摘要
相比于传统制造工艺生产的316L不锈钢零件,L-PBF技术具有更大的设计自由度和制造效率,可实现复杂几何形状金属零件的一次性成型,被广泛应用在核工业、汽车工业以及医疗卫生等领域。然而,L-PBF技术极快的冷却速率会导致其内部形成明显差异的微观组织结构,从而造成材料力学性能的各向异性。利用SEM、EBSD和TEM等表征技术,深入观察了L-PBF 316L不锈钢样品不同截面的微观组织的差异,从晶粒尺寸、晶体取向以及亚晶结构的变形机理3方面详细分析了其对材料力学性能的影响。研究表明,垂直于打印方向的晶体为明显的<110>织构,晶粒尺寸较小,且塑性变形时网络状的胞状亚晶和变形孪晶相互作用,形成了更小尺寸的三维立体钉扎结构,可有效抑制各个方向的位错滑移,明显增加了该方向的强度。然而,平行于打印方向为较粗大的柱状晶,晶体取向趋于随机,并且亚晶结构多为条状形貌。塑性变形时,当变形孪晶生长方向平行于亚晶的长边时,则无法对条状亚晶进行分割和细化,进而不能有效抑制平行于亚晶长边界的位错滑移,强化效果较弱,导致该方向强度较低。研究有利于更好地理解L-PBF 316L中各向异性的起源,为后续热处理提供了理论指导;同时有助于拓扑优化、晶格结构建模和增材制造过程中的热物理过程模拟等工作的模型搭建,提高模型的精度。
Compared to 316L stainless steel parts produced by traditional manufacturing processes,L-PBF technology offers greater design freedom and manufacturing efficiency,and can realize the one-time melding of metal parts with complex geometries,which is widely used in the nuclear industry,automotive industry,and healthcare.However,the extremely fast cooling rate of L-PBF technology leads to the formation of significantly different microstructures within it,thus causing anisotropy in the mechanical properties of the material.The differences in the microstructure of different sections of L-PBF 316L stainless steel samples were observed in depth by using characterization techniques such as SEM,EBSD and TEM,and their effects on the mechanical properties of the materials were analysed in detail from three aspects,namely,the grain size,the crystal orientation and the deformation mechanism of sub-grain structure.It is shown that the crystals perpendicular to the printing direction are obvious<110>weaving structure,with smaller grain size,and the network-like cytosolic sub-grains and deformation twins interact with each other during the plastic deformation to form a three-dimensional pinned structure with smaller size,which can effectively inhibit the dislocation slip in all directions,and obviously increase the strength in this direction.However,parallel to the printing direction for the coarser columnar crystals,the crystal orientation tends to be random,and the sub-grain structure is mostly strip-like morphology.During plastic deformation,when the growth direction of the deformation twin is parallel to the long edge of the sub-grain,it is not possible to segment and refine the barshaped sub-grain,which in turn cannot effectively inhibit the dislocation slip parallel to the long boundary of the subgrain,and the reinforcing effect is weak,resulting in a lower strength in this direction.This work is conducive to a better understanding of the origin of anisotropy in L-PBF 316L,which provides theoretical guidance for subsequent heat treatment;it also contributes to the model building for topology optimization,lattice structure modelling,and the simulation of thermophysical processes in the additive manufacturing process,improving the accuracy of the model.
作者
刘伟
刘成松
王勇
张华
倪红卫
LIU Wei;LIU Chengsong;WANG Yong;ZHANG Hua;NI Hongwei(The State Key Laboratory of Refractories and Metallurgy,Wuhan University of Science and Technology,Wuhan 430081,Hubei,China;Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education,Wuhan University of Science and Technology,Wuhan 430081,Hubei,China)
出处
《钢铁》
CAS
CSCD
北大核心
2024年第6期155-165,共11页
Iron and Steel
基金
国家自然科学基金面上资助项目(52074198,52374342)。
