During the development of Co-Cr-Mo as implant alloys, a higher surface hardness is required, in order to avoid the cracks originated by the presence of the chromium or molybdenum carbides in the alloys. Many different methods have been developed, being the surface coating with suitable intermetallic compounds. Surface coatings based on quaternary intermetallic compounds of the AlSiFeMn type have been successfully developed, taking advantage of the fact that chromium diffuses through the boundary layer of the intermetallic alloy, forming a well developed interface. The coatings obtained possess a high microhardness, apart from being continuous and well matched to the base alloy. This paper presents and discusses the methodology that was implemented to produce such coatings at temperatures in the range of 873 to 1123 K, under an applied stress. The coatings were characterized by the use of microprobe analysis, having determined the compositional effects of diffusion of the multiple elements on the coating quality.