TY - JOUR
T1 - Micromechanical behavior and thermal stability of a dual-phase α+α’ titanium alloy produced by additive manufacturing
AU - de Formanoir, Charlotte
AU - Martin, Guilhem
AU - Prima, Frédéric
AU - Allain, Sébastien Y.P.
AU - Dessolier, Thibaut
AU - Sun, Fan
AU - Vivès, Solange
AU - Hary, Benjamin
AU - Bréchet, Yves
AU - Godet, Stéphane
PY - 2019/1/1
Y1 - 2019/1/1
N2 - In order to improve the tensile properties of additively manufactured Ti-6Al-4V parts, specific heat treatments have been developed. Previous work demonstrated that a sub-transus thermal treatment at 920 °C followed by water quenching generates a dual-phase α+α′ microstructure with a high work-hardening capacity inducing a desirable increase in both strength and ductility. The present study investigates the micromechanical behavior of this α+α′ material as well as the thermal stability of the metastable α’ martensite. To that end, annealing of the α+α′ microstructure is performed and the resulting microstructural evolution is analyzed, along with its impact on the tensile properties. A deeper understanding of the micromechanics of the multiphase microstructure both before and after annealing is achieved by performing in-situ tensile testing within a SEM, together with digital image correlation for full-field local strain measurements. This approach allows the strain partitioning to be quantified at a microscale and highlights a significant mechanical contrast between the two phases. In the α+α′ microstructure, the α′ phase is softer than the α phase, which is confirmed by nanoindentation measurements. Partial decomposition of the martensite during annealing induces a substantial hardening of the α′ phase, which is attributed to fine-scale precipitation and solution strengthening. A scale transition model based on the iso-work assumption and describing the macroscopic tensile behavior of the material depending on the individual mechanical behavior of each phase is also proposed. This model enables to provide insights into the underlying deformation and work-hardening mechanisms.
AB - In order to improve the tensile properties of additively manufactured Ti-6Al-4V parts, specific heat treatments have been developed. Previous work demonstrated that a sub-transus thermal treatment at 920 °C followed by water quenching generates a dual-phase α+α′ microstructure with a high work-hardening capacity inducing a desirable increase in both strength and ductility. The present study investigates the micromechanical behavior of this α+α′ material as well as the thermal stability of the metastable α’ martensite. To that end, annealing of the α+α′ microstructure is performed and the resulting microstructural evolution is analyzed, along with its impact on the tensile properties. A deeper understanding of the micromechanics of the multiphase microstructure both before and after annealing is achieved by performing in-situ tensile testing within a SEM, together with digital image correlation for full-field local strain measurements. This approach allows the strain partitioning to be quantified at a microscale and highlights a significant mechanical contrast between the two phases. In the α+α′ microstructure, the α′ phase is softer than the α phase, which is confirmed by nanoindentation measurements. Partial decomposition of the martensite during annealing induces a substantial hardening of the α′ phase, which is attributed to fine-scale precipitation and solution strengthening. A scale transition model based on the iso-work assumption and describing the macroscopic tensile behavior of the material depending on the individual mechanical behavior of each phase is also proposed. This model enables to provide insights into the underlying deformation and work-hardening mechanisms.
KW - Additive manufacturing
KW - Heat treatment
KW - Martensite
KW - Ti-6Al-4V
KW - Work-hardening
UR - http://www.scopus.com/inward/record.url?scp=85054362685&partnerID=8YFLogxK
U2 - 10.1016/j.actamat.2018.09.050
DO - 10.1016/j.actamat.2018.09.050
M3 - Article
AN - SCOPUS:85054362685
VL - 162
SP - 149
EP - 162
JO - Acta Materialia
JF - Acta Materialia
SN - 1359-6454
ER -