基于纳米划刻实验的单晶锗切削机理的研究

Study on the Cutting Mechanism of Monocrystalline Germanium Based on Nano Scratch Experiment

摘要:

本文选用 Berkovich 压头，使用纳米压痕仪对单晶锗进行了变载荷纳米刻划试验，利用SEM观测了刻划过程中沟槽表面形貌特征，将划刻过程中材料的去除机制分为延性域、脆塑转变域和脆性域三个阶段，并分析了在各个阶段的力学特征。根据断裂力学理论，以切向力的首次下降作为脆塑转变发生点，由此获得单晶锗脆塑转变的临界载荷及临界深度，并分析了裂纹的产生与扩展过程。对于纳米划刻过程中法向力、切向力、摩擦因数与划刻深度的函数关系进行非线性拟合，由相关系数的计算结果表明，划刻力与划刻深度之间存在强相关性。基于赫兹接触理论计算单晶锗划刻过程中临界弹塑转变深度，其大小为1.33 nm。基于脆朔转变临界载荷，建立了表征单晶锗材料脆塑转变临界深度的表达式，结果表明其脆塑转变临界深度为561 nm。由此对于单晶锗划刻过程中不同阶段确立了量化区分方法。

Abstract:

The Berkovich indenter was selected to perform an varied load nano-scratching experiment for monocrystalline Germanium by using nano indentation test. The surface morphology of the groove was observed by SEM, which was found that there are three regimes in nano scratching process, i.e. the ductile regime, the brittle-ductile transition regime and the brittle regime, and the mechanical characteristics at each regime was analyzed. According to the theory of fracture mechanics, the first drop of tangential force was taken as the occurrence point of brittle-ductile transition, thus the critical load and critical depth for monocrystalline Germanium were obtained, and the crack generation and propagation process were also analyzed. Non-linear fitting method was used to figure out relationship between normal force, tangential force, friction factor and scratch depth respectively during nano-scratching process, the calculation results of the correlation coefficient show that there is a strong correlation between scratch force and scratch depth. Based on the Hertzian contact theory, the critical elastic-plastic transition depth during the scratch process for monocrystalline Germanium is calculated, and the value is 1.2 nm. Based on the critical load of brittle-ductile transition, An equation for characterizing the phenomenon is established, the results show that the transition depth is 561 nm. Therefore, a quantitative method for distinguishing different regimes of monocrystalline Germanium is established.