Hydrogen-Aided Microstructural Engineering of Additively Manufactured Ti–6Al–4V

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 54; no. 6; pp. 3451 - 3461
• Main Authors: Draelos-Hagerty, Lara, Paramore, James D., Butler, Brady G., Nandwana, Peeyush, Srivastava, Ankit
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.12.2023; Springer Nature B.V; ASM International
• Subjects: Additive manufacturing; characterization; Characterization and Evaluation of Materials; Chemistry and Materials Science; Dehydrogenation; Electron beam melting; Equiaxed structure; Heat treatment; hydrogen processing; MATERIALS SCIENCE; Mechanical properties; Metallic Materials; Microstructure; Morphology; Nanotechnology; Original Research Article; phase transformation; Phase transitions; Strain localization; Structural Materials; Surfaces and Interfaces; tensile testing; Thin Films; titanium alloys; Titanium base alloys
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-023-02924-z

Electron beam melting (EBM) additive manufacturing of Ti–6Al–4V subjects the material to complex thermal cycles, resulting in a columnar morphology of the prior β grains (PBGs). While the columnar PBGs of EBM-processed Ti–6Al–4V can be transformed to an equiaxed morphology through a super-transus ( i.e. , above the β -transus temperature) heat treatment, this also leads to the formation of a coarse lamellar two-phase microstructure. Such a microstructure is prone to strain localization and premature fracture. Herein, we present a thermohydrogen post-process treatment that achieves equiaxed PBG morphology in EBM-processed Ti–6Al–4V without sacrificing mechanical properties. Our results show that a three-step thermohydrogen post-process treatment can transform the columnar PBG morphology to an equiaxed morphology with fine microstructure, and strength and ductility levels comparable to those of the most optimum as-fabricated samples. This three-step thermohydrogen post-process treatment involves hydrogenation and phase transformation treatment in a hydrogen atmosphere, and subsequent dehydrogenation treatment in vacuum. Notably, all these treatments are carried out at temperatures well below the β -transus temperature of hydrogen-free Ti–6Al–4V.