Prior β grain evolution and phase transformation of selective laser melted Ti6Al4V alloy during heat treatment

• Published in: Journal of alloys and compounds 2022-09, Vol.914, p.165235, Article 165235
• Main Authors: Lu, S.L., Zhang, Z.J., Liu, R., Qu, Z., Wang, B., Zhou, X.H., Eckert, J., Zhang, Z.F.
• Format: Article
• Language: English
• Subjects: Beta phase; Evolution; Grain boundaries; Heat treating; Heat treatment; High temperature; Laser beam melting; Martensite; Microhardness; Microstructure; Phase transformation; Phase transitions; Rapid prototyping; Selective laser melting; Ti6Al4V alloy; Titanium base alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.165235

Prior β grain evolution and phase transformation of selective laser melted (SLM) Ti6Al4V alloy after subtransus and supertransus solution heat treatments are investigated. A method based on the special angle grain boundaries (in the range of 15–55° and 70–85°) is proposed for a clear and straightforward description of the prior β mesostructure. Post solution treatments below β transus retain the prior β grains and alter the fully martensitic microstructure into a mixture of α and α’/β phases. A non-traditional “bimodal structure” consisting of αP and αS’ phases is produced by subtransus treatments at a relatively high temperature. While treatments above β transus lead to the growth of prior β grains and transform the martensitic α’ phases into β phases first, and then back into α’ martensites again during quenching, leading to a new martensitic microstructure. The microhardness is determined by the α lath thickness and the amount of α’ martensite, and the latter is more predominant. [Display omitted] •Prior β grain can be described by grain boundaries in the range 15–55° and 70–85°.•Subtransus solution have no influence on the prior β mesostructure.•Solution at 900 ℃, α’ martensites between the primary α laths are produced.•Microhardness is determined by: amount of α’ martensite> α lath thickness.