Evolution of microstructural complex transitions in low-modulus β-type Ti-35Nb-2Ta-3Zr alloy manufactured by laser powder bed fusion

• DOI: 10.1016/j.addma.2021.102376
• Publication Date: 2021-10-04T13:09:52Z
• Authors: Noman Hafeez; Daixiu Wei; Lechun Xie; Yujin Tang; Jia Liu; Hidemi Kato; Weijie Lu; Lai-Chang Zhang; Liqiang Wang
• Keywords: Shear modulus; Titanium alloy; Diffusionless transformation

Abstract Low modulus β-type Ti-35Nb-2Ta-3Zr alloy scaffold was fabricated by laser powder bed fusion ( L -PBF). The complex microstructure and mechanical properties were characterized systematically. The martensitic interstitial complex transitions (ICTs) from β to α" (β→α"), α" to ω (α"─ω), and β to α" and ω (β→α''─ω) phases are accompanied by dislocation pile-ups and twins in a heterogeneous manner. A homaloidal transition was observed with astraddle ω and α"M nanolayers and partial nanolayers along the boundaries of the α"T martensitic twin. Crystallographic characterization confirmed that {332}〈113〉 and {112}〈111〉 twinning and shear stress assisted the α─ω and β→α" transitions at the interface of the β region. Both the αꞌꞌ martensitic twin and ω formation were observed adjacent to the {332}〈113〉 type twinning mode. The [332] twinning were instigated and nucleated through ω-phase formation. The secondary [112] twins amid the primary [332] twinning were instigated and nucleated through ω-phase formation. Multiple slip bands were identified on the surface of the micropillar after the microcompression testing. Moreover, high-density dislocations and dislocation pile-ups were found alongside the twins and grain boundaries. In addition, {112}〈111〉 twinning was identified amongst dislocation pile-ups. This work reveals a novel complex phase transformation that could play a significant role in applications such as biomedical implants.