A.r de Arellano-Lopez ef al /Internatonal Journal of efractory Metals& Hard Matenals 16(1998)337-341 339 grain size Is≈ I um and TiC particle size is≈5um.In situ whisker lengths are typically below 10 un Results and discussion 500 3. 1. Elastic modulus Variation of Youngs modulus(E)with temperature shown in Fig. 2. The value of E at room temperature for the composite was approximately 2.5% higher than 300 E for pure AlO3 [15]. The value of 1/E(dEldT) fror 25to1000cwas8.5×103, almost equal to the让 value of 8. x 10-C- found for Al O3 in the same 200400600800100012001400 temperature range [15]. The SiC and TiC. additions, therefore seem to have had little effect on e T 3. 2. Fracture strength temperature fracture strength is plotted as a function of tempera 1200C(Fig. 4(b)) indicate that fracture was a combination of intergranular and transgranular. Thus, ture in Fig. 3. The strength of 440 MPa measured at the dominant fracture mechanism was independent of room temperature is considerably lower than that temperature reported previously [10]. Fractures originated at processing flaws. The discrepancy between these measurements performed on polished samples and our previous measurements must reflect variability in processing or sample preparation and will require further investigation. Strength was virtually indepen dent of temperature to 1000C, but decreased slightly at 1200'C, which is probably the limit of practical use of this material because creep could be excessive at higher temperatures. This result is consistent with finding for Al O,/TiC composites [16]. Surfaces of samples fractured at room temperature(Fig. 4(a)and 380 370 200 400 600 8001000 Fig 4 SEM photomIcrographs of fracture surfaces at(a)room Fig 2 Vanation of E as a function of temperature mperature and(b)1200.CA. R de Arellano-L6pez et al /Internatzonal Journal of Refractory Metals& Hard Materials 16 (1998) 337-341 339 grain size is ~ 1 #m and TiC particle size is ~ 5 #m. In situ whisker lengths are typically below 10/~m. 3. Results and discussion 3.1. Elastic modulus Variation of Young's modulus (E) with temperature is shown in Fig. 2. The value of E at room temperature for the composite was approximately 2.5% higher than E for pure A1203 [15]. The value of 1/E (dE/dT) from 25 to 1000°C was 8.5 x 10 5 o C 1, almost equal to the value of 8.3 x 10 .5 °C -1 found for AlzO3 in the same temperature range [15]. The SiC and TiC additions, therefore, seem to have had little effect on E. 3.2. Fracture strength Fracture strength is plotted as a function of tempera￾ture in Fig. 3. The strength of 440 MPa measured at room temperature is considerably lower than that reported previously [10]. Fractures originated at processing flaws. The discrepancy between these measurements performed on polished samples and our previous measurements must reflect variability in processing or sample preparation and will require further investigation. Strength was virtually indepen￾dent of temperature to 1000°C, but decreased slightly at 1200°C, which is probably the limit of practical use of this material because creep could be excessive at higher temperatures. This result is consistent with finding for A1203/TiC composites [16]. Surfaces of samples fractured at room temperature (Fig. 4(a)) and D. v t-- e" .i..a .i..a o u.. Fig 600 500 400 300 ''1'''1'''1'''1'''1'''1''' 200 , , I , , , I , , , I , , , I , , , I , , , I , , , 0 200 400 600 800 1000 1200 1400 T (°C) 3 Four-point-bend fracture strength as a function of temperature 1200°C (Fig. 4(b)) indicate that fracture was a combination of intergranular and transgranular. Thus, the dominant fracture mechanism was independent of temperature. Q.. UJ 410 ' , i I i i i I i i i I i i ~ I ' ' ' [ 400 390 380 370 0 200 400 600 800 1000 T (°C) Fig 2 Variation of E as a function of temperature Fig 4 SEM photomacrographs of fracture surfaces at (a) room temperature and (b) 1200°C