Preparation And Properties Of Ni-based Self-lubricating Coating On Mold Copper Plates

In order to solve the problem of surface wear,thermal shock cracks and low life in the continuous casting mold manufacturing process,a composite coating structure with a bonding layer and a working layer was designed,and Al-Ni material was selected as the bonding layer,Ni-C and Ni-BN materials were used as the working layers.Ni-C and Ni-BN self-lubricating coatings were fabricated on the surface of Cr-Zr-Cu substrate by using supersonic plasma spraying.The bonding strength and microhardness of the coatings were evaluated,and the thermal shock resistance of the self-lubricating coating at different temperatures was studied.The friction and wear properties of the self-lubricating coating under different loads and different temperatures were studied.The wear mechanism and lubrication mechanism of the self-lubricating coating under different test conditions were revealed,and the formation mechanism of the lubrication film during the friction was clarified.Ni-C and Ni-BN self-lubricating coatings prepared by supersonic plasma spraying technology could be well combined with the Cr-Zr-Cu alloy of the mold copper plate material.The two self-lubricating coatings have low microhardness and good thermal shock resistance.Under different loads,the wear mechanism of Ni-C coating is mainly based on abrasive wear,and mainly based on the lubrication of graphite.Ni-C coating exhibits lower friction coefficient and wear mass.As the load increases,the coefficient of friction increases significantly.It is possible to solve this problem by reducing the size range of Ni-C powders.Nickel oxide is easily generated around the graphite phase of Ni-C coating at room temperature under the same experimental conditions.The friction coefficient of Ni-BN coating is higher than that of Cr-Zr-Cu substrate at room temperature,but its wear quality is lower than that of Cr-Zr-Cu substrate,and the friction and wear properties of Ni-BN coatingsare poor at room temperature.In the high temperature test conditions,although the friction coefficient of Ni-C coating increases,it is still smaller than the friction coefficient of Cr-Zr-Cu matrix at room temperature,and the wear mechanism changes from abrasive wear to oxidative wear,and nickel oxide is the main lubricant.The friction coefficient of Ni-BN coating decreases obviously at high temperature,and the wear mechanism is different between the center of the grinding groove and the edge of the grinding groove.The center of the grinding groove is mainly oxidation wear and nickel oxide plays a major role in lubrication,the edge of the grinding groove is dominated by abrasive wear,and the BN phase plays a major role in lubrication.The mechanism of the lubricating film during the friction process of the self-lubricating coating include four stages: The first stage is the lubrication phase exposure stage.Friction surface forms a discontinuous lubrication film in the second stage.In the third stage,a continuous lubricating film is generated on the friction surface,and lubrication plays a major role in lubrication.In the last stage,the friction surface is heavily oxidized,nickel oxide covers the lubricating phase,hindering the formation and spreading of the lubricating film,and oxide plays a major role in lubrication.Ni-C and Ni-BN self-lubricating coating prepared by supersonic plasma spraying technology can significantly improve the wear resistance of Cr-Zr-Cu alloy.The coating has good thermal shock stability.This study can provide new ideas and practical basis for surface treatment of mold copper.