Effect of Dislocation Slip Mechanism under the Control of Oxygen Concentration in Alpha-Case on Strength and Ductility of TC4 Alloy

Abstract

The oxygen diffusion layer (alpha-case) is generally considered to have a negative impact on the mechanical properties and applications of titanium alloys. In this study, TC4 alloy specimens with four types of different oxygen concentrations in alpha-case were obtained by controlling the oxygen diffusion process parameters. Scanning electron microscopy and glow discharge spectrometry were employed to characterize the microstructure and oxygen concentration of alpha-case. The effect of alpha-case on strength and ductility of TC4 alloy was investigated via tensile test and new insights were provided. The results indicate that with the increase in the oxygen concentration in the alpha-case, the ductility of the TC4 alloy gradually decreased. Interestingly, the strength of TC4 alloy with the alpha-case first increased and then decreased, resulting in the existence of a peak corresponding to a lower oxygen concentration before the decline of strength. Furthermore, a relatively good ductility match was also observed at the peak. When the oxygen concentration was relatively high, both the strength and ductility decreased. This phenomenon is attributed to the fact that dislocations in the alpha-case controlled by the oxygen concentration were modified from wavy slip to planar slip. Finally, the dislocation’s slip morphology was characterized by transmission electron microscopy.

Keywords

• TC4 alloy
• alpha-case
• strength and ductility
• embrittlement
• slip mechanism