THE INDENTATION AND WEAR PROPERTIES OF A THERMAL-DIFFUSION-BORONIZED CO-CR-W-C ALLOY

Vickers and ultralow-load indentation and unlubricated sliding wear properties of a commercially produced, diffusion-boronized layer deposited over a wrought Co-Cr-W-C alloy have been investigated using both commercially available and custom-built instruments. Cross-sectional micro- and ultralow-load indentation measurements using commercially available Vickers and mechanical properties microprobe (MPM) apparatus respectively, demonstrated the extreme hardness of the diffusion layer; the latter technique produced an elastic modulus maximum of 420 GPa. Typical modulus values were found to depend on the coating microstructure and measurement depth beneath the free surface and ranged from 366 to 410 GPa. Vickers microhardness measurements of the boronized layer yielded an average hardness value of 3200 kg mm-2 (31 GPa), compared with a maximum MPM hardness of 38 GPa at a depth of 6-mu-m beneath the free surface. The presence of the boronized layer resulted in great improvements in the unlubricated sliding wear performance against monolithic Al2O3, reducing the extent of wear attributable to the mechanisms of abrasion and adhesion through increases in hardness and modifications to the surface chemistry and structure respectively.