Abstract
The main objective of the present study was to understand the oxygen ingress in titanium alloys at high temperatures. Investigations reveal that the oxygen diffusion layer (ODL) caused by oxygen ingress significantly affects the mechanical properties of titanium alloys. In the present study, the high-temperature oxygen ingress behavior of TC21 alloy with a lamellar microstructure was investigated. Microstructural characterizations were analyzed through optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Obtained results demonstrate that oxygen-induced phase transformation not only enhances the precipitation of secondary α-phase (αs) and forms more primary α phase (αp), but also promotes the recrystallization of the ODL. It was found that as the temperature of oxygen uptake increases, the thickness of the ODL initially increases and then decreases. The maximum depth of the ODL was obtained for the oxygen uptake temperature of 960 °C. In addition, a gradient microstructure (αp + β + βtrans)/(αp + βtrans)/(αp + β) was observed in the experiment. Meanwhile, it was also found that the hardness and dislocation density in the ODL is higher than that that of the matrix.
Highlights
Studies reveal that oxygen is one of the most important interstitial solutes in titanium alloys, which has a significant impact on the microstructure and mechanical properties of Ti alloys
Recent investigations demonstrated that the disadvantages induced by the oxygen ingress in titanium alloys are much greater than its advantages
A dilatometer (DIL-805 A/D, Bahr, Oslo, Norway) was applied to measure β-transus temperature (Tβ ), and a temperature of 955 ◦ C was obtained in this regard
Summary
Studies reveal that oxygen is one of the most important interstitial solutes in titanium alloys, which has a significant impact on the microstructure and mechanical properties of Ti alloys. Further investigations reveal that the existence of oxygen in titanium alloys significantly decreases stress-corrosion, cracking resistance, and fracture toughness in Ti alloys [2]. It is worth noting that different methods, including grinding, polishing, and chemical milling can be applied to remove the oxidized surface layer. These processes remarkably increase the manufacturing cost of titanium workpieces in comparison with other structural materials such as steel and aluminum alloys. Investigating the oxidation characteristics of titanium alloys has become a research hot spot in recent years [7]
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