Gel'atko Matúš, Hatala Michal, Botko František, Vandžura Radoslav, Hajnyš Jiří, Šajgalík Michal, Török Jozef
Faculty of Manufacturing Technologies, Technical University of Košice, 080 01 Prešov, Slovakia.
Center of 3D Printing Protolab, Department of Machining, Assembly and Engineering Technology, Faculty of Mechanical Engineering, VSB-TU Ostrava, 17. Listopadu 2172/15, 708 00 Ostrava, Czech Republic.
Materials (Basel). 2023 Sep 28;16(19):6461. doi: 10.3390/ma16196461.
Residual stress occurs in the materials after different methods of processing due to the application of pressure and/or thermal gradient. The occurrence of residual stresses can be observed in both subtractive and additive-manufactured (AM) materials and objects. However, pressure residual stresses are considered, in some cases, to have a positive effect; there are applications where the neutral stress state is required. As there is a lack of standards describing the heat treatment of AM materials, there is a need for experimental research in this field. The objective of this article is to determine the heat treatment thermal regime to achieve close to zero stress state in the subsurface layer of additively manufactured AM316L stainless steel. The presented objective leads to the long-term goal of neutral etalons for eddy current residual stress testing preparation. A semi-product intended for the experiment was prepared using the Selective Laser Melting (SLM) process and subsequently cut, using Abrasive Water Jet (AWJ) technology, into experimental specimens, which were consequently heat-treated in combination with four temperatures and three holding times. Residual stresses were measured using X-ray diffraction (XRD), and microstructure variations were observed and examined. A combination of higher temperature and longer duration of heat treatment caused more significant stress relaxation, and the original stress state of the material influenced a degree of this relaxation. The microstructure formed of cellular grains changed slightly in the form of grain growth with randomly occurring unmolten powder particles, porosity, and inclusion precipitation.
由于压力和/或热梯度的作用，在经过不同加工方法后，材料中会产生残余应力。在减材制造和增材制造（AM）的材料及物体中都能观察到残余应力的产生。然而，在某些情况下，压力残余应力被认为具有积极作用；存在需要中性应力状态的应用。由于缺乏描述增材制造材料热处理的标准，因此该领域需要进行实验研究。本文的目的是确定热处理热制度，以使增材制造的AM316L不锈钢表层达到接近零应力状态。提出的这一目标指向了用于涡流残余应力测试准备的中性标准样件的长期目标。使用选择性激光熔化（SLM）工艺制备了用于实验的半成品，随后利用磨料水射流（AWJ）技术将其切割成实验试样，然后将这些试样在四种温度和三种保温时间的组合下进行热处理。使用X射线衍射（XRD）测量残余应力，并观察和检查微观结构变化。较高温度和较长热处理持续时间的组合导致更显著的应力松弛，并且材料的原始应力状态影响这种松弛的程度。由胞状晶粒形成的微观结构以晶粒生长的形式略有变化，伴有随机出现的未熔粉末颗粒、孔隙率和夹杂物析出。
