The Effect of Hydrogen on the Deformation and Fracture of Polycrystalline Nickel

Abstract

Polycrystalline nickel (grain size 140 μm) containing 9 ppm hydrogen has been mechanically tested over the range − 196 to + 100° C (77 to 373K) and at strain rates from 0·1 to 0·0001 s⁻¹. The hydrogen causes serrated yielding between − 130 and − 30° C (145 and 245 K), an increase in work-hardening rate between − 160 and + 100° C (115 and 373K), but no increase in yield stress. Hydrogen also weakens the nickel grain boundaries under all testing conditions. The resultant intergranular embrittlement is most marked below − 50° C (225 K) and appears to be enhanced by the occurrence of serrated yielding and grain-boundary shears. It is suggested that a very thin layer of hydride weakens the grain boundaries, but there is no direct evidence to support this.