Impact of CatalyticMetals on the Ceramic ConversionTreatment of Ti-6Al-2Sn-4Zr-2Mo Alloy

Ti-6Al-2Sn-4Zr-2Mo alloys (Ti6242) offer a high strength-to-weight ratio of up to 550 °C. Ceramic conversion treatment (CCT) is employed to enhance the titanium alloys with a ceramic layer and improve their poor tribological properties. However, longer treatment times and higher temperatures can have detrimental impacts on the materials. In this study, we predeposited various metallic layers like Ag, Au, V, Ag/V, Pd, and Ag/Pd on the surface of Ti6242 samples before CCT to compare their impact on catalyzing the treatment. CCT was carried out at 670 °C for 10 or 120 h. After treatment, the surface roughness/morphology, microstructure, and phase constituents were characterized. Surface hardness and nanohardness depth distribution were measured. Finally, reciprocating sliding tribological tests were carried out to study the friction and wear of the surface layers. CCT at 670 °C for 120 h created a compact oxide layer of less than 1 μm, which entitled the surface to high hardness and good tribological properties before the oxide layer was rubbed away. In a short treatment time of 10 h, vanadium was most effective in encouraging the oxidation of Ti6242, followed by Pd, Au, and Ag. Furthermore, Ag together with V or Pd boosted the growth of the oxide layer additionally. In the meantime, Ag, Pd, Au, and AgPd lowered the friction of the surface oxide layer and enhanced the wear resistance remarkably. In balance, gold helped to convert the surface of Ti6242 into a quality ceramic oxide layer efficiently with better tribological properties.