Metallurgical Abstracts on Light Metals and Alloys vol. 58

On the enhanced creep performance in Ti6246 achieved through Laser Powder Bed Fusion (LPBF) processing

Prince Valentine Cobbinah^a, Sae Matsunaga^a, Yoshiaki Toda^b, Ryosuke Ozasa^c, Takuya Ishimoto^c,d, Takayoshi Nakano^c,
Tsutomu Ito^e and Yoko Yamabe-Mitarai^a
^a Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo,
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
^b Center for Basic Research on Materials, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan
^c Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565- 0871, Japan
^d Aluminium Research Center, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
^e Department of Mechanical systems Engineering, Faculty of Engineering, Toyama Prefectural University, Kurokawa 5180, Imizu, Toyama, 939-0398, Japan

[Published in Metall. Mater. Trans. A, 56A (2025) 2057-2073]

https://doi.org/10.1007/s11661-025-07759-8
E-mail: mitarai.yoko[at]edu.k.u-tokyo.ac.jp
Key Words: Near-α Ti alloy, Lameller structure, Compression strength, Creep, Deformation mechanism

In this study, the creep performance (at 500°C) of Ti6246 fabricated from three different LPBF processing conditions and heat-treated (HT) at 885°C were investigated. In the as-built state, all the LPBFed-Ti6246 exhibited columnar microstructures with crystallographic lamellar-like microstructure (CLM), a near single crystal-like microstructure (SCM), and polycrystalline microstructure (PCM) textures, respectively. At low applied stresses (100 – 300 MPa), diffusional creep was the dominant deformation mechanism and its resistance depended on grain size. The reference β-forged-HT Ti6246, characterized by large equiaxed grains, exhibited the lowest strain rate compared to the columnar microstructure of SX1 (CLM)-HT, SX2 (SCM)-HT, and SX3 (PCM)-HT. Conversely, dislocation slip governed deformation at high applied stresses (400 – 580 MPa) and its efficacy depended on the α/β interfaces in the microstructures. Disjointed columnar grains in SX1 (CLM)-HT and the deformation of the polycrystalline grains in SX3 (PCM)-HT indicated that the melt pool boundaries were unstable in the LPBFed-Ti6246. SX2 (SCM)-HT exhibited the longest creep life due to the relatively stable melt pool boundaries and the near <001> SCM crystallographic texture parallel to the applied stresses. Shallow ductile dimples and tears and the observation of laser scan tracks characterized the fracture surfaces of the LPBFed-Ti6246. These indicated that failure occurred by intergranular ductile fracture resulting from the formation of microvoids at the melt pool boundaries.