MICROSTRUCTURE AND HIGH-TEMPERATURE TENSI LE PROPERTIES OF TIC TI5SI3/TI3SIC2 FINE COMPOSITES PREPARED BY MECHANICAL ALLOYING/

Microstructure and tensile properties at elevated temperatures of fine composites prepared by mechanical alloying of Ti and SiC powders have been investigated. Mixtures of elemental Ti and SiC powders in the co mposition of Ti-24 mass%SiC are milled under an Ar atmosphere using an attritor ball mill. After milling for 36 ks, formation of TiC and Ti5 Si3 is observed and further milling adding n-heptane for 3.6 ks makes the powder particles finer. Milled powders are consolidated by hot pre ssing at 1773 K for 10.8 ks under 70 MPa and hot isostatic pressing at 1773 K for 10.8 ks under 196 MPa. The compact consists of mostly equi -axed TIC and Ti5Si3 grains of an average diameter of 0.86 mu m partia lly mixed with plate-like phase of T3SiC2. The compact shows elongatio n of 130% at tensile test at 1773 K with an initial strain rate of 4.0 x 10(-4) s(-1) with the strain rate sensitivity exponent of 0.38. Mos t grains remain equi-axed after tensile test, while random orientation s of plate-like phases of Ti3SiC2 turn parallel along the tensile axis . The large elongation observed above 1773 K is likely due to the supe rplasticity, while rotation of the plate-like phase accompanies deform ation of the surrounding matrix.