Thermal oxidation of a porous Ti[sbnd]23Nb alloy for wear related biomedical applications: Effect of oxidation duration.

In this study, an attempt has been made for tailoring the surface features of an 18 vol% porosity containing Ti 23Nb alloy manufactured via powder metallurgy method. The aim was enhancing the wear resistance without sacrificing the mechanical properties. For this purpose, porous Ti 23Nb alloys having hardness of 280 HV 0.025 were subjected to thermal oxidation (TO) at 600 °C in air for two different holding times. TO duration of 6 h, which introduced a ~ 0.5 μm thick TiO 2 -rutile type exterior oxide layer (OL), provided surface hardness of 620 HV 0.025. Extension of TO duration to 60 h caused covering of the surfaces with a ~ 3.0 μm thick OL and increase of surface hardness to 980 HV 0.025. As the result of the increased surface hardness, TO'ed. alloys showed superior sliding wear resistance coupled with a reduction in friction coefficient (COF) against alumina ball in 1.5× simulated body fluid (SBF) when compared to the as-sintered state. Despite having the highest surface hardness, the alloy TO'ed. for 60 h exhibited slightly higher wear loss and COF than the alloy TO'ed. for 6 h. More important than this, the alloy TO'ed. for 60 h collapsed at a compressive stress well below the yield strength of the alloy TO'ed. for 6 h, which exhibited almost similar compressive stress-strain curve with that of the as-sintered alloy. From this perspective 6 h appeared as a promising TO duration for the examined porous alloy to be used in biomedical applications as it preserves the mechanical properties while providing remarkable enhancement in the wear resistance. [Display omitted] • Surface hardness of 18 vol% porosity containing Ti 23Nb increased upon TO • Wear resistance is remarkably increased after TO at 600 °C in air for 6 and 60 h • TO duration of 60 h dramatically reduced the compressive strength • TO of 6 h provided the lowest wear rate and COF without sacrificing strength [ABSTRACT FROM AUTHOR]