不同溅射技术制备MoN涂层的结构、力学和摩擦学性能研究

Structural,Mechanical and Tribological Properties of MoN Coatings by Different Sputtering Techniques

目的沉积条件对MoN涂层的微观结构、力学性能及摩擦学性能的影响至关重要,溅射技术决定了涂层的沉积条件,研究不同溅射技术对MoN涂层的结构及性能的影响。方法采用射频、脉冲和中频反应磁控溅射技术在单晶硅片和W18Cr4V高速钢上制备MoN涂层,利用X射线衍射、能谱仪、场发射扫描电镜、划痕仪、纳米压痕仪和高温摩擦磨损试验机等探究不同溅射技术制备的MoN涂层在显微结构、力学性能和摩擦学性能等方面的差异。结果采用射频电源制备的MoN涂层以六方相δ-MoN为主,采用中频直流电源和脉冲直流电源制备的MoN涂层以面心立方相γ-Mo_(2)N为主。随着氮气流量的增加,采用射频电源制备的MoN涂层的硬度先增加后减小,最大硬度为22 GPa,采用中频直流电源和脉冲直流电源制备的MoN涂层的硬度逐渐减小。采用射频电源制备的MoN具有最高的膜基结合力,临界载荷(FLc_(2))达到20 N以上,采用其他2种电源制备的MoN涂层的膜基结合力较低。在室温下,采用不同电源制备的MoN涂层的摩擦因数均较大。在300℃时,在磨痕内检测到β-MoO_(3),脆性氧化层容易磨损,导致摩擦因数增加。随着温度的升高,涂层表面发生氧化,生成了大量具有润滑作用的α-MoO_(3),摩擦因数逐渐下降。结论溅射技术对MoN涂层的微观结构和力学性能有着重要影响,采用射频电源制备的MoN涂层呈现出最优的力学性能和摩擦学性能。

The effect of deposition conditions on the microstructure,mechanical properties,and tribological properties of MoN coatings is crucial.Whereas the sputtering technique determines the conditions under which the coating is deposited,the aim of this work is to study the differences in the structure and properties of MoN coatings by different sputtering techniques.MoN coatings were prepared on monocrystalline silicon wafers and W18Cr4V high-speed steel using RF,pulsed and medium frequency reactive magnetron sputtering techniques.The structure of the coatings was analyzed by X-ray diffraction.The elemental content of the coating was analyzed by energy spectrometer.The morphology of the coatings was analyzed by field emission scanning electron microscopy.The mechanical properties of the coatings were analyzed by scratchmeter and nanoindentation,and the tribological properties were investigated by high-temperature friction and wear testing machine.The MoN coatings prepared by the RF power supply were mainly dominated by the hexagonal phaseδ-MoN phase with(200)preferential orientation,while the MoN coatings prepared by the MF DC power supply and the pulsed DC power supply were mainly dominated by the face-centered cubic phaseγ-Mo_(2)N phase with(111)preferential orientation.With the increase of nitrogen flow rate of the MoN coatings prepared by RF power supply,due to the nitriding of Mo target surface,the phenomenon of"target poisoning"occurred,resulting in a gradual decrease in the thickness of the coatings,whereas the thickness of the MoN coatings prepared by MF DC power supply and pulsed DC power supply increased with the increase of the nitrogen flow rate of the coatings in general.With the increase of nitrogen flow rate,the hardness of the MoN coatings prepared by RF power supply first increased and then decreased,with the maximum hardness of 22 GPa.The hardness of the MoN coatings prepared by MF DC power supply and pulsed DC power supply decreased gradually.This was because as the nitrogen flow rate increased,the grain size increased,reducing the grain boundary area and preventing dislocations and intergranular slip.The MoN coatings prepared by RF power supply had the highest membrane base bonding with critical load values(FLc_(2))reaching more than 22 N.The other two power sources prepared MoN coatings with lower membrane base bonding,the H3/E2 values of the MoN coatings prepared by RF power supply were higher than those of MF DC power supply and pulsed DC power supply,the coatings were more resistant to crack extension,and therefore,the membrane base bonding of the coatings was better than that of the coatings prepared by the other two power supplies.The hexagonalδ-MoN phase had higher hardness,modulus of elasticity and superior membrane base bonding compared with the face-centered cubic phaseγ-Mo_(2)N.At room temperature,the friction coefficients of the MoN coatings prepared by different power sources were large.At 300℃,β-MoO_(3) was detected within the wear marks,and the brittle oxide layer was prone to wear,leading to an increase in the coefficient of friction.When the temperature increased to 500℃,oxidation occurred on the surface of the coating,α-MoO_(3) dominated on the surface of the coating,the softening process of the oxides started,and the coefficient of friction decreased slowly.At a maximum temperature of 800℃,the coefficient of friction was reduced to about 0.4 to 0.5 because MoO_(3) sheared easily at high temperature.The wear rate of MoN coatings prepared by RF power supplies at elevated temperature was an order of magnitude lower than that of MF DC power supplies and pulsed DC power supplies.Sputtering technology has an important influence on the microstructure and mechanical properties of MoN coatings.The MoN coatings prepared by RF power supply present optimal mechanical and tribological properties.