# Fileset

[20251013MRS2026Abstract-Mitarai.docx](https://mdr.nims.go.jp/filesets/18d94ea0-66ca-40eb-b631-16d3f80e5946/download)

## Creator

Yoko Yamabe-Mitarai, [Yoshiaki Toda](https://orcid.org/0000-0002-8343-2890), Tetsuya Matsunaga, Ryosuke Ozasa(, Takuya Ishimoto, Tsutomu Ito, Takayoshi Nakano

## Rights

[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

## Other metadata

[Creep deformation mechanism of LPBFed near α, and near β-Ti alloys](https://mdr.nims.go.jp/datasets/966d3970-f9d2-4683-bc80-866ed01092bf)

## Fulltext

ABSTRACT DETAILSControl ID: 4429011Presentation Preference: Invited SpeakerSymposium: MF02: Creation of Materials by Super-Thermal Field in Additive ManufacturingAbstract Title: Creep deformation mechanism of LPBFed near α, and near β-Ti alloysPresenter: Yoko Yamabe-MitaraiAuthors: Yoko Yamabe-Mitarai(1); Yoshiaki Toda(2); Tetsuya Matsunaga(3); Ryosuke Ozasa(4); Takuya Ishimoto(5); Tsutomu Ito(6); Takayoshi Nakano(4)Institutions: 1. The University of Tokyo, Kashiwa, Japan. 2. National Institute for Materials Science, Tsukuba, Japan. 3. JAXA, Sagamihara, Japan. 4. The University of Osaka, Osaka, Japan. 5. University of Toyama, Toyama, Japan. 6. Toyama Prefectural University, Imizu, Japan.Abstract Body: Abstract BodyIn this study, near α (hcp) -Ti alloy (Ti-6Al-4Nb-4Zr, wt%) and near β (bcc) - Ti alloy (Ti-6Al-2Sn-4Zr-6Mo) were focused on since Ti alloys have been used as jet engine compressor components due to their lightweight and excellent mechanical properties at high temperatures.The laser powder bed fusion (LPBF) was applied for near α and near β - Ti alloys to investigate microstructure evolution depending on scanning conditions and creep deformation behavior related with microstructure. The melting pool boundaries that are formed by cyclic heating due to cyclic scanning of the laser beam were clearly observed in the as-built state in both alloys. The crystallographic orientation of the β phase was random in near α -Ti alloys 1, 2), while columnar microstructures with crystallographic lamellar-like microstructure (CLM), a near single crystal-like microstructure (SCM), and polycrystalline structures (PCM) were observed under the specific scanning condition in near β -Ti alloys 3, 4). The martensite transformation from the β to α phase occurred during rapid cooling during LPBF. The fine martensitic a phase was formed inside the melting pool. In near α Ti-Alloy, a fine a phase formed with decrease of energy density, VED, as shown by , where is laser power, is scan speed, is powder layer thickness, is hatch distance 1, 2), while in near β -Ti alloy, the opposite behavior was observed; that is, a fine α phase formed at higher VED 3, 4).The creep deformation mechanism is dislocation creep, which depends on the microstructure in the molten pool rather than the grain size in both alloys. Even so, grain size dependence of creep life was observed in near a -Ti alloy 1, 2). Creep lives of LPBFed near α -Ti alloy (100~300 μm in melting pool size) were between those of the forged sample with bimodal structure (10 μm in grain size) and with lamellar structure (550 μm in grain size) 1, 2). It was also found that the Hot Isostatic Press (HIP) is helpful for improving creep life by eliminating micro-defects 1). In near β -Ti alloy, the creep strain was larger at low stress in the LPBFed samples compared with the forged sample, but the creep life was slightly longer in the LPBFed samples than in the forged sample. There is no significant difference in creep deformation between SCM, CLM, and PCM. In addition, a creep rupture surface was observed at the melt-pool boundary, suggesting that the α phase, which continuously forms on the melt-pool boundary in near β -Ti alloy, is the crack formation site.References:T. Kuroda, H. Masuyama, Y. Toda, T. Matsunaga, T. Ito, M. Watanabe, R. Ozasa, T. Ishimoto, T. Nakano, M. Shimojo, Y. Yamabe-Mitarai, Mater. Trans. 64, 1 95-103 (2023).Y. Yamabe-Mitarai, T. Inoue, T. Kuroda, S. Matsunaga, Y. Toda, T. Matsunaga, T. Ito, R. Ozasa, T. Ishimoto, T. Nakano, Mater. Trans., 64, 6 1175-1182 (2023).P. V. Cobbinah, S. Matsunaga, Y. Toda, R. Ozasa, M. Okugawa, T. Ishimoto, Y. Liu, Y. Koizumi, P. Wang, T. Nakano, Y. Yamabe-Mitarai, Smart Materials in Manufacturing. 2 100050 (2024).P. V. Cobbinah, S. Matsunaga, Y. Toda, R. Ozasa, T. Ishimoto, T. Nakano, T. Ito, Y. Yamabe-Mitarai, Metall. Mater. Trans. A. 56, 2057-2073 (2025).Acknowledgement: This work was supported by Grants-in-Aid for Transformative Research Area A [grant number JP21H05198] and for Scientific Research [grant number JP23H00235] from the Japan Society for the Promotion of Science (JSPS), and by The Light Metal Educational Foundation (Japan).