ZrB2-MoSi2 ceramics: A comprehensive overview of microstructure and properties relationships. Part II: Mechanical properties

摘要

The mechanical behavior of ZrB2-MoSi2 ceramics made of ZrB2 powder with three different particle sizes and MoSi2 additions from 5 to 70 vol% was characterized up to 1500 degrees C. Microhardness (12-17 GPa), Young's modulus (450-540 GPa) and shear modulus (190-240 GPa) decreased with both increasing MoSi2 content and with decreasing ZrB2 grain size. Room temperature fracture toughness was unaffected by grain size or silicide content, whilst at 1500 degrees C in air it increased with MoSi2 and ZrB2 grain size, from 4.1 to 8.7 MPa m(1/2). Room temperature strength did not trend with MoSi2 content, but increased with decreasing ZrB2 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 degrees C, flexure strength for ZrB2 with MoSi2 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 ZrB2 powders increased with increasing MoSi2 content, 250-450 MPa. Ceramics made with coarse ZrB2 displayed the highest strengths, which decreased with increasing MoSi2 content from 600 to 450 MPa.