Study On Properties And Technology Of Ni-P-SiC Electroless Composite Coating

Titanium alloy is a new kind of structural material, that compared with the traditional steel material or aluminum alloy. It was widely used for its lightweight, high specific strength, especial application in the field of aerospace. There are many different kinds of titanium. For example Ti6Al4 V is the earliest development of titanium alloy and used up to now. Titanium and its alloys possess excellent comprehensive properties. However in some special conditions, the use of the titanium alloys are restricted because of its oxidation and poor wear-resisting.It can change the properties of the surface of the titanium alloys wear resistance by using of electroless nickel plating technology. Electroless nickel plating also can broaden the used scope of the alloys for the Ni-P coating high hardness and excellent corrosion resistance. The wear resistance of the materials have a direct relationship with the apparent hardness. In order to ascension of the surface hardness, this paper discusses the Ni-P-Si C composite coating properties and propagation. By the way of additive insoluble Si C hard particle in electroless nickel plating bath, the Si C particle codeposition with Ni-P coating formation composite coating, to improve the surface hardness.Based on the instability of low phosphorus nickel plating bath, it was the first to be researched that the effect of the stabilizer thiourea. The result is that additive 0.5mg/L thiourea can obtain a more stable bath. The phosphorus content of the Ni-P coating is 3.35%, and it was crystallized face-centred cubic structure. And optimization of low-phosphorus bath formula is: Nickel sulfate: 18~28g/L, Sodium hypophosphite: 20~30 g/L, Complexing agent: 16 ml/L, Complexing agent B: 20ml/L, Accelerator: 1g/L, Thiourea: 0.5mg/L, Ammonia(adjustment p H). conditions: p H =7.0±0.2, plating temperature: 85±2℃, plating loading: 0.5~1 dm2 / L.In order to obtain the stable composite coating properties,the Si C particle should disperse uniformly in the electroless nickel plating bath when the Ni-P-Si C coating deposit. So the dispersion of the Si C has been studied by using the ultrasonic dispersion and high shear separate physical methods. The result as follows: the ultrasonic method, ultrasonic frequency 50 k Hz and time 60 min, Si C particle size distribution range from 0.2 to 0.8μm; High shear method, high shear speed 4500 r/min, time 30 min,Si C particle size range from 50 nm to 100 nm. The effect of the high shear dispersion is better than that of the ultrasonic method.The properties of the Ni-P-Si C coating were detected by Scanning Electron Microscope(SEM), Laser Scanning Confocal Microscope(LSCM), Energy Dispersive Spectroscopy(EDS), X-Ray Diffraction(XRD), respectively. The properties of the Ni-P-Si C composite coating has been studied. The composite coating hardness is 750 HV, and after 400℃ heat treatment,the hardness is 1230 HV. The composite plating bath is as below:low-phosphorus electroless nickel plating and 1g/L Si C additive. The condition is as below: p H =7.0 ± 0.2, plating temperature: 85 ± 2 ℃, stir rate 15r/min,plating loading: 0.5~1 dm2 / L.