Research On The Process Of Electroless Ni-P And Performance Of Coating On Cr12MoV

With the rapid development of die industry, the requirements for higher quality and longer using life for dies have been put forward. Cr12MoV is extensively used material of cold working die, it has an excellent property of wear resistance, but wear failure is still main failure form in the using process. Therefore, it is necessary to improve the anti-wear properties of the cold-working steels by various surface engineering technologies for the purpose of decreasing cost and enhancing life of working dies. Electroless nickel plating have many advantages such as simple operating technics, good shape imitated property, high-hardness, good corrosion and wear resistance, it has been widely used in many fields such as petroleum, chemical, aerospace, electronics components, automobile and so on. So electroless nickel plating will become an effective surface treatment method that improved anti-wear performance of working dies.The effects of different pretreatment processes on surface morphology of Cr12MoV and coating, hardness and combining strength of coating were systematically studied in this paper. On the base of single factor experiment and orthogonal experiment, the formulations and processes of electroless plating on Cr12MoV were obtained. The effects of heat treatment on organization and performance of coating were investigated. In addition, the effects of tribological parameters on antiwear properties of the coating and the wear mechanisms under the different conditions were systematically studied. There are some important conclusions listed as follows:(1) The pretreatment processes played an important role in obtaining high quality surface of coating, particularly acid washing and activated processes. The better the surface of Cr12MoV by pretreatment processes, the coating was more compact, and had higher hardness and higher binding strength. to Cr12MoV steel. The optimized process is listed as follow: acid washing (15ml/L HNO3, 12ml/L HF, the acid time is one minute), activated liquid (8g/L NH4HF2, 18g/L C7H6O6·2H2O, 25℃, the activated time is 30 seconds).(2) The optimal plating parameters in high phosphorus electroless nickel plating were gained by single factor experiment and orthogonal experiment: NiSO4 30g/L, NaH2PO2 30g/L, PH 4.7, C3H3O3 20mL/L and NaAc 16g/L.(3) With an increasing of heat-treated temperature, the coating gradually changed from non-crystal structure to crystal, the hardness of coating firstly increased, and then decreased while attaining the biggest value. The temperature for attaining the highest hardness value is 450℃, and the hardness value is 986HV, which increased 227 HV comparing with the heat-treated Cr12MoV.(4) Electroless plating Ni-P alloy coating after heat treatment had smaller coefficient of friction and better anti-wear ability than Cr12MoV steel after heat treatment. The experiment results showed the wear volume of the coating was one thirteenth of Cr12MoV steel.(5) Load, sliding velocity and wear time were very important factors that affected anti-wear performance of coating. Wear volume increased with an increased of load, and the wear mechanisms changed from abrasive wear to adhesive wear and abrasive wear with an increase of load. Wear volume increased with an increased of sliding velocity, and the wear mechanisms changed from abrasive wear to oxidative wear, adhesive wear and abrasive wear with an increase of sliding velocity. Wear volume increased with an increased of wear time, but the increased extent continuously decreased; the wear mechanisms changed from the mixture of adhesive wear and abrasive wear to abrasive wear with an increase of wear time.