HYDROGEN EMBRITTLEMENT IN PRE-DEFORMED NI3AL ALLOY

Hydrogen embrittlement has been investigated in continuous cast sheet of a Ni3Al alloy (Ni77.82Al21.73Zr0.34B(0.1)) after imparting various amounts of pre-deformation. The specimens (25.4 mm long, 4.4 mm wide and 1 mm thick) were deformed in tension and then taken out of the testing rig for charging hydrogen cathodically for 120 min with a current density of 50 mA cm(-2). Upon testing again in tension, the specimens charged with hydrogen always failed after yielding, which occurred at the final pre-deformation stress. For instance, a specimen pre-deformed to 26% elongation and subsequently charged for 120 min failed (during tensile-testing at the strain rate of 5.8 x 10(-5) s(-1)) at a true stress of 1611 MPa, which is comparable to the true fracture stress (1753 MPa) of the uncharged specimen. However, the elongation at which the charged specimens failed decreased drastically from 5.4% to 1.3%, as the predeformation increased from zero to 2.0%. The fracture surface of the charged specimen consisted of regions of intergranular, quasi-cleavage and dimple fracture. The proportion of intergranular fracture decreased with the increasing pre-deformation, while that of dimple fracture increased. Our results suggest that grain boundaries in B-doped Ni3Al were not weakened by hydrogen, rather ductility-related voids and cracks were involved in hydrogen embrittlement of B-doped Ni3Al alloy.