Modelling of and solidification behaviour during laser surface alloying of ferrous alloys with CrB₂

Abstract

A continuous wave CO₂ laser was used to alloy the surface of AISI 1045 steel and α 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.

MST/1941