Microstructures of Al coatings prepared through magnetron co-sputtering with microcrystalline Ti doping

Abstract

Sintered NdFeB magnets are being utilised in numerous applications because of the excellent magnetic properties. However, due to its main components are Fe, B and rare earth metals. There is a potential difference between the neodymium rich phase, boron rich phase and the main phase, which was very easy to form a primary battery and cause electrochemical corrosion on the surface of the material. After the materials are easy to be corroded or the components and structures change, the performance of the materials will become weak or even lost, which will affect the service performance and life of the devices or equipment. According to the requirements of surface protection technology for NdFeB magnets, the preparation of protective coating by magnetron sputtering was an efficient means to enhance the corrosion resistance of magnets. Pure Al coating was deficient in microstructure, hardness and corrosion resistance, and the preparation of composite coating by doping co-sputtering had become a development trend. In the current work, AlTi coatings with various Ti contents were prepared from an Al target and a Ti target using direct and radio frequency hybrid magnetron co-sputtering. The surface morphology, microstructure, and elemental compositions of the AlTi coatings were explored through XRD (X-ray diffraction), SEM (scanning electron microscopy), and EDS (energy dispersive spectroscopy). The anticorrosion performances of the AlTi coatings were evaluated by performing electrochemical tests. According to SEM and EDS, the AlTi composite coating was denser and more homogeneous than that of the Al single layer. Furthermore, the results demonstrated that microcrystalline Ti doping reduced the grain size of Al coatings. Therefore, the corrosion current density of the sintered NdFeB magnets plated with Al(120w)/Ti(10w) was approximately more than a hundred times inferior to that of the pure Al layer, and the hardness of AlTi composite coatings also improved.