Hot deformation behavior and microstructure evolution of a high-temperature titanium alloy modified by erbium
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Isothermal compression testing of Ti–5.8Al–3Sn–5Zr–0.5Mo–1.0Nb–1.0Ta–0.4Si–0.2Er titanium alloy is performed on a Gleeble-3500 thermal simulator, and the corresponding microstructures are analyzed to clarify the softening mechanism and participates evolution. A constitutive equation compensated by strain has been established to describe the hot deformation behavior of the alloy. The deformation activation energies are calculated to be 369760.93–699310.86 J/mol in a 1 b two-phase region and 268030.03–325800.41 J/mol in b single-phase region. At a temperature of 880 °C, the main softening mechanism is the continuous dynamic recrystallization of lamellar a colony, controlled by the mechanical rotation of the sub-grain followed by dislocation climbing and annihilation by diffusion. Meanwhile, the dominant softening mechanism is the discontinuous dynamic recrystallization of b phase during the deformation at temperatures of 920 °C–1080 °C. Silicide containing Er with an average diameter of 20 nm is formed during the water quenching.
I. INTRODUCTION
Lightweight is an attractive way to improve its thrustweight ratio of engine in aircraft.1 High temperature titanium alloys have been applied in fabricating the compressor discs and blades at a temperature of 600 °C because of their high specific strength, excellent mechanical properties up to high temperature and good corrosion resistance,2 such as IMI685,3 IMI834,4 and Ti-11005 alloy. To increase the flight speed, the elevation of service temperature should be promoted as well as the remained mechanical properties at a higher temperature. In general, the Ti–Al–Sn–Zr–Mo–Si series titanium alloy has been accepted to be applied at a temperature of 600 °C, which belongs to near a titanium. Compared with the common Ti–Al–Sn–Zr–Mo–Si series titanium, Ti-60 was prepared with the addition of Nd to meet the requirements of thermal stability and oxidation resistance.6 Ti-600 exhibited excellent creep resistance by the inclusion of 0.1% Y element and increase in the content of silicon.7 Moreover, BT36 was added high-meltingpoint W element and rare-earth Y to perform improved creep resistance.8 However, to develop a titanium used in the higher temperature encountered two main difficulties: (i) the improved elevated-temperature strength by increase alloying degree was at the expense of thermal
Contributing Editor: Jürgen Eckert Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.33
stability; (ii) the creep resistance and fatigue property would deteriorate because of the oxidation of alloy’s surface.9 Therefore, it is the crucial difficulty in developing elevated-temperature titanium alloys to balance the effective strengthening and toughness. Micro-alloying and improving the microstructure are effective ways to solve such difficulties. Rare earth elements, such as Nd and La, have been added into the Ti–Al–Sn–Zr–Mo–Si series titanium alloy to improve the creep resistance and fatigue property, which strengthened the all
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