On the observation of annealing twins during simulating β-grain refinement in Ti-6Al-4V high deposition rate am with in-process deformation

DOI: 10.1016/j.actamat.2020.01.009

Authors: J. Donoghue (University of Manchester) , A. E. Davis (University of Manchester) , C. S. Daniel (University of Manchester) , A. Garner (University of Manchester) , F. Martina (Cranfield University) , J. Quinta Da Fonseca (University of Manchester) , P. B. Prangnell (University of Manchester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Materialia

State: Published (Approved)
Published: January 2020
Diamond Proposal Number(s): 13994

Abstract: Additive Manufacture (AM) of Ti-6Al-4V frequently leads to undesirable, coarse, columnar β-grain structures with a strong <100> fibre texture. In Wire-Arc AM (WAAM), it has been found that the application of a low plastic strain, by methods such as inter-pass rolling, can disrupt β columnar growth and produce a refined, equiaxed grain structure that is more randomly orientated. The origin of this desirable effect has been investigated by thermo-mechanical simulation, direct in-situ EBSD observation, as well as by real-time synchrotron X-ray diffraction (SXRD) during rapid heating. These complementary approaches have shown that, when starting with a WAAM microstructure, the grain refinement process produces a unique micro-texture represented by a four-pole motif symmetrically centred on the parent grain {100} orientations. These new β-grain orientations can be reproduced by a double {112}<111> twinning operation, which produces 12 new, unique, β-orientation variants. High-resolution orientation-mapping techniques and in-situ SXRD heating simulations suggest that the prior β does not twin during deformation, but rather the grain refinement and related texture may be caused by annealing twinning during β re-growth on rapid re-heating of the deformed AM microstructure. Although this is the first time such a unique texture has been observed in a deformed and β annealed Ti-6Al-4V material, it was only found to dominate under the unusual conditions that occur in AM of rapid heating – a fine, lightly deformed α transformation microstructure, with a very coarse starting β-grain structure.

Journal Keywords: Additive manufacture; Titanium; Grain size; Recrystallization; Texture

Diamond Keywords: Additive Manufacturing

Subject Areas: Materials, Engineering


Instruments: I12-JEEP: Joint Engineering, Environmental and Processing

Added On: 15/01/2020 09:54

Documents:
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Discipline Tags:

Aerospace Materials Science Engineering & Technology Metallurgy

Technical Tags:

Diffraction