Laser surface hardening of structural ferrous alloys

Laser surface alloying is a technique for altering the surface properties of a substrate without affecting those of the bulk, by simultaneously melting the surface of the substrate and adding alloying elements to it. By applying the proper combination of processing parameters and alloying elements, a surface can be modified to accommodate a wide variety of properties. Alloying with Cr and Ni improves the resistance to oxidation and corrosion and increases the hardness. Boronising with the aid of a laser results in a brittle layer, exhibiting very high hardness and low wear rates but a low corrosion resistance due to the cracked surface. The addition of high melting point carbides to the surface leads to increased hardness and wear resistance, except when the matrix is very soft. In this review the microstructure and properties are presented in detail.