Room-temperature environmental embrittlement in a TiAl alloy

A two phase gamma TiAl alloy with the composition Ti--47.5Al--2.5Nb--2Cr--0.5Mn--0.5Si (at.%) was used to determine the effect of the environment on tensile properties. Tensile tests were performed at room temperature in air, vacuum, and pure oxygen environments. Fracture surfaces were examined using a scanning electron microscope. Optical microstructure was determined from the shoulder part of the fractured specimens. The alloy exhibited a plastic strain to fracture of 0.2% in air, 0.5% in vacuum (4 x 10 exp --4 ), and 1.2% in pure O (66 kPa). The results indicated that the alloy is prone to moisture induced environmental embrittlement at ambient temperatures. The embrittlement is thought to involve the reaction of Ti and Al atoms with moisture in air, resulting in generation of atomic hydrogen that penetrates into crack tips and reduces overall tensile ductility. No apparent change in fracture mode with test environment was observed in this aluminide alloy.