HYDROGEN EMBRITTLEMENT IN DUCTILE NI3AL-EFFECTS OF HYDROGEN CONTENT, STRAIN-RATE AND PRE-DEFORMATION

Hydrogen embrittlement has been studied in continuous cast sheet of an Ni3Al alloy (Ni77.83Al21.73Zr0.34B0.1). When tensile tests were performed at the initial strain rate of 5.8 x 10(-5) s-1, the elongation decreased from 32.7% for no charging to 1.9% for 330min of cathodic charging with 50 mA/cm2 current, but the yield stress did not change. The fracture mode changed partially from dimple to intergranular and cleavage modes. At a faster strain rate of 5.8 x 10(-3) s-1, hydrogen embrittlement was less pronounced, but the yield stress increased with hydrogen content and multiple cracks were generated. Plastically pre-deformed (2-26% elongations) and subsequently charged specimens failed after yielding, which occurred at the final pre-deformation stress. Our results suggest that the grain boundary or the interior of the grain was not weakened by hydrogen, rather hydrogen-enhanced localized plasticity caused the loss of ductility in B-doped Ni3Al alloy.