Influence of electrochemically charged hydrogen on mechanical properties of Ti–6Al–4V alloy additively manufactured by laser powder-bed fusion (L-PBF) process

Abstract

Ti–6Al–4V alloy parts were obtained by laser powder bed fusion (L-PBF) process. The influence of electrochemically charged hydrogen on the microstructure, phase identification, and mechanical properties of as-charged Ti–6Al–4V alloy parts from printing and deposition directions was studied. The impact of hydrogen desorption on L-PBF Ti–6Al–4V alloy parts was characterized with oxygen nitrogen hydrogen analyzer, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that as-built Ti–6Al–4V alloy was composed of a unique structure of a kind of equiaxed α (hcp) + intergranular β (bcc) dual-phase. The average surface roughness values for Ra and Rq were 10.1 ± 1.0 μm and 12.6 ± 1.3 μm, respectively. After electrochemically charged hydrogen, the phase in the part was composed of a solid solution of hydrogen in α-phase, and δ-TiH2 and δ-TiHx hydride phases. The mechanical properties of as-printed Ti–6Al–4V alloy part from deposition direction were higher than those of as-built part from printing direction. After electrochemically charged hydrogen, the hydrogen content in the as-built Ti–6Al–4V alloy part increased significantly. The mechanical properties of the as-charged parts from printing and deposition directions were decreased significantly. The susceptibility to hydrogen embrittlement significantly depended on the orientation of additively manufactured Ti–6Al–4V alloy parts, the as-printed part from deposition direction had a higher resistance to hydrogen embrittlement compared with printing direction. After electrochemically charged hydrogen, Ti–6Al–4V alloy parts from printing direction was prone to brittle fracture and form the microcracks in α phase or along α/β interface in the as-built part.