Innovative Process
1. Manipulated powder mixture:
• Two alumina powder and two zirconia powder were mixed to manipulate
material properties of powder mixture
• Sintered dimension similarity could be obtained for the three layers
• Possible to eliminate cracks and camber
Fabrication of Alumina/Zirconia
Functionally Graded Materials (FGM)
Adam Sneller, Li Sun
Advisor: Dr. Patrick Kwon
Background:
(a)
(b)
Figure 2 (a) particle size distribution for each powder and (b)
Diameter of sintered samples with varying powder
composition, the powder composition located between
two blue lines have the potential to achieve similar final
dimension
• A functionally graded material features a concentration gradient
• the proportion each material varies throughout the object
• Useful for circumstances when remote parts of an object are
exposed to different conditions
Objective:
• Create a 3-layered FGM made of alumina and zirconia powders:
1. Pure zirconia (Layer Z)
2. Half zirconia, half alumina (Layer M)
3. Pure alumina (Layer A)
2. Design of Interface:
Three different interfaces were investigated:
1. Natural – created using flat punch
2. Smooth – created by pressing powder with a flat punch, then rotating to make surface smoother
3. Occlusive – created using the punch shown in Fig. 3
– A quasi-continuous shift from one layer to the next is possible
3. Optimized compaction load and temperature changing rate
See Table 1
Problem:
• Cracks form between layers
• The entire object warps in shape (camber)
Final Solution with Transient
Sintering Behavior Analysis
Table 1. Optimized parameters to achieve
a flat 3-layer Al2O3/ZrO2 FGM without cracks
Structure
(a)
Figure 3. Punch used to
produce occlusive interface
between powder layers
(b)
Figure 1. FGM samples with (a) a crack and (b) camber
(a)
(b)
Figure 4. (a) The shrinkage rate and (b) densification
rates can be seen to be similar for all three layers
Reason:
• During sintering, thermal reactions may differ between layers
• Mismatch in densification rate
• Mismatch in thermal expansion
• Results in residual stress which causes cracks or camber
• Unavoidable in using only one powder for each layer
Layer Z
60% TZ3YS, 40% CERAC
Interface Z/M
Occlusive
Layer M
46% CR-15, 4% TMDAR;
30% TZ3YS, 20% CERAC
Interface M/A
Smooth
Layer A
94% CR-15, 6% TMDAR
Forming load
60 MPa
Rate of temperature
change
10˚C/min
• The transient sintering behaviors of three chosen powder mixtures under optimized experimental condition
are almost same.
• This similarity ensures that no large dimension mismatch could occur at any time during sintering
References
1. Cai, P.Z., et al. 1997. “Constrained densification of alumina/zirconia hybrid laminates, I: experimental observations of processing defects,” J. Am. Ceram. Soc., 80(8): 1929–1939.
2. Torrecillas, R., et al. 2000. “Functionally graded zircon-molybdenum materials without residual stresses,” J. Am. Ceram. Soc., 83(2): 454–456.
3. Lance, D., et al. 2004. “Correlation between densification rate and microstructural evolution for pure alpha alumina,” J. Eur. Ceram. Soc., 24(9): 2749–2761