Martensitic transformations in Ti-6Al-4V (ELI) alloy manufactured by 3D Printing

• Published in: Materials characterization Vol. 146; pp. 101 - 112
• Main Authors: Kazantseva, N., Krakhmalev, P., Thuvander, M., Yadroitsev, I., Vinogradova, N., Ezhov, I.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.2018
• Subjects: HEAT TREATMENTS; Laser sintering; MARTENSITE; MARTENSITIC STEELS; Material or constituting phase(s); Material or constituting phase(s) Titanium alloys Laser sintering Metastable phases Mechanical properties; Materials Engineering; MATERIALS SCIENCE; Materialteknik; MECHANICAL PROPERTIES; MECHANICAL TESTS; Metastable phases; MICROSTRUCTURE; ORTHORHOMBIC LATTICES; PHASE TRANSFORMATIONS; POWDERS; TITANIUM ALLOYS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; Mechanical properties; Titanium alloys; Metastable phases; Material or constituting phase(s); Laser sintering
• ISSN: 1044-5803; 1873-4189; 1873-4189
• DOI: 10.1016/j.matchar.2018.09.042

In the present investigation, Ti-6Al-4V ELI samples were manufactured by the powder-bed fusion (PBF) process using the laser sintering (LS) technology. Microstructure, chemical and phase constitution, and mechanical properties were studied by means of the transmission electron microscopy, atom probe tomography, X-ray diffraction, nanoindentation and mechanical testing. It was found that the structure of LS samples consisted of two different variants of metastable phases, namely the hexagonal α′ martensitic phase and small amounts of the orthorhombic α″ martensitic phase. The martensitic α′-phase was formed because of the high cooling rates of the LS method. The {101¯2} ⟨1¯011⟩ hexagonal martensite tensile twins were observed in the microstructure of the as-build alloy. Small areas with inner twinning martensitic plates, which are typical for the metastable orthorhombic martensitic phase in titanium alloys, were identified by the transmission electron microscopy. Atom probe tomography (APT) confirmed localization of β-stabilizing elements at interfaces, presumably at the twin or lamella boundaries. The structure and origin of the martensitic phases in 3D printed Ti-6Al-4V alloys are discussed with respect to in-situ heat treatment during manufacturing. [Display omitted] •Two metastable martensitic phases, namely α′′ and α′ may be formed in Ti-6Al-4V during 3D manufacturing process.