The effect of grain size on the deformation resistance of nickel

The effect of the grain sizel of commerical nickel on the lower yield point, _y, and flow stress, _f , has been investigated. From the relationship between _y andl ^–1/2 and between _f andl ^–1/2, and also by extrapolation, the parameters ₁( _i ^f ) and k_y(kf), which occur in Petch's well-known expression, were determined. It was found that the values of these parameters depend on the previous history of the samples. It is suggested that the more marked dependence of the deformation resistance of nickel on grain size arising from certain thermal treatments is due to the segregation of impurities to the grain boundaries. It is shown that this is in accord with the presence of grain-boundary hardening and with its dependence on quenching temperature.