Massive transformation in Ti–6Al–4V additively manufactured by selective electron beam melting. (1st February 2016)

• Record Type: Journal Article
• Authors: Lu, S.L.; Qian, M.; Tang, H.P.; Yan, M.; Wang, J.; StJohn, D.H.
• Is Part Of: Acta materialia. Volume 104(2016)
• Page Start: 303
• Page End: 311
• Publication Date: 2016-02-01
• Subjects: Ti–6Al–4V -- Massive transformation -- Additive manufacturing -- Selective electron beam melting; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2015.11.011
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: The occurrence of the β (bcc) to αm (hcp) massive transformation in Ti–6Al–4V (wt.%) during additive manufacturing (AM) by selective electron beam melting (SEBM) has been identified. A variety of patch-shaped massive grains including both grain boundary (GB)-crossing and non-GB-crossing instances were characterised and their formation temperature and growth rate were estimated. In contrast to conventional Ti–6Al–4V, the massive grains in SEBM-fabricated Ti–6Al–4V consist of ultrafine lamellar α and β phases (100 nm wide β strips) due to in-situ decomposition of the massive grains during AM. The resulting ultrafine α-β lamellae obey the typical Burgers orientation relationship established for the lamellar α-β structure in conventional Ti–6Al–4V. These findings show that the β (bcc) to αm (hcp) massive transformation significantly contributes to development of the Ti–6Al–4V microstructure during AM by SEBM, providing an alternative microstructural design strategy for AM of Ti–6Al–4V and other titanium alloys. Graphical abstract: (a) EBSD colour inverse pole figure (IPF) showing both non-GB-crossing (i.e.③) and GB-crossing (i.e. ④ and ⑤) massive phase grains. (b) Multiple-spot TEM BF image showing the ultra-fine α-β microstructures within the massive phase grain. The inset in (a) is an EBSD band-contrast map showing the original prior-β GB. The side arrow in (a) represents the SEBM building direction.