Effect of Phosphorous Content on Microstructure and Wear Resistance of Electroless Ni-P Alloy Coatings on Titanium Alloy

Ni-P alloy coatings with different P contents were successfully prepared on the surface of TC4 titanium alloy by making use of electroless plating technology.The morphology and microstructure of as-prepared Ni-P alloy coatings were analyzed by scanning electron microscopy,energy dispersive spectrometry and X-ray diffraction.Furthermore,the hardness as well as wear mass loss and friction coefficient of as-prepared Ni-P alloy coatings was measured in relation to the effect of P content,and the wear mechanism of the alloy coatings was discussed.It was found that the amount of hump-like structure and grain boundary of Ni-P coatings gradually decreased with increasing P content,and the size of the grains gradually increased therewith,which was accompanied by crystal to amorphous transformation.Besides,the hardness and friction coefficient of the alloy coatings declined with increasing P content,and their wear mass loss rose therewith.In the meantime,as-prepared electroless Ni-P coatings with low P contents were dominated by abrasive wear and mild adhesion wear,while those with moderate and high P contents were dominated by severe adhesion wear and abrasive wear.