Deterioration of Mechanical Properties Caused by Omega Phase in Major Alloyed TiAl-based Alloys

摘要

The addition of 1.0 at.% boron has successfully reduced the lamellar colony size to 50 μm for alloy Ti-44Al-8Nb-1B and to 80 μm for alloy Ti-44Al-4Nb-4Zr-0.2Si-1B. However, the latter is found to have a considerable amount of omega phase precipitated from retained β under as-HIPped conditions. In order to understand the effects of omega phase, mechanical performance in tensile, fatigue and fatigue crack growth resistance tests has been assessed for these two alloys, and has been combined with detailed TEM examination. Omega particles existing as a network around retained beta cells are deduced to be favoured sites for microcrack initiation under both monotonic and cyclic loading conditions. On the other hand, no influence on the fatigue crack growth resistance has been found as a result of the presence of omega phase. The relationships between microstructure and mechanical properties for the two alloys are discussed.