This document discusses how lasers can be used to generate high-pressure shock waves in metals in order to improve their mechanical properties. Specifically:
1) Lasers with energies up to 500 Joules are used to generate stress waves exceeding 5 GPa in pressure in metals covered with transparent overlays like quartz or water.
2) These high pressures, above the elastic limit of most metals, cause dislocation networks that strengthen the metal.
3) Experiments showed strengthening of aluminum alloys and stainless steel through increased hardness and strength as well as improved fatigue properties.
A Literature Review on Fiber Laser Cutting on Stainless Steel-304ijsrd.com
the recent up gradation of newer and high strength materials have made the machining task in fiber laser cutting is quite challenging. Thus for the optimum use of all the resources it is essential to make the required mechanical properties, accuracy and quality. This paper reviews the various notable works in field of Fiber Laser Cutting and magnifies on effect of machining parameters on strength, kerf width and surface roughness.
A Literature Review on Fiber Laser Cutting on Stainless Steel-304ijsrd.com
the recent up gradation of newer and high strength materials have made the machining task in fiber laser cutting is quite challenging. Thus for the optimum use of all the resources it is essential to make the required mechanical properties, accuracy and quality. This paper reviews the various notable works in field of Fiber Laser Cutting and magnifies on effect of machining parameters on strength, kerf width and surface roughness.
Characterization of microstructure, mechanical properties and corrosion behav...HarisChang
Laser beam welding with full penetration was performed on two (1 mm thick, 50x50 mm) identical Inconel 625 metal sheets. The sheets are butt joined together with the geometry of the weld close to a convex shape. The mechanical, microstructural, X-ray diffraction and corrosion tests are conducted on the sample to determine the integrity of the sample.
Fundamentals of Laser Welding. Learn what laser welding is and how it can help you. For more information on Miyachi Unitek laser welders please visit our site at http://www.miyachiunitek.com/Products_LaserWelding
Annealing and Microstructural Characterization of Tin-Oxide Based Thick Film ...Anis Rahman
Abstract. The sheet resistance of tin oxide based thick-film resistors exhibits two regions of temperature dependence,
described by hopping (23°C-200°C) and diffusion mechanisms (200°C-350°C), respectively.
Annealing these samples causes the sheet resistance to increase in both regions. In the post-annealed samples,
the hopping conduction range is extended by 50°C (23°C-250°C) while the hopping parameter, To, is decreased by
more than 50%. The activation energy of diffusion (0.60 eV) is the same for both pre- and post annealed samples, but
the magnitude of resistance in the diffusion controlled region is increased significantly as a result of annealing. These
changes are explained in terms of a net decrease in the concentration of tin ions in the glass matrix. From a careful
microstructural study it was found that a conduction path composed of tin-oxide grains or their clusters in contact
with each other does not exist in the present system. HREM micrographs showed the presence of nanocrystalline
tin-oxide particles in the glass phase separating the tin-oxide grain clusters. Estimated average separation between
the nanocrystals in 4 nm, consistent with a variable-range hopping conduction via the dissolved tin ions in the glass
matrix.
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.
Production and characterization of nano copper powder using electric explosio...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Welding performance of a 2 kw continuous wave supermodulated ndyag laser incr...JK Lasers
Welding performance of a 2 kw continuous wave supermodulated ndyag laser increased weld speed, weld penetration and reduced porosity with supermodulated output power white paper from JK Lasers.
Electricity-free Thermopneumatic Single Dose Micropump for Low-Resource Setti...dharmakarma
This presentation describes a proposed design for a novel electricity-free thermopneumatic single-dose micropump that can be used for point-of-care lab on a chip applications in low resource settings. This device utilizes water as the only input necessary for actuation. It is intended to be tunable, multipurpose, cost-effective and compatible with low-cost microfluidic systems.
the effect of nickel incorporation on some physical properties of epoxy resinINFOGAIN PUBLICATION
The J-E characteristics of samples of epoxy resins mixed with nickel powder in different concentrations have been tested and a log-log straight line behaviour in both the low- and high field regions is observed. Ni-concentration has significant influence on the calculated constants of the J-E relationship. The d.c. electrical resistivity (ρ) of the samples are measured from the room temperature up to about 400 K. The variation of ρ with T obeys the exponential relation of ordinary dielectrics in three temperature regions. The parameters characterizing the ρ -T dependence change considerably with Ni-concentration. Due to the existence of nickel in different concentration a "true" compensation effect is observed with three characteristic compensation temperatures. The mechanical hardness of the samples was investigated as a function of Ni-concentration.
From this PPT you'll know much about Taiyi laser welding machine ,such as the various of models,the technical parameters,applicable materials,the advantage of fiber transmission etc.
Thank you for focus !
Laser Shock Peening of Bulk Metallic GlassesDeepak Rajput
Final report on Laser Shock Peening of Bulk Metallic Glasses submitted by Deepak Rajput at the University of Tennessee at Knoxville.
This experiment was not so fruitful. Also, there is a mistake in the concept of "overlap". However, this was the first ever attempt on laser shock processing of bulk metallic glasses.
Characterization of microstructure, mechanical properties and corrosion behav...HarisChang
Laser beam welding with full penetration was performed on two (1 mm thick, 50x50 mm) identical Inconel 625 metal sheets. The sheets are butt joined together with the geometry of the weld close to a convex shape. The mechanical, microstructural, X-ray diffraction and corrosion tests are conducted on the sample to determine the integrity of the sample.
Fundamentals of Laser Welding. Learn what laser welding is and how it can help you. For more information on Miyachi Unitek laser welders please visit our site at http://www.miyachiunitek.com/Products_LaserWelding
Annealing and Microstructural Characterization of Tin-Oxide Based Thick Film ...Anis Rahman
Abstract. The sheet resistance of tin oxide based thick-film resistors exhibits two regions of temperature dependence,
described by hopping (23°C-200°C) and diffusion mechanisms (200°C-350°C), respectively.
Annealing these samples causes the sheet resistance to increase in both regions. In the post-annealed samples,
the hopping conduction range is extended by 50°C (23°C-250°C) while the hopping parameter, To, is decreased by
more than 50%. The activation energy of diffusion (0.60 eV) is the same for both pre- and post annealed samples, but
the magnitude of resistance in the diffusion controlled region is increased significantly as a result of annealing. These
changes are explained in terms of a net decrease in the concentration of tin ions in the glass matrix. From a careful
microstructural study it was found that a conduction path composed of tin-oxide grains or their clusters in contact
with each other does not exist in the present system. HREM micrographs showed the presence of nanocrystalline
tin-oxide particles in the glass phase separating the tin-oxide grain clusters. Estimated average separation between
the nanocrystals in 4 nm, consistent with a variable-range hopping conduction via the dissolved tin ions in the glass
matrix.
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.
Production and characterization of nano copper powder using electric explosio...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Welding performance of a 2 kw continuous wave supermodulated ndyag laser incr...JK Lasers
Welding performance of a 2 kw continuous wave supermodulated ndyag laser increased weld speed, weld penetration and reduced porosity with supermodulated output power white paper from JK Lasers.
Electricity-free Thermopneumatic Single Dose Micropump for Low-Resource Setti...dharmakarma
This presentation describes a proposed design for a novel electricity-free thermopneumatic single-dose micropump that can be used for point-of-care lab on a chip applications in low resource settings. This device utilizes water as the only input necessary for actuation. It is intended to be tunable, multipurpose, cost-effective and compatible with low-cost microfluidic systems.
the effect of nickel incorporation on some physical properties of epoxy resinINFOGAIN PUBLICATION
The J-E characteristics of samples of epoxy resins mixed with nickel powder in different concentrations have been tested and a log-log straight line behaviour in both the low- and high field regions is observed. Ni-concentration has significant influence on the calculated constants of the J-E relationship. The d.c. electrical resistivity (ρ) of the samples are measured from the room temperature up to about 400 K. The variation of ρ with T obeys the exponential relation of ordinary dielectrics in three temperature regions. The parameters characterizing the ρ -T dependence change considerably with Ni-concentration. Due to the existence of nickel in different concentration a "true" compensation effect is observed with three characteristic compensation temperatures. The mechanical hardness of the samples was investigated as a function of Ni-concentration.
From this PPT you'll know much about Taiyi laser welding machine ,such as the various of models,the technical parameters,applicable materials,the advantage of fiber transmission etc.
Thank you for focus !
Laser Shock Peening of Bulk Metallic GlassesDeepak Rajput
Final report on Laser Shock Peening of Bulk Metallic Glasses submitted by Deepak Rajput at the University of Tennessee at Knoxville.
This experiment was not so fruitful. Also, there is a mistake in the concept of "overlap". However, this was the first ever attempt on laser shock processing of bulk metallic glasses.
Since the conventional Battery Ignition System has many drawbacks so, this Laser Ignition System is helpful in improving the efficiency of the engine as well it helps to reduce the emission from the engine.
Laser ignition is an alternative method for igniting compressed gaseous mixture of fuel and air. The method is based on laser devices that produce short but powerful flashes regardless of the pressure in the combustion chamber. Usually, high voltage spark plugs are good enough for automotive use, as the typical compression ratio of an otto cycle internal combustion engine is around 10:1 and in some rare cases reach 14:1. However, fuels such as natural gas or methanol can withstand high compression without self ignition. This allows higher compression ratios, because it is economically reasonable, as the fuel efficiency of such engines is high. Using high compression ratio and high pressure requires special spark plugs that are expensive and their electrodes still wear out. Thus, even expensive laser ignition systems could be economical, because they would last longer
Laser shock peening produces a compressive residual stress in the surface of metallic materials, which significantly increases fatigue life in applications where failure is caused by surface-initi ated cracks. Laser shock peening is applied by using a high energy pulsed laser to create a high amplitude stress wave or shock wave on the surface to be treated. This stress wave propagates into the material, causing the surface layer to yield and plastically deform, and thereby, develop a residual compressive stress. Where comparisons have been made to shot peening, the magnitude of the residual stresses at the surface are similar, but the compressive stresses from laser peening extend much deeper below the surface than those from shot peening. The resulting fatigue life enhancement is often greater for laser peering than it is for shot peening. In addition to fatigue strength improvement, laser peering can also locally strain harden thin sections of parts or strain harden a surface
Ahmed ibrahim razooqi...corrosion conduct of austenitic stainless steel 316 l...ahmed Ibrahim
Corrosion conduct of Austenitic stainless steel 316L subjected
to surface treatment.
Abstract. The influence of low temperature liquid nitriding as a surface heat treatment analogy
with laser peening treatment at the various of throbs on pitting corrosion of the “AISI 316L
Austenitic stainless steel” is investigated in this paper. According to typical ASTM (G71-31) a
number of corrosion examination samples are equipped with the measurements of (15 * 15 * 3)
mm which distributed into the many groups. Three sets were exposed to liquid nit riding
process at temperatures of (500, 400, 300) Co for one hour. The specimens (without coating)
were exposed to a number of the throbs (1,2,3) by laser peening. Microstructure varia tions,
compression residual stress, hardness, were inspected in this work. The corrosion and its
variables (potential cell, current density) were also evaluated using the potential stat
examination and applying the Tafel method using saltwater solution (3.5% NaCl). Tafle
equation was used to compute the corrosion degree. The results revealed that the liquid
nitriding participated to raise the corrosion rate at (500) Co, compared to the original metal
because of chromium nitride and also leaser peening participated to the increase in the
corrosion rate due to plastic deformation which led to the heterogeneity in the microstructure
but liquid nitriding at temperature (400) oC gave the best result where it was closer to the parent
metal’s, also laser peening at one throb showed the lower corrosion rate.
The effect of Deep cryogenic treatment (DCT) on the metallurgical and mechani...Dr.M BALA THEJA
The effect of Deep cryogenic treatment (DCT) on the metallurgical and mechanical properties of Aluminium 6061-T6 is investigated in the present work
The test castings were solutionized at 525°C for 08 hrs and water quenched to room temperature. One set of samples were subjected to cryogenic treatment at -196°C in Cryo- treatment unit, while the other set is subjected to age hardening at 160°C for durations of 3 hrs, 5hrs and 7hrs. Again cryogenic treated specimens were subjected to age hardening at 165°C for durations of 3hrs, 5 hrs and 7hrs. All the samples were taken for Mechanical properties evaluation.
The total duration of the Cryogenic treatment cycle was 36 hrs, which includes 3hrs of cooling from room temperature to -196°C, 24hrs of holding and 09 hrs of warming to room temperature. The Cryogenic treatment was carried out in a specially designed Cryogenic unit
Implementation of Generalized Regression Neural Network to Establish a Relati...IOSR Journals
Abstract: This paper presents implementation of Generalized Regression Neural Network to establish a
relation between vibration parameters and properties of vibration welded joints. During the welding of metals
along with mechanical vibrations, uniform and finer grain structures can be produced. This increases the
toughness and hardness of the metals, because of solidification effects at the weld pool surface. So, physical
experiments have been conducted on the homogeneous welded joints by providing vibrations during the welding
period. The voltage used to generate the vibration and the time of vibration are used as vibration parameters.
Hardness of the welded joint is considered as one of the mechanical properties of the welded joint.
Keywords: Vibratory welding, Neural Networks, Hardness
surface characteristics and electrochemical impedance investigation of spark-...mohammad fazel
In this study, the surface characteristic of oxide films on Ti-6Al-4V alloy formed by an anodic oxidation treatment at potentials higher than the breakdown voltage was evaluated.
Corrosion: A Discussion and Empirical Demonstration
Use of Laser Generated Shocks to Improve Metals & Alloys
1. Copyright 1977 by the Society of Photo-Optical Instrumentation Engineers, Box 1146, Palos Verdes
Estates, California 90274 USA.
This paper was published in Vol. 86-Industrial Applications of High Power Laser Technology and is made
available as an electronic reprint with permission of SPIE. Single print or electronic copies for personal
use only are allowed. Systematic or multiple reproduction, or distribution to multiple locations through an
electronic listserver or other electronic means, or duplication of any material in this paper for a fee or for
commercial purposes is prohibited. By choosing to view or print this document, you agree to all the
provisions of the copyright law protecting it.
USE OF LASER GENERATED SHOCKS TO IMPROVE
THE PROPERTIES OF METALS AND ALLOYS*
B. P. Fairand and A. H. Clauer
Battelle Columbus Laboratories
Columbus, Ohio 43201
Abstract
Pulsed lasers are being used to generate high amplitude stress waves in metals and change
their mechanical properties. Peak pressures greater than 5 GPa are generated in a metal or alloy
when it is covered with a transparent material. These pressures exceed the Hugoniot elastic limit
of most metals and produce networks of tangled dislocations in the metals substructure, which is
the source of the observed change in material properties. The strength, hardness, and fatigue
properties of 7000 series aluminum alloys are improved in this manner. Weld zones in aluminum
are strengthened up to the bulk level and the surface hardness of stainless steel is increased.
Introduction
Laboratory studies have established that the mechanical properties of different aluminum
and iron base alloys can be improved by laser shock treatment. When the energy from a powerful
pulsed laser is trained on the surface of a metal, a high amplitude stress wave is generated. This
wave propagates into the material and alters its microstructure, which is the source of the
observed improvement in the metal’s mechanical properties. The ability to generate stress waves
in materials with short duration bursts of laser energy has been known for some time, (1-6) but it
has only been in recent years that these stress waves have been shown to provide an effective
*
The research work leading to this paper was supported in part by the National Science
Foundation (NSF).
1
2. method of altering the in-depth mechanical properties of metals. (7) Various methods have been
used to increase the amplitude and duration of these stress waves in order to increase the depth
and degree of change introduced into the metal. (8-15) These techniques have generally taken the
form of adding to the surface of the material various coatings and layers of material which may be
opaque or transparent to the incident laser energy. The most effective method found up till now
for increasing the efficiency of converting laser energy into mechanical stress wave energy has
involved the use of transparent overlays. This technique has produced pressure with peak values
several times greater than the Hugoniot elastic limit of most metals and alloys. When a pressure
of this amplitude propagates through a material, the metal is plastically deformed in a manner
similar to that observed in explosively shocked materials.
This paper discusses methods of generating high amplitude stress waves in materials with
pulsed lasers and demonstrates by selected examples how these stress waves can be used to
improve the properties of metals and alloys.
Laser Generation of Stress Waves
Two different Q-switched neodymium glass lasers were used in the laser generated stress
wave studies. The high energy experiments were performed with a CGE VD-640 Q-switched
neodymium glass laser, which consists of an oscillator followed by six amplifier stages. This
system is capable of emitting up to 500 J of laser energy in a pulse with a full width at half-
maximum (FWHM) of up to 200 nanoseconds. A 5 joule AO Model 30 Q-switched neodymium
glass laser with a pulse width at one-half maximum of 40 nanoseconds was used in the low energy
experiments. Dielectric beam steering optics were used in all of the experiments and simple
convex convergent optics were used to focus the laser radiation on the specimens.
The change in the stress wave environment introduced by different transparent overlays
and addition of absorbent films of material to the metal surface were investigated. A solid in the
form of fused quartz and liquid water were selected for the transparent overlays. Because quartz
has a much higher acoustic impedance than water, it was expected to produce higher amplitude
stress waves in the shocked metal than those obtainable with water. However, liquids appear to
provide a more flexible and practical overlay material for future laser shock processing
applications and, therefore, water was included in the study. The results of adding various
absorbing materials to the metal surface are reported elsewhere. (16) Results of these studies
have shown that coatings do not significantly affect the magnitude of the laser generated stress
wave over the range of laser power densities investigated except at the lower laser power
densities where reflection of laser radiation from a bare metal surface becomes significant. Even
though coatings were not observed to enhance the size of the stress wave, their use is still
important in those cases where melting and vaporization of the metal is not desirable.
2
3. All of the laser generated stress wave experiments reported in this paper were performed
in an air environment at ambient conditions, and pressures were measured with commercially
available X-cut quartz crystal transducers.
Pressure Measurements
The variation in the measured peak pressures through thin aluminum foils is shown in
Figure 1 as a function of the overlay material and laser peak power density. The curves shown in
Figure 1 represent extrapolations of lines drawn through pressure measurements made at lower
laser power densities. (14,16) Earlier studies with iron targets and quartz overlays suggested that
the peak pressure was approximately proportional to the square root of the laser peak power
density.(15) However, the curves shown in Figure 1 predict that peak pressure is nearly
proportional to the laser peak power density. Calculations with a one-dimensional radiation
hydrodynamic computer cede are presently being undertaken in an effort to explain the reasons
behind the linear relationship between pressure and laser power. The fact that peak pressure is a
more sensitive function of laser power than previously expected is a positive feature insofar as the
future applicability of laser shock processing of materials is concerned. For example, examination
of the data shown in Figure 1 shows that it may be possible to achieve pressures as high as 10
GPa at laser power densities as low as 4 x l09 W/cm2.
As noted earlier, the higher peak pressures generated with a quartz overlay compared to
water was an expected result. However, the degree of difference between the pressures is not as
great as one might expect on the basis of the large difference in the acoustic impedances of the
two materials, i.e., ∼10.
Because rate dependent effects play an important role in the property changes introduced
by laser stress waves the duration as well as magnitude of the pressure wave affects the process.
A consistent feature in all pressure pulse measurements is the observation that the shape of the
stress wave measured near the front surface of the laser irradiated metal corresponds to the shape
of the laser pulse, particularly during the initial rise of the pulse to its peak value. By increasing
the duration at the laser pulse it is possible to increase the duration of the pressure pulse. An
example of this feature is shown in Figure 2. The laser pulses corresponding to these pressure
pulses are shown in Figure 3.
As a laser generated stress wave propagates into a metal or alloy, its amplitude and shape
will change because of attenuation and dispersive effects. An example of this effect is shown in
Figure 4, which shows the pressure pulse measured through a vapor deposited aluminum target
and after propagating through two thicknesses of a 5086 aluminum alloy. The laser peak power
densities were about 109W/cm2 and FWHM of the laser pulse was approximately 26
nanoseconds. An interesting feature in Figure 4 is the two component structure of the pressure
3
4. wave at 0.127 cm. The leading edge of this pressure pulse is due to the elastic precursor, which is
followed by the slower moving plastic wave component.
Laser Shock Induced Changes in Material Properties
Aluminum Alloys
Initial studies of laser shock induced changes in material properties were conducted with a
7075 aluminum alloy. (7) The alloy was studied in its peak aged (T6) and overaged (T73)
conditions. The 7075 T73 alloy, which has excellent stress corrosion resistance properties but
lower yield and tensile strength properties than the 7075 T6 alloy, was the main reason for
conducting these tests. Effects of explosively initiated shocks on this alloy were previously
investigated by Jacobs. (17) He was able to improve the strength properties of the 7075 T73
alloy by explosive shocking and, apparently in the process, did not decrease its excellent stress
corrosion properties. The results of the laser shock experiments on the 7075 T73 alloy also were
quite encouraging. The ultimate tensile strength was increased to a value somewhat greater than
the T6 alloy and the 0.2 percent yield strength was increased by about 30 percent over the
unshocked value. The improvement in the ultimate strength of the T73 alloy is particularly
interesting since this parameter is related to the fatigue properties of the alloy, and alloys that
exhibit an increase in ultimate strength may also show an improvement in fatigue properties.
Recent laser shock experiments on a 7475 aluminum alloy in the T73 condition have
demonstrated that the low cycle fatigue properties were improved by at least 100 percent over the
unshocked value.
Another area where laser generated stress waves can be used to improve the properties of
materials is shock hardening of weld zones in aluminum alloys. The weld and adjacent heat
affected zone in welded aluminum structures quite often are weaker than the remaining structure.
Post weld heat treatment or mechanical working can be used in some instances to improve the
strength of these regions. Laser shocking offers another approach that is particularly amenable
for treating formed structures. The effect of laser shocking on weld zones in two common
structural aluminum alloys (5086 H32 and 6061 T6) have been investigated. After laser shocking,
the yield strength of 5086 H32 was increased to the bulk value and the yield strength of 6061 T6
was raised midway between the welded and bulk value. Transmission electron micrographs taken
from the center section of laser shocked specimens showed the heavy dislocation tangles typical
of cold working. An example of the change in the microstructure of a 5083 H32 alloy from laser
shocking is shown in Figure 5. The bulk microstructure is shown in Figure 5a. A region in the
heat affected zone near the weld is shown in Figure 5b, and the same region after laser shocking is
shown in Figure 5c.
4
5. Iron Base Alloys
The first iron base material to be analyzed for laser shock induced changes in its
microstructure and mechanical properties was an Fe-3wt% Si alloy. (18) It was selected primarily
as a model material because it can be readily etch pitted to show the magnitude and distribution of
plastic deformation. (19) Quartz overlays were used in these studies and peak laser power
densities ranged from 5 x 108 W/cm2 to approximately 2 x l09 W/cm2. The study showed that
shock-induced strain could be introduced through 3-mm-thick material, although the average
strain intensity was of the order of 1 percent equivalent tensile strain. Deformation of the Fe-
3wt% Si alloy occurred by both slip and twinning. Thin sections of the material (about 0.02-cm
thick) were uniformly hardened by as much as 25 percent over the hardness of the unshocked
material.
Strain hardenable stainless steels are another class of alloys where a laser shock treatment
could be beneficial. The surface of these materials tend to cold flow and gall when subjected to
high load situations which has limited their applicability as bearing members. Only limited laser
shock studies have been conducted on these alloys. However, initial experiments with a 316
stainless steel have demonstrated that surface hardness can be improved by 20 percent over a
machine worked surface and by more than a factor of two over the bulk hardness.
Conclusions
Pulsed lasers can generate sufficiently intense stress waves in metals and alloys to change
their in-depth mechanical properties. This can be done in an air environment at ambient
conditions. The laser energy requirements to treat a unit area of material are quite modest and for
a laser pulse less than 100 nanoseconds long, they typically do not exceed 100 J/cm2.
References
1. Askar’yan, G. A., and Moroz, E. M., JETP Lett. Vol. 16, p. 1638. 1963.
2. Neuman, Frank, Appl. Phys. Lett. Vol. 4, p. 167. 1964.
3. Gregg, David W., and Thomas, Scott J., J. Appl. Phys. Vol. 37, p. 2787. 1966.
4. Skeen, C. H., and York, C. M., Appl. Phys. Lett. Vol. 12, p. 369. 1968.
5. Fox, Jay A., and Barr, Dallas N., Appl. Phys. Lett. Vol. 22, p. 594. 1973.
6. Lowder, J. E., and Pettingill, L. C., Appl. Phys. Lett. Vol. 24, p. 204. 1974.
7. Fairand, B. P., Wilcox, B. A., Gallagher, W. J., and Williams, D. N., J. Appl. Phys.
Vol. 43, p. 3893. 1972.
8. Anderholm, N. C., Appl. Phys. Lett. Vol. 16, p. 113. 1970.
9. Yang, L. C., and Menichelli, Vincent J., Appl. Phys. Lett. Vol. 19, p. 473. 1971.
5
6. 10. O'Keefe, J. D., and Skeen, C. H., Appl. Phys. Lett. Vol. 21, p. 464. 1972.
11. Siegrist, M., and Kneubuhl, F. K., Appl. Phys. Vol. 2, p. 43. 1973.
12. O'Keefe, J. D., and Skeen, C. H., J. Appl. Phys. Vol. 44, p. 4622. 1973.
13. Fox, Jay A., Appl. Phys. Lett. Vol. 24, p. 461. 1974.
14. Yang, L. C., J. Appl. Phys. Vol. 45, p. 2601. 1974.
15. Fairand, B. P., Clauer, A. H., Jung, R. G., and Wilcox, B. A., Appl. Phys. Lett. Vol. 25,
p. 431, 1974.
16. Fairand, B. P., and Clauer, A. H., Optics Communications, Fall 1976.
17. Jacobs, A. J., Fundamental Aspects of Stress Corrosion Cracking (National Association
of Corrosion Engineers, Houston, Tex. 1969), p. 530.
18. Clauer, A. H., Fairand, B. P., and Wilcox, B. A., Metallurgical Transactions, A,
submitted April 1976.
19. Hahn, G. T., Mincer, P. N., and Rosenfield, A. R., Exp. Mech. Vol. 1, p. 284. 1971.
6