Two-phase Flow Simulation Of Ni-P-Diamond Electroless Composite Plating And Study On Its Plating Techniques

Electroless Composite Plating (ECP) is a kind of surface treatment technology, which is carried out by adding functional inert particles to electroless plating solutions, leading to the inert particles co-deposited with Ni-P alloy to gain differently physical and chemical performances of platings. Since specific surface area of nano-particles is so large that nano-particles agglomerate easily during the plating process, so it is necessary to study the distribution and dispersion of nano-particles in ECP solutions in order to improve the quality of platings.In this paper, Firstly, fluid mechanical model was established based on traditional stirring method of electroless plating. Computational Fluid Dynamics (CFD) method was taken to analyse the distribution properties of particles in the plating solutions and the effect of stirring speed and size of particles on the distribution of particles. Then, structure of plating tank was optimized and fabricated. By adopting optimized bath and orthogonal experiment design method, the influence of diamond concentration, species and concentration of surfactants, and stirring speed on the properties of ECP with explosive detonation nano-diamond was studied. Single-factor method was also used to study the influence of stirring speed on deposition speed of composite plating and the influence of concentration of diamond particles on the wear resistance of composite plating. TEM, SEM, XRD, microhardness tester and rub tester, and so on, were employged to analyse the distribution of diamond particles in the plating solutions, surfical morphologies of the composite platings, microstructures, microhardness, abrasion resistance and the effect of heat treatment on the microstructure of platings.Results obtained from CFD nerical simulation are as follows:1. Inert particle size has obvious effect on its distribution in plating solutions—the distribution uniformilty of particles decreasese with the increase of its size, while, the effect of stirring speed on particle distribution is also obvious—particles distribute more uniformly in the solution when stirring speed increases.2. After adding a set of baffle into the bath, the uniformity of velocity field in plating bath increases efficiently, turbulence in plating solution diffuses considerably, turbulence intensity and reynolds shear stress increases, and the unifority of fine particles in plating solution improves greatly.Results obtained from ECP experiment are as follows:1. The optimal parameters for the ECP with nano-diamond are: the concentration of diamond being 6g/L, with SHP 1:10 and stirring speed about 450rpm when the average flow speed of palting solution 0.1m/s and onflow intensity 4%.2. When the stiring speed increases from 0 to a large value, the deposition speed firstly increases and then decreases in Ni-P deposition, while the deposition speed decreases with the increase of stirring speed in Ni-P codeposition with nano-diamond even when stirring speed is very high.3. The hardness of the composite plating increases with the diamond concentration in the plating bath, while abrasion resistance improves with the increase of the diamond concentration only in a certain range.