不同热处理TiN/Ti多层涂层冲蚀损伤特征与机理

Erosion Damage Characteristics and Mechanism of TiN/Ti Multilayer Coatings of Different Heat Treatment

目的通过研究分析不同热处理TiN/Ti多层涂层在冲蚀作用下的损伤特征,揭示不同热处理TiN/Ti多层涂层冲蚀损伤的机理。方法采用磁过滤阴极真空弧沉积技术在TC4钛合金表面制备TiN/Ti多层涂层,利用热处理炉对试样进行不同的热处理(300℃/40 min,空冷;400℃/40 min,空冷;300℃/40 min,空冷+300℃/40 min,空冷),采用划痕仪、显微硬度计、扫描电镜、能谱仪等设备对热处理试样涂层的结合力、显微硬度、涂层损伤形貌特征、元素分布等进行表征,并在冲蚀试验平台上通过砂尘冲蚀性能试验(速度130 m/s,角度45°)进行验证。结果TiN/Ti多层涂层在低温(≤400℃)下经短时间热处理后,涂层的物相未发生变化,仍以TiN(111)、TiN(200)、TiN(220)和TiN(311)为主,涂层结构完整,最外层的TiN涂层没有发生氧化现象,涂层结合力基本未发生改变,显微硬度略有下降,由2764.1HV分别降至2748.9HV、2493.2HV、2255.2HV。TiN/Ti多层涂层的抗冲蚀性能变化不大,冲蚀速率由0.117 mg/min分别变为0.100、0.156、0.120 mg/min。结论低温(≤400℃)短时热处理对TiN/Ti多层涂层冲蚀性能的影响不大,冲蚀损伤机理为环形裂纹引起分层剥落的脆性剥落。

Sand erosion causes serious damage to the compressor blades of military helicopter engine,which has become one of the factors restricting helicopters to carry out combat/rescue missions in sand environment.Alternating soft and hard multilayer ceramic coating can properly balance strength and toughness,which is an ideal material to improve the service performance of aero-engine compressor blade under sand erosion condition.The work aims to solve the problem that the erosion failure mechanism of TiN/Ti multilayer coatings at high temperature is still unclear,and investigate the erosion damage mechanism of TiN/Ti multilayer coatings with different heat treatment.In this study,TC4 titanium alloy with a size of 50 mm×20 mm×3 mm was selected as the matrix,and then polished with metallographic sandpaper until the surface roughness reached Ra<0.20μm.The TiN/Ti multilayer coatings were prepared on the surface of TC4 substrate by magnetic filter cathode vacuum arc deposition technology.The specimens were heated in a heat treatment furnace under different conditions(300℃/40 min,air-cooled;400℃/40 min,air-cooled;300℃/40 min,air-cooled+300℃/40 min,air-cooled)to simulate its performance change under the high temperature.The adhesion strength of the coatings was tested by scratch tester(WS-2005)with the load of 80 N,loading rate of 80 N/s,and scratch length of 5 mm.The microhardness was tested by microhardness tester(SCTMC)with the load of 300 g and loading time of 15 s.Moreover,the surface morphology and cross-section morphology of the coatings were observed by scanning electron microscope(Zeiss EVO-10),and the elements distribution on the surface of the sample was tested by energy dispersive spectrometer(Bruker Xflash 6130).Afterwards,the erosion performance tests were carried out at a speed of 130 m/s and an angle of 45°on the erosion test platform to obtain the erosion resistance evolution law of the coatings under different temperature.The results indicated that after short time heat treatment at low temperature(≤400℃),the multilayer coating structure was intact and the main phases of the coating remained unchanged,showing TiN(111),TiN(200),TiN(220)and TiN(311)textures.No oxidation phenomenon occured in the top TiN layer and the adhesion strength of the coatings before and after heat treatment remained roughly the same,which were 64.1,64.4,64.4,65.6 N,respectively.After heat treatment,the microhardness of the coatings decreased slightly,changing from 2764.1HV to 2748.9HV,2493.2HV and 2255.2HV,respectively.The variation of erosion resistance of TiN/Ti multilayer coatings was not significant.The erosion rate changed from 0.117 mg/min to 0.100 mg/min,0.156 mg/min and 0.120 mg/min,respectively.In conclusion,the effect of short time heat treatment at low temperature(≤400℃)on erosion damage mechanism of TiN/Ti multilayer coating is insignificant.Under the action of sand erosion,transverse cracks and longitudinal cracks form inside the coating,and the cracks develop continuously and new cracks are initiated with the further development of erosion.Then the cracks cross and form ring cracks,which leads to coating spalling and loss of protection to matrix.The erosion damage mechanism is brittle peeling failure mechanism caused by ring crack.