AlTiN涂层合金划痕测试的失效形式及其失效机理的有限元分析

Failure modes of AlTiN coated alloys during scratch test and the related mechanism by finite element analysis

为了研究硬质合金基体中硬质相和粘结相对涂层内聚失效抗力(LC1)和膜基结合力(LC2)的协同作用,设计制备了具有硬质相+粘结相两相结构的WC-10Co-0.65Cr_3C_2-0.35VC(10Co)、无金属粘结相WC-6Mo_2C-0.68Cr_3C_2-0.37VC(bWC)和无硬质相85.1Co-9.2W-4.7Cr_3C_2–1.0VC(CoW)合金。采用直流磁控溅射技术,在上述合金基体表面分别沉积了厚度约5μm的Al0.55Ti0.45N薄膜。通过划痕测试获得的LC1和LC2及其差值,对涂层的失效形式进行了表征。通过划痕测试过程中涂层应力分布的有限元分析,研究涂层合金划痕失效形式所对应的形成机理。在此,LC1对应涂层首次被剥离或基体首次被暴露时所对应的载荷,与涂层的内聚失效抗力呈正相关关系;LC2对应涂层被完全从基体剥离时的载荷,表征涂层合金的膜基结合强度。在此基础上,进一步研究WC–Co合金基体中WC晶粒度和Co含量对涂层合金划痕测试过程中涂层中应力分布的影响。结果表明,采用软质CoW合金基体,涂层的LC1和LC2均为最低;采用硬质bWC合金基体,涂层的LC2最大,但LC1和LC2差值也最大;采用10Co合金基体,涂层的LC1最大,LC1和LC2差值最小。涂层与基体的杨氏模量比和基体硬度是影响LC1和LC2的关键因素。降低硬质合金基体的晶粒度,选择适中的Co含量,均有利于LC1和LC2的同步改善。

To explore the synergistic effect of the hard phase and the ductile binder phase in cemented carbide substrates to the coating,WC-10Co-0.65Cr3C2-0.35VC(10Co)with hard phase+binder phase structure,WC-6Mo2C-0.68Cr3C2-0.37VC(bWC)and 85.1Co-9.2W-4.7Cr3C2-1.0VC(CoW)alloys were prepared.Al0.55Ti0.45N coating around 5μm in thickness was deposited by direct current magnetron sputtering technology.The failure modes of AlTiN coated alloys during scratch test were determined by the magnitude of critical loads LC1 and LC2 and the difference value between LC1 and LC2.LC1 and LC2 are the characterization parameters of the cohesive failure resistance of the film and the adhesion strength between the film and the substrate,respectively.The related failure mechanism was investigated by finite element analysis of the stress distribution in the coating during scratch test.Further,the effects of the WC grain size and the cobalt content in the cemented carbide substrates on the stress distribution in the coating during scratch test were also investigated.The results show that the coated alloy with ductile CoW substrate has the lowest value of LC1 and LC2.The coated alloy with hard bWC substrate has the highest LC2 and the highest difference value between LC1 and LC2.The coated 10Co alloy has the highest LC1 and the lowest LC1 and LC2 difference.The young modulus ratio of the film and the substrate and the hardness of substrate are the key factors affecting LC1 and LC2.Decreasing the grain size and choosing moderate cobalt content in cemented carbide substrate facilitate the synchronous improvement of LC1 and LC2.