| Laser surface alloying (LSA), a process of growing interest for local surface modification, relies upon a suitable composition and microstructure for satisfactory on-the-job performance. The LSA technique was used to form in situ Fe-Cr-C alloys on AISI 1018 steel substrate. In this process Cr powder of different particle sizes were mixed together to get optimum packing density and deposited onto the substrate surface. The surface was then melted by using a 2kw CW CO{dollar}sb2{dollar} laser.; The processing conditions were related to solute (Cr) content, microstructural refinement of the laser alloyed zones as well as the heat affected zone (HAZ). Similarly the existence and the nature of defects such as cracks and porosity in alloyed region are reported. Solute content was of principal concern as it is the single most important factor affecting the properties of laser surface alloys. The effects of varying the laser power, beam diameter, traverse speed and height of Cr powder deposit on the Cr content are reported. Interaction between process parameters are discussed with a simplistic theoretical model. It is felt that such an approach would facilitate selection of processing conditions to obtain reproducibly the compositions and microstructures necessary for gainful utilization of laser surface alloys.; The microstructure of the laser surface alloyed region was investigated by optical, scanning and transmission electron microscopy, and x-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying element. This process produced a fine distribution of complex type of carbide, (M{dollar}sb{lcub}23{rcub}{dollar}C{dollar}sb6{dollar}) precipitate in the martensite-ferrite matrix because of the high cooling rate. An alloy of this composition does not show any retained sustenite phase.; Finally, the nature of alloying and chemical diffusion profile as a function of intertrack separation distance affects the final content of alloying element in surface layer. The ratio of number of laser tracks to width can be optimized to get minimum of cracking, maximum hardness and most uniform alloying of species. |
