SURFACE ALLOYING OF COPPER WITH CHROMIUM BY CO2-LASER

Surface modification of copper using a laser is suggested in the prese nt work to improve strength and wear resistance of pure copper at elev ated temperatures without sacrificing its electrical properties. In pa rticular, Cu-Cr alloyed layers were produced on a pure copper substrat e using a 2.5-kW CO2 laser. By irradiating a laser beam onto chromium powder beds or a plasma spray-coating deposited on the substrate surfa ce, we obtained alloyed layers of thickness 100 to 200 mu m and chromi um concentration of approximately 20 mass.%. Since solid solutions in both chromium and copper have very limited solid solubility, the laser process causes pure chromium particles to crystallize and be finely d ispersed upon rapid cooling. The alloyed layers were strengthened by d ispersing the particles. The layers had relatively high hardness, abov e 120 Hv in most cases, in comparison with 60-70 Hv for pure copper ha rdness at room temperature. The hardness of the alloyed layers was thr ee to four times that of pure copper at 873 K. Thus, forming an alloye d layer appears to be a promising method to improve the strength and w ear resistance of copper at elevated temperatures.