In this study, we investigated characteristics and mechanical properties of SKD61 repaired using the direct energy deposition (DED) process. Mechanical properties of the repaired product can vary depending on the base material and powder used in the DED process. To prepare for DED repairing for a damaged part, we conducted experiments using two different powders (H13 and P21). Experimental results showed that both powders were deposited without defects in the surface or interface between the deposited zone and the substrate. Hardness measurements indicated that the repaired region of the Repaired-H13 sample exhibited higher hardness than the base material, while the Repaired-P21 sample showed a sharp increase in hardness in the heat-affected zone (HAZ). Additionally, tensile test results revealed that the Repaired-H13 sample had lower tensile strength and elongation than the base material, whereas the Repaired-P21 sample demonstrated higher tensile strength and yield strength with a higher elongation than the Repaired-H13 sample. In case of Repaired-H13, it was confirmed that interfacial crack occurred due to a high hardness difference between the repaired part and the substrate.

Additive manufacturing (AM) technology, also known as 3D printing, is a highly promising technology that can drive innovation in various industrial areas, including the nuclear industry. Although the nuclear industry is traditionally conservative when it comes to adopting new technologies, it is crucial that AM technology is eventually applied for a variety of reasons. To overcome the barriers that currently hinder the adoption of AM in the nuclear industry, it is essential to ensure the reliability of AM products. One key factor is ensuring that AM products have mechanical properties equivalent to those of traditionally manufactured products. This paper presents the results of mechanical property tests conducted on additive manufactured specimens of stainless steel 316 L after heat treatment. We performed tensile tests, hardness tests, and microstructure analysis on specimens produced using two types of metal AM technologies: powder bed fusion (PBF) and directed energy deposition (DED). The results of the tests indicate that certain weaknesses, such as anisotropy and brittleness, in AM products can be improved through three types of heat treatments. In particular, AM products produced using the PBF method and subjected to heat treatments show potential for application in the nuclear industry in terms of materials.

In this study, based on directed energy deposition (DED) technology, one of the additive manufacturing technologies, a porous material fabricated by mixing various aluminum alloys and foaming agent was manufactured. First, the foaming agent formed pores inside the deposited materials and differences in foaming characteristics were observed depending on the type of aluminum. Also, the foaming characteristics according to the laser power, which is a representative process variable, were analyzed. As a result, a closed-cell porous material with a maximum porosity at a laser power of 1,100 W was manufactured. Results of the compression test showed that the porous material made by the pores generated therein collapses to absorb energy, and the internal pores disappear to become high density. Therefore, Young’s modulus and yield stress were reduced by the pores inside the sample of pure aluminum and Al6063. However, it was found that the specific energy absorption, which is an advantage of the foamed materials, increased compared to non-porous materials. The findings of this study confirmed that it was possible to manufacture DED-applied foam materials using aluminum powder and a foaming agent.

The design of a substrate greatly affects the residual stress distribution and the deformation behavior of the repaired region by a directed energy deposition (DED) process. The objective of the present study was to investigate effects of edge length and slope of the substrate on residual stress and deformation characteristics in the vicinity of the repaired region for the repair of the straight damaged region using a DED process. Two-dimensional finite element analysis (FEA) was carried out using SYSWELD. Materials of the substrate and deposited powders were AISI 1045. The maximum residual stress during the deposition decreased when the edge length of the substrate increased, but increased when the slope of the substrate increased. The residual stress after a cooling state increased when the edge length and the slope increased. The displacement of the specimen increased when the slope of the substrate augmented. Finally, the methodology to select a proper edge length and slope of the substrate are discussed in this study.

Hybrid additive manufacturing (AM) refers to a combination of two metal AM techniques: material deposition by powder bed fusion (PBF) and additional building by directed energy deposition (DED). This study focused on different characteristics in accordance with relative deposition directions of PBF and DED during hybrid AM production. Characteristics of the sample fabricated by hybrid AM (i.e., hybrid sample) were compared with those of the sample fabricated by PBF or DED. Ferrite was dominant in the microstructure of PBF deposits with very fine retained austenite observed locally. In contrast, lath martensite and retained austenite were formed uniformly in the microstructure of DED deposits. Different microstructures in the two processes were attributed to differences of cooling rate. In DED deposits, microhardness was significantly decreased owing to a high retained austenite fraction. However, in the hybrid sample, microhardness was rapidly increased in the HAZ owing to aging heat treatment for long-term deposition. Principal wear mechanisms of PBF and DED samples were oxidative wear and plastic deformation, respectively.

Metal additive manufacturing processes such as directed energy deposition process (DED), can be used to manufacture high value metal parts, with improved mechanical properties and efficiency. However, parts produced by DED can suffer from excessive temperature gradients, and heat accumulation due to the deposition process. The purpose of this study was to investigate the impact of the deposited area on thermos-mechanical characteristics for the case of deposition of Inconel 718 powder, on the AISI 1045 substrate, using the DED process through finite element analyses (FEAs). Nine types of FE models were developed. Temperature dependent cooling conditions were analyzed, and applied to the model. Laser heat source was defined, as the three-dimensional volumetric heat source based on the Gaussian distribution model. Temperature dependent properties were assigned to the models. The influence of the width and the length of the deposited region, on residual stress distributions in the vicinity of deposited region were investigated. Additionally, the impacts of the deposited area on deformation characteristics were examined.

The directed energy deposition (DED) process has been used for enhancement of the mechanical property, repair, and part manufacturing. Post-process machining is required due to the low quality of the DED printed part. Even if the part is printed under similar conditions, dimensional variations occur frequently due to the accumulation of small printing errors. Due to tool overfeeding and the occurrence of the non-cutting area due to this variation, the quality of the finished part is not guaranteed. Therefore, the post-process machining should be carried out considering the actual printed part shape. Herein, the flexible post-process machining is proposed by utilizing the shape information through the on-machine measurement (OMM) of DED printed parts. The process margin for machining the design shape is calculated through the OMM of the geometric dimension of the printed part. Feedrate (Override) and machining path of each printing parts are flexibly determined depending on the process margin. This technique is applied to the pocket shape part printed with STS 316L material, and the rough and finish machining conditions are established. Rough machining time was reduced by adjusting the feedrate flexibly. The final form of accuracy and surface roughness were achieved under 30 and 0.25 μm, respectively.

It is compelling to realize that the additive manufactured part using wire feeding type directed energy deposition (DED) process is subjected to undesired thermal effects, and induced residual stress during the manufacturing process. In order to improve the quality of the manufactured part, the distributions of temperature and residual stress have to be understood to manage the results of the processing of these materials. The objective of this paper is to investigate the influence of the angle of corner deposition on the distributions of temperature and residual stress of the Ti-6Al-4V deposited bead, and the substrate via thermo-mechanical finite element analyses (FEAs). In the same fashion, the formation of the heat affected zone (HAZ) and the stress influenced region (SIR) are estimated from the measured results of the FEAs. Equally important, it can be stated that from the estimated HAZ and SIR regions, the overlapping of undesired thermal effects and residual stress between two beads fabricated by the wire feeding type DED process can be avoided at the design stage.