Vacancy formation in nickel and α-nickel-carbon alloy

Abstract

Positron lifetime measurements in pure nickel and in α-nickel-carbon alloy have been carried out. Vacancy formation enthalpy was determined to be H f v = (1.73 ± 0.07)eV in pure nickel. In the alloy the sample carbon content follows the line of solubility of the phase diagram. A large decrease in the effective formation enthalpy H f v,eff = (1.43 ± 0.1)eV due to carbon vacancy interaction is observed. This effect is ascribed to the formation of vacancy impurity complexes up to second order. In order to be applicable for interstitial alloys the model of Bérces and Kovács [1] has been modified. A solute-vacancy binding energy g B1 of (0.33 ± 0.07)eV has been determined. The attractive impurity-impurity interaction of Δ = (0.20 ± 0.15)eV is assumed to overcompensate the strain energy induced by interstitial carbon being located at the neighbor octahedral sites to the vacancy.