Influence of residual stresses on the crack propagation behavior in microstructurally graded samples manufactured by laser based additive manufacturing

残余应力对激光增材制造微结构梯度样品裂纹扩展行为的影响

• 批准号: 505457585
• 负责人: Dr.-Ing. Jens Gibmeier
• 金额: --
• 依托单位: Institut für Angewandte Materialien - Werkstoffkunde (IAM-WK)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/505457585?language=en
• 关键词: Influence; residual; stresses; crack; propagation

In additive manufacturing employing SLM (Selective Laser Melting), also termed laser based-powder bed fusion of metals (PBF-LB/M) according to EN ISO ASTM 52900, the structure and microstructure can be graded during component manufacturing through the appropriate choice of process parameters. It is possible to adapt this gradation specifically to the requirements that arise from the component application, so that complex component geometries with locally adapted micro-structure gradients can be manufactured. Local texturing can be used to specifically adapt the direc-tion-dependent strength and stiffness of local component areas to the prevailing loading situation. In preliminary work, it has already been shown that the fatigue behavior can also be substantially influenced by gradation of the microstructure. In particular, it has been shown that the cyclic crack propagation behavior can be influenced by local anisotropy. However, the role of the process-induced residual stress distributions on the local crack propagation behavior and, in particular, on the interaction between the crack and the interface remains absolutely unclear so far.The aim of the project, carried out in cooperation, is to assess the structural integrity of PBF-LB/M components, for which different gradations are specifically implemented through an adapted pro-cess design. This assessment is realized through the application of fracture mechanics concepts, tak-ing into account the local microstructure and the residual stresses. The single-phase austenitic steel 316L is initially used as a model material for the systematic investigations. In the further course of the project, the transfer to the Ni-base alloy IN718 takes place, so that a multiphase character is also considered. Rectangular profiles with wall thicknesses of 2 and 4 mm are considered as model com-ponents. The side surfaces of the profiles produced by means of PBF-LB/M are characterized in detail with respect to the existing local structure, crystallographic texture and residual stress gradi-ents in lateral and in depth directions. Following this systematic basic characterization, samples for crack growth analysis (CT samples) are taken from the side surfaces, taking into account the built direction of the components. The crack propagation behavior is analyzed on these CT samples based on cyclic stress-intensity-controlled crack propagation tests, whereby the development of the local residual stress distributions is determined for different stages of the crack propagation in interrupted test runs. On this basis, in the course of evaluating the elementary characteristics of crack growth, a model is derived that allows for describing the damage evolution of the specifically graded materi-als based on the local structure, residual stress state and microstructure (including grain orientations and crystallographic texture).

在采用SLM（选择性激光熔化）的增材制造中，根据EN ISO ASTM 52900，也称为金属的激光基粉末床熔合（PBF-LB/M），可以通过适当选择工艺参数在组件制造期间对结构和微观结构进行分级。可以使该梯度特别地适应于由部件应用引起的要求，使得可以制造具有局部适应的微结构梯度的复杂部件几何形状。局部纹理可用于专门调整局部组件区域的方向相关强度和刚度，以适应当前的负载情况。在初步工作中，已经表明，疲劳行为也可以受到微观结构分级的显著影响。特别是，它已被证明，循环裂纹扩展行为可以由局部各向异性的影响。然而，工艺引起的残余应力分布对局部裂纹扩展行为的作用，特别是对裂纹与界面之间的相互作用的作用，至今仍不清楚。该项目的目的是评估PBF-LB/M构件的结构完整性，通过调整工艺设计，对PBF-LB/M构件进行了不同等级的专门设计。这种评估是通过应用断裂力学概念，考虑到局部微观结构和残余应力来实现的。单相奥氏体钢316L最初被用作系统研究的模型材料。在项目的后续过程中，将过渡到镍基合金IN 718，因此也考虑了多相特性。壁厚为2 mm和4 mm的矩形型材被视为模型构件。本文详细地描述了PBF-LB/M型材侧面的局部结构、晶体学织构以及横向和深度方向的残余应力梯度。在系统的基本表征之后，从侧面采集用于裂纹扩展分析的样品（CT样品），同时考虑部件的构建方向。基于循环应力强度控制的裂纹扩展试验，对这些CT样品的裂纹扩展行为进行了分析，从而确定了在中断的试验运行中裂纹扩展的不同阶段的局部残余应力分布的发展。在此基础上，在评价裂纹扩展基本特征的过程中，导出了一个基于局部结构、残余应力状态和微观结构（包括晶粒取向和晶体学织构）描述特定梯度材料损伤演化的模型。