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.

Additive manufacturing has many positives, but its incorporation into functional parts production is restricted by the presence of defects. Eddy current testing provides solutions for their identification; however, some methodology and measurement standards for AM (additive manufacturing) products are still missing. The main purpose of the experiment described within this article was to check the ability of eddy current testing to identify AM stainless steel parts and to examine the data obtained by eddy currents variation under the influence of various types of designed artificial defects. Experimental samples were designed and prepared with SLM (selective laser melting) technology. Artificial defects, included in the samples, were detected using the eddy current testing device, taking the important circumstances of this non-destructive method into account. The presented research shows significant potential for eddy current testing to identify defects in AM products, with a resolution of various types and sizes of defects. The obtained data output shows the importance of choosing the right measurement regime, excitation frequency and secondary parameters setup. Besides the eddy current testing conditions, defect properties also play a significant role, such as their shape, size, if they are filled with unmolten powder or if they reach the surface.

The incorporation of additive manufactured (AM) metal parts to real assemblies is a crucial issue for the increasing of their industrial utilization. The presented research is devoted to the electron beam welding (EBW) of dissimilar steel joints. Dissimilarity is defined by the various types of steel and manufacturing processes used for the creation of specimens. Conventional AISI 316 stainless steel, selective laser melted (SLM) SS 316L stainless steel, and SLM M300 maraging steel were welded at variable parameters in the form of a welding current and a welding velocity. EBW joints were evaluated considering the macroscopic and microscopic characteristics, as well as a reached microhardness. The obtained preliminary results represent important input data for the follow-up experiments focused on the setting of optimal EBW parameters of welding the dissimilar joints including SLM products, with the consideration of their basic macroscopical and microscopical characteristics, mechanical properties, and residual stresses.

This paper deals with the application of the direct metal laser sintering (DMLS) process, which already has a dominant position in the area of additive manufacturing (AM). This DMLS technology is used in many branches of industry and medicine, especially in piece production, small series, and prototypes. The portfolio of used metal powder materials includes aluminum alloys, austenitic steels, maraging steels, special alloys of nickel and titanium. The properties of these products are very often improved by further heat treatment after printing, such as a hardening process, by which microstructure and hardness can be increased. Heat treatment processes of metal AM components are already described, but experiments focused on optimization of these processes are still missing. In the article, the maraging steel samples printed by the DMLS method are subjected to testing after hardening processes, which differ by reducing the maintaining time at a defined temperature, recommended by the manufacturer. The result of the evaluation will be the reaching of similar results, which are set by the powder manufacturer, however, with shorter time of samples treatment. Therefore, the elevated temperature is selected, with the purpose of monitoring the shortest possible time of a temperature impact. The experimental temperature was set 590 °C with different durations at this temperature, for 1, 2, 3, 4, 5 and 6 h. The cooling process runs controlled in the furnace or in the still air. The maintaining time proved to be the most ideal already at 1 h exposure and cooled in the still air, where a higher hardness value of around 50 HRC was reached. During the resulting microstructure evaluations, fine carbids and martensitic lamellae were observed. More uniform and finer lamellar microstructure occurred at 5 and 6 h temperature intervals.

The identification of residual stresses (RS) in components made by selective laser melting (SLM) is necessary for subsequent technological optimization. The presented research is devoted to evaluating the influence of the combination of laser power (P), scanning velocity (v) and the rarely considered number of layers (n_L) on surface residual stresses in SLM stainless steel SS 316L. Experimental parameters were set based on the Design of Experiment (DoE) method, with follow-up X-ray diffraction (XRD) measurements and data processing using analysis of variance (ANOVA) and regression analysis. The obtained data are a valuable stepping-stone for the subsequent design of research focused on the application of sustainable eco-friendly Abrasive Water Jet (AWJ) peening for RS modification in the evaluated material.

The paper deals with the application of abrasive water-jet cutting to composite material containing natural reinforcement—wood plastic composite. The specimens were cut through the application of four flows of different abrasive mass: 150, 200, 250, and 300 g·min⁻¹, respectively, and under different traverse speeds required to achieve the (expected) quality level Q1–Q5 (according to the SN 214001: 2010 standard). The output quality of Q1–Q5 was set in the CNC cutting programs and the real traverse speed values were calculated by machine control system according to change in the flow of the abrasive mass. The quality of surface topography was assessed using a tester (contact roughness) and an Inspectis digital zoom microscope. The results of topography–surface roughness parameters Ra presented here are compared with the values normalized for individual samples sets. The applied technology, i.e., the AWJ, eliminated the problem of tool wear and adhesion of the thermoplastic matrix to tool surfaces (compared to standard machining).