Additive Manufacturing (AM) using metallic material is expected as a processing method to create mechanical parts that are difficult with conventional machining, but conventional equipments are expensive. Therefore, a composite material with a metal filler and a ceramic material is used to obtain inexpensive and thermally conductive parts. In order to improve the thermal conductivity, the proportion of the metal filler should be increased. However, if the proportion is too high, the viscosity of the material becomes high, and unable to obtain a sufficient amount of extrusion. Then, an extrusion type AM by ultrasonic vibration is used and adjusted to have a sufficient extrusion rate and high thermal conductivity. By preparing a test piece and measuring the thermal conductivity, it is confirmed that metal filler improves thermal conductivity of the test piece.

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AlSi10Mg alloy products with a hydrogen content of approximately 3.9 or 5.6 cm³/100g-Al of hydrogen were fabricated by selective laser melting (SLM) using normal (as-received) and moist powders, and their non-reversible dimensional changes during heat treatment at 473 or 803 K were investigated. The linear dimensional change arising from the heat treatment at 473 K was approximately 0.22％ by 3.6 ks and remained constant thereafter. This behavior was independent of the amount of hydrogen in the SLM products, suggesting that the dimensional changes at 473 K were induced by precipitation of Si phase from the α-Al phase. However, the linear dimensional changes during the heat treatment at 803 K were comparatively large and continued to increase during the heat treatment. At the same time, the linear dimensional changes at 803 K also showed a dependence on the amount of hydrogen in the SLM products. These phenomena indicated that the porosity expansion and precipitation of Si phase occurred simultaneously at 803 K. For the SLM product with a hydrogen content of approximately 3.9 cm³/100g-Al, the linear dimensional change during the heat treatment at 803 K was 0.867％ at 18 ks, of which 0.116％ and 0.751％ were estimated to have been induced by the precipitation of Si phase and the porosity expansion, respectively. From gas analyses using different methods, it was elucidated that the hydrogen desorbed from the powder and was entrapped in the SLM products at the time of laser scanning, and then enriched to the porosities during the heat treatment at 803 K, causing the porosity expansion.

 

Mater. Trans. 64 (2023) 697-706に掲載

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金属を用いたAdditive Manufacturing（以下AM）の一つに金属材料とバインダの混合材料を，超音波加振を用いて空気圧により押し出す方式がある.しかし超音波の加振を続けることで材料温度が上昇し，造形に影響を及ぼすことが確認されている．本研究では超音波加振による材料温度が造形精度に及ぼす影響の評価を行い，水冷装置の提案と有効性を示す．

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 Recently, AM (Additive Manufacturing) process which can produce highly complex components have been gaining significant attention in both industry and academic research. Numerous metals and alloys have been processed by selective laser melting; Ti alloys, Ni alloys, and Co-Cr alloys have been the subjects of recent work. Ni-based superalloys have precipitated phases such as γ′ and γ″ phase and Ti alloys and Co-Cr alloys are the multiphase alloys which have phase transformation, thus it is difficult to clarify the influential factors of AM process on strengths of these alloys. In this study, we used SUS316L stainless steel which is a single-phase solid-solution alloy and does not have precipitated phase in order to clarify characteristic influential factors of AM compared with a conventional material. SUS316L was fabricated by selective laser melting by ytterbium fiber laser from fine metallic powder. It was found that the coarse columnar grains grew up along the built direction and the columnar cell structure of dislocations which are induced during the AM process. During the solution heat treatment, the dislocation recovery was observed. AM specimens showed higher tensile and creep strengths compared with the conventional (hot working) material because of the high-density of dislocations. Ductility of AM specimens was lower than the conventional material because of defects due to lack of fusion at molten pool boundaries; furthermore, the specimens whose loading direction corresponds to built direction showed lower strength and elongation than the specimens whose loading direction perpendicular to built direction due to the oriented defects.

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This work examined the behaviors of densification and microstructural formation of the Al-10 mass％ Si- 0.35 mass％ Mg alloy fabricated by Selective Laser Melting (SLM) method on the basis of experimental work and machine learning. Additionally, the effect of scanning repeated twice in each layer (double scanning) in the SLM process was also investigated. The SLM- Al-10 mass％ Si- 0.35 mass％ Mg alloy exhibited the columnar grained microstructure with an (α-Al-Si) eutectic cell structure. Refined microstructures were produced at an increasing scanning speed with a decreasing the energy density (J/mm3). Relative density tended to increase with an increasing of energy density for scan pitch conditions of 0.1 mm and 0.05 mm. And a scattering was obviously exhibited at a higher relative density more than 95％. The analysis based on machine learning revealed that a scanning pitch of 0.2 mm was just a condition to achieve a high relative density. Except for the condition at a scanning pitch of 0.2 mm, a scan speed was the most important factor in affecting the relative density. Thus, a machine learning approach enabled to identify the important processing factor for affecting the behavior quantitatively. Additionally, compared to a conventional single scanning process, it was found in this work that the double scanning resulted in a higher relative density with keeping the fine microstructural formation.

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