| Abstract:The main goal of the paper discussed preparation methods and mechanism of action for nickel pre-plating, which was appropriate for metal-ceramics complex coating.The experiment tried to prepare35-100μm nickel pre-plating on the surface of GH202alloy by means of electroplating and electro-less. Classical Watts plating bath was chose to Electroplate. After looking up relevant literature and experimental verification, appropriate electro-less solution recipe was ensured. The paper firstly investigated the effects of proportion of complexing agent CH3COONa and NH4C1on electro-less nickel-phosphorus deposition rate, surface morphology and phosphorus content. The change law of Ni2+and H2PO2-concentration in the solution was measured. Secondly, influences of SDS and bias voltage on resistance value in the process of Ni deposition were analyzed. Effects of different temperature on OCP, CV and EIS in the process of electro-less were investigated. And influences of different bias voltage on resistance value in the process of Ni-P electro-deposition were discussed.At last, the experiment prepared metal-ceramics complex coating for analyze mechanism of action and examine using effect of nickel pre-plating. Studied the founding process of glass and structure and morphology features of sintered complex coating. The type of pre-plating was primarily investigated in help of oxidation weight experiment and Vickers hardness test. Interface bonding strength between coating, pre-plating coating and matrix was evaluated by thermal shock experiments. Seriously analyzed the distribution of elements in the sample cross section by DSC. The whole paper could obtain the following conclusion:(1) Both electro-less and electroplating could successfully prepare nickel pre-plating on surface of GH202Alloy.The experiment determined electro-less nickel bath:NiSO4·6H2O80g/L, NaH2PO2·H2O24g/L, CH3COONa-H2O12g/L, NH4C16g/L, H3BO38g/L. The plating thickness could reach35～75μm and P%was around6.11wt%. The electroplating solution used Watts+50mg/L SDS and obtained pure nickel plating, the thickness of which could reach50-100μm.(2) It indicated that with the increase of CH3COONa, the electro-less deposition rate had peak relations and phosphorus content of the coating ranged from6.19wt%to10.45wt%. However, with the increase of NH4CI, deposition rate changed a little and phosphorus content of the coating showed downtrend.(3) With the increase of CH3COONa, quantities and size of cell synthesis on the plating surface apparently reduced. While inner-stress and micro-crack of the plating reduced with the increase of NH4C1. The best proportion of CH3COONa and NH4C1was2:1. With plating time, Ni2+and H2PO2concentration of plating solution gradually reduced, but H2PO2-concentration underspeed was faster.(4) In the electro-less bath, with temperature increased, the OCP turned negative, initial potentials of cathodic reduction obviously turned positive, and systematic resistance value gradually reduced. When temperature was above70℃, the OCP and resistance value observably reduced and lower frequency band of impedance spectroscopy appeared inductance arc. It related with process of nickel deposition.(5) Both SDS and increase of bias voltage could decrease resistance value of nickel deposition by analysis of EIS. When bias voltage was about-0.7V, it had apparently appeared nickel deposition reaction. The bias voltage bigger, the resistance value smaller for Ni-P electro-deposition. When bias voltage increase to about-0.59VSCE, resistance value of Ni-P electro-deposition trended to stabilize. It illustrated depositing reaction began to stabilize.(6) After thermal shock (room temperature-900℃) under uniform conditions, binding force between ceramic coating and different surface: coating-Ni plating>coating-Ni-P plating>coating-GH202alloy. While binding force of Ni plating-GH202alloy and Ni-P plating-GH202alloy could meet requirements. |
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