钨单晶纳米压痕尺寸效应研究

Study on Nanoindentation Size Effect of Tungsten Single Crystal

摘要:

利用纳米压痕仪和扫描探针显微镜对高纯钨单晶的载荷-位移曲线、弹性模量、压痕形貌、纳米硬度-加载深度以及弹性回复率的变化情况进行了研究。结果表明，W(111)晶面在加载和卸载过程中分别经历了弹性变形和塑性变形阶段，荷载-位移曲线未出现不连续现象，表明在加载过程中压痕内部未产生裂纹或脆性断裂；钨单晶的残余压痕表现出堆积形貌，表明钨单晶有较低的加工应变硬化趋势；采用连续刚度法测量了钨单晶的纳米压痕硬度以及弹性模量，结果表明，钨单晶纳米压痕硬度和弹性模量存在尺寸效应，即随着加载深度的增加，单晶的纳米压痕硬度和弹性模量减小；采用 Nix-Gao 模型对钨单晶的纳米压痕力学特征和进行了分析，计算了钨单晶的微观特征长度（h^*）为1490nm，无压痕尺寸效应时的纳米硬度值（H_0）为6.79GPa，尺寸效应因子（m）为0.18，即压入深度小于1490nm时，钨单晶具有明显的尺寸效应，当压入深度超过1490nm时，尺寸效应将减弱。当压入深度超过2450nm时，钨单晶的纳米尺寸效应将消失。

Abstract:

The load-displacement curves, elastic modulus, indent morphology, nanohardness and elastic recovery of high purity tungsten single crystal were investigated by nanoindentation and scanning probe microscopy. W (111) crystal plane undergoes elastic deformation and plastic deformation during the loading-unloading process, and the load-displacement curve does not show discontinuity, which demonstrates that cracks and brittle fracture are not formed in the indents. Moreover, the pile-up behavior around indents reveals that tungsten single crystal has the low work hardening tend. The nanohardness and elastic modulus of tungsten single crystal were measured by continuous stiffness measurement (CSM), and a size effect on the nanohardness and elastic modulus of tungsten single crystal was observed, which decrease with the increase of indentation depth. The Nix-Gao model was employed to analyze the nanoindentation mechanical characteristics of tungsten single crystals, and the characteristic length(h*), the intrinsic hardness in the limit of infinite depth(H0) and size effect index(m) were calculated to be 1490nm, 6.79GPa and 0.18 respectively, which indicates that tungsten single crystal has a significant size effect when the indentation depth is below about 1490nm, and the size effect becomes more insignificant when indentation depth is above 1490nm.When the impression is deeper than 2450nm, the nanoindentation size effect on the hardness will disappear.