Strain-rate dependence of surface/subsurface deformation mechanisms during nanoscratching tests of GGG single crystal
Strain-rate dependence of surface/subsurface deformation mechanisms during nanoscratching tests of GGG single crystal
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DOI：
10.1016/j.ceramint.2019.04.238
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发表时间：
2019-08-15
影响因子：
5.2
通讯作者：
Piao, Yinchuan
中科院分区：
文献类型：
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作者：
Li, Chen;Zhang, Feihu;Piao, Yinchuan
在不同划痕速度下对GGG单晶进行了等深度和变深度的纳米划痕实验。利用扫描电子显微镜对划痕槽和切屑的形貌进行了分析。实验结果表明，划痕速度越大，穿透深度越浅，残余深度越浅，连续切屑越大。提高划痕速度可有效提高GGG单晶的塑性，降低脆韧转变深度。基于分析试样与布氏压头的接触应力和接触面积，建立了考虑应变率效应和材料弹性恢复的侵彻深度预测模型。该模型进行了验证，使用恒定和变化的深度纳米划痕试验，预测和实验结果吻合良好。亚表面下的韧性表面的损伤，其特征在于使用透射电子显微镜。TEM结果表明，较高的刮擦速度使滑移面出现在更多的方向上，从而阻止了长滑移面的产生，降低了损伤层的深度。在100 μ m/s的划痕速度下，GGG的塑性变形由多晶纳米晶和非晶相主导，并且与低划痕速度下的塑性变形相似。这项研究提供了一个基本的理解应变率依赖的表面/亚表面变形机制GGG在超精密加工。
Constant- and varied-depth nanoscratching tests of GGG single crystal were carried out at different scratching velocities. The morphologies of the scratched grooves and chips were analysed using scanning electron microscope. The experimental results indicated that higher scratching velocity led to shallower penetration depth, shallower residual depth, and larger continuous chips. Increasing the scratching velocity could effectively improve the plasticity and reduce the brittle-to-ductile transition depth of GGG single crystal. Based on the contact stress and contact area between the analysed sample and Berkovich indenter, a model for predicting the penetration depth was developed, which took into account the strain rate effect and elastic recovery of materials. The model was verified using constant- and varied-depth nanoscratching tests, and the predicted and experimental results were in good agreement. Subsurface damage underneath the ductile surface was characterised using transmission electron microscope. The TEM results demonstrated that higher scratching velocity led to the slipping planes appearing in more directions, which prevented the generation of long slipping plane and reduced the depth of the damage layers. The plastic deformation of GGG at the scratching velocity of 100 mu m/s was dominated by poly-crystalline nanocrystallites and amorphous phases, and was similar to that at the low scratching velocity. This study provided a fundamental understanding of the strain-rate dependence of surface/subsurface deformation mechanisms of GGG during ultra-precision machining.