MODELING OF AND SOLIDIFICATION BEHAVIOR DURING LASER-SURFACE ALLOYINGOF FERROUS-ALLOYS WITH CRB2

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 techni que. 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 conten t of which depend on the laser parameters and on the thermophysical pr operties of the substrate. The typical microstructural components were : (i) columnar iron borides which formed on the residual chromium bori des; (ii) iron dendrites which grew on the substrate; (iii) eutectic; and (iv) a layer of iron boride which enveloped the residual CrB2 part icles. The solidification behaviour associated with the coexistence of these phases, and its dependence on the laser parameters are discusse d with the aid of a simplified mathematical model.