沉积偏压对AlCrTiN纳米复合涂层力学与抗高温氧化性能的影响

沉积偏压对涂层的结构与性能具有重要影响，为研究其对AlCrTiN纳米复合涂层成分、组织结构、力学与抗高温氧化性能的影响规律，采用磁控溅射技术，改变沉积偏压(-30、-60、-90、-120 V)制备四种AlCrTiN纳米复合涂层。利用X射线衍射仪、扫描电子显微镜、纳米压痕仪等仪器表征涂层的组织结构、成分、力学性能和抗高温氧化性能。研究结果表明：不同偏压下制备的AlCrTiN纳米复合涂层均为NaCl型fcc-(Al,Cr,Ti)N相结构。随着沉积偏压增大，涂层由沿(111)晶面择优生长转变为无明显的择优生长取向，晶粒尺寸降低，残余应力和硬度增大。偏压为-90 V与-120 V时，涂层表面更加致密，具有更高的硬度和弹性模量。在800℃与900℃氧化1 h后，所有涂层表面均生成一层连续致密的Al₂O₃膜。随着沉积偏压增加，氧化膜厚度逐渐降低，表明抗高温氧化性能逐渐增强，这是因为高偏压下涂层组织更致密，且晶粒更细小。研究成果对AlCrTiN纳米复合涂层的综合性能提升与工程化应用具有一定指导意义。

Effect of Bias Voltage on Mechanical and High Temperature Oxidation Resistance of AlCrTiN Nanocomposite Coatings

The bias voltage has a significant influence on the microstructure and properties of coatings deposited by physical vapor deposition. To investigate the effects of bias voltage on the chemical composition, microstructure, mechanical properties, and high-temperature oxidation resistance of AlCrTiN nanocomposite coatings, four different coatings were deposited by direct current and radio frequency magnetron sputtering at different bias voltages (-30, -60, -90, and -120 V). The coatings were characterized using X-ray diffraction, scanning electron microscopy, and nanoindentation techniques. The results show that all the AlCrTiN nanocomposite coatings possess NaCl-type fcc-(Al,Cr,Ti)N phase structure. The bias voltage considerably affects the preferred orientation and surface morphology of the AlCrTiN coatings. At -30 and -60 V, the preferential growth of the coating is along the (111) crystal plane. Furthermore, convex V-shaped columnar particles are formed on the surfaces of these coatings, with distinct voids at the particle boundaries. When the bias voltage is increased to -90 and -120 V, the diffraction peaks of the (111) crystal plane weaken, and the coatings exhibit no preferred orientation. Fine elliptical particles replace the V-shaped columnar particles, and no obvious pores are observed on the coating surface, indicating that the coating surface becomes smoother at higher bias voltages. The grain size decreases with increase in the bias voltage because of enhanced ion bombardment and formation of more defects. These defects hinder grain growth or serve as nucleation sites, resulting in a decreased grain size. The deposition rate also decreases with increase in the bias voltage because of possible resputtering of Al, Cr, or Ti atoms that arrive at the substrate surface with high kinetic energy. In contrast, the residual stress, hardness, and elastic modulus of the coatings rise with increase in the bias voltage. The improvement in hardness is attributed to the higher residual stress generated in the coating and the smaller grain size, which hinders the movement of dislocations. After oxidation at 800 and 900 degrees C for 1 h, a continuous and dense oxide film, predominately consisting of Al2O3, is formed on the surfaces of all the four coatings. Owing to the relatively high Al content (approximately 31 at%) of the coatings and the low Gibbs free energy of formation of Al2O3 (compared to that of Cr2O3 and TiO2), Al is preferentially oxidized at high temperatures. The dense oxide film effectively reduces the inward diffusion of oxygen and outward diffusion of the coating elements; this significantly decreases the oxidation rate of the coatings. The fcc-(Al,Cr,Ti)N phase is retained even after oxidation at 800 and 900 degrees C for 1 h, implying that all the four coatings possess good high-temperature oxidation resistance. The thickness of the oxide film decreases gradually with increase in the bias voltage, which indicates that the high-temperature oxidation resistance is enhanced at higher bias voltages. On the one hand, the voids formed on the surfaces of the coatings at low bias voltages (-30 and -60 V) provide a diffusion path for inward diffusion of oxygen and accelerate the oxidation of the coatings. On the other hand, the coatings deposited at higher bias voltages (-90 and -120 V) possess smaller grain sizes and more grain boundaries, which accelerate the formation of a protective oxide layer on the coating surface. Thus, the findings of this study are significant for improving the properties and applications of AlCrTiN nanocomposite coatings.