Effect of electrochemical hydrogen charging in corrosion medium on microstructural evolution and mechanical behavior of an as-forged Ti–6Al–4V (in wt.%) alloy

Combined with the hydrogen pre-charging and tensile testing methods, the effect of charged hydrogen content on the microstructure and mechanical behavior of an as-forged Ti–6Al–4V alloy was investigated. After performing hydrogen charging for 2, 4, 6, 8 and 10 h at a constant cathodic current density value of 75 mA/cm² in a corrosion medium of 3.5 wt.% NaCl solution, the hydrogen contents in the charged samples increased gradually from 73 × 10⁻⁴ to 230 × 10⁻⁴ wt.%. When the hydrogen content was less than 190 × 10⁻⁴ wt.%, the charged hydrogen atoms were present as the solute atoms in the matrix, resulting in the enhanced tensile strength due to the solid solution strengthening of hydrogen atoms. Moreover, the reduced axial ratio c/a for α-Ti matrix due to the hydrogen dissolution was beneficial to improving the ductility of the hydrogenated samples. The critical hydrogen content for simultaneously improving the ductility and strength is determined to be 99 × 10⁻⁴ wt.%. When the hydrogen content was 230 × 10⁻⁴ wt.%, a small number of δ-TiH_x hydrides and micro cracks formed in the localized areas of α-Ti matrix, resulting in the simultaneous decrease of ductility and strength.