Abstract
The precipitation behavior of the orthorhombic (O) phase during the slow cooling aging treatment of Ti-22Al-25Nb (at.%) alloy was investigated by microstructural characterization. Then the effect of O phase precipitation on the tensile properties was studied by room-temperature tensile tests. The results showed that the precipitation of the O phase transformed from both grain boundaries and intragranular to only grain boundaries with the temperature increasing. The nucleation mechanism of the O phase from intergranular is composed of sympathetic nucleation and interface instability nucleation. In addition, the results of tensile tests indicated that the ultimate tensile strength of the alloy decreases as the precipitation of the O phase increases. Meanwhile, from the tensile results, it is concluded that the optimum heat treatment process is slow cooling after aging at 950 °C for 1 h.
Highlights
As an important high temperature structural metal, Ti2 AlNb-based alloys have low density, high specific strength, high temperature strength, and excellent creep resistance [1,2,3]
Subsequent studies revealed that the orthorhombic Ti2 AlNb phase (O phase) has important effects on room temperature plasticity, creep resistance, and high temperature strength of Ti3 Al-based alloys [9]
Microstructure mainly consists of the O phase and B2 phase
Summary
As an important high temperature structural metal, Ti2 AlNb-based alloys have low density, high specific strength, high temperature strength, and excellent creep resistance [1,2,3]. Subsequent studies revealed that the O phase has important effects on room temperature plasticity, creep resistance, and high temperature strength of Ti3 Al-based alloys [9]. Former researches have shown that complicated phase transition pathways, the microstructure of Ti2 AlNb-based alloys is quite sensitive the and the mechanism of phase transitions the are level related to the temperatures of processing, tobehaviors the thermomechanical parameters. Age-treatments [17].ofThus, is of significance to reveal the relationship among the heat-treatment temperatures, microstructure, mechanical properties, especially effect of precipitation. The relationship between the content of the O phase and its tensile metallographic statistics based on the microstructure images, and the nucleation mechanism of the properties was established. The relationship between the content of the O phase and its tensile properties was established
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