Influence of grain boundary composition on the moisture-induced embrittlement of Ni-3(Si,Ti) alloys

Ni-3(Si,Ti) alloys containing different levels of boron were tensile tested in air at room temperature at two different strain rates. The grain bounda ry compositions and fracture modes of these alloys were determined by Auger spectroscopy and scanning electron microscopy, respectively. Tensile elong ation and fracture mode depend upon the fabrication procedure, heat treatme nt, and strain rate. Widely different boron concentrations were observed at the grain boundaries, depending on the fabrication procedure and heat trea tment. In addition, silicon and titanium were depleted while nickel was enr iched at the grain boundaries in all specimens examined. Tensile elongation s correlated well with the grain boundary concentration of boron and also w ith an embrittlement parameter defined as (Si+Ti-B)/Ti. A sharp brittle-duc tile transition was found to occur with increasing grain boundary concentra tion of boron and with decreasing values of the embrittlement parameter (Si +Ti-B)/Ti. The critical grain boundary concentrations corresponding to this transition were found to be sensitive to the strain rate. All the results can be explained in terms of the effect of grain-boundary composition on mo isture-induced environmental embrittlement. (C) 1999 Elsevier Science Ltd. All rights reserved.