Abstract
The hot deformation behavior and hot rolling based on the hot processing map of a nano-Y2O3 addition near-α titanium alloy were investigated. The isothermal compression tests were conducted at various deformation temperatures (950–1070 °C) and strain rates (0.001–1 s−1), up to a true strain of 1.2. The flow stress was strongly dependent on deformation temperature and strain rate, decreasing with increased temperature and decreased strain rate. The average activation energy was 657.8 kJ/mol and 405.9 kJ/mol in (α + β) and β region, respectively. The high activation energy and peak stress were contributed to the Y2O3 particles and refractory elements comparing with other alloys and composites. The deformation mechanisms in the (α + β) region were dynamic recovery and spheroidization of α phase, while the β phase field was mainly controlled by the dynamic recrystallization and dynamic recovery of β grains. Moreover, the constitutive equation based on Norton–Hoff equation and hot processing map were also obtained. Through the optimal processing window determined by the hot processing map at true strains of 0.2, 0.4 and 0.6, the alloy sheet with multi-pass hot rolling (1050 °C/0.03–1 s−1) was received directly from the as-cast alloy. The ultimate tensile strength and yield strength of the alloy sheet were 1168 MPa and 1091 MPa at room temperature, and 642 MPa and 535 MPa at 650 °C, respectively, which performs some advantages in current research.
Highlights
Due to the low density and high strength-to-weight ratio, titanium and titanium alloys have been widely used in the aerospace field [1,2]
Chen [16] investigated Ti60 alloy with the initial lamellar microstructure, the results show that the flow softening is attributed to the spheroidization of α lath at low strain rate or elevated temperature
A sharp drop after reaching peak stress at a very small strain is shown at 1030 ◦ C/0.1 s−1 and 1070 ◦ C/1 s−1 in Figure 3c,d, which is attributed to the competition of work hardening of high-density dislocations during the initial deformation processing and the softening by the dislocation annihilation and deformation heat at high strain rate; the dynamic spheroidization may be a non-negligible factor [21]
Summary
Due to the low density and high strength-to-weight ratio, titanium and titanium alloys have been widely used in the aerospace field [1,2]. As for the high-temperature titanium alloys, their outstanding high-temperature properties, such as creep-strength-toweight ratio and fatigue-strength-to-weight ratio, has a unique advantage on the elevated parts of the aircraft engine [3]. Replacing nickel-based high-temperature alloys with Ti alloys around 600 ◦ C can largely reduce the component weights under the same strength without affecting its serviceability [4]. Titanium alloys have considerable application potential in the high-temperature components of aerospace fields. The defects of the as-cast alloys are inherent problems, which can affect the high-temperature operating properties.
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