Features of the Structural-Phase State of the Alloy Ti-6Al-4V in the Formation of Products using Wire-Feed Electron Beam Additive Manufacturing

Introduction. The high cost of parts made of titanium alloys is determined by the high material consumption during machining, poor machinability caused by low thermal conductivity and high chemical reactivity with cutting tool materials, which is a factor limiting its widespread use. The use of additive technologies makes it possible to reduce production costs of titanium alloy components due to manufacturing of near-net shapes. At the same time, the key requirement in manufacturing the near-net shapes is to maintain high mechanical characteristics both of the base material and the component as a whole. Wire-feed electron beam additive manufacturing has a high potential, both in terms of high productivity and obtaining materials with a unique structure and high mechanical properties. Goal of this research is to study the structure, phase composition and microhardness of Ti-6Al-4V alloy samples obtained using wire-feed electron beam additive manufacturing. Results and discussion. Based on the data of optical, scanning electron microscopy and X-ray diffraction analysis, Ti-6Al-4V samples obtained after layer-bylayer formation have a heterogeneous microstructure which is composed of the system of orthogonal plates of the martensitic alpha'-phase, in addition to the columnar preceded beta-grains with the mean size of < 1.5 mm formed during epitaxial growth. At the same time, both thickness of the alpha'-phase plates and amount of the residual beta-phase are decreases in the direction at the top of the formed sample (from 4 mu m and 10 vol. % for the lower layer, up to 2 mu m and 5 vol. % for the upper layer). The effect of increasing the Vickers hardness with the increase in the height of the formed layers to values of the order of 3.5 GPa is found. A good agreement with the Hall-Petch ratio shows that the effect of increasing hardness in the direction of layer-by-layer formation is mainly due to a gradient microstructure formed during complex thermal history.