A continuous wave CO2 laser was used to alloy the surface of AISI 1045 steel and alpha iron plates with CrB2 via the powder injection technique. The CrB2 particles were partially dissolved in the bath, forming a melted layer of Fe-Cr-B-C or Fe-Cr-B, the thickness and boron content of which depend on the laser parameters and on the thermophysical properties of the substrate. The typical microstructural components were: (i) columnar iron borides which formed on the residual chromium borides; (ii) iron dendrites which grew on the substrate; (iii) eutectic; and (iv) a layer of iron boride which enveloped the residual CrB2 particles. The solidification behaviour associated with the coexistence of these phases, and its dependence on the laser parameters are discussed with the aid of a simplified mathematical model.
