Study Of The Preparation And Performance Of Ni-W-P Platings

Electroless Ni-W-P alloy platings have many advantages such as good wear resistance, corrosion resistance, film thickness uniformity, high hardness and so on. And hence, preparing good performance of Ni-W-P alloy coating becomes a hot topic in recent years at home and abroad. In this experiment, the performances of Ni-W-P alloy coating prepared on stainless steel substrate have been tested by a series of methods such as drip test, the deposition rate, micro-hardness, electrochemistry, scanning electron microscopy and so on.Electroless Ni-W-P alloy coatings were prepared on stainless steel. The sodium tungstate, nickel sulfate, sodium hypophosphite, lactic acid, temperature and other process parameters were studied on the deposition rate of electroless nickel plating layer, the influence of the bit time, the electrochemical properties, etc. The optimum formula acquired by combing with the single factor and orthogonal experiment method are as following: nickel sulfate 35g·L-1, sodium tungstate 15g·L-1, hypophosphite 35g·L-1, ammonium sulfate 30g·L-1, sodium citrate 32g·L-1, malic acid 8g·L-1, lactic acid 15ml·L-1, potassium iodate 2-5mg·L-1, thiourea 1mg·L-1, p H 4.8 to 5.1, temperature 88 ℃, time 1.5 h. The structure of Ni-W-P alloy plating is typical crystalline state with high content of P element(11.9%). The results showed that the corrosion risistance of Ni-W-P alloy plating(drip time 70s) is nearly to Ni-P alloy plating(drip time76s). The performances of the alloy coatings prepared in the optimum condition are as below: the bath life is five cycles and the value of hardness has increased 411.08 HV compared with substract hardness(268.1HV). And at the same time, the value of hardness increased about 117.04 HV compared with Ni-P alloy coatings(562.14HV).The performances of the platings treated under different temperature were tested by the same method. The results show that the structure of the plating change from amorphous state to crystalline state and the hardnesfirst increases and then decreases with the increasing heat treatment temperature. When the temperature reached 400 ℃, the diffraction peak enhanced, the process of crystallizing came to end, the hardness value is 1070.1 HV, and wear is 5.3 mg.The bath life is five cycles; the deposition rate is 11μm·h-1 and the value of hardness 670 HV.