What's New
2021（July－December）
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2021.10.29
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2021.10.27
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2021.9.28
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2021.9.13
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2021.9.11
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2021.9.5
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2021.9.3
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2021.9.2
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2021.8.19
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2021.8.16
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2021.8.1
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2021.7.23
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2021.7.12
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2021.7.8
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2021.7.7
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2021.7.3
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2021.10.29
We succeeded in forming high-melting-point W with reduced crack formation by changing the powder preparation method using laser metal 3D printing (L-PBF), and the paper proving it in cyber-physical space was published as an OA paper in AM Letters.
Ozkan Gokcekaya, Takuya Ishimoto, Tsubasa Todo, Pan Wang, Nakano Takayoshi*:
Influence of powder characteristics on densification via crystallographic texture formation: Pure tungsten prepared by laser powder bed fusion,
Additive Manufacturing Letters, 1, (2021), 100016; 1-8.
https://doi.org/10.1016/j.addlet.2021.100016Click here for this paper
Abstract
The laser powder bed fusion (LPBF) of pure tungsten for the fabrication of near-fully dense components is challenging owing to the intrinsic properties of tungsten. In this study, routine, gas-atomized, and plasma-processed tungsten powder samples were characterized for their powder shape, size distribution, tapped density, and flowability, and then used to fabricate parts using identical LPBF process parameters to evaluate the influence of the powder characteristics on the metal densification and microstructure. The plasma-processed W powder showed a relative density of 98.7%, the highest value yet to be reported, at a baseplate temperature of 80°C owing to the higher tapped density and improved flowability of the powder, which result in high-quality powder bed formation. In addition, numerical simulations were conducted to estimate the effect of the powder quality on laser energy absorption and, thus, melt pool formation. The results reveal that enhanced powder characteristics result in an increased density and prevent lack of fusion while tuning the grain boundary characteristics and strengthening the crystallographic texture, which resulted in decreased cracking owing to less crack-sensitive grain boundaries and increased hardness of the as-built W components.
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2021.10.27
【 paper 】We succeeded in forming high-melting-point W with reduced crack formation by changing the powder preparation method using laser metal 3D printing (L-PBF), and the paper proving it in cyber-physical space was published as an OA paper in Additive M
Ozkan Gokcekaya, Takuya Ishimoto, Tsubasa Todo, Pan Wang, Nakano Takayoshi*:
Influence of powder characteristics on densification via crystallographic texture formation: Pure tungsten prepared by laser powder bed fusion,
Additive Manufacturing Letters, 1, (2021), 100016; 1-8.
https://doi.org/10.1016/j.addlet.2021.100016Click here for this paper
Abstract
The laser powder bed fusion (LPBF) of pure tungsten for the fabrication of near-fully dense components is challenging owing to the intrinsic properties of tungsten. In this study, routine, gas-atomized, and plasma-processed tungsten powder samples were characterized for their powder shape, size distribution, tapped density, and flowability, and then used to fabricate parts using identical LPBF process parameters to evaluate the influence of the powder characteristics on the metal densification and microstructure. The plasma-processed W powder showed a relative density of 98.7%, the highest value yet to be reported, at a baseplate temperature of 80°C owing to the higher tapped density and improved flowability of the powder, which result in high-quality powder bed formation. In addition, numerical simulations were conducted to estimate the effect of the powder quality on laser energy absorption and, thus, melt pool formation. The results reveal that enhanced powder characteristics result in an increased density and prevent lack of fusion while tuning the grain boundary characteristics and strengthening the crystallographic texture, which resulted in decreased cracking owing to less crack-sensitive grain boundaries and increased hardness of the as-built W components. -
2021.9.28
A paper on the difference of powder bed fusion by using electron beam and laser beam as heat sources has been published as an open access paper in Additive Manufacturing (IF=11).
Shi-Hai Sun, Koji Hagihara, Takuya Ishimoto, Ryoya Suganuma, Yun-Fei Xue, Takayoshi Nakano:
Comparison of microstructure, crystallographic texture, and mechanical properties in Ti–15Mo–5Zr–3Al alloys fabricated via electron and laser beam powder bed fusion technologies
Additive Manufacturing, 47, (2021), 102329; 1-17.
https://doi.org/10.1016/j.addma.2021.102329Click here for this paper
Abstract
Depending on the application, establishing a strategy for selecting the type of powder bed fusion technology from electron beam (EB-PBF) or laser powder bed fusion (L-PBF)—is important. In this study, we focused on the β-type Ti–15Mo–5Zr–3Al alloy (expected for hard-tissue implant applications) as a model material, and we examined the variations in the microstructure, crystallographic texture, and resultant mechanical properties of specimens fabricated by L-PBF and EB-PBF. Because the melting mode transforms from the conduction mode to the keyhole mode with an increase in the energy density in L-PBF, the relative density of the L-PBF-built specimen decreases at higher energy densities, unlike that of the EB-PBF-built specimen. Although both EB-PBF and LPBF can obtain cubic crystallographic textures via bidirectional scanning with a 90° rotation in each layer, the formation mechanisms of the textures were found to be different. The <100> texture in the build direction is mainly derived from the vertically grown columnar cells in EB-PBF, whereas it is derived from the vertically and horizontally grown columnar cells in L-PBF. Consequently, different textures were developed via bidirectional scanning without rotation in each layer: the <110>and <100>aligned textures along the build direction in LPBF and EB-PBF, respectively. The L-PBF-built specimen exhibited considerably better ductility, but slightly lower strength than the EB-PBF-built specimen, under the conditions of the same crystallographic texture and relative density. We attributed this to the variation in the microstructures of the specimens; the formation of the α-phase was completely absent in the L-PBF-built specimen. The results demonstrate the importance of properly selecting the two technologies according to the material and its application. -
2021.9.13
A paper on kink strengthening of Mg-Zn-Y alloys containing LPSO layers as nanoplates has been published as an open access paper in Materials Research Letters.
Koji Hagihara*, Ryohei Ueyama, Toko Tokunaga, Michiaki Yamasaki, Yoshihito Kawamura, Takayoshi Nakano
Quantitative estimation of kink-band strengthening in an Mg–Zn–Y single crystal with LPSO nanoplates
Materials Research Letters, 9 (2021) 467-474.
https://doi.org/10.1080/21663831.2021.1974593Click here for this paper
Abstract
Kink-band strengthening was first quantitatively evaluated using an Mg–Zn–Y single crystal containing long-period stacking ordered (LPSO) nanoplates. The ability of a kink-band boundary to act as a barrier that hinders the motion of dislocations is high and comparable to that of a general random grain boundary. Nevertheless, a kink-band boundary is regarded as a simple tilt boundary in the dislocation model. One reason for the anomalous ability of kink-band boundary acting as barriers is related to its peculiar hierarchical structure, in which many small kink bands with high crystal rotation angles accumulate in a localized region. By the quantitative estimation using the single crystal, the origin of the anomalous ability of kink bands acting as barriers that hinder the motion of dislocation was elucidated. -
2021.9.11
A paper on the densification of tungsten by laser AM and the mechanism of crystal orientation control was published as an OA paper in Scripta Materialia (IF=5.6).
Tsubasa Todo, Takuya Ishimoto, Ozkan Gokcekaya, Jongyeong Oh, Takayoshi Nakano*:
Single crystalline-like crystallographic texture formation of pure tungsten through laser powder bed fusion,
Scripta Materialia, 206, (2022), 114252; 1-6.
https://doi.org/10.1016/j.scriptamat.2021.114252Click here for this paper
Abstract We successfully formed the first prominent crystallographic texture of tungsten using laser powder bed fusion (LPBF). It is difficult even to manufacture highly dense tungsten products using LPBF because of its extremely high melting point and high thermal conductivity. By tuning the laser process parameters, we succeeded in fabricating almost fully dense pure tungsten parts with a relative density of 99.1%, which is the highest value yet to be reported. More importantly, a single crystalline-like prominent crystallographic texture evolved, in which <011> preferentially oriented in the scanning direction. This texture was formed to reduce the crystal misorientation at the melt pool center, at which the solidification fronts from the right and left halves of the melt pool encounter. This texture formation mechanism is similar to that of conventional alloys with ordinary thermal properties; however, the crystal growth directionality that governs the crystallographic orientation differs according to the melt pool morphology.
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2021.9.5
A paper on deformation behavior of powder/solid composites with a honeycomb structure has been published in Crystals (MDPI: IF=2.6) as an open access article. The results on the control of crystallographic microstructure and mechanical properties of nick
Naoko Ikeo*, Tatsuya Matsumi, Takuya Ishimoto, Ryosuke Ozasa, Aira Matsugaki, Tadaaki Matsuzaka, Ozkan Gokcekaya, Yorinobu Takigawa, Takayoshi Nakano*:
Fabrication of Ti-Alloy Powder/Solid Composite with Uniaxial Anisotropy by Introducing Unidirectional Honeycomb Structure via Electron Beam Powder Bed Fusion,
Crystals, 11 [9], (2021), 1074;1-11.
https://doi.org/10.3390/cryst11091074Click here for this paper
Abstract:
In this study, a Ti–6Al–4V alloy composite with uniaxial anisotropy and a hierarchical structure is fabricated using electron beam powder bed fusion, one of the additive manufacturing techniques that enable arbitrary fabrication, and subsequent heat treatment. The uniaxial anisotropic deformation behavior and mechanical properties such as Young’s modulus are obtained by introducing a unidirectional honeycomb structure. The main feature of this structure is that the unmelted powder retained in the pores of the honeycomb structure. After appropriate heat treatment at 1020 °C, necks are formed between the powder particles and between the powder particles and the honeycomb wall, enabling a stress transmission through the necks when the composite is loaded. This means that the powder part has been mechanically functionalized by the neck formation. As a result, a plateau region appears in the stress–strain curve. The stress transfer among the powder particles leads to the cooperative deformation of the composites, contributing to the excellent energy absorption capacity. Therefore, it is expected that the composite can be applied to bone plates on uniaxially oriented microstructures such as long bones owing to its excellent energy absorption capacity and low elasticity to unidirectionally suppress stress shielding. -
2021.9.3
The results on the control of crystallographic microstructure and mechanical properties of nickel-based superalloy (Hastelloy-X) by the LPBF method have been published as an open access article in Crystals (MDPI, IF=2.6).
Shinya Hibino*, Tsubasa Todo, Takuya Ishimoto, Ozkan Gokcekaya, Yuichiro Koizumi, Kenichiroh Igashira, Takayoshi Nakano*:
Control of Crystallographic Texture and Mechanical Properties of Hastelloy-X via Laser Powder Bed Fusion,
Crystals, 11(9), (2021), 1064;
https://doi.org/10.3390/cryst11091064
*: Corresponding authorClick here for this paper
Abstract
The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like microstructure with <100>//build direction (BD) (<100>-SCM), single crystalline-like microstructure with <110>//BD (<110>-SCM), crystallographic lamellar microstructure (CLM), or polycrystalline microstructure (PCM). These four crystallographic textures were realized in Hastelloy-X for the first time here to the best of our knowledge. The mechanical properties of the samples varied depending on their texture. The tensile properties were affected not only by the Schmid factor but also by the grain size and the presence of lamellar boundaries (grain boundaries). The lamellar boundaries at the interface between the <110>//BD oriented main layers and the <100>//BD-oriented sub-layers of CLM contributed to the resistance to slip transmission and the increased proof stress. It was possible to control a wide range of crystallographic microstructures via the LPBF process parameters, which determines the melt pool morphology and solidification behavior. -
2021.9.2
A joint research paper with Tokyo Dental College was published in the International Journal of Implant Dentistry.
Yuto Otsu*, Satoru Matsunaga, Takehiro Furukawa, Kei Kitamura, Masaaki Kasahara, Shinichi Abe, Takayoshi Nakano, Takuya Ishimoto, Yasutomo Yajima
Structural characteristics of the bone surrounding dental implants placed into the tail-suspended mice
International Journal of Implant Dentistry, 7, (2021), 89;1-10.
https://doi.org/10.1186/s40729-021-00374-3Click here for this paper
Abstract
[ Background ] There are many unclear points regarding local structural characteristics of the bone surrounding the implant reflecting the mechanical environment.
Purpose: The purpose of this study is to quantitatively evaluate bone quality surrounding implants placed into the femurs of mice in an unloading model, and to determine the influence of the mechanical environment on bone quality.
[ Methods ]: Twenty 12-week-old male C57BL6/NcL mice (n = 5/group) were used as experimental animals. The mice were divided into two groups: the experimental group (n = 10) which were reared by tail suspension, and the control group (n = 10) which were reared normally. An implant was placed into the femur of a tail-suspended mouse, and after the healing period, they were sacrificed and the femur was removed. After micro-CT imaging, Villanueva osteochrome bone stain was performed. It was embedded in unsaturated polyester resin. The
polymerized block was sliced passing through the center of the implant body. Next, 100-μm-thick polished specimens were prepared with water-resistant abrasive paper. In addition to histological observation, morphometric evaluation of cancellous bone was performed, and the anisotropy of collagen fibers and biological apatite (BAp) crystals was analyzed.
[ Results ]: As a result, the femoral cortical bone thickness and new peri-implant bone mass showed low values in the tail suspension group. The uniaxial preferential orientation of BAp c-axis in the femoral long axis direction in the non-implant groups, but biaxial preferential orientation of BAp c-axis along the long axis of implant and femoral long axis direction were confirmed in new bone reconstructed by implant placement. Collagen fiber running anisotropy and orientation of BAp c-axis in the bone surrounding the implant were not significantly different due to tail suspension.
[ Conclusions ]: From the above results, it was clarified that bone formation occurs surrounding the implant even under extremely low load conditions, and bone microstructure and bone quality adapted to the new mechanical environment are acquired.
Keywords: Tail suspension, Femur, Bone quality, Biological apatite orientation, Collagen fiber, Dental implant -
2021.8.19
A paper on the difference of surface residual stress and phase stability between laser beam and electron beam in β-type titanium alloy was published as an open access article in Additive Manufacturing (IF=11).
Aya Takase*, Takuya Ishimoto, Ryoya Suganuma, Takayoshi Nakano*:
Surface residual stress and phase stability in unstable β-type Ti-15Mo-5Zr-3Al alloy manufactured by laser and electron beam powder bed fusion technologies,
Additive Manufacturing, 47, (2021), 102257; 1-14.
https://doi.org/10.1016/j.addma.2021.102257Click here for this paper
Abstract
The differences between the physicochemical properties of the laser and electron beam powder bed fusion (L- and EB-PBF) methods are yet to be explored further. In particular, the differences in the residual stress and phase stability of alloys with unstable phases remain unexplored. The present work is the first to systematically investigate how the heat source type and process parameters affect the surface residual stress and phase stability of an unstable β-type titanium alloy, Ti-15Mo-5Zr-3Al. The surface residual stress and β-phase behavior were studied using high-precision X-ray diffraction (HP-XRD). Significant differences were observed between the two methods. The L-PBF-made specimens exhibited tensile residual stresses of up to 400 MPa in the surface area. HP-XRD analysis revealed a stress-induced lattice distortion, interpreted as a transitional state between the β-phase and α”-phase. In contrast, the EB-PBF-made specimens showed no significant residual stress and had an undistorted β-phase coexisting with the hexagonal α-phase caused by elemental partitioning. This study provides new insights into the previously neglected effects of L-PBF and EB-PBF in unstable β-type titanium alloys.
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2021.8.16
A paper on the expression of anisotropic/isotropic mechanical functions by site-dependent control of shape using laser additive manufacturing has been published in "Crystals" as an open access article.
Naoko Ikeo#, *, Hidetsugu Fukuda#, Aira Matsugaki*, Toru Inoue, Ai Serizawa, Tadaaki Matsuzaka, Takuya Ishimoto, Ryosuke Ozasa, Ozkan Gokcekaya, Takayoshi Nakano*:
3D puzzle in cube pattern for anisotropic/isotropic mechanical control of structure fabricated by metal additive manufacturing,
Crystals, 11(8), (2021), 11(8), 959; 1-10.
https://doi.org/10.3390/cryst11080959.
#: These authors contributed equally to this work.
*: Corresponding authorClick here for this paper
Abstract
Metal additive manufacturing is a powerful tool for providing the desired functional performance through a three-dimensional (3D) structural design. Among the material functions, anisotropic mechanical properties are indispensable for enabling the capabilities of structural materials for living tissues. For biomedical materials to replace bone function, it is necessary to provide an anisotropic mechanical property that mimics that of bones. For desired control of the mechanical performance of the materials, we propose a novel 3D puzzle structure with cube-shaped parts comprising 27 (3 × 3 × 3) unit compartments. We designed and fabricated a Co–Cr–Mo composite structure through spatial control of the positional arrangement of powder/solid parts using the laser powder bed fusion (L-PBF) method. The mechanical function of the fabricated structure can be predicted using the rule of mixtures based on the arrangement pattern of each part. The solid parts in the cubic structure were obtained by melting and solidifying the metal powder with a laser, while the powder parts were obtained through the remaining nonmelted powders inside the structure. This is the first report to achieve an innovative material design that can provide an anisotropic Young’s modulus by arranging the powder and solid parts using additive manufacturing technology. -
2021.8.1
Our findings on the effect of gas atmosphere on sputtering during metal AM was published as an open access article in Materials Transactions.
Hiroki Amano, Yusuke Yamaguchi, Takuya Ishimoto, Takayoshi Nakano*:
Reduction of Spatter Generation Using Atmospheric Gas in Laser Powder Bed Fusion of Ti–6Al–4V,
Materials Transactions, 62, (2021), 1225-1230.
https://doi.org/10.2320/matertrans.MT-M2021059Click here for this paper
Abstract
Laser powder bed fusion (LPBF), a typical additive manufacturing (AM) process, is a promising approach that enables high-accuracy manufacturing of arbitrary structures; therefore, it has been utilized in the aerospace and medical fields. However, several unexplained phenomena significantly affect the quality of fabricated components. In particular, it has been reported that the generation of spatters adversely affects the stability of fabrication process and degrades the performance of the fabricated components. To realize high-quality components, it is essential to suppress the generation of spatters. Thus far, the suppression of spatter generation has been attempted based on the process parameters; however, this has not been adequately discussed in terms of the fabrication atmosphere. Therefore, in this study, we focused on the fabrication atmosphere and investigated spatter generation using gas with different physical properties rather than conventionally used argon. It was observed that the spatter generation during the fabrication of the Ti–6Al–4V alloy could be significantly suppressed by changing the atmospheric gas, even under constant LPBF process parameters. We proved that the fabrication atmosphere is an important factor to be considered, apart from the process parameters, in AM technology. -
2021.7.23
A study on microstructure control of stainless steel by electron beam additive manufacturing was published in Crystals as open access.
Yuichiro Miyata, Masayuki Okugawa*, Yuichiro Koizumi*, Takayoshi Nakano：
Inverse columnar-equiaxed transition in 304 and 316L stainless steels melt by electron-beam for additive manufacturing,
Crystals, 11 (8), (2021), 856: 1-13.
https://doi.org/10.3390/cryst11080856Click here for this paper
Abstract
According to Hunt’s columnar-to-equiaxed transition (CET) criterion, which is generally accepted, a high-temperature gradient (G) in the solidification front is preferable to a low G for forming columnar grains. Here, we report the opposite tendency found in the solidification microstructure of stainless steels partially melted by scanning electron beam for powder bed fusion (PBF)-type additive manufacturing. Equiaxed grains were observed more frequently in the region of high G rather than in the region of low G, contrary to the trend of the CET criterion. Computational thermal-fluid dynamics (CtFD) simulation has revealed that the fluid velocity is significantly higher in the case of smaller melt regions. The G on the solidification front of a small melt pool tends to be high, but at the same, the temperature gradient along the melt pool surface also tends to be high. The high melt surface temperature gradient can enhance Marangoni flow, which can apparently reverse the trend of equiaxed grain formation.
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2021.7.12
A paper on the improvement of tensile properties of TiAl alloy containing β-phase by cell precipitation using electron beam plastic forming (EBPBF) has been published in "Crystals" as an open access paper.
Ken Cho, Hirotaka Odo, Keisuke Okamoto, Hiroyuki Y. Yasuda*, Hirotoyo Nakashima, Masao Takeyama, Takayoshi Nakano:
Improving the tensile properties of additively manufactured β-containing TiAl alloys via microstructure control focusing on cellular precipitation reaction,
Crystals, 11 (7), (2021), 809; 1-13.
https://doi.org/10.3390/cryst11070809Click here for this paper
Abstract
The effect of a two-step heat treatment on the microstructure and high-temperature tensile properties of β-containing Ti-44Al-4Cr (at%) alloys fabricated by electron beam powder bed fusion were examined by focusing on the morphology of α2/γ lamellar grains and β/γ cells precipitated at the lamellar grain boundaries by a cellular precipitation reaction. The alloys subjected to the first heat treatment step at 1573 K in the α + β two-phase region exhibit a non-equilibrium microstructure consisting of the α2/γ lamellar grains with a fine lamellar spacing and a β/γ duplex structure located at the grain boundaries. In the second step of heat treatment, i.e., aging at 1273 K in the β + γ two-phase region, the β/γ cells are discontinuously precipitated from the lamellar grain boundaries due to excess Cr supersaturation in the lamellae. The volume fraction of the cells and lamellar spacing increase with increasing aging time and affect the tensile properties of the alloys. The aged alloys exhibit higher strength and comparable elongation at 1023 K when compared to the as-built alloys. The strength of these alloys is strongly dependent on the volume fraction and lamellar spacing of the α2/γ lamellae. In addition, the morphology of the β/γ cells. is also an important factor controlling the fracture mode and ductility of these alloys. -
2021.7.8
A study on quantitative comparison of crystallographic features and residual stresses of Ti-6Al-4V fabricated by metal 3D printing (L-PBF and EB-PBF) was published as an open access article in Crystals.
Aya Takase*, Takuya Ishimoto, Naotaka Morita, Naoko Ikeo, Takayoshi Nakano*
Comparison of phase characteristics and residual stresses in Ti-6Al-4V alloy manufactured by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques.
Crystals, 11(7), (2021), 796; 1-17.
https://doi.org/10.3390/cryst11070796
*: Corresponding authorCkick here for this paper
Abstract
Ti-6Al-4V alloy fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques have been studied for applications ranging from medicine to aviation. The fabrication technique is often selected based on the part size and fabrication speed, while less attention is paid to the differences in the physicochemical properties. Especially, the relationship between the evolution of α, α’, and β phases in as-grown parts and the fabrication techniques is unclear. This work systematically and quantitatively investigates how L-PBF and EB-PBF and their process parameters affect the phase evolution of Ti-6Al-4V and residual stresses in the final parts. This is the first report demonstrating the correlations among measured parameters, indicating the lattice strain reduces, and c/a increases, shifting from an α’ to α+β or α structure as the crystallite size of the α or α’ phase increases. The experimental results combined with heat-transfer simulation indicate the cooling rate near the β transus temperature dictates the resulting phase characteristics, whereas the residual stress depends on the cooling rate immediately below the solidification temperature. This study provides new insights into the previously unknown differences in the α, α’, and β phase evolution between L-PBF and EB-PBF and their process parameters. -
2021.7.7
Our joint research with Narushima Lab. of Tohoku University on the improvement of properties of CO-Cr-W-Ni stent alloys by adding Mn has been published in Metallurgical and Materials Transactions A as an open access article.
Soh Yanagihara*, Kosuke Ueki, Kyosuke Ueda , Masaaki Nakai, Takayoshi Nakano, Takayuki Narushima:
Development of low-yield stress Co-Cr-W-Ni alloy by adding 6mass% Mn for balloon-expandable stents,
Metallurgical and Materials Transactions A, (2021), in press.
https://doi.org/10.1007/s11661-021-06374-7Click here for this paper
Abstract
This is the first report presenting the development of a Co–Cr–W–Ni–Mn alloy by adding 6 mass pct Mn to ASTM F90 Co–20Cr–15W–10Ni (CCWN, mass pct) alloy for use as balloon-expandable stents with an excellent balance of mechanical properties and corrosion resistance. The effects of Mn addition on the microstructures as well as the mechanical and corrosion properties were investigated after hot forging, solution treatment, swaging, and static recrystallization. The Mn-added alloy with a grain size of ~ 20 µm (recrystallization condition: 1523 K, 150 seconds) exhibited an ultimate tensile strength of 1131 MPa, 0.2 pct proof stress of 535 MPa, and plastic elongation of 66 pct. Additionally, it exhibited higher ductility and lower yield stress while maintaining high strength compared to the ASTM F90 CCWN alloy. The formation of intersecting stacking faults was suppressed by increasing the stacking fault energy (SFE) with Mn addition, resulting in a lower yield stress. The low-yield stress is effective in suppressing stent recoil. In addition, strain-induced martensitic transformation during plastic deformation was suppressed by increasing the SFE, thereby improving the ductility. The Mn-added alloys also exhibited good corrosion resistance, similar to the ASTM F90 CCWN alloy. Mn-added Co–Cr–W–Ni alloys are suitable for use as balloon-expandable stents. -
2021.7.3
A study of new insights into the correlation between crystallographic symmetry and crystal orientation formed by metal 3D printing has been published as an open access paper in Scripta Materialia.
Koji Hagihara#, Takuya Ishimoto#, Masahiro Suzuki, Ryosuke Ozasa, Aira Matsugaki, Pan Wang, Takayoshi Nakano∗
Factor which governs the feature of texture developed during additive manufacturing; clarified from the study on hexagonal C40-NbSi2, Scripta Materialia, 203, (2021), 114111; 1-6.
https://doi.org/10.1016/j.scriptamat.2021.114111
#: The authors equally contributed to this study.
*: Corresponding authorClick here for this paper.
Abstract
C40-NbSi2 with a hexagonal unit cell is focused as a high-temperature structural material. We first at- tempted the fabrication of the bulk C40-NbSi2 products via selective laser melting (SLM) in additive manufacturing (AM) process. Strong crystallographic texture control wherein <0001> was parallel to the building direction, i.e. development of the so-called basal fiber texture, was achieved in this study. The texture developed in products does not largely vary by changing the scanning strategy, unlike the textures of C11b -MoSi2 with a tetragonal unit cell and a β-Ti alloy with a cubic unit cell. A comparison of these results led us to the conclusion that crystal symmetry, i.e., the multiplicity of the preferential crystal growth direction, is one of the primary factors that governs the features of the textures developed in AM-built materials.