Nuclear microprobe characterization of surface hardening by precipitation of chromium carbides after laser beam treatment of a Ni-Cr substrate

Surface treatment by laser provides interesting solutions to the problems of accelerated wear of materials. The aim of the present study is the characterization of chromium carbide-rich surface alloys after laser beam melting of an Ni70Cr30 carbon-precoated substrate. Transmission electron microscopy investigation shows the structure of the carburized zone, and electron diffraction shows the type of carbides formed. Carbon profiling of the lasered surface was performed by nuclear microprobe using the 12C(d, po)13C reaction; Ni and Cr (more precisely, the ratio Ni/Cr) were evaluated semi-quantitatively by means of particle-induced X-ray emission. The specificity of the method and the experimental conditions are explained. Wear results are very satisfactory and close to those obtained by injection of chromium carbide powders into the laser beam in the case of a Nimonic alloy: wear rates are divided by tow orders of magnitude. (author)