Wear Resistance of Titanium Boride Coated Titanium Alloy Against Alumina

There is considerable interest in developing a hard and durable surface layer on the surfaces of titanium components for biomedical applications. One potential surface layer is a double layer coating (consisting of a monolithic TiB2 layer combined with a TiB whisker layer) which can be formed on Ti and titanium alloys. In this work, the wear and friction properties of titanium alloy (Ti-6Al-4V) ball bearings with such a double layer coating mated against alumina has been determined using ball-on-disk wear testing. The behavior was compared to that of a 97% dense alumina ball. The friction and wear volume were measured using a load cell and optical measurement of wear spot diameters, respectively. The wear mechanisms were determined using scanning white light interferometry (SWLI), optical microscopy, and scanning electron microscopy (SEM). The bonded balls showed a 40-fold reduction in wear compared to the alumina balls and showed slightly lower friction values. The superior wear properties are attributed to the hardness and unique structure of the double layer TiB2 + TiB coating and the subsequent smoothness of the wear surface that emerges during wear testing. The wear mechanism was determined to be abrasive in nature for the boride coated balls, whereas the alumina balls exhibited grain fracture and removal.