Zeng Wu, Yang Junjie
School of Aerospace Engineering, Tsinghua University, Beijing 100084, China.
Institute for Aero Engine, Tsinghua University, Beijing 100084, China.
Materials (Basel). 2020 Mar 21;13(6):1437. doi: 10.3390/ma13061437.
Surface hardening treatment can usually introduce severe grain distortion with a large gradient in the surface layer. It results in mechanical properties being difficult to accurately determine through macroscopic tests due to the non-uniformity of the shot-peened material. In this study, the mechanical behavior of uniformly pre-deformed nickel-based superalloy IN718 was investigated with monotonic tensile tests and instrumented indentation tests. For the shot-peened material, the hardness distribution of the surface hardening layer after shot peening was identified through the instrumented indentation method. According to the stress-strain results of pre-deformed materials, Ramberg-Osgood model parameters could be presented with plastic deformation. Assuming the power-law relationship between hardness and plastic deformation, the plastic deformation distribution along the depth of the surface hardening layer was clarified. Based on the results, a method to identify the stress-strain relationships of hardened material at different depths was established. Finally, the finite-element simulations of the instrumented indentation test considered residual stress and strain hardening were built to verify the method presented herein. The results show that the solution to evaluate the mechanical properties of hardening layer materials in the microscopic zone is feasible, which can provide the foundation for the failure analysis of shot-peened materials.
表面硬化处理通常会在表层引入严重的晶粒畸变，并伴有较大的梯度。由于喷丸处理材料的不均匀性，通过宏观试验难以准确测定其力学性能。在本研究中，通过单调拉伸试验和仪器化压痕试验研究了均匀预变形镍基高温合金IN718的力学行为。对于喷丸处理的材料，采用仪器化压痕法确定喷丸后表面硬化层的硬度分布。根据预变形材料的应力-应变结果，可以给出考虑塑性变形的Ramberg-Osgood模型参数。假设硬度与塑性变形之间存在幂律关系，阐明了沿表面硬化层深度的塑性变形分布。基于这些结果，建立了一种识别不同深度硬化材料应力-应变关系的方法。最后，建立了考虑残余应力和应变硬化的仪器化压痕试验的有限元模拟，以验证本文提出的方法。结果表明，该方法用于评估微观区域硬化层材料力学性能是可行的，可为喷丸处理材料的失效分析提供依据。
