Ta. Parthasarathy et al., HIGH-TEMPERATURE DEFORMATION OF SIC-WHISKER-REINFORCED MGO-PSZ MULLITE COMPOSITES, Journal of the American Ceramic Society, 79(2), 1996, pp. 475-483
The effect of 33.5 vol% SIC whisker loading on high-temperature deform
ation of 1 wt% MgO-38.5 wt% zirconia-mullite composites was studied be
tween 1300 degrees and 1400 degrees C. At strain rates of 10(-6) to 5
x 10(-4)/s the creep resistance of zirconia-mullite composites without
SIC reinforcement was inferior to monolithic mullite of similar grain
size, Analysis of the results suggested that the decreased creep resi
stance of mullite-zirconia composites compared to pure mullite could b
e at least partially explained by mechanical effects of the weaker zir
conia phase, increased effective diffusivity of mullite by zirconia ad
dition, and to the differences in mullite grain morphology, With SLC w
hisker reinforcement, the deformation rate at high stress was nearly t
he same as that of the unreinforced material, but at low stress the cr
eep rates of the SiC-reinforced material were significantly lowered, T
he stress dependence of the creep rate of unreinforced material sugges
ted that diffusional creep was the operative mechanism, while the rein
forced material behaved as if a threshold stress for creep existed, Th
e threshold stress could be rationalized based on a whisker network mo
del. This was supported by data on other whisker-containing materials;
however, the threshold stress had a temperature dependence that was o
rders of magnitude higher than the elastic constants, leaving the phys
ical model incomplete, The effects of residual stresses and amorphous
phases at whisker/matrix interfaces are invoked to help complete the p
hysical model for creep threshold stress.