Unique crystallographic texture formation in Inconel 718 by laser powder bed fusion and its effect on mechanical anisotropy

Fracture and fatigue in additively manufactured metals

Fatigue strength of additively manufactured 316L austenitic stainless steel

Development of TiNbTaZrMo bio-high entropy alloy (BioHEA) super-solid solution by selective laser melting, and its improved mechanical property and biocompatibility

This is the first comprehensive study on the development of a cubic crystallographic texture in pure chromium (Cr) manufactured using laser powder bed fusion (LPBF) with different laser energy densities to alter its microstructure and high-temperature oxidation behavior. An increase in the laser energy density led to the formation of a strong crystallographic texture, which was preferentially oriented in the (100) plane, and there were microstructural improvements in the pure Cr. The grain size of the (100)-oriented Cr was larger than that of the randomly oriented Cr. In addition, the high-angle grain boundary and coincident site lattice (CSL) boundary characteristics were altered. The (100)-oriented Cr exhibited a decrease in the oxide thickness that was due to the decrease in the grain boundary density with a larger grain size and an increase in the CSL boundary ratio. In contrast, the Cr with a random texture showed higher oxidation kinetics and spallation of the oxide layer. The oxidation kinetics of the pure Cr manufactured using LPBF obeyed the parabolic rate law. However, the crystal orientation affected the oxidation of the Cr as the (100)-oriented pure Cr displayed a lower parabolic rate constant, indicating that the (100)-oriented Cr was oxidation-resistant. This is the first report to demonstrate the cubic crystallographic texture formation and the improvement of high-temperature oxidation resistance in Cr manufactured using LPBF.

Crystallographic orientation control of pure chromium via laser powder bed fusion and improved high temperature oxidation resistance

Metal additive manufacturing (AM) has attracted the most attention in recent years among various metal processing technologies. Conventionally, metal AM has been characterized by its flexible shaping ability and relatively high processing speed. Taking advantage of such features of AM, metal AM technology has been applied to the fabrication of products with hollow structures, three-dimensional complex porous bodies, and tailor-made products, among others.1,2) Meanwhile, in recent studies, metal AM has emerged as a methodology for controlling the crystallographic texture of metallic materials3–5) in addition to controlling the shape of products. Crystallographic texture, which is an important material parameter for metallic materials, is a major factor that affects the functionality of a product, independent of shape parameters. The mechanical properties of metallic materials are the most significant factor controlled by the crystallographic texture. Highly texturized materials with preferential crystallographic orientations can feature mechanical anisotropies, such as Young’s modulus,6,7) yield stress and elongation,8) fatigue resistance,9) and creep resistance.10) The single crystalline form, in which the anisotropy based on the atomic arrangement is manifested to the limit, exhibits Crystallographic Orientation Control of 316L Austenitic Stainless Steel via Selective Laser Melting

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Crystallographic Orientation Control of 316L Austenitic Stainless Steel via Selective Laser Melting

In metal additive manufacturing, the microstructures and associated mechanical properties of metal specimens can be controlled over a wide range. Although process parameters are considered important in the fabrication of functional parts, the effect of atmospheric gas has not been comprehensively documented. In laser powder bed fusion (LPBF), gas flow is used to eliminate fumes generated by laser irradiation. Simultaneously, the gas removes heat from the laser-irradiated part, which is exposed to high temperature. In this study, we investigated the capacity of helium as an alternative to argon, which is conventionally used as the LPBF atmosphere gas. He has a higher thermal conductivity and lower gas density than Ar, which may result in enhanced heat removal from the Ti-6Al-4V alloy during fabrication. Numerical simulations suggest a greater cooling rate under He flow. Further, the material built under He flow contained finer α' martensite grains and showed improved mechanical properties compared to those fabricated under Ar flow, despite the identical laser irradiation conditions. Thus, He gas is advantageous in LPBF for fabricating products with superior mechanical performance through microstructural refinement, and this is a result of its capacity for cooling and fume generation inhibition. Therefore, this study reveals the importance of the choice of atmospheric gas because of its effects on the characteristics of metallic specimens fabricated using LPBF.

Effect of a helium gas atmosphere on the mechanical properties of Ti-6Al-4V alloy built with laser powder bed fusion: A comparative study with argon gas

Reduction of Spatter Generation Using Atmospheric Gas in Laser Powder Bed Fusion of Ti–6Al–4V

レーザ積層造形(Selective Laser Melting: SLM)法は、粉末 床溶融(Powder Bed Fusion: PBF)方式の付加製造(Additive Manufacturing: AM)技術の一種である。主に金属材料造形 に適用され、任意形状の構造物を精度よく製造することを 得意とする最先端のデジタルモノづくりシステムである。 すでに、航空機関連部材を含む産業機器分野や医療機器分 野等への適用に向けた研究開発が進められ、一部では実用 化が開始されている。 従来 SLMをはじめとする AM技術は、外形状制御によ る高付加価値化を期待されてきたが、近年では形状のみな らず、結晶集合組織や結晶粒性状といった金属材料の材質 制御による高機能化部材の作製を可能とする方法論として の認識が拡大している。例えば、レーザ走査条件や層 ごとのレーザ走査パターンの組み合わせを意味するスキャ ンストラテジーによって、集合組織の強度や優先配向方向 が制御可能であり、それに依存して造形物の力学特性 が制御可能となる 。このように、金属 AMを活用して、 形状と材質の両面からの高機能化設計が可能となりつつあ る 。 一方で、こうした高度な機能制御においては、造形過程 で形成される欠陥が大きな問題となる。欠陥の形成は部材 の特性を劣化させ、部材の品質管理に不確実性をもたらし、 様々な産業における AM適用の実用化を妨げる要因とも なっている。欠陥形成の主要因の一つに、スパッタの発 生が挙げられる 。Fig. 1には、造形中のスパッタ発生の 例を示す。スパッタの発生は、スパッタがレーザ光路を通 過することでレーザのエネルギー効率を低下させること、 さらには、レーザ照射前の粉末層にスパッタが飛散するこ とで造形物中にスパッタが取り込まれ、造形物の材質特性 に影響を与える可能性が考えられる。さらには、SLM法で は通常未溶融粉末を回収し再利用す るが、回収粉末中にス パッタが含有し、次の造形に影響を与える可能性がある。 したがって、スパッタの発生量を低減することが、SLMに おける造形物の品質管理には重要であると言える。 しかしながら、スパッタ発生に関しては未解明な事象が 多く、その制御法は確立されてはいない。本研究では、造 レーザ積層造形における雰囲気中の酸素がスパッタ発生に与える影響

Effect of Oxygen Concentration on the Generation of Spatter during Fabrication via Selective Laser Melting

The purpose of the present invention is to provide a manufacturing device and a manufacturing method with which it is possible to manufacture a metal object with superior mechanical properties and design for external appearance as well as a metal powder recovery method with which it is possible to easily reuse powder not affected by heat Provided is a device (20) for manufacturing a metal object for manufacturing a metal object (X) by irradiating the surface layer of metal powder (M), which fills a fabrication tank (12) of a fabrication stage (10), with laser light (L) and fabricating and laminating layers of metal, said device being characterized by comprising a calculation unit (4) for calculating a second region which is a region surrounding a first region irradiated by the laser light (L) and an elimination mechanism (5) for eliminating metal powder included in the second region, which is calculated by the calculation mechanism, from the fabrication tank (12)

Amano Hiroki

Papers

Crystallographic Orientation Control of 316L Austenitic Stainless Steel via Selective Laser Melting

Effect of a helium gas atmosphere on the mechanical properties of Ti-6Al-4V alloy built with laser powder bed fusion: A comparative study with argon gas

Reduction of Spatter Generation Using Atmospheric Gas in Laser Powder Bed Fusion of Ti–6Al–4V

Effect of Oxygen Concentration on the Generation of Spatter during Fabrication via Selective Laser Melting

Manufacturing device for metal object, manufacturing method for metal object, and metal powder recovery method