ZrB 2 -MoSi 2 ceramics: A comprehensive overview of microstructure and properties relationships. Part II: Mechanical properties

The mechanical behavior of ZrB 2 -MoSi 2 ceramics made of ZrB 2 powder with three different particle sizes and MoSi 2 additions from 5 to 70 vol% was characterized up to 1500 °C. Microhardness (12–17 GPa), Young's modulus (450–540 GPa) and shear modulus (190–240 GPa) decreased with both increasing MoSi 2 content and with decreasing ZrB 2 grain size. Room temperature fracture toughness was unaffected by grain size or silicide content, whilst at 1500 °C in air it increased with MoSi 2 and ZrB 2 grain size, from 4.1 to 8.7 MPa m ½ . Room temperature strength did not trend with MoSi 2 content, but increased with decreasing ZrB 2 grain size from 440 to 590 MPa for the largest starting particle size to 700–800 MPa for the finest due to the decreasing size of surface grain pullout. At 1500 °C, flexure strength for ZrB 2 with MoSi 2 contents above 25 vol% were roughly constant, 400–450 MPa, whilst for lower content strength was controlled by oxidation damages. Strength for compositions made using fine and medium ZrB 2 powders increased with increasing MoSi 2 content, 250–450 MPa. Ceramics made with coarse ZrB 2 displayed the highest strengths, which decreased with increasing MoSi 2 content from 600 to 450 MPa.