双划痕实验中单晶锗的去除机制和损伤行为

Removal mechanism and damage behavior of single crystal germanium in double scratch test

采用纳米压痕仪对单晶锗开展变载荷与定载荷双划痕实验。通过扫描电子显微镜(SEM)观察了单晶锗的划痕形貌,并对划痕深度、残余深度、弹性回复率和摩擦因数等进行分析;同时结合双划痕应力场模型,揭示单晶锗材料的去除机制和损伤行为。结果表明:变载荷刻划时,材料会发生塑性变形、脆塑转变和脆性断裂;双次刻划过程中材料的脆塑转变临界深度减小,并更容易发生脆性去除。定载荷刻划时,减小划痕间距,材料的脆性断裂程度增加,导致第二次刻划时的划痕深度和残余深度曲线波动增大,但是弹性回复率没有发生改变。这些现象产生的主要原因是双次刻划会使划痕附近材料的最大主应力迅速增加,并且最大主应力随划痕间距的减小而增大,这将导致裂纹扩展并相互作用,最终造成材料发生严重的脆性断裂。

The nano-indenter was used to conduct the double scratch experiment of single crystal germanium under variable and constant load.Scanning electron microscope(SEM)was used to observe the scratch morphology of single crystal germanium,and the scratch depth,residual depth,elastic recovery rate and friction coefficient were analyzed.Also,the removal mechanism and damage behavior of single crystal germanium materials were revealed combined with the double scratches stress field model.The results show that the material undergoes plastic deformation,ductile-brittle transition and brittle fracture under the variable load scratching,the critical depth of the ductile-brittle transition of the material under the double scratching reduces,and brittle removal is more likely to occur.The reduction of the scratch interval in constant load scratching will lead to an increase of brittle fracture of the material,which results in the increase of the fluctuation of scratch depth and residual depth curves during the second scratching,but the elastic recovery rate does not change.The reason for these phenomena is that double scratching will promote the maximum principal stress of the material near the scratch,and it increases as the scratch interval decreases,which will lead to the propagate and interaction of cracks,and eventually severe brittle fracture occurs.