What's New
2024（January－June）
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2024.4.16
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2024.4.13
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2024.4.3
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2024.3.27
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2024.3.1
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2024.2.23
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2024.2.20
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2024.1.27
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2024.1.27
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2024.1.17
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2024.1.4
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2024.4.16
A paper on grain size dependence of martensitic transformation in beta titanium alloys has been published as OA in Materials Science and Engineering A (IF=6.4).
Chenyang Wu, Xiaoli Zhaoa*, Mengrui Zhang, Hideki Hosoda, Takayoshi Nakano , Mitsuo Niinomi, Nan Jia, Zhiwen Shao , Deliang Zhang:
Strong grain size effect on tensile behavior of the body-centered-cubic Ti-30Zr-5Mo alloy with stress-induced α' martensitic transformation,
Materials Science and Engineering A, 900, (2024), 146455, 1-13.
https://doi.org/10.1016/j.msea.2024.146455
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Abstract
In this study the grain size effect on mechanical properties of a body-centered-cubic Ti-30Zr-5Mo alloy was investigated. Double yielding behavior in the stress-strain curves and four-stage behavior in the strain hardening rate curves can be seen in all Ti-30Zr-5Mo materials with different average grain sizes ranging from 6 to 475 μm, which is attributed to the occurrence of the stress-induced α′ transformation. The static Hall-Petch coefficient (k) for phase transformation was calculated to establish the relationship between grain size and trigger stress of the various materials. With the increase of strain, the hindrance of αʹ/β grain boundaries and αʹ/αʹ grain boundaries to dislocations gradually replaced β/β grain boundaries, thus the work hardening ability and k value changed. β grains were segmented by α′ martensite, resulting in a dynamic Hall‒Petch effect. Combined with a large stress field in the fine-grained materials with an average grain size of 6 μm, the highest work hardening rate with a value of 13 GPa was obtained. As the β grain size increased, the ultimate strength gradually decreased, while both trigger stress of the stress-induced αʹ transformation and elongation fluctuated. The trigger stress can be adjusted between 211 and 464 MPa by controlling the grain size. The grain size has little effect on the amount of the stress-induced αʹ phase. With a high trigger stress of 464 MPa in the material with the finest grains, the excellent ductility of 21% is obtained. The best comprehensive mechanical properties with a strength-ductility index value of 252 MPa is obtained in the material with an average grain size of 113 μm.
Keywords
Ti-30Zr-5Mo alloy; Grain size; Stress-induced phase transformation; αʹ martensite; Mechanical properties; Grain refinement; α′ phase; Titanium alloys
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2024.4.13
A paper on the deformation behavior of two-dimensional special lattice structures fabricated by AM has been published as OA in Materials & Design (IF=8.4).
Zana Eren, Ozkan Gokcekaya, Demet Balkan, Takayoshi Nakano, Zahit Mecitoğlu:
Comparison of in-plane compression of additively manufactured Ti6Al4V 2D auxetic structures: Lattice design, manufacturing speed, and failure mode,
Materials & Design, 241, (2024), 112885, 1-19.
https://doi.org/10.1016/j.matdes.2024.112885
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Abstract
The metal-based 2D auxetic lattice structures hold the potential for multifunctional tasks in aerospace applications. However, the compression response of those manufactured by powder bed fusion process is underexplored. This study proposes a comprehensive comparison of in-plane quasi-static compression performance of 2D auxetic lattice structures, utilizing three designs (anti-tetrachiral (ATC), double arrow-headed (DAH), and tree-like re-entrant (TLR)), manufactured with stiff Ti6Al4V by the electron beam powder bed fusion process (PBF-EB) with various manufacturing speeds. The results revealed unique failure patterns and superior energy absorptions among 2D lattice structures in the literature. TLR design enhanced energy absorption by overcoming failures between DAH columns and exhibited the lowest standard deviations in specific energy absorption (SEA) values (9.75 -12.62 ). Besides, Kernel average misorientation (KAM) values followed the order of DAH, TLR, and ATC, and inversely correlated with SEA values. ATC structures with the lowest KAM outperformed DAH and TLR by 47.5 and 6.44 , respectively. Scan speed variations affected SEA and porosity values differently for each lattice design while exhibiting similar microstructure characteristics. The findings in this study propose a significant contribution to the development of aerospace sandwich structures where harsh environments exist and employment of 2D topologies are required.
Keywords
Auxetic structures; Additive manufacturing; Energy absorption; Compressive failures; Residual stress -
2024.4.3
A computer simulation study on the segregation behavior of a nickel-based heat-resistant alloy (Hastelloy-X) has been published as an OA paper in the journal "Additive Manufacturing" (IF=11).
Masayuki Okugawa*, Kenji Saito, Haruki Yoshima, Katsuhiko Sawaizumi, Sukeharu Nomoto, Makoto Watanabe, Takayoshi Nakano, Yuichiro Koizumi*:
Solute segregation in a rapidly solidified Hastelloy-X Ni-based superalloy during laser powder bed fusion investigated by phase-field and computational thermal-fluid dynamics simulations,
Additive Manufacturing, 84, (2024), 104079, 1-13.
https://doi.org/10.1016/j.addma.2024.104079
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Abstract
Solute segregation significantly affects material properties and is a critical issue in the laser powder-bed fusion (LPBF) additive manufacturing (AM) of Ni-based superalloys. To the best of our knowledge, this is the first study to demonstrate a computational thermal-fluid dynamics (CtFD) simulation coupled multi-phase-field (MPF) simulation with a multicomponent-composition model of Ni-based superalloy to predict solute segregation under solidification conditions in LPBF. The MPF simulation of the Hastelloy-X superalloy reproduced the experimentally observed submicron-sized cell structure. Significant solute segregations were formed within interdendritic regions during solidification at high cooling rates of up to 1.6 × 106 K s−1, a characteristic feature of LPBF. Solute segregation caused a decrease in the solidus temperature (TS), with a reduction of up to 38.4 K, which increases the risk of liquation cracks during LPBF. In addition, the segregation triggers the formation of carbide phases, which increases the susceptibility to ductility dip cracking. Conversely, we found that the decrease in TS is suppressed at the melt-pool boundary regions, where re-remelting occurs during the stacking of the layer above. Controlling the re-remelting behavior is deemed to be crucial for designing crack-free alloys. Thus, we demonstrated that solute segregation at the various interfacial regions of Ni-based multicomponent alloys can be predicted by the conventional MPF simulation. The design of crack-free Ni-based superalloys can be expedited by MPF simulations of a broad range of element combinations and their concentrations in multicomponent Ni-based superalloys.
Keywords
Laser powder-bed fusion; Hastelloy-X nickel-based superalloy; Solute element segregation; Computational thermal-fluid dynamics simulation; Phase-field method -
2024.3.27
Smart Materials in Manufacturing (Elsevier) published a paper as OA on the unique microstructure and hardness variation of Ti-6Al-2Sn-4Zr-6Mo alloys by metal additive manufacturing.
Prince Valentine Cobbinah*, Sae Matsunaga, Yoshiaki Toda, Ryosuke Ozasa, Masayuki Okugawa, Takuya Ishimoto, Yuheng Liu, Yuichiro Koizumi, Pan Wang, Takayoshi Nakano*, Yoko Yamabe-Mitarai*:
Peculiar microstructural evolution and hardness variation depending on laser powder bed fusion-manufacturing condition in Ti-6Al-2Sn-4Zr-6Mo,
Smart Materials in Manufacturing, 2, (2024), 100050, 1-10.
https://doi.org/10.1016/j.smmf.2024.100050
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Abstract
This study aims to comprehensively analyze the phase and microstructure evolution and related hardness variations of the Ti-6Al-2Sn-4Zr-6Mo wt.% (Ti6246) alloy produced by laser powder bed fusion (LPBF) under various laser conditions and to gain insight into the mechanisms of these changes using numerical thermal analysis. Higher laser volumetric densities (VEDs) resulted in a finer α/α' microstructure and increased hardness, exhibiting a positive correlation with the VED, except under extremely high conditions. This contrary trend, reported for the first time, is attributed to the solid-phase transformation from the β phase to metastable α' martensite during LPBF induced by rapid cooling. Despite the finer microstructure, the samples under very high VED conditions showed lower hardness, deviating from the overall trend. The X-ray diffraction peaks in the high-VED samples suggested a partial decomposition of α' to α + β owing to laser-induced reheating of the underlying layers, which is considered a contributing factor to the hardness reduction. The numerical analysis showed that the underlying layer was exposed to high temperatures for a relatively long time under high-VED conditions. It was revealed that the hardness of LPBF-fabricated Ti6246 was influenced by unique thermal processes: rapid cooling and reheating of the pre-solidified part, leading to the formation of a metastable α' phase and partial decomposition into α + β. These findings provide insights for tailoring Ti6246 with desired physical properties via LPBF.
Keywords
LPBF; Ti6246; Polycrystalline microstructure; Metastable phase; Rapid cooling; Thermal history -
2024.3.1
A paper proposing the world's first (R≥2.0) super high entropy alloy (SHEA) was published as OA in Materials Chemistry and Physics (IF=4.6).
Tadaaki Matsuzaka, Akira Hyakubu, Yong Seong Kim, Aira Matsugaki, Takeshi Nagase, Takuya Ishimoto, Ryosuke Ozasa, Hyoung Seop Kim, Tomoji Mizuguchi, Ozkan Gokcekaya, Takayoshi Nakano:
Development of an equiatomic octonary TiNbTaZrMoHfWCr super high-entropy alloy for biomedical applications,
Materials Chemistry and Physics, 316, (2024), 129120; 1-7.
DOI: https://doi.org/10.1016/j.matchemphys.2024.129120
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Abstract
A super-high-entropy alloy (SHEA) with ΔSmix ≥ 2.0R (where R is the gas constant) was designed to produce metallic materials with superior mechanical properties to conventional alloys. As an alternative to conventional quinary high-entropy alloys (HEAs), herein, octonary SHEAs for biomedical applications (BioSHEAs) are proposed for the first time, and the TiNbTaZrMoHfWCr BioSHEA was fabricated. Arc-melted BioSHEA exhibited an extremely high yield strength of 1953 ± 84 MPa, which was approximately 550 MPa higher than that of the quinary TiNbTaZrMo BioHEA. This yield strength is considerably higher than that estimated by the rule of mixtures for pure metals, confirming the achievement of significant solid-solution strengthening induced by a supermulticomponent solid solution composed of elements with different atomic radii. Its biocompatibility was comparable to that of pure Ti and the quinary BioHEA, and superior to that of SUS316L. This study demonstrates the validity of a novel entropy-based guideline for increasing the mixing entropy to achieve metallic materials with ultrahigh strength.
Keywords
Super-high-entropy alloys (SHEAs); Octonary system; Supermulticomponent; Solid-solution strengthening; BioSHEAs -
2024.2.23
An international collaborate research on the microstructure of pure Cr produced by L-PBF and the effect of HIP on wear has been published in the International Journal of Refractory Metals and Hard Materials (IF=3.6).
Asli Gunay Bulutsuz*, Buse Gulec, Ozkan Gokcekaya*, Johannes Gardstam, Takayoshi Nakano, Hakan Yilmazer:
An investigation over microstructure and HIP processing effects on wear performance of pure chromium parts fabricated by laser powder bed fusion,
International Journal of Refractory Metals and Hard Materials, 120, (2024), 106616, 1-10.
DOI: https://doi.org/10.1016/j.ijrmhm.2024.106616
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Abstract
Chromium (Cr) and its alloys have long been valued for their exceptional properties, including corrosion resistance and high-temperature stability, rendering them indispensable in industrial applications such as chemical processing, energy production, and aerospace. However, due to the difficulties in Cr-based alloy manufacturing, there is a need for novel manufacturing methodologies. Additive Manufacturing (AM) emerges as a promising approach, particularly Laser Powder Bed Fusion (LPBF), which allows for intricate designs, reduced material waste, and simplified assembly. However, certain issues still need to be addressed, including defects like cracks and porosities in the manufactured parts. Post-processing techniques such as Hot Isostatic Pressing (HIP) have gained prominence for enhancing the material properties and quality of AM parts, including those produced using LPBF. HIP treatments are effective in eliminating internal pores, although some challenges remain, notably the presence of trapped argon and grain coarsening side effects of HIP process parameters. This study focuses on LPBF-processed pure chromium parts with crystallographic texture and investigates their properties after HIP treatment, including microstructure, hardness, and tribological performance. According to the obtained results: the HIP process reduced cracks, especially in the center region, but increased gaps in the side region. HIP also hindered grain realignment, limiting grain growth, and resulting in high HAGB density and low MUD values. Elevated HIP processing pressure negatively affected tribological performance due to increased grain size, and reduced hardness. This study, for the first time, realized the effect of HIP conditions on the microstructure and tribological performance of LPBF-processed pure Cr.
Keywords
Laser powder bed fusion; Pure Cr; Crystallographic texture; Hot isostatic pressing; Wear performance -
2024.2.20
Research on the development of low elasticity antimicrobial Ti-Nb-Cu alloys for biological applications was published in Materials Today Communications (IF=3.8).
Qiang Li*, Qizhen Peng, Qi Huang, Mitsuo Niinomi, Takuya Ishimoto, Takayoshi Nakano:
Development and characterizations of low-modulus Ti-Nb-Cu alloys with enhanced antibacterial activities,
Materials Today Communications, 38, (2024), 108402, 1-8.
DOI: https://doi.org/10.1016/j.mtcomm.2024.108402
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Abstract
Avoiding infection is a requirement for the long-term stability and safety of implants, but most Ti alloys for implantation hardly inhibit the bacterial proliferations. Cu works as a β stabilizer in Ti alloys, and Cu ion can kill bacteria. To obtain antibacterial activities in low-modulus Ti alloys, Ti-35Nb-(0, 1, 2, 3, 4)Cu (wt%) alloys were prepared by non-consumable arc melting following by homogenization, hot rolling, and solution treatment. They were then subjected to phase analysis, microstructure observation, tensile test and dynamic polarization. The cytotoxicity and antibacterial activities were finally evaluated. The results show that Cu stabilizes the β phase and inhibits the generation of α" phase during quenching. Ti-35 Nb and Ti-35Nb-1Cu consist of β and α" phases, and Ti-35Nb-(2, 3, 4)Cu alloys have a single β phase. The Ti-Nb-Cu alloys exhibit the Young's moduli ranging from 57 to 72 GPa. All the alloys show passivation behavior with a low passive current density. Cytotoxicity is hardly observed in the alloys. The antibacterial rates of Ti-35Nb-(1, 2, 3, 4)Cu alloys against E. coli are 62.8%, 68.9%, 70.9% and 73.2%, respectively, and the antibacterial rates against S. aureus are 63.4%, 69.7%, 72.8% and 74.7%, respectively. The developed β-type Ti-35Nb-4Cu alloy shows a relatively low Young's modulus and good antibacterial properties, and is a candidate for biomedical applications.
Keywords
Biomedical Ti alloys, Mechanical properties, Corrosion resistance, Cytotoxicity, Antibacterial properties -
2024.1.27
Bone (IF=4.1) published an OA article showing that bone matrix orientation has a stronger effect on bone mechanical function adaptation than bone density.
Jun Wang, Takuya Ishimoto, Tadaaki Matsuzaka, Aira Matsugaki, Ryosuke Ozasa, Takuya Matsumoto, Mikako Hayashi, Hyoung Seop Kim, Takayoshi Nakano*:
Adaptive Enhancement of Apatite Crystal Orientation and Young's Modulus Under Elevated Load in Rat Ulnar Cortical Bone,
Bone, 181, (2024), 117024: 1-10.
https://doi.org/10.1016/j.bone.2024.117024
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Abstract
Functional adaptation refers to the active modification of bone structure according to the mechanical loads applied daily to maintain its mechanical integrity and adapt to the environment. Functional adaptation relates to bone mass, bone mineral density (BMD), and bone morphology (e.g., trabecular bone architecture). In this study, we discovered for the first time that another form of bone functional adaptation of a cortical bone involves a change in bone quality determined by the preferential orientation of apatite nano-crystallite, a key component of the bone. An in vivo rat ulnar axial loading model was adopted, to which a 3-15 N compressive load was applied, resulting in approximately 440-3200 μɛ of compression in the bone surface. In the loaded ulnae, the degree of preferential apatite c-axis orientation along the ulnar long axis increased in a dose-dependent manner up to 13 N, whereas the increase in BMD was not dose-dependent. The Young's modulus along the same direction was enhanced as a function of the degree of apatite orientation. This finding indicates that bone has a mechanism that modifies the directionality (anisotropy) of its microstructure, strengthening itself specifically in the loaded direction. BMD, a scalar quantity, does not allow for load-direction-specific strengthening. Functional adaptation through changes in apatite orientation is an excellent strategy for bones to efficiently change their strength in response to external loading, which is mostly anisotropic.
Keywords
Functional adaptation; Bone strength; Apatite orientation; Bone quality: In vivo loading -
2024.1.27
An international collaborate research on improving the antimicrobial properties of Ti by Zn coating with improved adhesion has been published in Materials Today Communications (IF=3.8).
Ming Li, Qiang Li*, Jiawei Yang, Mitsuo Niinomi, Takayoshi Nakano:
Preparation and Antibacterial Activity of Zn Coating on Pure Ti with Enhanced Adhesion,
Materials Today Communications, 38, (2024), 1-10
https://doi.org/10.1016/j.mtcomm.2024.108149
click here for this paper.
Abstract
A titania nanotubes layer was prepared as an intermediate layer on pure Ti via anodic oxidation, and subsequently, a Zn-containing coating was electrochemically deposited. The influence of the deposition parameters on the Zn content was studied using an orthogonal experiment. The obtained coatings were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and their adhesion was measured using a scratch test. The deposition time had the greatest effect on the Zn content of the electrodeposited samples, whereas the deposition temperature had the smallest effect. After the electrodeposition, Zn was uniformly distributed on the surface and existed mainly as a simple substance. The adhesion was only 10.9 N in the Zn-free sample; it increased with increasing Zn content of the samples, and reached a maximum value of 22.4 N in the sample with a Zn content of approximately 16%. The samples with Zn-containing coatings exhibited strong antibacterial effects against E. coli and S. aureus, and the antibacterial effect increased with increasing Zn content. Cell viability was above 80%, indicating that the Zn-containing coating is a good candidate as an antibacterial coating for biomedical applications.
Keywords
Zn-containing coating; Electrochemical deposition; Orthogonal experiment; Adhesion; Antibacterial property; Pure Ti -
2024.1.17
A paper was published as OA in The International Journal of Advanced Manufacturing Technology (IF=3.4).
Ozkan Gokcekaya*, Ali Günen, Ferhat Ceritbinmez, Abdollah Bahador, Takayoshi Nakano, Melik Çetin:
Wire-EDM performance and surface integrity of Inconel 718 with unique microstructural features fabricated by laser powder bed fusion,
The International Journal of Advanced Manufacturing Technology, (2024), 1-16
https://doi.org/10.1007/s00170-023-12924-7
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Abstract
Inconel 718 alloy is difficult to machine using conventional methods due to its physical properties. Thereby, additive manufacturing (AM) of IN718 components with near-net shapes has been extensively studied. Even though AM processes provide shape and size accuracy, there is still the need for the machining of the AM-processed components to achieve the final shape of a component. Laser powder bed fusion (LPBF) has been successfully utilized to fabricate near-net shape IN718 components; moreover, the microstructure of LPBF-IN718 was unique owing to the AM processing, resulting in differences in grain size, grain boundary characteristics, and grain orientations. Furthermore, these microstructural characteristics are expected to alter the machining performance of IN718. Therefore, this study investigated the wire electro-discharge machining (WEDM) performance of LPBF-718 samples compared to wrought IN718 while focusing on the unique microstructure characteristics of LPBF-IN718 samples (lamella, single-crystal, ploy-crystal). Three different cutting strategies (rough, semi-finish, and finish) were implemented to understand the performance of the multi-pass cutting phenomenon and its effect on the surface of IN718. For all samples, rough (single pass) cutting displayed high roughness, while finish (three passes) cutting exhibited good surface quality. Compositional analyses on the machined surface showed debris formation including Zn and Cu-containing recast material, indicating wire erosion. The surface of single-crystal LPBF-IN718 after the WEDM process was smooth owing to its large grain size and less amount of grain boundary, resulting in slow cutting speed but a good surface finish. Thus, this study, for the first time, investigated the effect of unique microstructural characteristics of LPBF-fabricated IN718 on WEDM performance and machined surface quality. -
2024.1.4
The Journal of the Mechanical Behavior of Biomedical Materials (IF=3.9) published the results of our collaborate research with Shanghai University of Science and Technology and Dr. Niinomi on the suppression of infection by surface deposition of iodine.
Qiang Li*, Shuaishuai Li, Hao Sun, Mitsuo Niinomi, Takayoshi Nakano:
Preparation and Characterizations of Antibacterial Iodine-containing Coatings on Pure Ti,
Journal of the Mechanical Behavior of Biomedical Materials, 151, (2024), 106366, 1-8.
https://doi.org/10.1016/j.jmbbm.2023.106366
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Abstract
Iodine-containing coatings were prepared on pure Ti surfaces via electrochemical deposition to enhance their antibacterial properties. The factors influencing iodine content were analyzed using an orthogonal experiment. The electrochemically deposited samples were characterized using scanning electron microscopy with energy dispersive spectroscopy and X-ray photoelectron spectroscopy, and their antibacterial properties and cytotoxicity were evaluated. The results showed that changing the deposition time is an effective way to control the iodine content. The iodine content, coating thickness, and adhesion of the samples increased with deposition time. Iodine in the coatings mainly exists in three forms, which are I2, I3−, and pentavalent iodine. For samples with iodine-containing coatings, the antibacterial ratios against E. coli and S. aureus were greater than 90% and increased with increasing iodine content. Although the samples with iodine-containing coatings showed some inhibition of the proliferation of MC3T3-E1 cells, the cell viabilities were all higher than 80%, suggesting that iodine-containing coatings are biosafe.