Ni-Co-P/Si3N4 electroless composite plating and its hardness
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Abstract:
Ni-Co-P/Si3N4 composite coating on Al alloy is prepared by electroless composite plating in order to improve the minohardness of Al alloy. The influence of electroless plating process parameters on the micro-hardness of Ni-Co-P/Si3N4 coating on a hyper-eutectic Al-Si casting alloy is studied by an orthogonal experiment. The effects of process parameters, such as pH and mole ratio of Co 2+/（Co 2+ +Ni2+）,Si3N4 concentration in electroless plating bath and plating temperature,on the micro-hardness of composite layer are obtained. It is indicated that the hardness of coatings can be increased by increasing pH, plating temperature,Si3N4 concentration and keeping mole ratio of Co2+/（Co 2+ +Ni2+）moderate. Moreover, the influence of heat treatment on the micro-hardness of coatings is also investigated. It is found that the hardness of films increases with the heat treatment temperature rising below 400 ℃ but decreases when temperature is over 400 ℃.
