Fundamental investigation into mass transfer process and microstructural transformation pathways in Ti-6Al-4V via underwater wire-laser directed energy deposition

ABSTRACT

The in-situ analysis of mass transfer behaviours in a novel underwater wire-laser directed energy deposition (ULDED) technique was conducted using in-situ X-ray high-speed imaging. By creating a stable local dry cavity within the water environment, three distinct mass transfer modes were identified: droplet transfer, liquid bridge transfer and spreading transfer modes. The mass transfer behaviours were effectively managed by maintaining the liquid bridge mode to enhance the formability of the metal deposits. The inherent heat treatment effect in ULDED provides a unique opportunity to tailor microstructures and mechanical properties in situ with establishing a thermal environment conducive to the preferred lamellar α+β microstructure instead of the acicular α′ martensite. With increasing heat input, the diffusion-controlled transformation pathway gave rise to the lamellar α+β instead of the martensite decomposition, underpinned by the microstructure morphological characteristics and the crystallographic orientations of constituent phases.

KEYWORDS:

• Underwater wire-laser directed energy deposition
• mass transfer
• formability
• microstructure transformation pathway
• mechanical properties

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data presented in this study are available on request from the corresponding author.

Additional information

Funding

The authors are grateful for the financial support for this study from ‘National Key R&D Program of China' (grant number 2022YFB4601800), ‘National Natural Science Foundation of China' (grant number 52305346), ‘Natural Science Foundation of Shandong Province' (grant number ZR2023QE168), ‘CGN-HIT Advanced Nuclear and New Energy Research Institute' (grant number CGN-HIT202219), ‘Scientific research and innovation fund' (grant number 2022KYCXJJ08), the ‘Fundamental Research Funds for the Central Universities’ (grant number HIT.OCEF.2021036).