Tribology of titanium boride-coated titanium balls against alumina ceramic: Wear, friction, and micromechanisms

The tribological performance of titanium alloy (Ti-6Al-4V) balls coated with a dual boride layer comprised of titanium diboride (TiB2) and titanium boride (TiB) whiskers mated against alumina ceramic disks has been determined using lubricated ball-on-disk wear testing. Measurements of coefficient of friction values and volumetric wear were made and electron microscopic investigation of wear spots and tracks was performed. The wear rate of the boride-coated titanium alloy balls was 40 times less than that of 97% dense alumina balls. Measurements of wear track width and depth corroborated this result. The superior wear resistance is attributed to the hardness and the unique structure of the dual (TiB2 + TiB) whisker layer and the consequent smoothness of the wear surface created during the wear process. The material removal mechanism is abrasive in nature in the boride-coated balls compared to grain fracture and pullout in alumina.