TiB_(2)/WS_(2)复合薄膜退火处理下的结构演变与磨损失效分析

Structural Evolution and Friction Loss Effect Analysis of TiB_(2)/WS_(2) Composite Films under Annealing Treatment

在严苛的航空航天工况环境下,WS_(2)基复合薄膜在减摩耐磨方面的结构演变和失效规律仍须进一步探索。为扩展其在温域上的应用范围,采用磁控溅射技术在硅片和718高温合金块上沉积TiB_(2)/WS_(2)复合薄膜,分别在200、450和600℃大气环境下对复合薄膜进行退火处理。利用扫描电子显微镜、透射电镜、X射线衍射仪、拉曼光谱仪、纳米压痕仪和球盘高温摩擦试验机等分析技术对退火处理前后薄膜的组分、结构、力学性能和摩擦磨损性能进行研究。结果表明:随着退火温度的升高,复合薄膜中硫元素的分解率增大,S/W比降低,薄膜氧化程度增加。未退火处理薄膜在摩擦过程中由于形成易于剪切滑移的WS_(2)(002)晶体取向结构保持了低且稳定的摩擦因数。200℃退火处理后薄膜的致密性增加,硬度得到明显的提升,显示良好的减摩耐磨性能[摩擦因数<0.075,磨损率为9.21×10^(-6)mm^(3)/(m·N)量级]。450℃退火处理后薄膜中生成的氧化相WO_(3)、TiO_(2)导致摩擦因数波动上升,磨损率增加。600℃退火处理后薄膜瞬时失效,主要是由于薄膜中硫元素的大量分解流失难以形成润滑相和薄膜表面形成松散堆积结构所造成的。通过观察退火处理前后复合薄膜微观结构的变化明确了其在不同温度下的磨损失效演化规律。

The exploration of structural evolution and failure patterns in WS_(2)-based composite films,especially regarding their friction and wear reduction capabilities under harsh aerospace conditions,still requires further investigation.To widen their application across various temperature ranges,TiB_(2)/WS_(2) composite films,aimed at adapting to a broad temperature domain,were deposited onto silicon wafers and 718 high-temperature alloy substrates using a magnetron sputtering method.These films were then annealed at 200℃,450℃,and 600℃in atmospheric conditions.Detailed analyses of the films,both before and after the annealing processes,were performed using a range of analytical techniques,including scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),Raman spectroscopy,nanoindentation,scratch testing,and ball-on-disk high-temperature friction testing.The study focused on the effects of annealing temperatures,ranging from 0 to 600℃,on the films'elemental composition,microstructure,hardness,and frictional wear properties.It was determined that the films,deposited by non-equilibrium magnetron sputtering,were characterized by a cabbage-like morphology on the surface,a columnar growth structure in the cross-section,and an amorphous state overall.An increase in annealing temperature was associated with an accelerated decomposition rate of sulfur elements,a significant reduction in the S/W ratio,a noticeable rise in film oxidation,and a wear rate that decreased initially but then increased with the annealing temperature.At an annealing temperature of 200℃,the films exhibited the lowest number of surface defects and the most compact structure,which slightly enhanced mechanical properties and maintained stable tribological performance,demonstrating effective friction and wear reduction(with a coefficient of friction<0.075 and wear rate of 9.21×10–6 mm^(3)/m·N).Excellent tribological properties were exhibited by the film during dynamic and continuous temperature increases(RT of approximately 600℃),and thereby,excellent thermal stability and continuous lubricity were realized.Mechanisms of destabilization in composite films before and after undergoing annealing treatments at various temperatures were observed:A low and stable coefficient of friction was maintained by the unannealed film during the friction process due to the formation of a shear-slip friendly WS_(2)(002)crystal orientation structure.Increased densities and significantly improved hardness,along with optimal tribological properties,were observed after the annealing treatment at 200℃.A significant fluctuation in the coefficient of friction was displayed by the composite film after the annealing treatment at 450℃,as WS_(2) starts to oxidize at 450℃,leading to the formation of a small amount of oxide phases WO_(3) and TiO_(2) on the composite film surface.These oxide phases,being higher in the coefficient of friction than the lubricant phase WS_(2),partake in the friction process,causing the coefficient of friction to fluctuate and gradually increase,and the wear rate to rise.Failure of the composite films annealed at 600℃occurs within a very short period,attributed on one hand to the destruction of the microstructure and mechanical properties by high-temperature annealing,and on the other hand to the instantaneous failure of the S element in the composite films due to a high temperature decomposition rate of 92.9%and the difficulty in forming the lubricant phase during the friction process in the absence of the S element.The evolution of frictional wear loss at different temperatures was clarified by investigating the changes in the microstructure of the composite films before and after the annealing treatment.