Laser surface alloying using metal salt precursors

Abstract

Surface alloys are of great interest for improving the mechanical and/or chemical properties of the near-surface region of metallic materials. A new method is described to achieve surface alloys under laser irradiation, consisting of the chemical reduction of metallic salts followed by alloying in the liquid state. The surface of the workpiece is first covered with a film containing concentrated salts of the elements to be alloyed and a thickening agent showing reducing capability. When the covered surface is irradiated by the laser beam, the temperature rise leads to decomposition of the salts and formation of the native metals which are immediately dissolved into the melted substrate, leading to the desired surface alloy. By this process, Fe-Ni, Ti-Ni and Fe-Ni-Cr surface alloys were achieved on mild steel and titanium substrates. The samples were studied by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray analysis, and hardness measurements were performed on cross-sections. This laser surface-alloying process gives rise to a variety of possibilities for improving the homogeneity of complex melts to tailor surface properties.