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A novel two-phase titanium alloy based on Ti-6.5Al-3.3Mo-0.3Si (VT8) (wt%) having the composition VT8-20Zr-0.1B has been studied in the present paper. Modifying with boron and alloying with zirconium led to refinement of prior β grains and α/β colonies by a factor of about ten. Alloying with 20 wt% of zirconium resulted in significant decreasing the β-transus temperature that along with the refinement of the as-cast structure facilitated ingot breakdown and formation of fine grained structure during forging. After multidirectional hot forging and hardening heat treatment the strength of the VT8-20Zr-0.1B alloy at 20–500 °C was found to be higher by 30–40% as compared with that of the VT8 alloy after similar treatment while retaining near the same ductility of the alloys. For the VT8-20Zr-0.1B alloy with the duplex structure the following tensile properties have been attained: σ UTS /σ 0.2 =1560/1400 MPa and δ=4.2% at room temperature, σ UTS /σ 0.2 =1230/1090 MPa and δ=14% at Т =500 °С. The density normalized strength reached at Т =500 °С is the highest even obtained at this temperature for currently known titanium alloys. The novel alloy in the fine lamellar condition showed quite reasonable creep resistance at temperatures near the maximum service temperature. Solution treatment in the β or the α+β temperature field followed by water quenching was revealed to result in the martensitic β→α′′ transformation with retained β phase. Subsequent ageing led to formation of fine lamellar or duplex structure with nanosized lamellar spacings that in turn promoted achieving extraordinary high strength properties. [ABSTRACT FROM AUTHOR]

The effects of boron additions in an amount of 0.1–2 wt%, thermomechanical processing and heat treatment on microstructure and mechanical properties of a two-phase titanium alloy Ti–6.5Al–3.3Mo–0.3Si alloy have been investigated. Depending on the boron amount, the materials under study were divided into two groups: (1) boron modified alloys containing ~0.1 wt% of boron and (2) discontinuously reinforced metal matrix Ti–TiB based composites containing 1.5–2 wt% of boron. Boron additions led to formation of TiB whiskers, which were predominantly located along boundaries of prior β-grains and α-colonies resulting in refined as-cast microstructure. Multiple 3D forging at T =650–700 °C applied for the boron modified alloys resulted in formation of ultrafine-grained microstructure and intensive breaking of TiB whiskers. Tensile properties of the Ti–6.5Al–3.3Mo–0.3Si–0.2 wt% B alloy after multiple 3D forging followed by β-heat treatment were found to be appreciably higher than those of the alloy free of boron after the same processing route that was ascribed to better controlling the β-grain size during β heat treatment. The composite materials were subjected to multiple isothermal 2D forging at T =950 °C that provided effective alignment of TiB whiskers while retaining their high aspect ratio. The hot forged composites demonstrated appreciably higher strength, creep resistance in comparison with those of the base alloy without drastic reduction in ductility. The effect of TiB whiskers orientation and morphology on the tensile properties of the composite materials is discussed. [ABSTRACT FROM AUTHOR]

This paper is devoted to comparative investigation of recrystallization behavior during uniaxial hot compression at 600–900 °C of cast commercially pure titanium (CP-Ti) modified with boron and free of boron as well as of CP-Ti in initial wrought condition. Using optical microscopy and EBSD analysis it has been revealed that the boron addition in an amount of 0.2 wt% promoted much more uniform strain development and intensive dynamic recrystallization during hot compression in cast CP-Ti modified with boron as compared with cast CP-Ti free of boron. At the same time, hot compression led to similar fine-grained microstructures in cast CP-Ti modified with boron and wrought CP-Ti. The obtained results suggest that the boron additions to CP-Ti may reduce postcast processing steps and thus reduce the overall cost of produced fine-grained materials out of CP-Ti by means of hot working. [ABSTRACT FROM AUTHOR]