) used for all further experiments in a transregional Collaborative Research Center (CRC) were to be examined. The most simple investigation methods were chosen deliberately to allow a better statistical support of correlations between introduced strains and material reactions for a wide variation of process parameters. Since the visual effects by light microscopy in AISI 4140 were very small, the experiments were repeated with german grade 18 CrNiMo 7-6 (comparable to AISI 4820). This paper focuses on the micro structural changes in defined deep rolled surface regions due to an increase in temperature. The work described is part of the Collaborative Research Center “Process Signatures”, collaboration between Bremen University, Technical University Aachen, Germany and Oklahoma State University Stillwater, USA.
A Review: Effect of Laser Peening Treatment on Properties And Life Cycle of D...IOSRJMCE
- In this review, the effect of laser peening process with and without protective coating is discussed over the different material and it is observed that the residual stress are induced in material surface up to some depth according to process parameters of LSP. Fatigue strength and micro-hardness of material are enhance by inducing residual stresses which further depends on process parameters and material properties.
Coating thickness and interlayer effects on cvd diamond film adhesion to coba...The University of Alabama
In this study, diamond coating adhesion on cobalt-cemented tungsten-carbide (WC–Co) substrates was investigated using scratch testing. In particular, a methodology was applied to evaluate the effects of the coating thickness and the interlayer on diamond coating delaminations. In the coating thickness effect research, substrate surface preparations, prior to diamond depositions, were common chemical etching using Murakami solutions. On the other hand, to study the interlayer effect, Cr/CrN/Cr and Ti/TiN/Ti, were deposited to WC–Co substrate surfaces (no chemical etching) by using a commercial physical vapor deposition (PVD) system in a thickness architecture of 200 nm/1.5 μm/1.5 μm, respectively. Diamond films were synthesized by using a hot-filament chemical vapor deposition (HFCVD) reactor at a fixed gas mixture
with varied deposition times.Scratch testing was conducted on the fabricated specimens using a commercial instrument. It is noted that the onset of coating delamination can be clearly identified by high-intensity acoustic emission (AE) signals and high tangential force fluctuations when such events occur, which can be used to determine the criticalload for coating delaminations. Scratched track morphology was also characterized by scanning electron microscopy and white light interferometry.The results show that the adhesion of diamond coatings on WC–Co substrates increases with the increased coating thickness, with a nearly linear relation. The trend is consistent with the findings from a previous study that experimentally evaluated the coating thickness effect on the diamond-coated tool performance. Scratched tracks were characterized by diamond coating cracking and coating delaminations once the adhesion critical load is reached. For the two types of interlayer materials tested, neither of them seems to be effective and the diamond coating with the Ti-interlayer shows poor adhesion compared to the Cr-interlayer coatings.
Interface characterizations of diamond coated tools by scratch testing and si...The University of Alabama
n this study, micro-scratch tests were conducted on diamond-coated tungsten-carbide substrates to investigate coating adhesion. During the scratch testing, high intensity acoustic emission (AE) signals can be clearly detected when the coating delamination occurs. It is also found that the tangential force increase gradually with the normal force, but fluctuates significantly when the critical load of coating delamination is reached. A three-dimensional (3D) finite element (FE) model with a cohesive-zone interface was developed to simulate the scratch process, and by comparing with the delamination critical load from the experiment, the interface characteristic length, the maximum strength and the fracture energy can be obtained. The preliminary results indicate that it is feasible to use the FE simulation combined with scratch tests to evaluate the coating interface behaviors.
Presentation at icotom17 dresden 20140826Xiaodong Guo
ICOTOM stands for International Conference on Textures of Materials. it is the biggest conference in the field of texture and microstructure of materials in the world.
Structural Changes in the Surface Layer of Deep Rolled Samples Due to Thermal...IJERA Editor
Deep rolling processes initiate plastic deformations in the surface layer. The local characteristics of deformation are dependent on the induced stress expressed by the local stress tensor. Equivalent stresses above yield strength cause plastic deformation. Additionally the intrinsic energy, e. g. the dislocation density, is enhanced and the residual stress state is changed. The effects to a deep rolled surface from an increase in temperature are mainly dependent on the material, the microstructure, the initial residual stress state, the inclusion density, the distribution of soluted alloying elements and the plastic deformation. In the described experiments the interactions between deformation and temperature of the steel grade AISI 4140 (42 CrMo 4) used for all further experiments in a transregional Collaborative Research Center (CRC) were to be examined. The most simple investigation methods were chosen deliberately to allow a better statistical support of correlations between introduced strains and material reactions for a wide variation of process parameters. Since the visual effects by light microscopy in AISI 4140 were very small, the experiments were repeated with german grade 18 CrNiMo 7-6 (comparable to AISI 4820). This paper focuses on the micro structural changes in defined deep rolled surface regions due to an increase in temperature. The work described is part of the Collaborative Research Center “Process Signatures”, collaboration between Bremen University, Technical University Aachen, Germany and Oklahoma State University Stillwater, USA.
A Review: Effect of Laser Peening Treatment on Properties And Life Cycle of D...IOSRJMCE
- In this review, the effect of laser peening process with and without protective coating is discussed over the different material and it is observed that the residual stress are induced in material surface up to some depth according to process parameters of LSP. Fatigue strength and micro-hardness of material are enhance by inducing residual stresses which further depends on process parameters and material properties.
Coating thickness and interlayer effects on cvd diamond film adhesion to coba...The University of Alabama
In this study, diamond coating adhesion on cobalt-cemented tungsten-carbide (WC–Co) substrates was investigated using scratch testing. In particular, a methodology was applied to evaluate the effects of the coating thickness and the interlayer on diamond coating delaminations. In the coating thickness effect research, substrate surface preparations, prior to diamond depositions, were common chemical etching using Murakami solutions. On the other hand, to study the interlayer effect, Cr/CrN/Cr and Ti/TiN/Ti, were deposited to WC–Co substrate surfaces (no chemical etching) by using a commercial physical vapor deposition (PVD) system in a thickness architecture of 200 nm/1.5 μm/1.5 μm, respectively. Diamond films were synthesized by using a hot-filament chemical vapor deposition (HFCVD) reactor at a fixed gas mixture
with varied deposition times.Scratch testing was conducted on the fabricated specimens using a commercial instrument. It is noted that the onset of coating delamination can be clearly identified by high-intensity acoustic emission (AE) signals and high tangential force fluctuations when such events occur, which can be used to determine the criticalload for coating delaminations. Scratched track morphology was also characterized by scanning electron microscopy and white light interferometry.The results show that the adhesion of diamond coatings on WC–Co substrates increases with the increased coating thickness, with a nearly linear relation. The trend is consistent with the findings from a previous study that experimentally evaluated the coating thickness effect on the diamond-coated tool performance. Scratched tracks were characterized by diamond coating cracking and coating delaminations once the adhesion critical load is reached. For the two types of interlayer materials tested, neither of them seems to be effective and the diamond coating with the Ti-interlayer shows poor adhesion compared to the Cr-interlayer coatings.
Interface characterizations of diamond coated tools by scratch testing and si...The University of Alabama
n this study, micro-scratch tests were conducted on diamond-coated tungsten-carbide substrates to investigate coating adhesion. During the scratch testing, high intensity acoustic emission (AE) signals can be clearly detected when the coating delamination occurs. It is also found that the tangential force increase gradually with the normal force, but fluctuates significantly when the critical load of coating delamination is reached. A three-dimensional (3D) finite element (FE) model with a cohesive-zone interface was developed to simulate the scratch process, and by comparing with the delamination critical load from the experiment, the interface characteristic length, the maximum strength and the fracture energy can be obtained. The preliminary results indicate that it is feasible to use the FE simulation combined with scratch tests to evaluate the coating interface behaviors.
ICMCTF2012:Coating thickness and interlayer effects on cvd-diamond film adhes...The University of Alabama
In this study, diamond coating adhesion on cobalt-cemented tungsten-carbide (WC-Co) substrates was investigated using scratch testing. In particular, the methodology was applied to evaluate the effects of the coating thickness and interlayer on coating delaminations. In the coating thickness effect study, substrate surface preparations, to remove the surface cobalt, prior to diamond depositions was common chemical etching using Murakami solutions. On the other hand, to study the interlayer effect, by halting the catalytic effect of the cobalt binder, two different interlayers, Cr/CrN/Cr and Ti/TiN/Ti, were deposited to WC-Co substrate surfaces (no chemical etching) by using a commercial physical vapor deposition (PVD) system in a thickness architecture of 200nm/1.5µm/1.5µm, respectively. Diamond films were synthesized by using a hot-filament chemical vapor deposition (HFCVD) reactor at a gas mixture of 6 sccm of CH4 and 60 sccm of H2, with varied deposition times.
Scratch testing was conducted on the fabricated specimens using a commercial machine, at a maximum normal load of 20 N and a speed of 2 mm/min. It is noted that the onset of coating delamination can be clearly identified by high-intensity acoustic emission (AE) signals when such events occur, which can be used to determine the critical load. Scratched track geometry was also characterized by scanning electron microscopy.
The results show that the adhesion of the diamond coating increases with the increased coating thickness, with a nearly linear relation, in the range tested. For the two types of interlayer materials tested, either of them seems to be effective and the diamond coating with Ti-interlayer shows poorer adhesion comparing to the Cr-interlayer coating.
Final Year Project Presentation (June 2015) : INVESTIGATION OF SHEAR BEHAVIOU...Asadullah Malik
It was a 20 min presentation made to participate in the Rector's Gold Medal Competition for the best undergrad project, in which our research based project won 2nd position.
Correlation between the Interface Width and the Adhesion Strength of Copper F...IOSRJAP
The present study has been conducted in order to determine the influence of negative bias voltage applied to substrate on adhesion of copper films deposited on carbon steel substrates. The adhesion strength has been evaluated by the scratch test. Coatings were deposited by a DC magnetron sputtering system. The substrates were firstly mechanically polished and then ion-etched by argon ions prior to deposition. Adhesion was found to increase with the bias voltage. The critical load had a value of 9.5 g for an unbiased substrate and reached 18.5 g for a bias voltage of 600 V. Equally important, the interface width, measured using Auger electron spectroscopy, increased as a function of the bias voltage. The width of the interface is related to the time of ion milling in the Auger spectrometer. The size of this width is obtained from the Auger elemental depth profiles through measuring the depth of the interface coating/substrate. The width had a value of 335 min with a bias of 600 V whereas it didn't exceed 180 min when the substrate was unbiased. Therefore, the effect of the bias voltage was to expand the interface because of the diffusion phenomenon and physical mixing of materials at the interface. Moreover, the critical load increased with the increase of the interface width.
To ensure good adhesion between a 200 nm thick silicon dioxide layer and a 4.5 μm thick hardcoat polymeric coating, a better understanding of mechanisms of adhesion at this interface is needed. To reach this purpose, focus is placed on two axes: characterizing mechanical properties of materials composing the system and in parallel, finding an applicable and effective method to quantify adhesion. Small dimension of SiO2 thin film makes it challenging to accurately characterize it. Hence the use of both nano-indentation and AFM to attempt assessment of SiO2 thin film elastic modulus Ef; taking into account limitations and uncertainty associated with each technique. Elastic modulus of SiO2 thin film determined by nano-indentation is roughly 50 GPa on a wafer substrate and 15 GPa on a lens substrate. As for AFM, modulus measured is approximately 56 GPa on a wafer substrate and 22 GPa on a lens substrate. This highlights significant influence of substrate for both techniques. Impact on mechanical properties between SiO2 thin films under different intrinsic stresses was also investigated. Results suggest that higher density of SiO2 thin film leads to higher elastic modulus.
To quantify adhesion, micro-tensile and micro-compression tests were performed. Micro-tensile experiments give ultimate shear strengths of hardcoat-substrate interface ranging from 9 to 14 MPa. Values of energy release rates of SiO2 / Hardcoat, range from 0.1 J/m² to 0.5 J/m², depending on moduli values found on wafer or lens substrate.
Improvement of Surface Roughness of Nickel Alloy Specimen by Removing Recast ...IJMER
Abstract: In this investigation, experimental work and computational work are combined to obtain improvement in the surface roughness of nickel alloy specimen, the machining is carried out by means of CNC wire electric discharge machining (WEDM). Brass wire is used as the tool electrode and nickel alloy (Inconel600) is used as the work piece material. The machining parameters such as Pulse-On time (Ton), Pulse-Off time (Toff), Peak Current (Ip), and Bed speed are considered as input parameters for this project. Surface roughness and Recast layer are considered the output parameters. The experiments
with the pre-planned set of input parameters are designed based on Taguchi’s orthogonal array. The surface roughness is measured using stylus type roughness tester and the thickness of the Recast layer is measured using Scanning Electron Microscope (SEM). The results obtained from the experiments are fed to the Minitab software and optimum input parameters for the desired output parameters are identified. The software uses the concept of analysis of variance (ANOVA) and indicates the nature of effect of input parameters on the output parameters and confirmation is done by validation
experiments. Once the recast layer thickness is obtained Chemical Etching and abrasive blasting is performed in order to remove the recast layer and again the surface roughness is measured by using stylus type roughness tester. Finally from the obtained results it was found that there was significant improvement in the Surface roughness of the nickel alloy material. In addition using regression analysis this work is stimulated by computational method and the results are obtained
Analyzing Adhesion of Epoxy/Steel Interlayer in Scratch TestIJERA Editor
The aim of this paper is to investigate use of an experimental technique to determine which parameters effects
on the interfacial durability performance of adhesive on the metallic adherends as zinc plated mild steel (S235)
by using Taguchi method. The experimental layout has been used four scratch force parameters using the L16
(41x23) orthogonal array. The statistical methods of signal to noise ratio (SNR) and the analysis of variance
(ANOVA) were applied to examine effects of surface treatment, adhesive type, blade angle and thickness on
scratch force and scratch energy. Besides, the surface analysis was carried out the morphological modifications
as well as to perform elemental analyses of the pre-treated surfaces. Results of this study indicate that the
thickness and surface treatment are main parameters influencing scratch force (by 52.4% and 19.9%) and
scratch energy (by 44.0 % and 25.6%), respectively.
Influence of contact friction conditions on thin profile simulationVan Canh Nguyen
The paper presents the development of the Finite Element model for simulation of thin
aluminium profile extrusion of both solid and hollow shapes. The analysis has shown that the material
flow in simulation is very dependent on the friction model. Experimental and theoretical studies show
that friction traction on the interface between the tool and the deformed material can be represented as
a combination of adhesive friction force and the force that is required to deform surface asperities. In
aluminium extrusion we can clearly distinguish two different areas with respect to friction conditions
such as sticking and sliding and transient zones between them. The lengths of these zones are also
dependent on variation of the choke angle and actual thickness of the profile. To get these values the
material flow problem is to be coupled with the simulation of the tools deformation. A series of
experiments with specially designed tools have been done to investigate how the bearing length and
choke angle may influence the extension of different friction zones and by these means vary the
material flow pattern. The friction models have also been tested with industrial profiles of complex
shapes and have shown good correspondence to reality.
In-situ TEM studies of tribo-induced bonding modification in near-frictionles...Deepak Rajput
A presentation on "In-situ TEM studies of tribo-induced bonding modification in near-frictionless carbon films" made by Deepak Rajput. This presentation was based on "critical review of a paper," in All Things Carbon course offered at the University of Tennessee Space Insitute at Tullahoma in Fall 2009.
International Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
MSEC2014-4063 THERMOMECHANICAL INVESTIGATION OF OVERHANG FABRICATIONS IN ELEC...The University of Alabama
Electron beam additive manufacturing (EBAM) is one of
powder-bed-fusion additive manufacturing processes that are capable of making full density metallic components. EBAM has a great potential in various high-value, small-batch productions in biomedical and aerospace industries. In EBAM, because a build part is immersed in the powder bed, ideally the process would not require support structures for overhang geometry. However, in practice, support structures are indeed needed for an overhang; without it, the overhang area will have defects such as warping, which is due to the complex thermomechanical process in EBAM. In this study, a thermomechanical finite element model has been developed to simulate temperature and stress fields when building a simple overhang in order to examine the root cause of overhang warping. It is found that the poor thermal conductivity of Ti- 6Al-4V powder results in higher temperatures, also slower heat dissipation, in an overhang area, in EBAM builds. The retained higher temperatures in the area above the powder substrate result in higher residual stresses in an overhang area, and lower powder porosity may reduce the residual stresses associated with building an overhang.
Adhesion analysis and dry machining performance of cvd diamond coatings depos...The University of Alabama
This paper investigates the effects of different surface pretreatments on the adhesion and performance
of CVD diamond coated WC–Co turning inserts for the dry machining of high silicon aluminum alloys.
Different interfacial characteristics between the diamond coatings and the modified WC–Co substrate
were obtained by the use of two different chemical etchings and a CrN/Cr interlayer, with the aim to
produce an adherent diamond coating by increasing the interlocking effect of the diamond film, and
halting the catalytic effect of the cobalt present on the cemented carbide tool. A systematic study is
analyzed in terms of the initial cutting tool surface modifications, the deposition and characterization
of microcrystalline diamond coatings deposited by HFCVD synthesis, the estimation of the resulting
diamond adhesion by Rockwell indentations and Raman spectroscopy, and finally, the evaluation of the
dry machining performance of the diamond coated tools on A390 aluminum alloys. The experiments
show that chemical etching methods exceed the effect of the CrN/Cr interlayer in increasing the diamond
coating adhesion under dry cutting operations. This work provided new insights about optimizing the
surface characteristics of cemented carbides to produce adherent diamond coatings in the dry cutting
manufacturing chain of high silicon aluminum alloys.
An investigation into interface behavior and delamination wear for diamond-co...The University of Alabama
The goal of this research is to enhance the diamond-coated cutting tool performance through fundamental understanding of the interface adhesion of chemical vapor deposition (CVD) diamond-coated tungsten carbide cutting tools. CVD diamond-coated cutting tools have the advantages of superior tribological properties and low cost in fabrications compared to polycrystalline diamond tools. However, the applications of diamond-coated tools are limited by interface delamination. Therefore, it is necessary to not only accurately detect interface delamination events, but also understand the delamination behavior affected by coating fractures. The primary objectives of this research are: (1) to utilize acoustic emission (AE) signals for wear monitoring of diamond-coated tools in machining, (2) to develop a finite element (FE) model of indentation for investigating the interface adhesion related to coating-substrate system parameters, (3) to combine micro-scratch testing and FE sliding model to assess the interface cohesive characteristics, and (4) to investigate the interface delamination considering coating cracking by developing a 3D indentation/sliding model using the extended finite element method (XFEM). The research methods include: (1) machining test A359/SiC-20p composite with an acoustic emission sensor, (2) finite element (FE) modeling and analysis of indentation and sliding with different configurations, and (3) scratch testing on diamond-coated tools. The major results are summarized as follows. (1) The short-time Fourier transform method has a potential for monitoring diamond coating failures. (2) In scratch testing, the tangential force and AE signal intensity vary significantly when the coating delamination critical load is reached. (3) Increasing the coating elastic modulus will reduce the delamination length and a thicker coating tends to have greater resistance to the interface delamination. (4) Coating cracking will decrease the interface delamination size, while the deposition stress will increase the delamination radius and critical load of interface failures. The contributions of this study include the following. (1) This study correlates the AE frequency response during machining with diamond-coated tool failures. (2) A cohesive zone model has been incorporated in FE modeling of indentation and scratch processes on a diamond-coated tool in evaluating coating adhesion with interface characteristics. (3) XFEM models of indentation and scratch simulations on a diamond-coated tool with an embedded cohesive layer are developed to simultaneously study coating cracking and interface delamination.
Diamond coated cutting tools have a potential to replace costly polycrystalline diamond tools. However, coating delaminations remain the primary wear mode that often results in catastrophic tool failures, causing to poor part quality and possible damage to machine tools. Moreover, delamination events are difficult to be precisely predicted. Thus, tool delamination identification is necessary for process monitoring.
Following a previous work, this study examines the acoustic emission (AE) signal evolutions during machining by diamond coated tools, in particular, the frequency response along cutting time as well as during a specific cutting pass. The intent was to correlate the characteristics of the AE spectral components with coating delaminations. The results are summarized as follows. Though AE root-mean-square values have been used to monitor tool failure, it may not show clear transition registered to coating delamination in some cases. The fast Fourier transformation (FFT) spectra of AE data along cutting time generally show decreased intensity for low frequency peaks, but increased intensity for high frequency peaks. In addition, the AE FFT spectra of sub-divided time zones during one cutting pass may clearly indicate the coating failure transition.
MSEC2010: Short-time fourier transform method in ae signal analysis for diamo...The University of Alabama
Coating failures due to delaminations are the primary life-limiting criteria of diamond-coated tools in machining. Process monitoring to capture coating failures is thus desired to prevent from poor part quality and possible production disruption. Following previous studies of AE signal analysis for diamond coating failure monitoring in machining applications, this research applied a short-time Fourier transformation (STFT) method to capture the coating failure transition during cutting. The method uses sub-divided signal segments, in a continuous manner, for the fast Fourier transform (FFT) analysis and computes the amplitude ratio of high vs. low frequencies as a function of cutting time during a cutting pass. The results show that during the coating failure pass, a clear sharp increase of amplitude ratio (value change over one) of high/low frequency occurs along the cutting time. On the other hand, the amplitude ratio only exhibits a certain low range fluctuations in other passes, e.g., initial cutting and prior to failure passes. Thus, it can be suggested that the applied STFT method has a potential for diamond coating failure monitoring. However, for coating failure associated with a smaller tool wear (less than 0.8 mm flank wear-land width), the amplitude ratio plot from the STFT analysis may not clearly show the failure transition.
Residual stresses in diamond coatings grown on WC-Co substrate have been investigated by
X-ray diffraction (XRD) method. Nano-diamond coatings were deposited by microwave
plasma-enhanced chemical vapor deposition technique (MP-CVD). To measure residual stress,
we tried different peak selection and instrument setting mode (χ mode and ω mode). For getting
reliable residual stress value, sin2ψ-method with omega-tilting mode (χ=0) was employed. The
(311) plane of CVD diamond was used with tilting angle (ψ) from -40 to 40 degrees. A
compressive stress of 1.65GPa was obtained by linear fitting the mean d-spacing values of
positive and negative tilting. The occurrence of “ψ-splitting” demonstrates the existence of
non-zero shear stress normal to the surface.
Book chapter: Analysis of acoustic emission signal evolutions for monitoring ...The University of Alabama
In this study, the characteristics of acoustic emission (AE) signals acquired during machining of an aluminum matrix composite using diamond-coated cutting tools were analyzed in various ways. The AE signals were analyzed in both the time and the frequency domains under various machining conditions and at different cutting times. The results from machining experiments and analysis indicate that it may be feasible to use AE signals to monitor the condition of diamond-coated tools in machining. AE root-mean-squared (RMS) values decrease considerably once coating delamination occurs. The results also indicate a correlation between tool condition and the fast Fourier transformation (FFT) spectra of AE raw data. The AE-FFT spectra with cutting time generally show a decreased intensity for the low-frequency peaks, but increased intensity for the high-frequency peaks. In addition, AE-FFT analysis of data from various time periods during one cutting pass clearly indicate coating failure transition. Further research using the short-time Fourier transform (STFT) method shows that during the coating failure pass, there is a clear increase in the amplitude ratio (1/value change) of the high- vs. low-frequency component with cutting time, which captures the coating failure transition. Repeatable results indicate that the applied STFT method has the potential for monitoring of diamond-coated tool failure during machining. However, for coating failures associated with less tool wear (flank wear-land width <0.8 mm), the amplitude ratio plot from the STFT analysis may not clearly identify the failure transition.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Literature Review Basics and Understanding Reference Management.pptxDr Ramhari Poudyal
Three-day training on academic research focuses on analytical tools at United Technical College, supported by the University Grant Commission, Nepal. 24-26 May 2024
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
HEAP SORT ILLUSTRATED WITH HEAPIFY, BUILD HEAP FOR DYNAMIC ARRAYS.
Heap sort is a comparison-based sorting technique based on Binary Heap data structure. It is similar to the selection sort where we first find the minimum element and place the minimum element at the beginning. Repeat the same process for the remaining elements.
We have compiled the most important slides from each speaker's presentation. This year’s compilation, available for free, captures the key insights and contributions shared during the DfMAy 2024 conference.
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
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NAMRC39: Micro-scratch testing and simulations for adhesion characterizations of diamond-coated tools
1. Proceedings of NAMRI/SME, Vol. 39, 2011
Micro-Scratch Testing and Simulations for Adhesion
Characterizations of Diamond-coated Tools
Ping Lu
Mechanical Engineering Department
The University of Alabama
Tuscaloosa, Alabama, USA
Xingcheng Xiao and Michael Lukitsch
Research & Development Center
General Motors Corporation
Warren, Michigan, USA
Kevin Chou
Mechanical Engineering Department
The University of Alabama
Tuscaloosa, Alabama, USA
ABSTRACT
In this study, micro-scratch tests were conducted on a diamond-coated tungsten-carbide substrate to investigate the coating
adhesion. High intensity Acoustic Emission (AE) signals were detected once the coating delamination initiated during the
scratch test. It has also been found that the tangential force increased gradually with the normal force, but varied significantly
when the critical load of coating delamination was reached. A finite element (FE) model with a cohesive-zone interface was
developed to simulate the scratch process and the coating delamination phenomena. The preliminary results indicate that it is
feasible to use the FE combined with scratch tests to evaluate the coating interface characteristics.
KEYWORDS
Adhesion, Cohesive zone interface, Diamond-coated tool, Delamination, Finite element, Scratch testing.
INTRODUCTION
Applying hard coatings such as diamond on cutting
tools is an ideal approach for enhancing tool lifetime and
improving the machining quality due to diamond’s high
hardness/strength, low friction coefficient, and chemical
stability, etc. Diamond-coated tools excel in cost and
flexibility to various tool geometry and size comparing to
synthetic polycrystalline diamond (PCD) tools (Hu, 2007),
which are also commonly used in the manufacturing
industry. Thus, diamond-coated cutting tools have a
potential to replace costly polycrystalline diamond tools.
However, in tooling applications, diamond coating
delamination remains the primary wear mode that often
result in catastrophic tool failures (Lu, 2009, Qin, 2009).
Coating delamination is due to insufficient adhesion
between the coating and substrate. Many approaches have
been developed to enhance the coating adhesion such as
etching cobalt (Co) phase off from the tool surface before
diamond depositions. In addition, reliable experimental
methods to quantitatively characterize the coating adhesion
are critical to compare and further optimize different
interface approaches.
There are several methods used to examine the adhesion
of coatings (Perry, 1983). For example, Bouzakis et al.
applied an inclined impact test to evaluate the cohesion and
adhesion properties of thin coatings (Bouzakis, 2004).
Scratch testing is one of the most practical means of
evaluating the adhesion of a hard, thin coating on a
substrate (Bull, 1992, Ollendorf, 1999), since it is reliable,
simple to perform and no special specimen shape or
preparation are required. Adhesion is measured when a
critical load is reached at which coating failure occurs.
Provided that the failure is adhesive, this critical normal
load is taken as a measure of the coating–substrate
adhesion, or the work of adhesion is derived from the
2. Proceedings of NAMRI/SME, Vol. 39, 2011
critical normal load (Jaworski, 2008, Nakao, 2007). Figure
1 is a schematic illustrating a scratch test on a coated
specimen. During scratch testing, a spherical indenter tip
slides over the surface of the coating to generate a groove
under incremental or constant normal loads. The tangential
force is measured during the test and the morphology of the
scratches can be observed simultaneously or afterwards.
When the mean compressive stress over an area in the
coating exceeds a critical value, the coating detaches from
the substrate to lower the elastic energy stored in the
coating (Liu, 2009). The work of adhesion at the interface
between the coating and substrate is equal to the energy
release rate from coating detachment and this rate is a
function of the mean compressive coating stress over the
detaching area at the instant of detachment. Thus, the
critical mean compressive coating stress responsible for the
detachment could be a measure of coating–substrate
adhesion. On the other hand, diamond coatings are very
brittle. While a coating can withstand compressive stresses
induced by the indenter to a certain extent, it may fracture if
a high tensile or shear stress field is induced
simultaneously, in particular, at the interface such as
delamination (Xie, 2002).
Figure 1. A schematic illustrating a scratch test on a coated
specimen (http://www.pvd-coatings.co.uk/scratch-adhesion-
tester.htm).
This study aims at better understanding the adhesion of
diamond-coated carbide tools by micro-scratch testing;
critical load for coating delamination and the corresponding
process signals were focused. In addition, a finite element
(FE) model was developed to simulate the scratch process,
with emphasis on the interface behavior, and to evaluate the
adhesion between the coating and substrate using interface
characteristics, which can be further applied in studies at
different loading conditions such as cutting.
EXPERIMENTAL DETAILS
The specimen was a diamond-coated tool. The substrate is
co-cemented tungsten carbide (WC-Co), submicron grains,
6% Co, with coating thickness around 4 µm, provided by
University of South Florida. The surface roughness of the
samples was about 0.38 µm Ra. A Micro-scratch tester
from CSM Instruments, model Micro-Combi, was used for
the experiments at the room temperature. Testing was
conducted in typical laboratory temperature/humidity
environments,
The diamond indenter with a tip radius of 50 µm was
utilized. The scratch speed was 2 mm/min with the
progressive loading method. The scratch length for each
test was 5 mm. During the scratch test, tangential forces,
acoustic emission (AE) signals, and the depth of the scratch
were acquired. A KEYENCE digital microscope (VHX-
600X) was used to observe the scratch marks and
delamination after the test. In addition, a white-light
interferometer (WLI) was used to acquire the morphology
of scratch grooves. To determine the critical load for the
tested diamond-coated tool, scratch tests were carried out
with a progressive load, maximum normal force of 10 N, 15
N, 20 N, 25 N and 30 N. Figure 2 below shows the overall
images of 5 scratch grooves at the corresponding load (1:
10 N, 2: 15 N, and 3: 20 N, etc.)
Figure 2. Digital microscopic images of scratch grooves on
the sample.
RESULTS AND DISCUSSION
Figure 3 shows the AE signal and tangential force (Ft)
vs. the applied normal load (Fn) during the scratch test with
a progressive load of maximum 10 N. From the figure, it is
observed that the tangential force increases smoothly when
the normal force is less than 5.4 N, but varies considerably
once the load exceeds 5.4 N. It is also observed that an
abrupt amplitude increase of AE signals (Spot 1) exists at
the load around 5.4 N, followed by a series of continuous
high-amplitude AE peaks. This implies coating
delamination initiation occurred around 5.4 N.
3. Proceedings of NAMRI/SME, Vol. 39, 2011
Figure 3. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a maximum load of 10 N.
After testing, the scratched groove was observed in the
digital microscope at 500X. From the relation between the
load and the distance, the location corresponding to the high
force variation and sudden intensity increasing (Spot 1) can
be examined and verified whether coating delamination has
initiated at that point. Figure 4a shows the digital
microscopic image at Spot 1 and the corresponding normal
load is around 5.4 N. It can be clearly confirmed that
coating delamination has initiated at such a force, clearly
exposing the substrate layer of WC, near Spot 1. Figure 4b
shows the digital microscopic image at the end of scratch
test. It is shown that coating delamination continued, once
initiated, to the end of the final load, with a comparable
delamination width.
Figure 4. The digital microscopic images of (a) Spot 1
around 5.4 N, and (b) the end of the scratch for scratch test
under maximum load of 10 N.
For the conditions of different final normal loads, the
tangential force/AE data show similar behaviors as the 10 N
load, i.e., gradual increasing of tangential force and AE
signals followed by an abrupt jump, and followed by large
variations of force/AE magnitudes. For example, Figure 5
shows the AE signals and tangential force (Ft) vs. the
normal load (Fn) during the scratch with a 30 N final load.
Spot1
(b)
(a)
4. Proceedings of NAMRI/SME, Vol. 39, 2011
Figure 5. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a maximum scratch load of 30 N.
Further, using the approach described earlier, the
corresponding critical load of delamination for each
condition can be estimated. It is found that the critical load
of delamination initiation is around 4 to 6 N for all tested
loads, indicating that the delamination critical load is not
sensitive to the load rates currently applied. Figure 6a
shows the digital microscopic image at Spot 1 (for 30 N
load scratching) with the normal load around 3.9 N. It is
clearly seen that coating delamination has been initiated at
this point (near Spot 1), an area of coating layer detached
from the WC substrate. Figure 6b shows the digital
microscopic image at the end of scratch test (maximum
load 30 N). It is also noted that coating delamination
continues spreading at the end of the scratches, and the
delamination width becomes larger compared to at the
beginning of delamination. Therefore, the coating
delamination becomes more severe with the increased
normal load. From the scratch test results, the evaluated
diamond-coated tool with a coating thickness of 4 µm has a
critical load for delamination in the range of 4 to 6 N.
Figure 6. Digital microscopic images of (a) Spot 1 around
3.9 N, and (b) the end of the scratch (30 N load).
The white-light interferometer has also been used to
obtain quantitative information of the scratched geometry.
Figure 7 below shows a 3D surface contour image of part of
the scratched track, at ~3 mm distance from beginning (20
N maximum load). It clearly shows coating delamination
propagated outward. Figure 8 is the 2D profile analysis of
the scratched mark at the same location. It is estimated that
the delamination width is about 88 µm and the depth of the
track is about 7 µm.
Figure 7. WLI image (3D) at 3 mm scratch distance for 20
N maximum load, showing coating delamination.
Spot1
(a)
(b)
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Figure 8. 2D scratch track profile analysis at 3 mm scratch distance for 20 N maximum load.
SCRATCH PROCESS SIMULATIONS
A 3D FE model has been developed to study the micro-
scratch test by using ABAQUS 6.8. A half model is used
because of the symmetry of the problem. The geometric
model of the specimen shown in Figure 9a is 3000 µm in
length and 200 µm in width. The thickness of the diamond
coating and the carbide substrate is 4 µm and 60 µm,
respectively. The diamond indenter is assumed to be rigid
with a tip radius of 50 µm. Figure 9b shows the details of
the model around the indenter. The smallest mesh size
underneath the indenter is 0.6 µm for the coating and 5.0
µm for the substrate. Further, a cohesive layer with zero
thickness was included to model the mechanical behavior of
the interface between the coating and the substrate.
The materials of the specimen, both the coating and the
substrate, were modeled as an elastoplastic solid with
isotropic hardening. According to the Ramberg-Osgood
law, the stress-strain relation can be described as
,
where , and the strain-hardening exponent is
generally in the range of 0 to 0.5 (Xu, 2005). The yield
strength of WC-6wt%Co is in the range of 1.45 to 5.76 GP
(Renaud, 2009, Mittal, 2001), and the yield strength of the
WC-Co is assumed as 3.605 GPa in this study. Other
properties of WC are identical with those in a previous
study (Renaud, 2009). The yield strength and hardening
exponent of the diamond can be obtained by the method
proposed by Suresh (Giannakopoulos, 1999, Ramamurty,
1999, Venkatesh, 2000) based on the experimental data of
nanonindentation on diamond (Chowdhury, 2004). In this
study, the Young’s modulus of the coating is 1200 GPa,
other properties of the coating and substrate are listed in
Table 1. The friction coefficient was set as 0.1. The
cohesive zone properties such as the strength and
characteristic length are derived from a previous study (Hu,
2008) with adjusted property values: 543 MPa maximum
strength, 0.43 µm characteristic length and 117 J/m2
fracture energy density, to approximate the critical load
observed from the experiments.
6. Proceedings of NAMRI/SME, Vol. 39, 2011
Figure 9. 3D FEA model for the scratch test: (a) overall model, and (b) details around the indenter.
Table 1. Properties of the substrate and coating for the diamond-coated cutting tools
Part Material
Young’s
modulus/GPa
Poisson’s
ratio
Yielding
strength/GPa
Hardening
exponent
Substrate
WC-6 wt.
% Co
619.5 0.24 3.605 0.244
Coating Diamond 1200 0.07 26.7 0.23
Figure 10 shows the normal force and tangential force
development along with the indenter location from the
scratch simulation. The spherical indenter first moves
downward in contact with the coating, then slides along the
surface of the coating, at a speed of 500 µm/s, with a
linearly increased depth, and the sliding distance is 500 µm.
At the end, the slider moves upward until fully unloaded.
Figure 10. Normal and tangential forces at different
locations for the maximum load of 14 N.
Figure 11 shows (a) the maximum principal stress and
(b) the equivalent plastic strain in the specimen, around the
indenter, during the initial sliding period, corresponding to
around 2 N of the normal force. It can be seen that high
compressive stresses, around 6 GPa, occur near the indenter
and the maximum equivalent strain is 0.024. In addition,
there is a small area with tensile stresses. As to be shown
later, no delamination has been generated at this location.
Figure 12 shows (a) the maximum principal stress and (b)
the equivalent plastic strain in the specimen at the onset of
coating delamination. It can be observed that high
compressive stresses, around 20 GPa, occurred in the
coating near the indenter and the maximum equivalent
strain is 0.082. Moreover, high tensile stresses occur in the
wake of the slider. The corresponding load at this location
is about 4 N. And the delamination has just initiated, to be
shown later. Figure 13 shows (a) the maximum principal
stress and (b) the equivalent plastic strain in the specimen at
the end of the sliding period. It can be seen that
compressive stresses are as high as around 25 GPa,
occurred in the coating near the indenter and the maximum
equivalent strain is 0.34.
Indenter
Coating
substrate
Cohesive zone
(b)
(a)
7. Proceedings of NAMRI/SME, Vol. 39, 2011
Figure 11. (a) Maximum principal stress (unit: 1000 GPa)
and (b) Equivalent plastic strain at the initial scratching.
Figure 12. (a) Maximum principal stress (unit: 1000 GPa)
and (b) Equivalent plastic strain at the onset of
delamination.
Figure 13. (a) Maximum principal stress (unit: 1000 GPa)
and (b) Equivalent plastic strain at the end of scratching.
(a) (b)
(a)
(b)
(a)
(b)
8. Proceedings of NAMRI/SME, Vol. 39, 2011
Figure 14 illustrates the normal stress distribution in the
cohesive-zone layer at different times: (a) initial scratch, (b)
onset of delamination and (c) end of scratch. At the initial
period, though the normal stress of the cohesive zone has
reached the cohesive zone strength (543 MPa), the damage
evolution has not resulted in the cohesive zone failure.
Thus, the interface is still intact. On the other hand, at
around 4 N of normal load, the cohesive-zone layer has
shown some damage initiated; the cohesive zone normal
separation has reached its characteristic length (0.43 µm).
Figure 14c shows a large delamination area at the end of
scratch testing. The coating delamination crack has spread
in both the sliding and transverse directions.
Figure 14. Cohesive zone stress distribution (unit: 1000 GPa) at the interface: (a) initial scratch, (b) onset of delamination,
and (c) end of scratch.
Figure 15 further shows the cohesive-zone normal stress
vs. normal separation traced along the scratch time at two
different locations. Figure 15a is for a location where the
interface remains attached. The normal stress is first
compressive when the slider is approached to that location
and quickly changes to tensile and reaches the interface
strength. Then, the stress is reduced in a short time, but with
the normal separation increased. Finally, as the slider
moves away from this location, the stress is reduced, also
the separation, but does not return to zero at the end. On the
other hand, Figure 15b is for a location where the interface
has been delaminated. The normal stress vs. separation
curve follows the typical traction-separation behavior and
the normal separation has reached the maximum separation
and results in the interface failure. In a previous study of
(a) (b)
(c)
9. Proceedings of NAMRI/SME, Vol. 39, 2011
diamond-coated carbides (Hu, 2008), the ideal cohesive
zone properties (as an upper bound) were estimated from
the substrate (WC) toughness. For the current study, note
that the cohesive-zone properties have been modified (1/3
of the upper-bound fracture energy) to approximate the
critical load measured from the experiments. Therefore, the
estimated cohesive-zone characteristics may be used to
indicate the interface capacity related to the delamination
behaviors.
Figure 15. Normal stress vs. separation behavior along the
scratch time: (a) location without delamination, and (b)
location with delamination.
Note that, it is known that during machining, the
temperature will be substantially higher than the room
temperature testing conducted here. The temperature
increases may affect coating properties and the deposition
thermal stress (Bouzakis, 2010). However, as the first step,
this study attempted to establish the room-temperature
adhesion data for general evaluation purposes.
CONCLUSIONS
Scratch tests of diamond coatings deposited on a WC
substrate have been carried out using a micro-scratch tester.
During the scratch tests, the normal force, the tangential
force, the acoustic emission signals and the penetration
depth were acquired. After scratch tests, the scratch marks
were also observed in a digital microscope and analyzed by
a white-light interferometer. Moreover, to characterize the
interface mechanical behavior, an FE model including the
interface cohesive zone was developed to simulate the
scratch process. The results are summarized as the
following:
(1) Coating delamination can be clearly detected by AE
signals. It was observed that the abrupt AE peak jumps
followed by several continuous AE high-amplitude
peaks are associated with coating delamination. The
tangential force increases smoothly with the normal
force before the initiation of coating delamination, but,
varies considerably once coating delamination
initiated. Therefore, tangential force may also be used
to monitor the coating delamination during scratch
tests.
(2) The width of coating delamination would increase with
the increased loads after delamination initiated, this is
confirmed by the scratch images under digital
microscope, which show that the coating delamination
becomes more severe with the increased load.
(3) The critical load for the tested diamond-coated WC
tools was in the range of 4 to 6 N, which has been
confirmed by repeated tests.
(4) The simulation results indicate that it is feasible to use
the FE model combined with scratch tests to evaluate
the coating interface characteristics.
ACKNOWLEDGEMENTS
This study was conducted under an NSF-funded joint
project (CMMI 0928627) - GOALI/Collaborative Research:
Interface Engineered Diamond Coatings for Dry
Machining, between The University of Alabama, General
Motors and University of South Florida.
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