TY  - JOUR
AU  - Simonelli, Marco
AU  - Zou, Zhiyi
AU  - Barriobero Vila, Pere
AU  - Tse, Yau Yau
TI  - The development of ultrafine grain structure in an additively manufactured titanium alloy via high-temperature microscopy
JO  - Materialia
VL  - 30
IS  - I-20210694
SN  - 2589-1529
CY  - Amsterdam
PB  - Elsevier
M1  - PUBDB-2023-04603
M1  - I-20210694
SP  - 101856 -
PY  - 2023
AB  - Microstructures dominated by acicular α' martensitic phase, such as in the case of Ti-6Al-4V fabricated by laser powder-bed fusion (PBF-LB), are known to suffer from reduced ductility and low toughness. The decomposition of such metastable microstructures into α+β lamellar structures during PBF-LB requires either specific laser regimes that are often challenging to be attained or post-process heat treatments which might lead, instead, to undesirable coarsening of the grain structure. Here we propose a novel route for the formation of ultrafine lamellar α+β microstructures and demonstrate the associated advantages in terms of tensile strength and ductility. Our approach is based on a suitable modification of constitution of Ti-6Al-4V with additions of Fe, a known potent β stabiliser of high intrinsic diffusivity. After printing, this alloy presents a microstructure dominated by metastable β phase. We investigate the details of its decomposition using a combination of in-situ high-energy synchrotron X-ray diffraction and high temperature microscopy up to the β transus temperature. The microstructure evolution is comprised by homogeneous decomposition of the metastable β phase via ω-assisted nucleation of α phase, α grain growth sustained by early diffusion of Fe in the β phase followed by a conventional partitioning of V. The understanding of this transformation pathway enables the development of ultrafine grained α+β lamellar microstructures that exhibit outstanding tensile behaviour. The presented approach is machine-agnostic and offers a novel alloy design strategy for development of high-strength alloys in additive manufacturing.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:001047590000001
DO  - DOI:10.1016/j.mtla.2023.101856
UR  - https://bib-pubdb1.desy.de/record/587907
ER  -