近年來奈米壓痕廣泛應用於量測奈米尺度之機械性質，而傳統機械性質係以拉伸測試獲得應力-應變曲線，為了獲得奈米尺度之應力-應變曲線。因此，本研究主要目標為以奈米壓痕獲得應力-應變曲線。在面心立方的金屬中，疊差能對變形機制、機械性能和微觀結構皆有重要的影響，而中低疊差能的金屬於均勻的變形過程中，具較高的加工硬化及延展性，並容易產生變形雙晶。此外，奈米壓痕由於變形區域的侷限性以及應力和應變場的分布複雜。本研究其次目標為探討疊差能對壓痕變形行為的影響仍須進一步的研究，使用兩種疊差能差分別為125 mJ/m2的純鎳單晶以及22 mJ/m2的純銀單晶。
本研究研究方法首先藉由逆分析中的球形奈米壓痕應力和應變方法，以及有限元素法模擬之球形奈米壓痕變形，進而提取奈米壓痕之應力應變曲線。接著，利用掃描式電子顯微鏡、電子背向散射繞射儀和電子穿隧對比影像來觀察壓痕周邊的變形組織。
研究結果顯示，有三種壓痕應力-應變的組合成功預測拉伸應力應變曲線，分別為σH-εM、σO-εA以及σX-εK，而其壓痕應力約束因子分別為2.6、3.4和3.4。此三種組合得到的加工硬化率分別為0.173、0.248以及0.306，而傳統拉伸曲線之硬化率為0.214。
此外，在球形奈米壓痕的試驗中，{110}純鎳晶粒的變形機制以差排滑移，主要差排滑移系統為(111)[10-1]和(11-1)[101]，其臨界分解剪應力為386.18±64.14 MPa。{314}純銀晶粒的變形機制以雙晶變形，其主要變形雙晶系統為(1-11)[1-1-2]，其臨界分解剪應力為90.90±9.61 MPa。最後，{253}純鎳晶粒中，維式壓痕所引起的變形是由八種差排滑移系統所主導，分別為五個螺旋螺旋差排系統，包含(111)[-110]、(111)[10-1]、(1-1-1)[110]、(1-1-1)[101]及(-11-1)[011]，以及三個刃差排系統，包含(-11-1)[-101]、(1-1-1)[101]及(-1-11)[-10-1]。其中，滑移系統(1-1-1)[-1-10]、(111)[1-10]、(1-1-1)[101]及(-1-11)[101]，因其Burgers 向量沿著z軸向上，所以導致壓痕周邊產生凸起行為(pile-up)，相反地，具有向下的Burgers 向量之滑移系統(-11-1)[0-1-1]、(1-1-1)[-10-1 ]和(-11-1)[10-1]引起沉入行為(sink-in)。

Stacking fault energy (SFE) of face-centered cubic (FCC) materials is considered as a crucial influence for deformation mechanisms, mechanical properties and microstructures of metals. The reduction of SFE improves the ability of work-hardening behavior, ductility, and the formation of deformation twins in the metals during the deformation process. However, the effect of SFE on the indentation behavior has not been well understood because of the complicated distributions of stress and strain fields and deformation inhomogeneity. Therefore, we choose single crystals of Ni and Ag with the SFE of about 125 mJ/m2, and 22 mJ/m2 to study the relationship between SFE and deformation behavior under the indentation test.
At first the indentation stress and strain of the spherical nanoindentation were investigated to extract the uniaxial stress-strain curve using the finite element method. Then, the deformation microstructures around the indentation were observed by the scanning electron microscopy (SEM), the electron backscatter diffraction (EBSD) based techniques, and the electron channeling contrast imaging (ECCI).
As a result, three types of the indentation stress-strain of σH-εM, σO-εA, and σX-εK with the stress constraint factor of 2.6, 3.4, and 3.4, reveal good agreements with the simulated stress-strain curve of tension test. The power-law fitting of the work-hardening exponent in these three combinations is equal to 0.173, 0.248, and 0.306, and having the deviations of 19.16, 15.89, and 42.99% by comparing with that of the simulated tensile stress-strain curve of 0.214.
For the case of {110}-oriented Ni and {314}-oriented Ag under the spherical nanoindentation test, the deformation mechanism were dominated by the dislocation slip in the Ni, and by the deformation twin in Ag. Then, the critical resolved shear stresses of Ni and Ag were measured as 386.18±64.14, and 90.90±9.61 MPa, respectively. In addition, the activated slip systems of Ni were (111)[10-1], and (11-1)[101], and the dominant deformation twin system of Ag was (11-1)[1-1-2].
Additionally, the slip systems induced by Vickers indentation were identified as (111)[-110], (111)[10-1], (1-1-1)[110], (1-1-1)[101], and (-11-1)[011] with screw type, and (-11-1)[-101], (1-1-1)[101], and (-1-11)[-10-1] with edge type in the {253}-oriented Ni. The slip systems of (1-1-1)[-1-10], (111)[1-10], (1-1-1)[101], and (-1-11)[101] with the upward Burgers vectors resulted in the pile-up pattern, and in the opposite, that of (-11-1)[0-1-1 ], (1-1-1)[-10-1 ], and (-11-1)[10-1] with downward Burgers vectors caused the sink-in behavior.

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