压头半径对玻璃表面薄有机涂层划痕试验结果的影响

纳米划痕是一种薄膜力学性能的评价方法,然而,当膜层厚度小于10 nm时,压头大小对划痕的深度、宽度及变形状态影响较大,较难保证试验结果的有效性。为了快速对超薄膜层进行纳米划痕测试,采用不同半径的压头,在施加不同载荷的情况下,研究了压头半径对玻璃表面薄有机涂层纳米划痕试验结果的影响。利用纳米划痕仪和扫描电子显微镜(SEM)对划痕形貌及伴随的力学信号转换进行了分析和研究。结果表明:施加从6 mN线性增加至10 mN的载荷,在10μm半径压头所得划痕中,涂层失效包含塑性形变、裂纹、撕裂和剥离等4种模型,并且在各临界点的法向力Fn和划痕深度Pd均有清晰的转换信号;在2μm半径压头所得划痕中,压头较早地撕裂涂层,导致Fn和Pd信号只出现短暂的小幅波动,并且在涂层剥离失效之前,Pd超过压头半径r,压头两侧对涂层变形的影响大于压头半径,因此试验结果缺乏有效性;而在50μm半径压头所得划痕中,尽管直至试验结束之前,Pd未超过r,然而Fn和Pd转换信号不明显,这不利于对涂层形变过程中力学性能的分析。该研究结果可为纳米划痕试验中压头半径的选择以及对划痕试验结果有效性的评估提供决策支持。

Influence of Indenter Tip Radius on the Scratch Resistance of Thin Organic Clear Coatings on Glass Surface

Nanoscale-scratch is a method to evaluate the mechanical properties of nano-films.However,when the film is less than 10 nm,indenter tip radius has great effects on the depth and width of scratch in thin films,leading to an unreliable test result.For achieving effective results quickly,the influences of indenter tip with different radii on the scratch resistance of an organic clear coating on glass surface was investigated with various progressive loads in this work.Morphologies of the scratches and accompanied mechanical signal transduction were examined by using nano-scratch tester and scanning electron microscopy(SEM).Results showed that failure modes of the scratch with 10μm radius spherical indenter involved plastic deformation,cracking,tearing and exfoliation.Furthermore,both the normal load signal(Fn)and penetration depth signal(Pd)had clear indicators of coating fracture at different critical positions.For the smallest radius(2μm)scratch,Fn andPdboth presented fluctuation within a narrow range for a relatively short time,andPdexceeded the radius(r)of the indenter before the delamination,then the sidewalls of the cone exerted a greater influence on the coating deformation than the actual radius of the tip,which resulted into an invalid scratch.For the biggest radius(50μm)scratch,Pddid not exceed the radius(r)of the indenter till the end of the tests,but bothFnandPddid not present clear indicators of coating fracture at critical position,which was not in favor of the analysis of mechanical properties.This work was conducive to the decision of the radius of the indenter and the validity assessment of scratch on thin organic clear coatings.