The aim of the diploma thesis is to study fatigue properties of EN AW-2618A aluminium alloy produced by selective laser melting (SLM). S-N diagrams of reference alloy and SLM material depending on manufacturing conditions were constructed. Reference alloy had the same chemical composition as the SLM material, but it was made by traditional technology (by extruding). While testing, acoustic emission (AE) and resonant frequency of loading was monitored. Fractographic analyses of fracture surfaces were performed. It was found, that SLM material has significantly worse fatigue performance. Fatigue properties are strongly dependent on SLM process parameters settings and precise observance of procedure. The most significant differences in cyclic degradation were found in the length of the stages of fatigue. The more homogeneous the material is, the longer the nucleation stage compared to the total lifetime is. The main source of AE in case of the reference material is plastic deformation on the tip of the crack. For SLM testing, stronger acoustic activity was recorded, because brittle fracture of the material between discontinuities, which is stronger AE source, is more frequent.

This diploma thesis deals with finding copper alloy suitable for processing SLM technology and determining the process parameters leading to a relative density close to the full material. The theoretical part provides an insight into additive technology and the processing of new alloys in SLM. Work also contains a search report of processed copper alloys used in SLM. Based on the theoretical part were designed test samples and method of evaluation. Samples were produced by melting metallurgical powder using ytterbium laser with an output power 400 W. The testing is divided into three stages; Determination of the parameters of the SLM process, Debug strategies for larger parts, Geometric precision and mechanical testing. Based on the results was determined dependence of relative density on the input parameters. For the best parameters were determined geometric precision correction and mechanical properties.

3D printing, also known as additive manufacturing (AM), has got rapidly developed since 1987. Compared with conventional manufacturing methods, 3D printing provides some advantages such as increasing material utilization and less waste of material. Maraging steel provides good strength and toughness without losing ductility, which has been used for the 3D printing technique. Selective laser melting (SLM) is one of the 3D printing methods, which is mostly used for metal and alloy powder. In this thesis, selective laser melting will be used for maraging steel. 3D printing maraging steel is a new material, the research about the properties of 3D printing maraging steel is still ongoing. Corrosion resistance is one of the most important properties of maraging steel due to the high cost of corrosion. So this thesis will focus on the corrosion behavior of 3D printing maraging steel. The purpose of this thesis was to find the best heat treatment condition for high corrosion resistance and to find the relationship between microstructure and corrosion behavior of maraging steel. In this thesis, several kinds of maraging steel samples with different heat treatment conditions were used. SLM, SLM austenized&quenched, SLM aged, conventional austenized&quenched, and conventional aged. Besides, two kinds of solutions were produced, NaOH (pH=11.5) and Na2SO4 (pH=6.5). To observe the microstructure, an optical microscope was used. The grain size is different between SLM and conventional samples, and also different between the samples with different heat treatment conditions. The potentiodynamic polarization method was used to measuring the corrosion behavior. SLM samples have much lower current density, and the passivation potential and the corrosion rate are similar compared with conventional samples. But due to the lack of further experiments, the relationship between corrosion behavior could be affected by the combined effect of several factors.

Selective laser melting has shown incredible growth as a metallic additive manufacturing process in recent years. While it does provide many solutions and new ways to approach challenges, it does not come without issues of its own, namely, surface roughness. In the as-printed state, the surface roughness of selectively laser melted parts is unacceptable for use in engineering applications. Additionally, selective laser melting is used to produce complex geometries with hard to reach features, preventing conventional mechanical polishing from being successful. Therefore, it is necessary to evaluate non-mechanical polishing processes as treatments for surface roughness. In this study, electrochemical and laser polishing were investigated as potential start-to-finish treatments for the surface roughness of selectively laser melted parts. Following this preliminary study, a follow-up study investigating the effect on the mechanical strength of a lattice design that electropolishing would have. Electropolishing was found to significantly reduce the surface roughness of the as-printed part, but not to a usable value. Additionally, electropolishing was found to be unacceptable for use on lattice parts. Laser polishing was found to significantly reduce the surface roughness of the part but had feature size issues preventing a perfectly smooth surface.

A drill tool body operates under tough cutting conditions where it is subjected to severe rubbing at the drill flute margin by the sliding chips. The tool wear caused by the contact stresses of the high-speed sliding chips is one of the common damage mechanisms observed in drill tool bodies. The present investigation is aimed at evaluating the wear properties, mechanical properties and tribological characteristics of the selective laser melting (SLM) produced drill bodies of Co-alloyed tool steels. Two different maraging steel powders, Modified 18Ni300 and Osprey MAR were the materials of interest in this work. A ranking was obtained after a detailed examination to select the most suitable cutting tool body material for drilling application. The microstructures of SLM-produced materials after aging were carefully characterized and analyzed. The result shows that both the materials are composed of fine dendritic cellular structures and even exhibit melt pool boundaries. The microhardness values taken on the as-polished samples indicate that Modified 18Ni300 is marginally harder than Osprey MAR. The material pick-up tendency, friction characteristics and wear properties of the two material samples at room temperature were also evaluated using a scratch tester and a pin-on-disc tribometer. The wear volume for the scratch test and the pin-on-disc test was quantified by a 3D optical profilometer. The overall coefficient of friction (COF) and the wear volume was considerably higher for Osprey MAR than Modified 18Ni300 in scratch testing. The increase in COF for Osprey MAR can be attributed to the build-up edge adhered to the moving stylus. Wear characterization of the scratched surface shows secondary plowing which validates the adhesion tendency of Osprey MAR. The results from the pin-on-disc test conform to the scratch results displaying marginally lower COF and wear volume for the Modified 18Ni300 disc specimen. The higher volume loss of pin manufactured from workpiece material SS2541 used against Modified 18Ni300 disc substantiates the better wear characteristics of this material. Characterization of wear on the surface and cross-section of disc samples suggests that the total wear is the result of adhesion by delamination and build-up edge, abrasion, and cellular fracture at the interacting interface. Machining application tests were also conducted to study the chip wear characteristics and facilitate the ranking of the materials concerning wear resistance. Chip breaker wear test was performed with chip breakers of two different surface topography, milled and ground, to evaluate the effect of surface texture and roughness on the wear behavior. The result shows adhesion on the chip breaker surface for both the materials of interest. The wear is higher in Osprey MAR than Modified 18Ni300 in both milled and ground conditions. A series of actual drill tests from SLM-produced drill bodies indicates wear at the drill flute margin. The drill body material at the chip flute margin is abraded by the sliding chips for Osprey MAR exhibiting greater wear than Modified 18Ni300 in which case the flute margin is intact. Adhesion is also seen at the flute surface for both materials. EDS analysis undertaken at the site of wear confirms the adhered material is of the workpiece SS2541. The results from all the aforementioned tests suggest that Modified 18Ni300 has better wear resistance than Osprey MAR. It also indicates that the cellular microstructure of SLM-produced maraging steels is not suitable for sliding wear resistance.

Selective laser melting (SLM) is a method of additive manufacturing that has become increasingly popular in recent years for fabricating complex components, especially in the medical and aerospace industries. By fabricating components in a layerwise fashion, SLM provides users the freedom to design components based on their desired functionality rather than their manufacturability. The current state-of-the-art for SLM is limited though, as defects induced by the SLM process have proven to greatly alter the material properties of fabricated parts. In addition, traditional post-process nondestructive inspection methods have experienced significant difficulty in accurately detecting these process-induced defects. Therefore, the objective of this study is to investigate methods of processing and analysis for optical in-situ monitoring data recorded during SLM fabrication of six test samples. Four of the samples were designed with seeded (i.e., intentional) defects located at their center to serve as a reference defect signatures in the resulting in-situ data. An off-axis optical tomography (OT) sensor was used to capture near-infrared (NIR) melt pool emissions during the fabrication of each layer. Image analysis was subsequently performed using a custom squared difference (SD) operator to enhance defect signatures in the OT data. Results from the SD operator were then used to perform k-means clustering to partition the data into k relevant clusters, where the optimal number of k clusters for each image is employed as metric for detecting the onset of defects in the samples. By employing OT image data from samples containing seeded intentional defects, the k-means clustering approach was investigated as a method of defect detection for the in-situ OT images. Results showed that the SD operator is capable of elucidating anomalous signatures in the in-situ data. However, variations within the SD distributions ultimately limited detection capabilities as the output from k-means clustering was unable to accurately distinguish the seeded defects from the fused regions of material.

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Subscription articles: Theses and dissertations which contain embedded PJAs as part of the formal submission can be posted publicly by the awarding institution with DOI links back to the formal publications on ScienceDirect.doi:10.1016/j.msec.2015.10.069 / 京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19578号 / 医博第4085号 / 新制||医||1013(附属図書館) / 32614 / 京都大学大学院医学研究科医学専攻 / (主査)教授 安達 泰治, 教授 開 祐司, 教授 妻木 範行 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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