Fabrication of Alumina/ZirconiaFunctionally Graded Materials (FGM)

Adam Sneller, Li Sun Advisor: Dr. Patrick Kwon

Background:• 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

Innovative Process

Problem:• Cracks form between layers• The entire object warps in shape (camber)

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

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

(a) (b)

Figure 1. FGM samples with (a) a crack and (b) camber

3. Optimized compaction load and temperature changing rate See Table 1

Figure 3. Punch used to produce occlusive interface between powder layers

Structure

Layer Z 60% TZ3YS, 40% CERAC

Interface Z/M Occlusive

Layer M46% 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

(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

Table 1. Optimized parameters to achieve a flat 3-layer Al2O3/ZrO2 FGM without cracksFinal Solution with Transient

Sintering Behavior Analysis

• 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

2. Design of Interface:Three different interfaces were investigated:

1. Natural – created using flat punch2. Smooth – created by pressing powder with a flat punch, then rotating to make surface smoother3. Occlusive – created using the punch shown in Fig. 3

– A quasi-continuous shift from one layer to the next is possible

Figure 4. (a) The shrinkage rate and (b) densification rates can be seen to be similar for all three layers

(a) (b)

References1. 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

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)