Microstructure and nanoindentation behaviour of Ni surface modified Ti6Al4V

The Ni modified layers were prepared on the surface of Ti6Al4V substrate by plasma surface alloying technique. The surface and cross-section morphology, composition distribution and phase structure of the modified layers were analysed. Nanoindentation tests were performed not only on the surface and cross-section of the Ni modified Ti6Al4V but also on the substrates of the treated and untreated Ti6Al4V plates. The residual indentation profiles of the Ni modified layers were also investigated. The results show that the Ni modified layers were uniform and compact. The Ni modified layers consisted of an outer Ni deposition layer, a middle Ni rich layer and an inner Ni poor layer. The concentration of Ni gradually decreased from the surface to interior. The maximum content of Ni atoms was nearly 95%. The Ni modified layers were composed of TiNi, Ti2Ni, Ni3Ti, Al3Ni intermetallic compounds and pure Ni as well as Ti phases. Comparing to the untreated Ti6Al4V, the Ni rich layer and Ni poor layer had higher hardness, elastic modulus and remained relatively fine plasticity. The strengthened mechanism of the Ni modified Ti6Al4V was discussed in this paper.