Metal additive manufacturing (AM) process induces residual stress which can hinder the applicability of AM. Residual stress build-up causes part failure due to the crack initiation and growth, and also distortion during or after fabrication. Consequently, it is of great importance to accurately and rapidly predict residual stress within the AM parts. During the thermal loading, the grain size is altered at the subsurface through dynamic recrystallization (DRx) and subsequent recovery. The yield strength of the alloys is largely determined by the size of nucleated grains, and it has a substantial influence on residual stress build-up. In this work, a physics-based analytical model is proposed to predict the residual stress considering the microstructure of the additively manufactured part. The thermal signature of this process is predicted using a transient moving point heat source. Due to the high-temperature gradient innate in this process, material may experience high thermal stress which often exceeds the yield strength. The thermal stress is obtained from Green’s functions of stresses due to the point body load. The modified Johnson-Cook flow stress model is used to predict the yield surface. In this flow stress model, the yield strength parameter is modified to incorporate the effect of grain size using Hall-Petch equation. The dynamic recrystallization and the resultant grain size are predicted by utilizing the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model for IN718 alloy. Moreover, a grain refinement model is used to include the effect of the rapid solidification on grain size. Then, as a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is precited from incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with equilibrium and compatibility conditions. Results from the analytical residual stress model showed good agreement with X-ray diffraction measurements used to determine the residual stresses in the IN718 specimens. Moreover, the phases present in the IN178 samples built via direct metal disposition (DMD) are evaluated using X-ray diffraction.

金属增材制造 (AM) 工艺会产生残余应力，这会阻碍增材制造的适用性。由于裂纹萌生和扩展，以及制造过程中或制造后的变形，残余应力的积累会导致零件失效。因此，准确快速地预测增材制造零件内的残余应力非常重要。在热载荷期间，通过动态再结晶 (DRx) 和随后的恢复，在表面下改变晶粒尺寸。合金的屈服强度在很大程度上取决于成核晶粒的大小，它对残余应力的积累有重大影响。在这项工作中，提出了一种基于物理的分析模型来预测考虑到增材制造零件的微观结构的残余应力。使用瞬态移动点热源预测该过程的热特征。由于此过程中固有的高温梯度，材料可能会经历高热应力，通常会超过屈服强度。热应力由点体载荷引起的应力的格林函数获得。修正的 Johnson-Cook 流动应力模型用于预测屈服面。在这个流动应力模型中，屈服强度参数被修改，以使用 Hall-Petch 方程结合晶粒尺寸的影响。利用 IN718 合金的 Johnson-Mehl-Avrami-Kolmogorov (JMAK) 模型预测动态再结晶和所得晶粒尺寸。此外，使用晶粒细化模型来包括快速凝固对晶粒尺寸的影响。然后，由于循环加热和冷却以及材料屈服的事实，残余应力的积累是根据与平衡耦合的塑性变形体积不变性的性质，从金属的增量塑性和运动硬化行为中推导出来的和兼容性条件。分析残余应力模型的结果与用于确定 IN718 样品中残余应力的 X 射线衍射测量结果非常吻合。此外，通过直接金属沉积 (DMD) 构建的 IN178 样品中存在的相使用 X 射线衍射进行评估。根据与平衡和相容性条件耦合的塑性变形体积不变性的性质，残余应力的积累是从金属的增量塑性和运动硬化行为中推断出来的。分析残余应力模型的结果与用于确定 IN718 样品中残余应力的 X 射线衍射测量结果非常吻合。此外，通过直接金属沉积 (DMD) 构建的 IN178 样品中存在的相使用 X 射线衍射进行评估。根据与平衡和相容性条件耦合的塑性变形体积不变性的性质，残余应力的积累是从金属的增量塑性和运动硬化行为中推断出来的。分析残余应力模型的结果与用于确定 IN718 样品中残余应力的 X 射线衍射测量结果非常吻合。此外，通过直接金属沉积 (DMD) 构建的 IN178 样品中存在的相使用 X 射线衍射进行评估。