Environmental effects on the fracture toughness of the ternary cubic (L12) titanium trialuminide intermetallics

To understand the effect of environment on the fracture toughness of cubic titanium trialuminide (based on Al3Ti) intermetallics a wide program of fracture toughness testing using the single-edge-precracked-beam (SEPB) and chevron-notched-beam (CNB) in three-and four-point bending was carried out in air, vacuum (similar to 1.3x10(-5) Pa), oxygen, argon, water and liqiud nitrogen. The cubic titanium trialuminide (average composition 66at.% Al, 25at.% Ti and 9at.% Mn) modified with Mn, cast and HIP-ed at 1200 degrees C for 2h under 170 MPa was used for testing. Testing in air, vacuum and argon was carried out up to 1000 degrees C. It is shown that fracture toughness of cubic titanium trialuminides at ambient temperatures is not affected by the environments containing moisture (water vapour). It seems that at ambient temperatures these materials are completely immune to the water-vapour hydrogen embrittlement and their cause of brittleness is other than environment. At the intermediate temperature range of approx. 200-600 degrees C trialuminides tested in air and vacuum exhibit a mild but discernible peak of fracture toughness. However, testing in high-purity argon eliminates this peak and fracture toughness in argon is practically independent of temperature at the range from room temperature to 1000 degrees C.