FLEXURAL STRENGTH, FRACTURE-TOUGHNESS AND FATIGUE-CRACK GROWTH-BEHAVIOR OF CHROMIUM ALLOYED GAMMA-BASE TIAL

Mechanical properties of gamma-base titanium aluminides strongly depen d on microstructural parameters. Flexural strength, fracture toughness and fatigue crack growth properties were estimated for the cast and h eat-treated (HT-TiAlCr) and cast, heat treated and isothermal forged ( ITF-TiAlCr) chromium alloyed gamma-base titanium aluminides at room te mperature. HT-TiAlCr possessed superior fracture properties compared t o ITF-TiAlCr. Toughening due to microcracks, and crack bridging by unc racked ligaments were observed in the test materials. Presence of lame llar grains in HT-TiAlCr increased the crack growth resistance and con tributed positively to fracture properties. The coarse grain size prom oted large crack deflection and fracture surface mismatch and caused h igh levels of crack closure in HT-TiAlCr. Combined crack-tip blunting and bridging by ductile beta-phase was significant in the case of ITF- TiAlCr. Fracture mechanisms of test materials were investigated and co rrelated to the fracture properties.