Geng Haoqi, Du Wenhao, Wang Hui, Li Jiawei
Appl Opt. 2021 Aug 1;60(22):6639-6647. doi: 10.1364/AO.428127.
The understanding of mechanical behavior in magnesium aluminate spinel () at the nanoscale lays a foundation for its material removal mechanism in ultraprecision machining. Nanoindentation tests are carried out in the interior and boundary of spinel grain with different loads. An obvious indentation size effect exhibits in both of these areas. First, the nano-hardness and elastic modulus decrease, followed by stabilization due to an increase of pressure. The measured elastic modulus, hardness, and fracture toughness of the grain interior are 277.7±8.4, 19.79±0.83, and 1.12±0.02⋅, respectively. Deformation of spinel transits from elastic to plastic at approximately 0.8 mN load, which corresponds to the discontinuous steps of load-displacement curves. By comparing the fracture toughness and the residual indent morphology, the grain boundary exhibits lower brittleness than the grain interior. Radial cracks form on the grain surface as indentation load exceeds 29 mN, whose propagation is influenced by the loading conditions and the grain boundary effect.
对纳米尺度下铝酸镁尖晶石（）力学行为的理解为其在超精密加工中的材料去除机制奠定了基础。在不同载荷下对尖晶石晶粒的内部和边界进行纳米压痕试验。在这两个区域均呈现出明显的压痕尺寸效应。首先，纳米硬度和弹性模量降低，随后由于压力增加而趋于稳定。测得的晶粒内部弹性模量、硬度和断裂韧性分别为277.7±8.4、19.79±0.83和1.12±0.02⋅。在大约0.8 mN载荷下，尖晶石的变形从弹性转变为塑性，这与载荷-位移曲线的不连续台阶相对应。通过比较断裂韧性和残余压痕形态，晶界的脆性低于晶粒内部。当压痕载荷超过29 mN时，晶粒表面会形成径向裂纹，其扩展受加载条件和晶界效应的影响。
