Low-friction study between diamond-like carbon coating and Ti-6Al-4V under fretting conditions

Low friction between DLC coating and Ti-6Al-4V alloy was investigated under fretting conditions on a fretting-wear testing machine. The results indicated that, during the beginning period, the Ti-6Al-4V surface was damaged as a consequence of adhesion (and abrasion), leading to high friction coefficients of around 0.5. With the test ongoing, a tribofilm was formed on the rubbed Ti-6Al-4V surface. This tribofilm was derived from the wear product of Ti-6Al-4V alloy with oxidization. Its nano-hardness and reduced elastic modulus were greater than the Ti-6Al-4V matrix. Meanwhile, structural transformation occurred on the rubbed DLC surface. The tribofilm and transformed carbonaceous layer prevented the Ti-6Al-4V alloy and the DLC surface from direct contact and led to low friction coefficients (below 0.2).