High Temperature Bending Strength and Thermal Shock Resistance of Carbon-Ceramics Composites

Abstract

Carbon-ceramics composites were prepared from C-B4C, C-B4C-NbC, C-B4C-TaC and C-B4C-TiC mixed powder by hot-pressing under the pressure of 19.6 MPa at 2200°.After hot-pressing, NbC, TaC and TiC changed into borides through the reaction with coexisting B4C.Bending strength in the range from room temperature to 2000° and thermal shock resistance in the quenching temperature ranging from 0° to 1000°were measured for these carbon-ceramics composites.Bending strength of the composites prepared from C-B4C, C-B4C-NbC and C-B4C-TaC mixed powders increased monotonically with an increase of temperature up to 1600°-1700°.Its maximum value was 1.3-1.6 times that at room temperature.Bending strength decreased with temperature above 1600°-1700°.Bending strength of the composite prepared from C-B4C-TiC mixed powder also increased with an increase of temperature up to 1500°, but the amount of increase in strength at high temperatures was small in comparison with the strength increase for other composites.Bending strength also decreased above 1500° in this case.The carbon-ceramics composites showed very high thermal shock resistance.The critical quenching temperature difference of the composites prepared from 60 vol%C-30 vol%B4C-10 vol%NbC (or TaC or TiC) and 70 vol%C-20 vol%B4C-10 vol%NbC (or TaC or TiC) was 700°-900° and more than 1000° respectively.These values are much higher than those for such oxides as Al2O3 and ZrO2.From these experimental results, it is considered that these carbon-ceramics composites are possibly used at high temperatures up to 1500°-1700° under high stresses as a structural material.