Modification of α-phase of wire + arc additive manufactured Ti-6Al-4 V alloy with boron addition

Abstract

The deposition rate of the wire+arc additive manufacturing (WAAM) technique is high and its equipment and operating costs are low, making it suitable for fabricating large-size components with special-shape. For improving the high-strain-rate mechanical properties, 0.1 wt% boron was added to the Ti-6Al-4 V alloy wire to modify the microstructure of the boron-added titanium alloy fabricated via WAAM. In this study, the α-phase morphology and texture of as-built and β-annealed WAAM Ti-6Al-4 V-0.1B alloy were investigated by optical microscopy and electron backscatter diffraction technique. The addition of 0.1 wt% boron caused the length of the α-phase lamellae to reduce significantly in both the as-built and the annealed WAAM Ti-6Al-4 V-0.1B specimens. This was attributed to the combined action of the fine prior β-grains and the growth-inhibiting effect of the TiB particles on the α-phase. The continuous-grain-boundary α-phases were broken and even completely absent in both the as-built and the annealed WAAM Ti-6Al-4 V-0.1B specimens. Moreover, in both specimens, the α-phases exhibited two distinct fiber textures, 〈11−20〉 α and < 16 0–16 19 > α, parallel to the building direction. Further, the α-phases that had nucleated at the boundaries of the prior β-grains showed the appearance of the variant selection, which preferentially exhibited the former fiber texture.