Pb-Ni融液を用いたFeへのNi拡散被覆

Abstract

In order to obtain fundamental information on the development of a new Ni diffusion coating method using molten Pb as a medium for transfer of Ni atoms to an iron surface, solid state reactions of iron in molten lead containing various amounts of nickel at 1173 to 1373 K have been investigated.A dense and uniform diffusion layer composed of γ phase was obtained on the surfaces of iron specimens annealed in Pb-Ni melts. Pb could not be detected in the diffusion layer, although Pb particles adhered to the surface of the diffusion layer. The surface concentration of Ni in the diffusion layer increases with increasing Ni content of molten Pb and the maximum value of 95 mass% was obtained at more than 4 and 5 mass%Ni at 1173 and 1273 K, respectively. The thickness of the diffusion layer increases as the Ni content of molten Pb, annealing temperature and time increase, while the surface concentration of Ni in the diffusion layer decreases with increasing annealing temperature. These results are explained from the concentration dependence of Ni activity in molten Pb and the temperature dependence of interdiffusion coefficient in the γ phase. The method used here is applicable to Ni diffusion coating on iron and steel, if sticked molten Pb can be removed from the surface of the coatings.