The Preparation And Properties Of Surface Protective Coatings For NdFeB Protection

Owing to the outstanding magnetic properties,sintered NdFeB magnets have become the most compelling magnetic materials,and are widely used in the fields of electronics,electrical devices,medical equipment and aerospace,etc.However,the magnets have to be coated with an anticorrosive coating by electroplating for protection in usual industrial manufacturing due to their poor corrosion resistance.In recent years,with the increasing concerns on environmental protection and emissions in China,magnetron sputtering is considered as a potential substitute for the electroplating process due to its environmentally friendly feature and good coating adhesion.Al coatings prepared by magnetron sputtering have good anticorrosion properties but poor mechanical properties which affect the service life of NdFeB magnets.It is thus important to investigate the magnetron sputtering method for protective coatings of NdFeB and improve the mechanical properties of Al coatings with the implications to promote the application of magnetron sputtering for magnet protection.This paper mainly investigates the preparation of Al and Al-Ti coatings by ion beam assisted deposition(IBAD)via magnetron sputtering.The effects of ion beam,bias voltage,deposition process,sputtering power,etc.on the coating structure,mechanical properties and electrochemical properties are studied.The IBAD-Al-Ti alloy coatings are prepared with Ti contents from 1.2 to 8.9 at.%,and the effects of Ti content on the structure,hardness,wear and corrosion properties of Al coatings are discussed.The results show that the bias voltage has a grain refinement effect on Al grains,and ion beam assisted deposition can promote the structural transformation of the coating from columnar grains to equi-axed gains as well as the coating density increase and defect reduction.The IBAD-Al coating obtains a corrosion current density of one magnitude order lower than that for bare NdFeB,exhibiting a better anti-corrosion property,while it has a hardness of 0.7 GPa.A dense,homogeneous and well-bonded Al-Ti coating is achieved through ion beam assisted co-deposition of Al and Ti targets at a rotation rate of 8r/ min for the sample plate with an ion beam power of 150 V × 1A.With the increasing Ti content,the coating becomes denser and its grain size decreases.The SEM and TEM results show a uniform structure of Al-Ti solid solution for the coating while some Ti segregations are inspected with the increase of Ti content.Also,the hardness and wear property of coatings has been significantly improved with the increase of Ti content.When Ti content reaches 4.3at%,the hardness of Al-Ti coating is four times than that of pure Al coating.The polarization curves and EIS results show that the corrosion resistance of the Al-Ti coatings has also been improved compared with the pure Al coating.The optimum corrosion resistance of the Al-Ti coating is obtained when the titanium content is 4.3at%.