XIA and LANGDON: DEFORMAtION OF AN ALUMINA COMPOSITE 1423 AzO·93w寡siC|叫 a Fig 4. Creep strain vs time at 1773 K for a range of applied a stresses; for specimens bent to failure, the creep curves levels of the applied stress, o. These creep curves exhibit the normal three stages with a brief primary stage, a lengthy and well-defined steady-state con dition, and then a very brief tertiary stage of acceler ating creep before final catastrophic fracture(marked with x in Fig. 4). Using these creep data, Fig. 5 shows the instantaneous strain rate, t, plotted against strain for the same five specimens. This plot confirms the presence of a well-defined steady-state stage t It lso apparent that this material is capable of exhibit ing reasonable ductility with strains to failure of Fig. 2. Distribution of whiskers in Al,O3 9.3 voL. SiC(w) >10% under some experimental conditions at (a)low and (b) high magnifications: the hot-pressing Creep tests were conducted at temperatures from direction lies vertical in the plane of observatic 1673 to 1823 K, and Fig. 6 shows a logarithmic plot of the steady-state strain rate vs the applied stress. At each temperature, the datum points fall along straight lines, and the four lines are give an average value for the stress exponent, n, of ~3.8. Taking n=3.8, Fig. 7 shows a semi-logarithmic plot of the temper Fig 3. Whiskers located in the boundaries and at tril tFor the two specimens tested at the lower stresses in strains of 8%. Tests conducted stress levels mperatures revealed no significant further decrease in strain rate at strains ab 10 it is therefore reasor very close to the Instanta rain rate vs strain at 1773 KXIA and LANGDON: DEFORMATION OF AN ALUMINA COMPOSITE 1423 161 I AI203 - 9.3 vol I~, SiC (w) 14 I- .r ----T 7--T~--- • 17 -- 12j- ~" 0 39.8 -'-" u 32.8 | .-/ o 25.8 r~L ,,;" a 18.7 '~F ~ ~11.8 0# ,, ~ , t (hr} Fig. 4. Creep strain vs time at 1773 K for a range of applied stresses; for specimens bent to failure, the creep curves terminate with x. Fig. 2. Distribution of whiskers in AI203 9.3 vol.% SiC(w) at (a) low and (b) high magnifications: the hot-pressing direction lies vertical in the plane of observation. levels of the applied stress, a. These creep curves exhibit the normal three stages with a brief primary stage, a lengthy and well-defined steady-state con￾dition, and then a very brief tertiary stage of acceler￾ating creep before final catastrophic fracture (marked with x in Fig. 4). Using these creep data, Fig. 5 shows the instantaneous strain rate, ~, plotted against strain for the same five specimens. This plot confirms the presence of a well-defined steady-state stage.t It is also apparent that this material is capable of exhibit￾ing reasonable ductility with strains to failure of > 10% under some experimental conditions. Creep tests were conducted at temperatures from 1673 to 1823 K, and Fig. 6 shows a logarithmic plot of the steady-state strain rate vs the applied stress. At each temperature, the datum points fall along straight lines, and the four lines are reasonably parallel and give an average value for the stress exponent, n, of ~3.8. Taking n = 3.8, Fig. 7 shows a semi-logarithmic plot of the temperature compensated stress [20], Fig. 3. Whiskers located in the grain boundaries and at triple points. #For the two specimens tested at the lower stresses in Fig. 5, the tests were terminated without failure at strains of ~8%. Tests conducted at low stress levels at other temperatures revealed no significant further decrease in strain rate at strains above ~6-8%, and it is therefore reasonable to conclude that the slowest strain rates recorded in Fig. 5 are very close to the steady-state values. 10"3 t I I ~ I I I AI203 - 9.3 vo~% SiC (.) T=1773 K o'(MPa) o 39.8 ,F 432.8 10 -4 ~._ ,~ 025.8 t c ~"c-c--C°-'°~ / °18.7 / -- I0" i0-~ Fig. 5. Instantaneous strain rate vs strain at 1773 K