THE MICROSTRUCTURE AND MICROCHEMISTRY OF A THERMAL-DIFFUSION-BORONIZED CO-CR-W-C ALLOY

The microstructural and microchemical properties of a commercially produced, diffusion-boronized layer deposited over a wrought Co-Cr-W-C alloy have been investigated using several analytical techniques, including scanning electron microscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy and rotating-anode X-ray diffraction. Application of these analytical techniques revealed the presence of a complex and compositionally graded coating consisting of at least three distinct regimes: (1) an outer region containing either pure boron and/or B4C, (2) an intermediate region comprised of several probable stoichiometries, constituents and crystal structures, and (3) a rather diffuse and dilute, boron-containing transition region between the coating and the substrate. X-ray diffraction techniques suggest that the compounds of CrB and Co2B were present in significant concentrations. Furthermore, chromium-rich M7C3 carbides which resided in the boronized region were found to transform during the diffusion process into a borocarbide compound, quite probably having the Cr7BC4 stoichiometry.