Laser developed Al-Cr surface alloys: Microstructure, mechanical and wear behaviour

Surface alloys with composition ranging from 10 to 20% Cr were produced by laser surface alloying. Their microstructure consists of faceted plate-like Al4Cr intermetallic compound particles dispersed in a matrix of alpha-Al solid solution. During remelting, heterogeneous nucleation of eutectic Al7Cr/alpha-Al occurred in the undercooled liquid ahead of the columnar solid-liquid interface, followed by equiaxial solidification, resulting in a microstructure formed of equiaxed cells. Al-Cr alloys present Young's modulus and hardness values that increase with increasing volume fraction of intermetallic compounds. Wear resistance, measured in dry sliding conditions, increases with increasing load due to the protective effect of a stable mechanically mixed layer that forms at the surface of the samples and the steel counterbody. Alloys formed of equiaxed eutectic cells provide better wear resistance than those formed of large plate-like particles since a thinner, more stable and harder mechanically mixed layer is formed, which offers best protection against wear.