Hydrogen-Induced Phase Transformation and Microstructure Evolution for Ti-6Al-4V Parts Produced by Electron Beam Melting

• Published in: Metals (Basel ) 2018-05, Vol.8 (5), p.301
• Main Authors: Pushilina, Natalia, Panin, Alexey, Syrtanov, Maxim, Kashkarov, Egor, Kudiiarov, Viktor, Perevalova, Olga, Laptev, Roman, Lider, Andrey, Koptyug, Andrey
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Beta phase; Electron beam melting; Evolution; Hydrides; Hydrogen; Hydrogen storage; Hydrogenation; Intermetallic compounds; Microstructure; Phase plates; Phase transitions; Scanning electron microscopy; Titanium aluminides; Titanium base alloys; Titanium Ti-6Al-4V alloy; Transmission electron microscopy; X-ray diffraction
• ISSN: 2075-4701; 2075-4701
• DOI: 10.3390/met8050301

In this paper, phase transitions and microstructure evolution in titanium Ti-6Al-4V alloy parts produced by electron beam melting (EBM) under hydrogenation was investigated. Hydrogenation was carried out at the temperature of 650 °C to the absolute hydrogen concentrations in the samples of 0.29, 0.58, and 0.90 wt. %. Comparative analysis of microstructure changes in Ti-6Al-4V alloy parts was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Furthermore, in-situ XRD was used to investigate the phase transitions in the samples during hydrogenation. The structure of Ti-6Al-4V parts produced by EBM is represented by the α phase plates with the transverse length of 0.2 μm, the β phase both in the form of plates and globular grains, and metastable α″ and ω phases. Hydrogenation to the concentration of 0.29 wt. % leads to the formation of intermetallic Ti3Al phase. The dimensions of intermetallic Ti3Al plates and their volume fraction increase significantly with hydrogen concentration up to 0.58 wt. % along with precipitation of nano-sized crystals of titanium δ hydrides. Individual Ti3Al plates decay into nanocrystals with increasing hydrogen concentration up to 0.9 wt. % accompanied by the increase of proportion and size of hydride plates. Hardness of EBM Ti-6Al-4V alloy decreases with hydrogen content.