湿度对a-C:Ti/a-C:Si纳米多层薄膜摩擦学行为的影响

Effect of Humidity on Tribological Behavior of a-C:Ti/a-C:Si Nano-multilayer Films

目的沉积出具有纳米级多层结构的a-C:Ti/a-C:Si薄膜来改善非晶碳薄膜的湿度适应性。方法通过磁控溅射技术在硅片和304不锈钢试样表面交替沉积a-C:Ti薄膜和a-C:Si薄膜,并进行了薄膜截面形貌表征。通过纳米压痕测试表征了复合薄膜的力学性能,采用球-盘摩擦磨损试验机进行了不同湿度下摩擦学试验,测试薄膜的摩擦学性能。结合拉曼光谱和扫描电子显微镜,分析了摩擦试验后的磨痕形貌和磨斑。结果a-C:Ti/a-C:Si纳米多层结构增加了薄膜的异质界面,相比于a-C:Ti膜,a-C:Ti/a-C:Si纳米多层薄膜的弹性模量和残余应力随a-C:Si层厚度的增加而上升。在低湿度环境下,a-C:Si层引入后使a-C:Ti/a-C:Si纳米多层膜在摩擦过程中不易产生碳转移膜,薄膜的摩擦因数和磨损率随a-C:Si层沉积时间的增加而增加,薄膜的摩擦学性能略有下降。在高湿度环境下,由于磨屑的堆积抑制了碳转移膜的形成,不同制备工艺获得的a-C:Ti/a-C:Si纳米多层膜的摩擦因数均有所上升,但是a-C:Si层的存在使薄膜极易产生富硅转移膜,缓解了无碳转移膜的缺陷,降低了磨损率,提高了摩擦学性能。结论纳米多层结构有效地改善了非晶碳薄膜的湿度适应性。利用a-C:Ti层和a-C:Si层分别提升了非晶碳基复合薄膜在低湿环境下和高湿环境下的摩擦学性能。

The work aims to prepare a-C:Ti/a-C:Si films with nano-scale multilayer structure to improve the humidity adaptability of amorphous carbon films.The a-C:Ti and a-C:Si layers were deposited alternately on the surface of silicon wafer and 304 stainless steel by magnetron sputtering.The sizes of silicon wafer and 304 stainless steel were 10 mm×20 mm×0.33 mm and 12 mm×20 mm×1 mm,respectively.In addition,the cross-sectional morphology and the three-dimensional surface morphology of the films were also characterized.The hardness and elastic modulus of a-C:Ti/a-C:Si nano-multilayer films were determined by nano-indentation tests,and the adhesion between films and substrates was evaluated by the scratch method.The tribological properties of the films were evaluated by tribological tests at different humidity levels with a ball-disk friction and wear tester.Subsequently,the wear marks on the films were analyzed by Raman spectroscopy and scanning electron microscopy.The results showed that the multilayer structure made the interface of the film more complex.With the addition of a-C:Si layer,the hardness,elastic modulus and internal stress of the films increased to 19.6 GPa,186 GPa and 1.56 GPa,respectively.Moreover,the adhesion of a-C:Ti/a-C:Si nano-multilayer films decreased from 35 N to 25 N compared with a-C:Ti films.The friction coefficient and wear rate of a-C:Ti/a-C:Si nano-multilayer films increased with the increase of a-C:Si layer deposition time,and the wear rate increased to 3.48×10^(‒16)m^(3)/(N·m).This was due to the introduced a-C:Si layer,which made it difficult to form carbon transfer films during friction,and it was easier to produce debris.This result was similar to the tribological test results of a-C:Ti/a-C:Si nano-multilayer films at the humidity of 20%.However,when the humidity increased to 80%,this result showed a completely opposite trend.The longer the deposition time of a-C:Si layer,the lower the friction coefficient and wear rate of the film,and the wear rate was as low as 2.2×10^(‒16)m^(3)/(N·m).This was because the a-C:Si layer was likely to react with water molecules to form gel compounds SiOx(OH)y,which promoted the formation of silicon-rich transfer films and played a certain role in lubrication.By analyzing the facial distribution of the abrasion spot of the film at the humidity of 80%,it was found that there was a large amount of Si elements distributed on the film,which could confirm that the transfer films produced at this time was a silicon-rich transfer film.The formation of the silicon-rich transfer film reduced the defects of carbon-free transfer films,reduced the friction coefficient and wear rate of a-C:Ti/a-C:Si nano-multilayer films,and improves the tribological properties.At the same time,when the humidity increased from 20%to 80%,the variation of wear rate of a-C:Ti/a-C:Si nano-multilayer films decreased gradually with the a-C:Si layer deposition time,from 3.66×10^(‒16)m^(3)/(N·m)to‒1.4×10^(‒16)m^(3)/(N·m),showing good humidity stability.In a word,the nano-multilayer structure effectively enhances the environmental humidity adaptability of a-C films,and makes the films have better tribological properties in the environment with changing humidity.