Solid Solution Hardening and Precipitation Hardening of α₂-Ti₃Al in Ti-Al-Nb Alloys

Abstract

Microstructure and mechanical properties of Ti-Al-Nb-based alloys were investigated as they are important in the development of new generation high temperature Ti alloys due to good oxidation resistance. The alloy compositions Ti-15Al-2Nb (to obtain α 2 precipitates) and Ti-15Al-2Nb-0.5Si (at%) (to obtain solid-solution hardening by Si) were selected. Heat treatment at 1000 C after forging and rolling at 900 C transformed the β phase to α phase and α martensite during cooling. By heat treatment at 900 C, a single α phase was obtained in both alloys. The α 2 phase was formed by aging treatment at 600 and 700 C of Ti-15Al-2Nb and at 600, 700, and 800 C of Ti-15Al-2Nb-0.5Si. Compressive strength was investigated for samples heat treated at 900 C with a single α phase and those aged at 600, 700, 800 C with α 2 precipitates. The solid solution hardening effect of Si was found at all test temperatures. Precipitation hardening effect by α 2 precipitates was also observed in both alloys and the effect improved with Si addition. Peaks of precipitation hardening were obtained at 300 C in both alloys; the precipitation hardening effect decreased with increase of test temperature above 300 C. It is suggested that a shearing mechanism occurs up to 300 C, which changes to a bypass mechanism above 450 C.

Microstructure Evolution and Creep Behavior of Near-α Ti Alloy Produced by Thermomechanical Processing

“…5) Next, the effects of the precipitation hardening by the ¡ 2 -Ti 3 Al were investigated. 8) By precipitating the ¡ 2 phase in Ti15Al 2Nb, precipitation hardening was clearly observed within the moderate temperature range of 300°C to 450°C, and the precipitation hardening became weaker at 600°C or higher. This indicates that a strong solidsolution hardening is necessary to improve the strength of Ti alloy.…”

“…The addition of 2 at% of Zr into Ti10Al2Nb (at%) also improves the compression strength through solidsolution strengthening. 7,8) This means that Zr is an effective alloying element, improving both the oxidation resistance and the mechanical properties.…”

Correlation between Solution Treatment Temperature, MicroStructure, and Yield Strength of Forged Ti-17 Alloys

“…However, in the tensile tests at 450 and 600 • C, the effect of the secondary α phase was not observed; that is, the strengths of the solution-treated and the solution-treated-and-aged samples were approximately the same. At high temperatures, especially temperatures greater than 450 • C, the strength of the α phase is known decrease drastically [28]. Thus, the secondary α phase may be easily cut by dislocations at high temperatures.…”

Equiaxed α microstructure evolution in wrought Ti-10Al-1Zr-1Mo-1Nb alloy during annealing

“…[6] A new Snfree Ti-Al-Nb-Zr alloy has been proposed to increase the service temperature of near α-type titanium alloy, and the creep properties related to its microstructures have been investigated. [7][8][9] Influence of temperature and compression strain rate in the β-single-phase region for the microstructural evolution of the Ti-10Al-1Zr-1Mo-1Nb alloy was evaluated. The flow behavior of the alloy during high-temperature compressive deformation was evaluated by the Arrhenius-type constitutive model and discussed on the basis of microstructural evolution.…”