What's New
2024（July－December）
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2024.12.18
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2024.12.5
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2024.12.5
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2024.11.21
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2024.11.13
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2024.10.7
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2024.10.4
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2024.12.18
The Journal of Materials Engineering and Performance published an article on the effect of energy density on the functionality of Ti6Al-4V alloys formed by AM.
H. Yilmazer, Y. A. Sadikoglu, S. Kucuk, O. Gokcekaya, I. C. Turu, T. Nakano, B. Dikici*:
The effect of energy density on microstructural, mechanical, and corrosion characteristics of Ti6Al-4V alloy fabricated via selective laser melting (SLM) and electron beam melting (EBM) techniques,
Journal of Materials Engineering and Performance, (2024), 1-13.
https://doi.org/10.1007/s11665-024-10512-8
Click here for this paper.
Abstract
In this study, the effect of production parameters on Ti-6Al-4V alloys fabricated using selective laser melting (SLM) and electron beam melting (EBM) techniques was investigated. Through the variation of energy volume (12.5, 25, 37.5 J mm−3), these two additive manufacturing methods were compared in terms of microstructure, mechanical, and corrosion properties. Density was calculated using Archimedes' technique, while microstructure was characterized through optical microscopy (OM) and scanning electron microscopy (SEM). Mechanical properties were determined via micro-Vickers hardness and tensile tests. Electron backscatter diffraction (EBSD) and x-ray diffraction (XRD) analyses were performed on EBM and SLM samples for a comprehensive understanding. Corrosion susceptibilities of the alloys were evaluated using potentiodynamic scanning (PDS) tests in a 3.5% NaCl solution at room temperature. Microstructural analysis revealed that SLM-produced parts predominantly consisted of the α′ (martensite) phase, whereas EBM-produced parts primarily comprised the α phase with a small amount of the β phase. The strength values of all SLM samples exceeded 930 MPa, surpassing those of wrought Ti-6Al-4V ELI. However, only EBM samples fabricated with a 37.3 J mm−3 energy volume approached this standard. Corrosion susceptibility generally increased with higher energy volume in both EBM and SLM samples, with porosity volume and grain size variations influencing corrosion behavior.
Keywords
Corrosion; EBM; Energy density; Phase transformation; SLM; Ti-6Al-4V
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2024.12.5
The Journal of Alloys and Compounds published an OA paper on the results of joint research with Northeastern University, China.
Chenyang Wu, Xiaoli Zhao*, Takayoshi Nakano, Mitsuo Niinomi, Nan Jia, Deliang Zhang:
Grain size dependence of deformation behavior in Ti-15Mo alloy prepared by powder metallurgy
Journal of Alloys and Compounds, 1010, (2025), 177825: 1-12.
https://doi.org/10.1016/j.jallcom.2024.177825
Click here for this paper.
Abstract
To the best of our knowledge, this is the first report demonstrating grain refinement to 4 μm via a mass-production method for the Ti-15Mo alloy. Grain sizes ranging from 4 to 38 μm were achieved by controlling thermomechanical processing in powder metallurgy, combined with heat treatment using recycled coarse powders for additive manufacturing. The critical grain size for deformation twinning was investigated, alongside an analysis of the deformation behavior and mechanical properties of the Ti-15Mo alloy with various grain sizes. Upon refining the grain size to 7 μm, deformation twinning is inhibited, shifting the plastic deformation mechanism from mechanical twinning to dislocation slip. The yield strength can be adjusted between 921 and 715 MPa, with elongation ranging from 18.4% to 34.4%, by varying the grain size distribution ratio of small to large grains relative to 7 μm from 1.5 to 0.42. This strengthening effect primarily arises from dislocation strengthening, Mo solid solution, texture strengthening, and modifications in the Hall-Petch constant due to changes in deformation behavior during grain refinement.Keywords
Ti-Mo alloy; Power Metallurgy; Grain refinement; Mechanical properties; Mechanical twinning -
2024.12.5
A paper on microstructural changes and high temperature mechanical properties of titanium alloys was published in Materials Transactions.
Tomoki Kuroda, Haruki Masuyama, Yoshiaki Toda, Tetsuya Matsunaga, Tsutomu Ito, Makoto Watanabe, Ryosuke Ozasa, Takuya Ishimoto, Takayoshi Nakano, Masayuki Shimojo, Yoko Yamabe-Mitarai:
Microstructure Evolution and High-Temperature Mechanical Properties of Ti-6Al-4Nb-4Zr Fabricated by Selective Laser Melting,
Materials Transactions, 64 [1], (2024), 2022021; 348-356.
DOI: https://doi.org/10.2320/matertrans.MT-MLA2022021
Click here for this paper.
Abstract
Ti-6Al-4Nb-4Zr (mass%) was prepared by selective laser melting (SLM) under various conditions, and the microstructure evolution resulting from SLM processing and subsequent heat treatments was investigated. The effects of the unique SLM-induced microstructure on the high-temperature compressive strength and creep properties of the samples were then elucidated. Under rapid cooling conditions, the martensitic structure formed in a scale-like pattern, with a 100 µm in size, consistent with the laser scanning pattern. By contrast, under slow cooling conditions, the α/β lamellar structure formed in β grains with a 300 µm grain size instead of in a scale-like pattern. The martensitic structure drastically changed to a Widmanstätten structure during heat treatment. The equiaxed α phase also formed at the interface of the scale-like patterns. By contrast, the α/β lamellar structure did not exhibit a change in response to heat treatment. The compressive strength of the SLM samples was governed by the martensite α size and the grain size, both of which depended on the cooling rate. The dominant creep deformation mechanism at 600°C and under a loading stress of 137 MPa was grain boundary sliding. The creep life depended on the grain size. The HIP treatment improved the creep life because it eliminated pores introduced by the SLM process.
Keywords
selective; lasermelting; heat-resistant; Ti alloys; compression; strength; creep -
2024.11.21
A paper on our recent research on titanium alloys was published in the December issue of Materials Transactions.
Mitsuo Niinomi*, Takayuki Narushima, Takayoshi Nakano:
Recent Research and Development in the Processing, Microstructure, and Properties of Titanium and Its Alloy
Materials Transactions, 65 [12], (2024), 1600-1611.
https://doi.org/10.2320/matertrans.MT-M2024082
Click here for this paper.
Abstracts
The special issue on recent research and development in the processing, microstructure, and properties of titanium and its alloy contains four review articles on metal additive manufacturing (AM) focusing on the processing, microstructural and/or crystallographic control, and biomedical applications of titanium and its alloys, and seventeen regular articles on metal AM, refining, microstructural evolution, and mechanical and fatigue properties related to the microstructure, and biomedical applications of titanium and its alloys, which have been published in Materials Transactions in 2023. This study briefly addresses this issue.
Keywords
titanium and its alloys; additive manufacturing (AM); phase transformation; microstructure; mechanical properties; titanium based intermetallics; biomaterials; recycling -
2024.11.13
A paper on the successful laser fabrication of high-melting-point Cr in cyber/physical space has been published as an OA paper in the "Journal of Materials Research and Technology".
Sung-Hyun Park, Ozkan Gokcekaya*, Tatsuya Nitomakida, Takayoshi Nakano*:
Effects of heat accumulation strategies on defects and microstructure of pure chromium fabricated by laser powder bed fusion: An experimental and numerical study,
Journal of Materials Research and Technology, 33, (2024), 11.049; 1-12.
DOI: https://doi.org/10.1016/j.jmrt.2024.11.049
Clicl here for this paper.
Abstract
The process of employing laser powder bed fusion (L-PBF) process to refractory materials, such as chromium (Cr), remains challenging because of its high ductile-brittle transition temperature. Therefore, a strategy is required to increase the processing temperature to prevent defects. The focus of this study is to clarify the effect of the preheat temperature and scan length variations on defects during the L-PBF process with an experimental and numerical study. Applying a high preheat temperature and short scan length was effective in mitigating the defects. By tuning the heat accumulation strategies, the determined relative density measured by the Archimedes principle and optical measurement of pure Cr parts increased from 97.2% to 99.8% and 97.4% to 99.2%, respectively. The numerical study indicated that deepened and elongated melt pool geometry owing to heat accumulation promoted epitaxial growth. Strong crystallographic texture formation with epitaxial growth led to higher grain size, lower high-angle grain boundary misorientation, Kernel average misorientation, and Taylor factor, which resulted in densification by preventing defects. The hardness of L-PBFed Cr samples gradually decreased with the stronger crystallographic texture formation and compressive yield strength exhibited the same phenomenon. However, the high densification sample with strong crystallographic texture promised the highest compressive strength and strain because it allows single and multi-slip operation during the compressive deformation without premature fracture. This study is a pivotal moment in heat accumulation strategies to achieve high densification for brittle materials fabricated by the L-PBF process while proposing an approach to ensure the reliability of structural applications.
Keywords
Chromium; Laser powder bed fusion; Densification; Numerical simulation; Process-microstructure-property relationship -
2024.10.7
The results of joint research with Prof. Adachi et al. of Nagoya University were published in Materials Characterization.
Fei Sun*, Yoshitaka Adachi, Kazuhisa Sato, Takuya Ishimoto, Takayoshi Nakano, Yuichiro Koizumi:
Quantitative revealing the solute segregation behavior at melt pool boundary in additively manufactured stainless steel using a novel processing method for precise positioning by HAADF-STEM,
Materials Characterization, Materials Characterization, 217, (2024), 114435: 1-6.
https://doi.org/10.1016/j.matchar.2024.114435Click here for this paper.
Abstract
Laser-powder bed fusion (LPBF) enables the fabrication of complex metallic components by manipulating various laser scan strategies to control microstructure and texture. Multiple thermal cycling and rapid solidification lead to non-equilibrium, non-uniform microstructure, and micro-segregation at the melt pool boundary (MPB), whose accurate location is still invisible by transmission electron microscopy (TEM), and quantitative concentration remains imprecise. In this study, we proposed a novel method to make it clear by controlling the crystallographic texture of 316 L stainless steel through unique LPBF processing parameters to obtain a single-crystal-like microstructure of the cellular structures along the laser scanning direction. The accurate location of the track-track MPB is distinguishable by means of the transverse and longitudinal cellular dislocation structures on both sides. The edge-on state of the track-track MPB makes the quantitative concentration analysis precisely using high-angle annular dark-field scanning TEM with energy-dispersive X-ray spectroscopy, which is in good agreement with the Scheil-Gulliver solidification simulations.
Keywords
Additive manufacturing; Melt pool boundary; Cellular structure; Segregation -
2024.10.4
Materialia (Elsevier) published a paper on non-stoichiometric TiNbMoTaW high-entropy alloys that can be fabricated by an in-situ alloying method.
Yong Seong Kim, Ozkan Gokcekaya, Aira Matsugaki, Ryosuke Ozasa, Takayoshi Nakano*:
Laser energy-dependent processability of non-equiatomic TiNbMoTaW high-entropy alloy through in-situ alloying of elemental feedstock powders by laser powder bed fusion, Materialia, 38, (2024), 102241: 1-10.
https://doi.org/10.1016/j.mtla.2024.102241Click here for this paper.
Abstracts
Pre-alloyed powder, which is primarily used in laser powder bed fusion (LPBF), has the disadvantages of requiring time and high manufacturing costs. To overcome these limitations, in-situ alloying, which mixes pure elemental powders and alloys them in real-time during the LPBF process, has attracted attention. In particular, manufacturing high entropy alloys (HEA) containing high-melting-point refractory elements through in-situ alloying presents considerable challenges. In this study, a non-equiatomic single body-centered cubic (BCC) solid-solution HEA was fabricated via in-situ alloying with Ti, Nb, Mo, Ta, and W powders through the LPBF process. Specifically, by applying a high volumetric energy density (VED), we successfully mitigated the segregation of constituent elements, leading to an enhanced crystallographic texture. Consequently, the reduction in the residual stress and high-angle grain boundary (HAGB) density progressed, contributing to an increased relative density. Thus, this study marks a pioneering endeavor for in-situ alloyed HEA fabrication via LPBF, illustrating the efficacy of in-situ alloying utilizing mixed powders.
Keywords
High entropy alloys; Additive manufacturing; In-situ alloying; Segregation; Cracking