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

Ti-6Al-4V alloy parts were obtained by laser powder bed fusion (L-PBF) process. The influence of electro-chemically 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 alpha (hcp) + intergranular beta (bcc) dual-phase. The average surface roughness values for Ra and Rq were 10.1 +/- 1.0 mu m and 12.6 +/- 1.3 mu m, respectively. After electro-chemically charged hydrogen, the phase in the part was composed of a solid solution of hydrogen in alpha-phase, and 8-TiH2 and 8-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 alpha phase or along alpha/beta interface in the as-built part.

Automated summary

Ti-6Al-4V alloy parts obtained by L-PBF process were studied for their microstructure, phase identification, and mechanical properties after being electro-chemically charged with hydrogen. The results showed a unique dual-phase structure in the as-built alloy, while the as-charged parts exhibited a solid solution of hydrogen in alpha-phase, as well as hydride phases. Mechanical properties of the alloy were affected by the direction of deposition, with parts from the deposition direction showing higher resistance to hydrogen embrittlement. Furthermore, the as-charged parts experienced a significant increase in hydrogen content and a decrease in mechanical properties.