Of Az91 Magnesium Alloy Surface Of Diamond-like Carbon Films, Structure And Performance

Magnesium alloys are very prospective materials for applications in the automotive, communication and aerospace industry. However, the poor mechanical strength, the poor corrosion and wear resistance restrict their practical application. The protective hard coatings with excellent wear and corrosion resistance on the magnesium alloys are one of the most effective ways to overcome the drawbacks and enhance the performance for the magnesium alloy surface. Diamond-like carbon (DLC) film with high hardness, low coefficient, excellent wear and corrosion resistance is a promising function protective material.In this paper, the DLC films and titanium doped DLC films were deposited on AZ91Mg alloy surface by arc ion plating (AIP) in Ar gas atmosphere and different pulse bias voltage. The morphology, composition and microstructure of the deposited DLC films were characterized by scanning electron microscopy (SEM), atom force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS).The hardness, elastic modulus, friction behavior, thermal stability and corrosion resistance property of the DLC films were investigated.The results show that the dense and well adherent DLC films were successfully deposited on AZ91 magnesium alloy surface by AIP. The pulse bias voltage can affect the morphology and microstructure of the deposited DLC films. The sp3 bond content of the DLC film deposited in Ar gas atmosphere and-100V reached the maximum value up to 33.32%. Further increasing the pulse bias voltage, the ID/IG increases and sp3 bond content decreases.The hardness and elastic modulus of the deposited DLC films on AZ91 magnesium alloy are determined by sp3 bond content, the high sp3 bond content resulting in high hardness and modulus of the DLC film. At the deposition conditions of-100V and Ar gas atmosphere, the hardness and elastic modulus of DLC film both reached a maximum value of 28 and 300 GPa when the sp3 bond content was 33.32%.The shallow wear track and the friction coefficient as low as 0.14 measured by experiments indicated that the DLC film prepared by AIP is an ideal wear resistance material and can significantly improve the wear resistance of AZ91 magnesium alloy. Furthermore, the friction coefficient of DLC films varied with tribological conditions and deposition conditions. The high sliding velocity and low sp2 carbon bond content can result in low friction coefficient of DLC film. The low friction is related with the formation of transfer film during the friction process. The equilibrium corrosion potential of AZ91magnesium alloy can be improved from-1.59V to-1.53V by depositing DLC films on its surface, and titanium doping into DLC film can further enhance the corrosion resistance of AZ91 magnesium alloy. The microstructure of the DLC films exhibits good thermal stability when DLC films were annealed in atmospheric environment from 200 to 400℃.The results of vacuum annealing show that sp3 bond of DLC film changes into sp2 bond when the temperature is higher than 500℃, and leading to the graphitization of the DLC film.