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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 R a and R q 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-TiH 2 and δ-TiH x 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. [ABSTRACT FROM AUTHOR]

The influence of intercritical annealing plus tempering treatments on the microstructure and mechanical properties of a novel Nb–Mo bearing medium Mn steel was investigated in this work. Based on the experimental results, the microstructure of experimental steel affected by intercritical annealing plus tempering treatments could be included as follows: (1) the retained austenite (RA) fraction fluctuated slightly (~41%) when the samples tempered between 150 °C and 350 °C, then decreased up to 32% at 450 °C for the austenite decomposition; (2) RA mechanical stability increased with the increase in tempering temperatures; (3) (Nb,Mo) (C,N) precipitates density increased from 150 °C to 450 °C by decreasing mismatch degree between precipitates and ferrite; (4) the coarsening rate of (Nb,Mo) (C,N) precipitates decreased from 150 °C to 450 °C, which led to a decrease in mean size of precipitates. The increase in tempering temperatures from 150 °C to 450 °C led to the yield strength increasing from 581 MPa to 765 MPa. The total elongation increased from 29% to 37% with the tempering temperatures increased from 150 °C to 350 °C, then decreased up to 25% at 450 °C. [ABSTRACT FROM AUTHOR]

Microstructure evolution and austenite stability of a Fe-6.0Mn-0.2C-1.0Al-0.05Nb-0.20Mo alloy fabricated by a novel cyclic quenching treatment were investigated. According to the experimental results, the influences of cyclic quenching treatment on retained austenite could be described as follows: (1) turning austenite grain morphology from a mixture of lamellar and equiaxed grain to the lamellar grain with the increase in cyclic quenching passes, (2) increasing austenite stability for the grain refinement (up to 0.21μm) and higher C/Mn content in austenite. In addition, cyclic quenching treatment can increase the yield strength (YS), ultimate tensile strength (UTS) and total elongation (TE) of the experimental steel up to 172 MPa, 89 MPa and 8%, respectively. The average product of UTS and TE of the experimental steel after cyclic quenching treatment could reach up to 66.6 GPa·%. Moreover, the yield point elongation increased with the increase in cyclic quenching passes. [ABSTRACT FROM AUTHOR]