Oxygen content effect on mechanical properties and microstructure of TZM alloy

Abstract

A series of molybdenum‑titanium‑zirconium (TZM) alloys with continuous oxygen content gradients were fabricated by powder metallurgy and the correlation between microstructure and properties was investigated. By controlling the carbon source, TZM-like alloys with an oxygen content of 2000 ppm, 1000 ppm, and TZM alloy with an oxygen content of 300 ppm (±100) were obtained, followed by rolling and heat treatment, and the effect of oxygen on the development of the microstructure and the mechanical properties of the alloy was studied. The results show that the changing of the oxygen content has a significant impact on the mechanical properties and microstructure of the alloy. With the increase in oxygen content, titanium and zirconium are more inclined to combine with oxygen to form oxide particles of titanium and zirconium (TiO2, ZrO2), the secondary phase particles increase significantly, and the alloy strengthening mode changes from solid solution strengthening to secondary phase dispersion strengthening. Owing to the inhibition of grain boundary migration by the secondary phase, the grain size of the alloy decreases as its oxygen content rises, which causes an increase in hardness of around 10 HV0.1 for every 1000 ppm increase in oxygen content. According to the Hall-Petch relationship, the yield strength of the annealed alloy increased from 336 MPa (300 ppm) to 556 MPa (2000 ppm) with smaller grain size. Kernal Average Misorientation (KAM) is used to characterize the dislocation density of the alloy, and the results show that the value of KAM is negatively correlated with the toughness of the alloy. The KAM value of the alloy is the lowest at 1000 ppm and its greatest elongation reaching 16.8%. Dislocation cells formed in the long-striped grains with an oxygen content of 300 ppm, greatly enhancing the strength of the material and maintain good plasticity. TZM alloy with 300 ppm oxygen has the highest tensile strength of 866 MPa and has an elongation of 15%, which is the leading performance compared with ASTM-specification B386/B386M.