Study On Process And Properties Of Ni-P Coating On TC4 Titanium Alloy

Titanium alloy are widely used because of their advantages such as low density,high specific strength,good corrosion resistance and better biocompatibility.They have been widely used in the automotive,medical equipment and aerospace defense industry.However,the titanium alloy shows poor wear resistance in industrial applications for its surface hardness is low and easy to be oxidized,which greatly limits its application scope,so it is very important to modify the surface of titanium alloys.Ni-P coating because of its simple operation process and the characteristics of good wear resistance and corrosion resistance was used for the modification of metal surface,this paper uses the method of electroplating Ni-P plate on the surface of TC4 titanium alloy for modification to improve the surface properties of titanium alloy.Based on the summary of the preparation technology and research status of electroplating nickel phosphorus,studied the electroplating process of electroplating Ni-P plate on TC4 titanium alloy of nickel hypophosphite system,optimizing the technical formula and the technological parameter by orthogonal experiment,which was obtained as follows: NiSO₄·6H₂O 140g/L ? NiCl₂·6H₂O 16g/L ? NaH₂PO₂·H₂O 8g/L?H₃PO₄ 35g/L?pH 3.5?current density 4A/dm2?temperature 65?.Under this condition of TC4 titanium alloy electroplating Ni-P coating,not only the speed is fast and high hardness,but also the surface of the coating is bright ? smooth and high density.On the basis of orthogonal experiment,the influence of various parameters on the deposition rate,hardness and phosphorus content of Ni-P coating was studied by single factor experiment.In order to improve the properties of Ni-P coating,the surface pretreatment technology of titanium alloy was studied.According to the different pretreatment process under the coating surface morphology,hardness and bonding strength of the comparative analysis,to determine the best pretreatment process: grinding?chemical degreasing?pickling and activation?chemical pretreatment.The coating morphology,phase composition,hardness and wear resistance and corrosion resistance were studied,the results show that the coating surface is a cellular structure uniform,compact and smooth surface,the main components are Ni and P.With the increase of heat treatment temperature,coating by amorphous gradually converted to crystalline structure,heat treatment temperature at 400 ?,the coating of Ni₃P phase precipitation.Coating and P content and heat treatmenttemperature on hardness,coating hardness increased with the increase of P content showed a trend of decrease after the first increase,coating hardness has a maximum value when P content in 8%.The coating hardness with increasing heat treatment temperature increases first and then,after 400 ? heat treatment after coating hardness maximum.Coating wear-resisting corrosion resistance after 400 ? heat treatment significantly enhanced.