Papers by Author: M.R. Shagiev

Abstract: Mechanical properties of a Ti2AlNb-based intermetallic alloy both at room and elevated temperatures were considerably improved due to formation of a homogeneous microstructure with the average grain size of about 300 nm. At room temperature, elongations up to 25% were obtained and the ultimate strength reached 1400 MPa. The alloy exhibited superplastic behavior in the temperature range of 850-1000°C. The maximum elongation of 930% and steady state flow stress 50 of about 125 MPa were obtained at 900°C and strain rate of 4.210-3 s-1. The nanostructured material was used for production of intermetallic sheets and multilayer composite plates consisting of alternating layers of orthorhombic intermetallic and commercial high temperature titanium alloy. Ti2AlNb-based sheets and composites exhibited improved mechanical properties.

Abstract: Small additions of Sc and Zr may considerably improve both strength and ductility of 7000 series aluminum alloys, which is associated with precipitation of fine coherent Al3(Sc,Zr) particles. These particles also increase resistance to recrystallization and promote formation of a stable refined microstructure. Because of very low equilibrium solubility of Sc and Zr in Al alloys, a supersaturated solid solution of these elements in the Al matrix presented after casting is responsible for precipitation of the Al3(Sc,Zr) particles during subsequent heat treatment, while the strengthening effect depends on the particle size and number density. Therefore, it is necessary to optimize precipitation of the Al3(Sc,Zr) particles, in order to achieve superior balance of mechanical properties. In the present work, the effect of heat treatment conditions on microstructure and tensile properties of a developmental 7000 series Al alloy SSA018 modified with Sc and Zr was studied, with special emphasis on the analysis of size and number density of the Al3(Sc,Zr) particles, and their effect on the strength increase.

Abstract: Homogeneous nanocrystalline structure with the average grain size of about 300 nm was produced in Ti2AlNb-based intermetallic alloy by a thermomechanical processing which included multistep isothermal forging at temperatures below the β-transus and intermediate annealings. Nanostructured material possessed excellent mechanical properties. At room temperature, elongations up to 25% were obtained and the ultimate strength reached 1400 MPa. The alloy exhibited superplastic behavior in the temperature range of 850-1000°C. The maximum elongation of 930% and steady state flow stress σ50 of about 125 MPa were obtained at 900°C and strain rate of 4.2×10-3 s-1. The rolling temperatures of nanostructured alloy were defined from analysis of its mechanical behavior at a typical rolling strain rate of about 10-1 s-1 and intermetallic sheets with improved mechanical properties were produced.