Microstructural evolution during tempering of arc-evaporated Cr-N coatings

The thermal stability of are-evaporated Cr-N coatings has been investigated as a function of incident ion energy via tempering experiments. Coatings were grown onto high-speed steel substrates at two bias voltages, 50 and 300 V, and examined using x-ray diffraction, transmission electron microscopy, and Auger electron spectroscopy. A significant reduction in the as-deposited lattice defect density, accompanied by the formation of equiaxed grains, was observed after tempering the coatings slightly above the deposition temperatures. Phase evolution was also observed during tempering, characterized by beta-Cr2N phase formation above a time-dependent temperature, which suggests that a nonequilibrium excess of CrN1-x(x approximate to 0.17) was formed during growth. The apparent activation energy, Q, for defect relaxation was determined to be approximately 2.7+/-0.3 eV in the 50 V coating, which is in good agreement with published values for bulk diffusion of N in CrN. In the 300 V coating, however, Q was found to increase from 1.7+/-0.3 to 3.1+/-0.3 eV with decreasing defect concentration. These results are discussed in terms of different defect populations formed as a function of incident ion energy during deposition, and corresponding defect-mediated diffusion. (C) 2000 American Vacuum Society. [S0734-2101(00)01401-9].