Unlubricated sliding wear behaviour of nickel diffusion-coated Ti-6Al-4V☆

Abstract Electroless Ni-P alloy was deposited on to a commercial Ti-6Al-4V substrate and diffusion treated at 1123 K for 7 h. The structure of the coating consisted of five layers. The outer three layers were composed of various intermediate phases and of these the outermost layer was shown to be a mixture of Ni 3 Ti, Ti 1.7 P, Ni 3 P and Ni 5 P 2 , the hardness of which was about 900 KHN. The fourth layer was the transformation product of the β phase, which was formed at the diffusion temperature owing to the penetration of nickel, causing the original α + β aggregate to be transformed to a single-phase β material. An analysis of the layers is given. Unlubricated sliding wear tests were performed in air using upper and lower disk-shaped specimens both rotating in the counter-clockwise direction with a relative sliding velocity of 0.6 m s −1 and loads of 2.5–5 kgf. Coated and uncoated specimens were tested against a counterface made from heattreated 52100 steel. The wear rate of the coated specimens was significantly lower than that of the uncoated specimens. Examination of the wear tracks, wear debris and subsurface structure indicated that these two materials wear by entirely different mechanisms.