The effect of post-sintering heat treatment on the properties ofSiC–LaAlO3-chromium carbide ceramic material fabricated bya liquid phase sintering: II. Effect of heat-treatment at 1500°C on properties of SiC–LaAlO3-chromium carbide ceramic materials

SiC–LaAlO3-chromium carbide ceramic materials were prepared from 55–70 wt% β-SiC, 20–35 wt% LaCrO3 and 10 wt% Al2O3 by liquid phase sintering at 1700°C. The mechanical properties and microstructure of the SiC–LaAlO3-chromium carbide ceramics before and after heat-treatment at 1500°C were studied. During heat-treatment, a La–Al–Si–O glass phase was formed by reaction of LaAlO3 with residual silica. After heat treatment the sample prepared from 70 wt% SiC, 20 wt% LaCrO3 and 10 wt% Al2O3, showed a significant improvement in bending strength from 80 to 307 MPa and in fracture toughness from 3.4 to 4.9 MPa·m1/2. SEM observation showed that in the sample after heat-treatment, a La–Al–Si–O glass was present over large areas and formed the ramified structure. However, in the samples with a higher content of lanthanum oxide, a similar structure was not observed and the glass was found to be concentrated in local areas. The ramified structure of the glass phase is considered to enhance a bonding effect of the glass phase in the material and could cause improvement in strength.