functionally graded materials

1. DEPARTMENT OF MECHANICAL ENGINEERING
Characterization of functionally graded Al-SiCp
metal matrix composites manufactured by
centrifugal casting
By,
NIKHIL TT
M170389ME
MATERIAL SCIENCE &
TECHNOLOGY

2. introduction
What is fgm?
FGMs are innovative composite materials whose composition and
microstructure vary in space following a predetermined law. The
gradual change in composition and microstructure gives place to a
gradient of properties and performances.

3. introduction
The conventional approach of materials selection for component design and fabrication
is based on the list of existing engineering materials.
In case of FGM approach , an inverse design procedure is followed where the choice of
basic material ingredients and material processes are combined with three
diomensiona mechanical analysis to form the graded structures and components for
demanding applications.

4. introduction
WHY FGM?
Large number of engineering components and tools
require materials performance varying with location
The body of a gear must be tough, whereas it's surface must be
hard and wear resistant.
A knife needs only to be hard at it's cutting edge; elsewhere, the
material must be strong and tough.
Many of the most demanding current applications of materials
fall under this category.

5. Origin of fgm concept
The phenomenon of graded structures existed in nature.

6. Origin of fgm concept

7. Origin of fgm concept
The concept of functionally gradient materials (FGMs)
was proposed in 1984 by material scientists in the Sendai
area in Japan as a means of preparing thermal barrier
materials.
Interest in FGMs has recently escalated due
to the ability to produce materials with tailored properties which
are suitable candidates for numerous high tech applications such
as aerospace, bioengineering and nuclear industries

8. Applications of fgm

9. Fabrication methods
Gas based methods
Chemical vapour deposition/infiltration (CVD/CVI)
Thermal spray .
Surface reaction process
Liquid phase processes
Centrifugal casting
Combustion
Tape casting .
Slip casting
Gel-casting
Electrophoretic deposition
Chemical solution deposition (CSD)
Laser deposition .
Directional solidification
Sedimentation
Electrochemical gradation

10. Fabrication methods
Solid phase processes
Spark plasma sintering
Powder metallurgy

11. Centrifugal casting technique
variable frequency drive (VFD) to control the mould rotational speed in
the range of 500–2500 rpm
VFD to control the axial speed of the feeder tube in the range 5–50
mm/s

12. Centrifugal casting technique
Functionally graded aluminium-matrix composite prototype components: a cylinder liners
and gears; b brake rotor disc; c piston
Centrifugal casting of Al–graphite and Al–zircon
composites

13. Centrifugal casting technique

14. Production procedure
pure aluminium (99.97%, 25 BHN, 80 Mpa UTS) has been used as a matrix
material
Reinforcement is done by adding SiC particles
 WHY Al-SiCp?
The usage of Al-SiC Metal Matrix Composites is constantly
increasing in the last years due to their unique properties
such as light weight, high strength, high specific modulus,
high fatigue strength, high hardness and low density.

15. Production procedure
 Melting of the base metal in a graphite crucible at 670 °C and
heating to the pouring temperature of 725 °C.
SiC p powder is added at different weight percentages (0,2.5, 5,
7.5, 10 and 15 wt.%) of the molten metal weight.
1)
2)Three different SiC p sizes with average particle size of 16 µm, 23
µm or 500 µm were used.
3)
4)

16. Production procedure
 The SiC particles were mixed with stirrer at a speed of 100 rpm

 The mixture is poured into a centrifugal casting machine which has been
adjusted to different rotation speeds (800,900 or 1000 rpm) to produce
FGM tube with outer diameter of 230 mm, wall thickness of 12 mm and
length of 180 mm.

17. Characterization of material
Investigation of microstructure
Metallographic samples were sectioned from the cast FGM tubes through the
wall thickness
The samples have been polished and etched with 0.5% diluted Hydrofluoric
acid (HF).
Microscopic examination has been performed using Axiovert 25 CA compound
optical microscope.
The difference in distribution of SiC particles in the aluminium matrix has been
determined.

18. Characterization of material
Investigation of microstructure
Microstructure of FGM with 10 wt.% SiCp of 23 µm

19. Characterization of material
Investigation of microstructure
Microstructure of FGM with different weight fractions of SiC p of 16 µm

20. Characterization of material
Investigation of microstructure
Microstructure of FGM with 10 wt.% SiCp of 500 µm.

21. Characterization of material
Effect of the SiCp size on the distribution of particles
through thickness
Particle analysis
Image processing technique has been applied
Image J software program to analyse the distribution and the number of silicon
carbide particles
Automatic tools of particles detection have been applied to define
edges,adjust contrast, count the particles and calculate relative concentration
of SiCp

22. Characterization of material
Effect of particle size on distribution of SiCp at different weight fractions

23. Characterization of material
Effect of the mould rotational speed on distribution of particles

24. Characterization of material
Effect of the pouring mechanism feed on distribution of particles
Effect of feed on distribution of SiCp for different particle sizes.

25. Evaluation of mechanical properties
Brinell hardness test has been conducted on specimens of varying weight fraction
of SiCparticles
Hardness testing machine (Model MRB-250) has been used with a load of 62.5 N
and a steel ball indenter of 5 mm diameter.
Effect of reinforcement on hardness

26. Evaluation of mechanical properties
Effect of SiCp weight fraction on Brinell hardness at different zones

27. Evaluation of mechanical properties
Effect of SiCp weight fraction on Brinell hardness of outer zone.

28. Evaluation of mechanical properties
Effect of SiCp distribution on ultimate tensile strength
Example of tensile testing
specimen.
Locations of the cut samples.

29. Evaluation of mechanical properties
The samples were cut on a vertical milling machine
finished by fine emery paper (grit 600)
machined with the complete tube thickness to investigate the effect of
particle distribution through the thickness for each of the studied SiCp
weight percentages.
The tensile strength and the elongation at fracture were determined in a
tensile test.
ISO 1608:1995 (mechanical testing of metals tensile testing of materials)
on TUN-400 tensile testing machine.

30. Characterization of material
Effect of SiCp weight fraction on ultimate tensile strength.

31. Characterization of material
Effect of SiCp distribution on ductility
Effect of SiC p weight fraction on ductility.

32. Characterization of material
Effect of SiCp distribution on wear
Weight loss at different zones with increased SiCp weight fraction

33. Characterization of material
The relation between weight fraction and weight loss with
time

34. conclusion
 Investigation of microstructure reveals that the concentrations of the SiC
particles in the outer zone of the cast tubes reach its maximum value followed
by a gradual decrease in the direction of inner diameter.

 In case of large particle sizes and higher rotational speeds, all fabricated
tubes revealed high concentration of reinforcing particles in the outer zone
due to higher centrifugal force and particle mass.

 At higher axial speeds of feeding tube, the concentration at the outer zones is
higher than that obtained at lower feed speeds

 he gradient of concentration reduction inlower feed conditions is lower than
the gradient obtained at higher feeds and results in smoother change of
properties across the thickness

 Brinell hardness measurements reveal that high hardness is obtained on the
outer zone of all tested FGMs compared to that measured in chill,
concentration transition and inner zones

35. conclusion
 The hardness obtained in case of the smallest particle sizes is the highest
among all tested particle sizes.

 the increase in SiCp weight fraction resulted in a proportional increase in
outer zone hardness. The rate of increase decreases slightly beyond 10 wt%
SiCp

 By increasing the weight fraction of SiCp an increase in tensile strength of
FGMs samples cut through the whole tube thickness could be measured,
while ductility has decreased.

 The ultimate tensile strength has been found to be proportional to the
percentage of SiCp and inversely proportional to the size of the particles

 the highest wear resistance is achieved on the outer zones in all
investigated tubes

 Maximum improvement of wear resistance could be achieved in the range
7.5–10 wt.% SiCp

36. Reference
 E. Jayakumar, J.C. Jacob, T. Rajan, M. Joseph, B. Pai, Processing and
Characterization of Functionally Graded Aluminum (A319)-SiCp Metallic
Composites by Centrifugal Casting Technique, Metall. Mater. Trans. 47 (8)
(2016) 4306–4315.
 Q. Hu, H. Zhao, F. Li, Microstructures and properties of SiC particles reinforced
aluminum-matrix composites fabricated by vacuum-assisted high pressure die
casting, Mater. Sci. Eng. A (October) (2016) 1–8.
 Gupta, M. Ankit, Recent development in modeling and analysis of functionally
graded materials and structures, Progr. Aerosp. Sci. 79 (2015) 1–5.
 R. Kumar, D.C.N. Chandrappa, Synthesis and characterization of Al-SiC
functionally graded material composites using powder metallurgy techniques,
Int. J. Innov. Res. Sci., Eng. Technol. 3 (8) (2014) 15464–15471.
 T. P. D. Rajan • B. C. Pai,Developments in Processing of Functionally Gradient
Metals and Metal–Ceramic Composites: A Review, Acta Metall. Sin. (Engl.
Lett.), 2014,27(5), 825–838.

37. THANK YOU