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Abstract
A first stage study has been performed to investigate the potential for exploiting high deposition rate WAAM to print dual-alloy microstructures. Samples were built using alternating feed wires of commercially-pure Ti and Ti–6Al–4V. A high level of dilution occurred during deposition accompanied by effective liquid-phase mixing, producing a regular distribution of solidified melt tracks of approximate bimodal composition each less extreme than that of their respective constituent feed wires. The yield strength of the dual alloy composite material was approximately midway between that of the two alloys from which it was produced and exhibited a double inflection yield behaviour. Overall, because of the relatively coarse length scale there was not a significant property advantage in tensile loading above that of a chemically homogenous material, thus the main advantage of printing alternate alloys at this length scale is likely to reside more with increasing crack path tortuosity during fracture or fatigue loading. Importantly, the deposited material was found to have a refined β-grain structure suggesting that the composition gradients introduced by dual-alloy printing can disrupt the epitaxial columnar growth normally seen in WAAM deposits.
Highlights
Titanium alloys, like Ti–6Al–4V (Ti64), are in increasing demand for aerospace applications due to their high specific strength, corrosion resistance, damage tolerance, and compatibility with graphite fibre composite materials [1,2,3]
The results show that, similar to other continuously reinforced composite materials [59], the AACWAAM deposits gave a better all-round mechanical performance when tested parallel to the direction of alignment of the alternating alloy tracks, compared to when tested in the direction normal to the deposited layers (ND)
A first stage study has been performed to investigate the potential for exploiting high deposition rate additive manufacturing (AM) techniques to print dual alloy microstructures
Summary
Like Ti–6Al–4V (Ti64), are in increasing demand for aerospace applications due to their high specific strength, corrosion resistance, damage tolerance, and compatibility with graphite fibre composite materials [1,2,3]. Of the different approaches available, wire fed Directed Energy Deposition (DED) processes, like Wire-Arc AM (WAAM) [1,4,5,6], have several advantages over other technologies including: a high material utilisation (99% [7,8,9]) and energy efficiency (~ 70% [8,10,11]), lower capital equipment costs, high kilogram-per-hour deposition rates [9], and large build envelops of several meters In addition to their greater near-net-shape capability, AM technologies can add value by taking advantage of the layer-by-layer deposition principle to ‘print’ components with tailored microstructures and compositions [12,13,14,15,16,17,18,19]. Hernández-Nava et al [21] have demonstrated, using a novel electron beam melting and hot isostatic pressing technique, that two microstructure types could be engineered for site-specific properties in a single component, whereby coarse colony α could be produced for areas where fracture-resistant properties were desirable, and fine Widmanstatten α for high yieldstrength areas
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