Fabrication and characterization of TiB2/TiC and tungsten co-sputtered wear coatings

Co-deposited thin films of titanium carbide (TiC)/titanium diboride (TiB2) and tungsten (W) were fabricated using magnetron sputtering under conditions of varied working gas pressures and with different W metal concentrations. Coatings were characterized using scratch adhesion, indentation and sliding wear tests. Films exhibited very good adhesion with critical scratch adhesion values from 50 to 70 N, with slightly higher values measured for W-containing films. Observations from Rockwell C-Brale indentations, to compare relative toughness, suggest that adding a moderate amount (from 16 to 22 at.%) of W to the TiC/TiB2 coatings reduced the damage diameter around the indentations and resulted in a less severe cracking mode (fine radial cracking observed for W-containing films). This suggests that TiC/TiB2/W coatings have higher coating/substrate interfacial toughness than pure TiC/TiB2 coatings. Nanoindentation of the TiC/TiB2/W coatings resulted in hardness values in the range of 20–30 GPa, with higher values for coatings with higher W content. Reciprocating sliding wear tests were performed on the coatings using a tungsten carbide–cobalt (WC–Co) ball counterface. At a lower initial stress of 1.33 GPa, addition of W to the TiC/TiB2 matrix resulted in higher wear factors, whereas at a higher initial stress of 1.91 GPa, W-containing TiC/TiB2 films had lower wear factors than for the pure TiC/TiB2 coating. This behavior suggests a load (or stress) sensitive wear performance.