In wire arc additive manufacturing of Ti-alloy parts (Ti-WAAM) gas metal arc welding (GMAW) can be applied for complex parts printing. However, due to the specific properties of Ti, GMAW of Ti-alloys is complicated. In this work, three different types of metal transfer modes during Ti-WAAM were investigated: Cold Metal Transfer, controlled short circuiting metal transfer, and self-regulated metal transfer at a direct current with a negative electrode. Metal transfer modes were studied using captured waveform and high-speed video analysis. Using these modes, three walls were manufactured; the geometry preservation stability was estimated and compared using effective wall width calculation, the microstructure was analyzed using optical microscopy. Transfer process data showed that arc wandering depends not only on cathode spot instabilities, but also on anode processing properties. Microstructure analysis showed that each produced wall consists of phases and structures inherent for Ti-WAAM. α-basketweave in the center of and α-colony on the grain boundary of epitaxially grown β-grains were found with heat affected zone bands along the height of the walls, so that the microstructure did not depend on metal transfer dramatically. However, the geometry preservation stability was higher in the wall, produced with controlled short circuiting metal transfer.

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In this work, MIG process was utilized for the wire arc additive manufacturing of the wall-shaped parts, using NiTi shape-memory alloy. High-scale specimens consisting of 20 layers were deposited by using Ni-rich (Ni55.56Ti wt.%) wire as a feedstock on the NiTi substrate with the identical chemical composition. One of two specimens was heat-treated at a temperature of 430 °C for 1 h. The influence of such a heat treatment on the microstructure, phase transformation temperatures, chemical and phase compositions, microhardness, and tensile and bending tests’ results is discussed. As-deposited metal successfully demonstrates superelastic behavior, except in the lower zone. In regard to the shape-memory effect, it was concluded that both the as-deposited and the heat-treated samples deformed in liquid nitrogen completely restored (100%) their shapes at an initial strain of 4–5%. An occurrence of the R-phase was found in both the as-deposited and the heat-treated specimens. The phase transformation temperatures, microstructure, and tensile and bending tests results were found to be anisotropic along the height of the specimens. The presented heat treatment led to changes in the functional and mechanical properties of the specimen, provided with the formation of finely dispersed Ni4Ti3, NiTi2, and Ni3Ti phases.

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