EFFECT OF 3RD ELEMENTS ON HIGH-TEMPERATURE STRENGTH OF TIAL BASE ALLOYS

After the heat-treatment of 1473 K-10.8 ks, the yield stress of TiAl (gamma) base alloys, Ti-50 mol%Al, Ti-(50-C) mol%Al-C mol%X, and Al-(50-C) mol%Ti-C mol%X, was examined by the compression test as a function of temperature (295-1273 K) and the amount, C (0.5-2.0), of third elements, X (Cr, Ga, Zr, Nb, Sb, Hf, Pd, Pt, Ta). Micro-hardnesses of gamma in the alloys were measured at room temperature to confirm solid solution hardening. The microstructures were examined using OM, SEM, EPMA and XRD. The results obtained were examined with regression analysis and compared with the microstructures. The micro-hardness increased with the amount of additives. The increase was remarkable with increasing difference in atomic radius between Ti or Al and X atoms. In the temperature range of 295-1073 K, the yield stress is in proportion to the micro-hardness and influenced by the amount of Ti3Al phase and the grain size of gamma phase. At 1273 K, the effect of the microstructure on the yield stress decreased and the effect of solid solution hardening become prominent.