CrWN涂层中W元素含量对涂层纳米硬度和热稳定性的影响

目的 探究氮气退火环境下不同W含量CrWN涂层微结构、纳米硬度及热稳定性能的演变规律.方法 采用等离子增强磁控溅射技术,制备不同W含量的CrWN涂层,利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、透射电子显微镜(TEM)、纳米压痕、原子力显微镜(AFM)等分析方法,系统研究退火前后涂层的微结构、表面质量、尺寸精度、纳米力学与热稳定性能.结果 CrWN涂层由面心立方结构的CrN+W2N相组成,CrN层与W2N层交替沉积,并具有典型共格生长.随涂层中W含量的增加,涂层硬度从12.9 GPa增加至15.5 GPa,表面粗糙度降低,并趋于稳定.经过氮气环境退火后,随涂层中W含量的增加,与气氛中的微量杂质气体反应加剧,涂层硬度由13.5 GPa降低至5.2 GPa,表面氧化层WO3厚度增加,并导致涂层表面粗糙度和厚度增加.结论 CrWN涂层具有优异的表面质量及纳米力学性能,氮气退火过程中,氧化侵蚀反应导致CrWN涂层表面粗化、体积膨胀和力学降解.随涂层中W含量的增加,退火涂层表界面微结构损伤与性能退化效应加剧,氧化损伤是CrWN涂层玻璃精密模压成形应用中需考虑的关键因素之一.因此,CrWN涂层作为光学玻璃精密模压成形模具涂层使用时,应在高真空度或高纯惰性气体环境下工作.

Effect of W Content on the Nano-hardness and Thermal Stability of the CrWN Coating

This paper aims to investigate the evolution of microstructure, nano-hardness and thermal stability of the CrWN coating with different W content under the N2 annealing atmosphere. The CrWN coatings with different W contents were synthesized by the plasma enhanced magnetron sputtering technique. The microstructure, surface quality, dimensional accuracy, nano-mechanical property and thermal stability of the as-deposited and annealed CrWN coatings were investigated by the scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), nanoindentation and atomic force microscopy (AFM). The CrWN coating was composed of the face-centered cubic CrN+W2N phases, the CrN and W2N sublayers were deposited alternately, and showed a typical coherent growth. With the increase of W content, the nano-hardness of this coating increased from 12.9 GPa to 15.5 GPa, and its roughness decreased and tended to be stable. After the annealing treatment in nitrogen atmosphere, the reaction with the trace impurity gases in the atmosphere intensifies, the hardness of the CrWN coating decreased significantly with the increase of W content, from 13.5 GPa down to 5.2 GPa. Meanwhile, the WO3 phase in the oxide layer increased obviously with the increase of W content, which consequently resulted in the significant increase in surface roughness and thickness of the coating. The CrWN coating exhibited excellent surface quality and nano mechanical property, but suffered from the severe surface coarsening, volume expansion and mechanical degradation after the N2 environment annealing because of the oxidation erosion. The microstructure damage and performance degradation of the annealed coating were aggravated with the increase of the W content. The current results confirmed that the oxidation damage was a key factor to be considered in the glass precision molding application of the CrWN coating. Therefore, when CrWN coating is used as a coating for optical glass precision molding molds, it should work in a high vacuum or high purity inert gas environment.