Preparation And Performance Of Plasma Ni-alloyed Layers On Ti6Al4V Alloy Surface

Titanium alloys are widely used in the aerospace, automotive industries dueto its low density, excellent strength to weight ratio and high corrosionresistance. However, its lower hardness and poor wear resistance limit theapplication in erosion-wear condition. Therefore, the surface modification is oneof the effective methods to improve its performance. Using double glow plasmaalloying technique, the Ni alloyed layers were prepared on the surface ofTi6Al4V alloy. The plasma surface alloying process is optimized by analyzingthe effects of the processing temperature and pressure on the formation of Nialloyed layers. The surface and cross-section morphology, compositiondistribution and phase structure of the Ni alloyed layers were analyzed. Thenanoindentation behavior and erosion-wear property of Ni alloyed layers werestudied. The main research results are as follows:(1) A fine, compact Ni alloyed layers can be fabricated on Ti6Al4Vsurfaced by double glow plasma alloying technique. The process parameterswere optimized, which are temperature930℃, pressure35Pa, alloying time3h,voltage difference250V.(2) The surface of Ni alloyed Ti6Al4V demonstrates nodular units’morphology and its roughness increased. The Ni alloyed layers are triple layer structures. From the surface to the matrix, there are Ni deposited layer, Ni-richlayer and Ni-poor layer. Along the thickness direction, the concentration of Nielement presents three platforms and displays gradient layered distributions. TheNi alloyed layers are mainly composed of Ti, Ni, Ni3Ti, Ti2Ni, NiTi and AlNi3.The elemental Ni formed in Ni deposition layer and the Ni3Ti, Ti2Ni and NiTi inNi-rich layer.(3) The mechanical property and the erosion resistance of the Ni-rich layerhave improved obvious, and that of Ni-poor layer have little improved, but thatof Ni deposited layer and pitted area of Ni element have got worsen. So thethickness of Ni deposited should be as thin as possible.(4) Under different loads and angles conditions, Ni alloyed layers presentplastic erosion characteristics mainly. The erosion wear mechanism is mainlymicro-cutting, plough and crater wear.(5) The erosion angle influents the erosion resistance of Ni alloyed layersobvious. With the angle increasing, the erosion rate increases and the maximumwas got at90°.(6) The microstructure and mechanical property of Ni alloyed layers have abig influence of its erosion resistance. It is advantage to improve the erosionresistance of Ni alloyed layers that high values of H/E and H2/E3and largecontents of Ni3Ti, Ti2Ni and NiTi.