The effects of partial pressure and strain rate on water vapor- and hydrogen gas-induced embrittlement of Co 3Ti alloys

Abstract

The effects of partial pressure and strain rate on the embrittlement owing to water vapor and hydrogen gas are observed on Co23 mol% Ti and Co21 mol% Ti alloys by SP and tensile tests at room temperature. The Co 3Ti alloys are very susceptible to environmental embrittlement owing to water vapor and hydrogen gas. Critical partial pressures (CPPs) below which the embrittlement does not occur are determined for both testing atmospheres, both alloy compositions and three cross-head speeds. Also, critical strain rates (CSRs) beyond which the embrittlement does not occur are determined in air for both alloy compositions. The difference in the susceptibility to the embrittlement between water vapor and hydrogen gas is attributed to the difference in the decomposition rate on the alloy surface. The compositional dependence of the susceptibility to the environmental embrittlement is considered to be due to the difference in the intrinsic grain boundary cohesion between two alloy compositions, i.e. to the difference in the critical hydrogen content causing intergranular cracking.