Fracture toughness, crack-growth-rate and creep studies of alloy 276

Austenitic nickel-base Alloy 276 had been proposed to be a candidate structural material within the purview of the nuclear hydrogen initiative program. A mechanistic understanding of high temperature tensile deformation of this alloy has already been presented in an earlier investigation. The current investigation has been focused on the evaluation of crack-growth behavior, fracture toughness, stress-corrosion-cracking and creep deformation of this alloy as functions of different metallurgical and mechanical variables. The results of crack-growth study under cyclic loading indicate that this alloy exhibited greater cracking tendency with increasing temperature at a constant load ratio (R). However, the effect of temperature on crack-growth-rate was more pronounced within a temperature range of 100-150°C when the R value was kept at 0.1. The fracture toughness of this alloy in terms of JIC was significantly reduced at 100°C compared to those at higher temperatures. As to the cracking susceptibility of this alloy in an acidic solution, the average crack-growth-rate was gradually reduced with increasing exposure time probably reaching a near threshold value following eight months of testing. Limited data on creep testing suggest that Alloy 276 may be capable of withstanding time-dependent deformation at 750, 850 and 950°C under sustained loading equivalent to its 10 percent yield strength values at these temperatures. Finally, the extent of deformation under different modes of loading was analyzed by numerous state of the art characterization tools.