Microcrystalline surface layers created by laser alloying

Abstract

Laser alloying has been used to create hard surface layers on a ferritic stainless steel. Alloying elements were introduced very simply by painting the steel surface with a suitably charged paint. The materials obtained were examined by electron metallographic techniques and analysed by energy-dispersive spectroscopy and diffraction. Suitable control of laser conditions makes it possible to regulate the depth of substrate melting and the alloy composition. A second melting was necessary to homogenize the material and simultaneously to select the grain size. Microstructures obtained were typically equiaxed with grains of size 0.25–1 μm. The formation of this microstructure is analysed in terms of the existence of an undercooled molten pool containing nucleants for the heterogeneous nucleation of b.c.c. iron. Such microstructures are created because crystal growth requires diffusion and large undercoolings and because suitable nucleant particles are present.