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

Laser surface alloying (LSA) of Cu with pre-deposited Cr has been carried out using a high power continuous wave CO2 laser. Following LSA, the surface microstructure and composition have been correlated with the laser processing parameters. It is found that a judicious selection of laser power density (Q) and scan speed (v) (or interaction time, ti) is essential to obtain a defect-free and uniform alloyed zone (AZ) for a given pre-deposit thickness (tz). The AZ-depth is directly related to Q and ti. Microstructurally, the AZ consists of dispersed Cr-rich particles in the Cr-alloyed Cu-rich solid solution. Rapid quenching in the present LSA routines has extended the solid solubility of Cr in Cu to about 4 at.%. The total Cr content in the AZ varies inversely with Q and ti for a given tz. Finally, a process optimization diagram has been constructed to predict the microstructure and composition of the AZ for the present system for different conditions of LSA.