Wear Resistant Coatings Prepared By A Combined Cathodic Arc-magnetron Sputtering Technique

With the development of high performance thrust-weight ratio and large-scale aero-engines, solving the problem of wear and abrasion at high load conditions is increasing urgent. Diamond-like carbon coating has become the preffered material to solve the wear problems in military products due to the advantages of low friction, and high performance in wear resistance. But the monolayer structure of diamond-like carbon coating is prone to fracture, peeling off and then failure when used under high load,which is due to the poor bearing ability, the large internal stress and the poor adhesion between the coating and the substrate. In order to solve this problem, the solutions abroad is through constructing bonding layer (metal layer)+bearing layer (wear-resisting layer)+lubricating layer (diamond-like carbon coating) in the wear-resistant lubricating coating system. By building the functional gradient multilayer structure of bonding layer and supporting layer, it can realize the gradient change in composition and microstructure of the coating system along the growth direction of the coating, also it can improve the coating-substrate cohesion and load bearing ability of the coating significantly. On the other hand the international development trend of coating preparation technology is moving in large-area processing, composite processing and high quality of surface. Based on the backgroud, the paper firstly study the combined cathodic arc and magnetron sputtering technology, we try to solve the problem in large-area burning and controlling of the burning ablation trajectory. Then we combined the steered arc technique with the medium frequency magnetron sputtering technique, so as to realize large-area processing and high quality of surface processing. On the basis of above, we prepared the composite diamond like carbon coatings with high bearing capacity by constructing the coating system of adhesive layer+bearing layer+lubricating layer. This paper mainly includes the following parts:(1) First by designing the programmable coil power and using of the perturbation effect on the magnetic field produced by the coils, we optimized the structure of large area rectangular steered arc target (size of430mmx125mm), also achive the controllable of the ablation trajactory of the arc target according to a scanning type, which makes the target ablation uniformly and also greatly increasing the utilization of the target; Then we combined the steered arc target and the medium frequency magnetron sputtering to the same device in order to meet the demand for preparation of coatings with multilayer structure. For the combined equipment, the deposition enviroment is characterized by magnetic field testing and simulation and testing plasma density. Results show that the uniformity of plasma density is good for the combined equipment, the plasma density when the composite sources working is8.98×10/cm3, which is significantly higher than that of a single source working, the effective working area with plasma density larger than1011/cm3in the chamber isφ400×450mm2.Use the composite sources device, we prepared titanium nitride coatings by4different techniques, including the cathodic arc deposition, cathodic arc deposition after magnetron sputtering deposition, cathodic arc and magnetron sputtering co-deposition, magnetron sputtering deposition. Through the analysis of the surface and cross-section morphologies of the coatings, it can be seen that compared to the coating deposited by cathodic arc, the surface quality is obviously improved (with the roughness of0.056μφ) by the arc combined magnetron sputtering technique, at the same time, the organization structure has no columnar characteristics, instead it displays a compact laminated structure. Grinded at400N and WC for the contact ball, the coating deposited by the combined arc and magnetron sputtering technique has the longest wear-life,116s. This is maily due to the sample (also the sample holder) rotation during the deposition process allows the alternative deposition of the sample by arc target and the magnetron sputtering target, and which also allows the two techniques play a complementary role. All this make the coating exhibits the layered compact structure, and this type of structure is conducive to improve the wear resistance capability of the coating under high load.(2) Using the composie technique of cathodic arc and magnetron sputtering, we contrasitive study the different multilayer Cr/CrN coatings as the supporting layers of the composite diamond like carbon coatings, including different modulate periodic multilayers and gradient multilayers, so as to find out the optimum supporting structure scheme. Through the characterization of surface and cross-section, the crystal structures, chemical composition, hardness, cohesion, internal residual stress and the tribological properties of the coatings, we find that different modulate cycles affects the the crystal structure as well as the residual stress of Cr/CrN multilayer coatings, so influences the mechanical properties and the load bearing ability. The film-substrate cohesion, the hardness and abrasion resistance capacity are enhanced as the modulate layer number decreases. Compared to the Cr/CrN modulate periodic coatings, gradient Cr/CrN multilayer coatings has the highest hardness, nano-hardness of27.8GPa and Vickers hardness of972Hv (Vickers hardness is tested of2N load), the binding force is up to62N, the wear rate id the lowest of32.54x10-6mm3/Nm (grinded with WC ball at the load of100N without lubricant). During the preparation process of gradient Cr/CrN multilayer coating, the nitrogen flow rate is gradually increased to the vaccum chamber by the way of100sccm/step, and makes the continuous change in coating composition and hardness, there is also a good matching between the coating hardness and the internal stress for the gradient Cr/CrN multilayer. All this make the gradient Cr/CrN coating have the best performance in wear resistance property and load bearing ability, and the gradient Cr/CrN structure is the optimum selection as the supporting layer for the carbon based composite coatings with high load bearing ability.(3) On basis of the optimum structure of the supporting layer (gradient structure of Cr/CrN support layer), we prepare diamond like carbon coatings by building the bonding layer, bearing layer and anti-friction top layer with the technique of cathodic arc deposition, magnetron sputtering and chemical vapor decomposition C2H2gas. The structure of the multilayer is as Cr/(Cr/CrN gradient layer)/CrCN/CrC/Cr-DLC, in which the doping amount of Cr in the top Cr-DLC layer can be adjusted by controlling the current of the arc target so as to control the poisoning speed of the target. Through the contrasive study, we find that the coating of the top layer deposited at the target current of120A has the best comprehensive mechanical properties, such as nano-hardness is36.5GPa, the cohesion is52N, the content of sp3bond is the highest. By the comparasion study of Cr-DLC composite coatings with different supporting layers, friction and wear test is performed by ball on disc with no lubrication. After grinded with WC ball under100N loading for3600cycles, we find that the Cr-DLC composite coating with gradient supporting layer has the most shallow wear scar of7.24nm, and the lowest wear rate of13.8x10"7mm3/Nm. Compared with Cr-DLC composite coating without CrN supporting layer, the abrasion resistance capacity of Cr-DLC composite coating with Cr/CrN gradient supporting layer is enhanced by10times.Based on thought of functional gradient transition and element gradient doping, we prepare the Cr-DLC composite gradient multilayer coatings with athodic arc and magnetron sputtering composite technology, by employing the optimization structure scheme (bearing layer (Cr/CrN)+lubricating DLC layer), the Cr-DLC composite multilayer coatings with thickness more than13.5μm are prepared and the coatings show a good application prospect in high-loading work conditions.