Laser alloying of Cu and Cr

Abstract

CuCr multilayers, 0.5−1 /um total thickness, on Cu substrates have been laser irradiated. Threshold energy densities for complete alloying with different laser wavelengths and different multilayer structures were determined using Rutherford backscattering. Results are discussed in terms of absorbance of Cu and Cr as a function of laser wavelength, overall chemical composition, and thicknesses of the individual Cu and Cr layers. Also, x-ray diffraction was used to study the microstructure of the CuCr before and after laser irradiation. A method is outlined for unraveling the contributions to peak shift of stacking faults, stresses, and change in'chemical composition. The CuCr alloy produced by the laser irradiation consisted of small, very defective Cu-rich and Cr-rich crystallites. The CuCr layer was subjected to a high tensile stress. The distinct change in preferred orientation of crystallites on laser irradiation indicated a complete melting of the CuCr multilayer. A high tensile strength (> 935 MPa) of the CuCr before and after laser alloying is suggested by the microstructure as observed by x-ray diffraction and sustained by hardness measurements. In the Cu-rich crystals 4.0 at. % Cr was in solid solution, i.e., five times the maximum equilibrium solid solubility.