Faiyad Abrar, Munshi Md Adnan Mahathir, Islam Md Mahbubul, Saha Sourav
Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh.
Department of Mechanical Engineering, Wayne State University, 5050 Anthony Wayne Drive, Detroit, MI 48202, USA.
Phys Chem Chem Phys. 2021 May 5;23(17):10650-10661. doi: 10.1039/d0cp06614a.
Ni-based super alloy Inconel-718 is ubiquitous in metal 3D printing where a high cooling rate and thermal gradient are present. These manufacturing conditions are conducive to high initial dislocation density and porosity or voids in the material. This work proposes a molecular dynamics (MD) analysis method that can examine the role of dislocations, cooling rates, voids, and their interactions governing the material properties and failure mechanisms in Inconel-718 using the Embedded Atom Method (EAM) potential. Throughout this work, three different structures - nanowires (NWs), nanopillars (NPs), and thin-plates - are used. The strain rate is varied from 108 s-1 to 1010 s-1 and the temperature is varied from 100 K to 800 K. Different cooling rates ranging from 0.5 × 1010 K s-1 to 1 × 1014 K s-1 are applied. Our results suggest that the high cooling rates create regular crystalline structures which result in high strength and ductility. In contrast, the lower cooling rates form a non-crystalline structure that exhibits low strength and a brittle nature. This brittle to ductile transition is observed solely due to the cooling rate at the nanoscale. Elimination of voids as a result of heat treatment is reported as well. Shockley dislocation is observed as the key factor during tensile plastic deformation. Increasing strain rates result in strain hardening and a higher dislocation density in tension. Our computational method is successful in capturing extensive sliding on the {111} shear plane due to dislocation, which leads to necking before fracture. Furthermore, notable mechanical properties are revealed by varying the temperature, size and strain rate. Our results detail a pathway to design machine parts with Inconel-718 alloy efficiently in a bottom-up approach.
镍基超级合金因科镍合金718在存在高冷却速率和热梯度的金属3D打印中无处不在。这些制造条件有利于材料中产生高初始位错密度以及孔隙或空洞。这项工作提出了一种分子动力学（MD）分析方法，该方法可以使用嵌入原子法（EAM）势来研究位错、冷却速率、空洞及其相互作用在因科镍合金718中对材料性能和失效机制的影响。在整个工作中，使用了三种不同的结构——纳米线（NWs）、纳米柱（NPs）和薄板。应变率从10⁸ s⁻¹变化到10¹⁰ s⁻¹，温度从100 K变化到800 K。施加了从0.5×10¹⁰ K s⁻¹到1×10¹⁴ K s⁻¹的不同冷却速率。我们的结果表明，高冷却速率会形成规则的晶体结构，从而导致高强度和延展性。相比之下，较低的冷却速率会形成非晶体结构，表现出低强度和脆性。这种从脆性到韧性的转变仅在纳米尺度上是由于冷却速率引起的。还报道了热处理导致空洞的消除。肖克利位错被观察到是拉伸塑性变形过程中的关键因素。应变率增加会导致应变硬化和拉伸时更高的位错密度。我们的计算方法成功地捕捉到了由于位错导致的在{111}剪切面上的大量滑移，这导致在断裂前出现颈缩。此外，通过改变温度、尺寸和应变率揭示了显著的力学性能。我们的结果详细说明了一种自下而上高效设计因科镍合金718机器零件的途径。
