A study on the grain refinement mechanism of Ti-6Al-4V alloy produced by wire arc additive manufacturing using hydrogenation treatment processes

The effect of the hydrogen content of 0.48 wt% and 1.38 wt% on the refinement of the microstructure of Ti-6Al-4V alloy produced by wire arc additive manufacturing was studied, and the microstructure evolution of Ti-6Al-4V alloy after hydrogenation, heat treatment and dehydrogenation was revealed in this work. The result shows that the Ti-6Al-4V alloy prepared by wire arc additive manufacturing technology consist of coarse columnar beta grains with the lamellar alpha cluster inside. After hydrogenation treatment, the alpha clusters inside the beta grains become smaller, and hydrides were produced. Then alpha', alpha '' and metastable phase beta(M) were formed in the microstructure during the quenching from the temperature of Tp+ 10 degrees C. At last, the metastable phase and hydride were decomposed during the subsequent aging and dehydrogenation process, which significantly refines the alpha grains in the columnar beta grains, forming a large area of a fine-grained microstructure. The shape and size of the original and hydrogen-removed grains was observed by electron backscatter diffraction (EBSD). The result shows that the average size of the original lamellar alpha grains has been refined from 5.78 mu m to 0.84 mu m, especially, there were no original alpha grains with size above 4 mu m left. With the hydrogen content of 0.48 wt%, the morphology of alpha grains after hydrogen removal is fine needle-like, while, when the hydrogen content increases to 1.38 wt%, the morphology of alpha grains is equiaxed. (C) 2021 Published by Elsevier B.V.