Laser surface alloying of copper with chromium - I. Microstructural evolution

Laser surface alloying (LSA) of Cu with pre-deposited Cr has been carried o ut using a high pou cr continuous wave CO2 laser. Following LSA, the surfac e microstructure and composition have been correlated with the laser proces sing parameters. It is found that a judicious selection of laser power dens ity (Q) and scan speed (v) (or interaction timet t(i)) is essential to obta in a defect-free and uniform alloyed zone (AZ) for a given pre-deposit thic kness (t(z)). The AZ-depth is directly related to Q and t(i). Microstructur ally, the AZ consists of dispersed Cr-rich particles in the Cr-alloyed Cu-r ich solid solution. Rapid quenching in the present LSA routines has extende d the solid solubility of Cr in Cu to about 4 at.%. The total Cr content in the AZ varies inversely with Q and t(i) for a given t(z). Finally, a proce ss optimization diagram has been constructed to predict the microstructure and composition of the AZ for the present system for different conditions o f LSA. (C) 1999 Published by Elsevier Science S.A. All rights reserved.