Study On The Preparation And Properties Of Boron Carbide Films On The Gear Surface

Due to the superior mechanical and tribological properties of boron carbide thin films, it is hopeful to be a new kind of solid lubricant film and has the potential applications in the field of surface engineering such as being a protection coating for the gear.Magnetron sputtering is a common physical vapor deposition method, which has been extensively applied to the preparation of the films because of its numerous advantages, for example, it has more simple operation process, faster deposition speed, lower substrate temperature, better adhesion strength, denser film structure and lower internal stress.In this paper, boron carbide films were deposited on the gear steel(38CrMoAl) surface by closed-filed unbalanced DC magnetron sputter technique through adjusting the substrate negative bias, graphite target current and boron carbide target current. Moreover, the microscopic structure, mechanical and tribological properties of boron carbide films were characterized using scanning electron microscope(SEM), transmission electron microscopy(TEM), atomic force microscopy(AFM), X-ray photoelectron spectroscopy(XPS), X-ray diffraction(XRD), Raman spectroscopy(Raman), Nano indentation tester and tribo-meter, and the preparated amorphous boron carbide films in this experiment had good mechanical properties and excellent tribological properties.The main conclusions of paper as follows:(1) The mechanical properties of boron carbide films is greatly influenced with the substrate negative bias, as the bias is increased, the hardness, elastic modulus and adhesion strength of films increases first and then decreases, and the internal stress of films had the reverse effect. However, the tribological properties of boron carbide thin films are hardly affected by the substrate bias voltage.(2) The thickness, structure and properties of boron carbide films, especially the tribological properties can be significantly improved through sputtering boron carbide target together with graphite target.(3) The BCx/a-C films possessing columnar structure, compact and amorphous microscopic structure, excellent mechanical properties and tribological properties, which have been prepared successfully when the current of graphite target and boron carbide target are 3.5A and 0.5A. The adhesion strength, hardness and elastic modulus of films were 60 N, 15.7GPa and 195 GPa, respectively. Additionally, the friction coefficient of stable stage is lowed to 0.05, and the wear rate of films is as low as 5×10-8mm-3N-1m-1.(4) The BCx/a-C films exhibit great thermostability through the high temperature soaking in lubricant oil and cyclic thermal shock experiment. However, the reliability of films need to be improved in start and stop test under dry friction condition.(5) The BCx/a-C films possess better mechanical properties and more prominent tribological properties comparing to Cr/a-C films, especially BCx/a-C films exhibit excellent wear resistance in the high temperature environment.