The microstructure and mechanical properties (at room and elevated temperatures) of ultrafine-grained (UFG) 08Kh18N10T steel fabricated by equal-channel angular pressing (ECAP) at temperatures of 150 and 450°C are studied. The UFG steel is found to have a high α' martensite content, and σ-phase nanoparticles precipitate in it upon heating. The UFG steel is shown to have a high ultimate tensile strength and good ductility. The Hall–Petch coefficient of the UFG steel is found to decrease due to the fragmentation of δ-ferrite particles during ECAP.
The work presents the results of studies of the structure and microhardness during annealing of cast and microcrystalline (MC) Al–2.5%Mg–Sc–Zr alloys with a total Sc and Zr content of 0.32%. The Sc content varies from 0.1 to 0.22% with an interval of 0.02%, and the Zr concentration in the alloy changes proportionally. In the initial state, the cast alloys are characterized by a homogeneous coarse-grained macrostructure. MC alloys are obtained by equal-channel angular pressing (ECAP) and have a homogeneous fine-grained structure in the initial state. The temperature of the beginning of recrystallization of MC alloys is determined. The mechanisms and temperature of the beginning of solid-solution decomposition in the cast and MC alloys are determined according to the Johnson–Mehl–Avrami–Kolmogorov model. It is found that the partial replacement of scandium with zirconium leads to a steady increase in the thermal stability of solid solution of Sc and Zr in aluminum.
The effect of scandium on the superplasticity characteristics of Al–0.5Mg–Sc conductor aluminum alloys with a submicrocrystalline (SMC) structure is investigated. Large elongation to failure (~1060%) is achieved in the SMC alloys with 0.4 and 0.5% Sc at a deformation temperature of 500°C and a strain rate of 1 × 10–1 s–1. Intense pore formation is shown to occur during the superplasticity of the Al–0.5Mg–Sc SMC alloys. The kinetics of deformation-stimulated grain growth in the Al–0.5Mg–Sc SMC alloys is found to be determined by the mobility of junction disclinations and orientation-misfit dislocations.
t—The diffusion welding of ultrafine-grained pseudo-α-titanium Ti–4.73% Al–1.88% V alloy specimens has been performed by spark plasma sintering. It has been shown that the destruction of welded joints in the ultrafine-grained (UFG) specimens under hot salt corrosion (HSC) conditions has a two-stage character: intercrystallite corrosion (ICC) is developed at the first stage to turn into pitting corrosion at the following stage. It has been established that the resistance to intercrystallite corrosion is governed by the concentration of vanadium on grain boundaries, the size and volumetric content of β-phase particles, and the existence of pores in a welded joint. It has been demonstrated that the welded joints of the ultrafine-grained specimens have higher hardness and resistance to intercrystallite corrosion as compared to coarse-grained specimens.
The effect of severe plastic deformation by rotary forging on the mechanical properties and the corrosion resistance of a pseudo-α-titanium PT-7M alloy is studied. The corrosive character of fracture the fine-grained alloy under hot salt corrosion (HSC) conditions is found to change: pitting corrosion at the onset of recrystallization processes changes into intercrystalline corrosion. The HSC resistance of the fine-grained PT-7M titanium alloy is shown to depend on the structure–phase state of grain boundaries, whose intense migration with developing recrystallization leads to “sweeping out” of corrosion-hazardous alloying elements (aluminum, zirconium) from the crystal lattice of the titanium alloy.
The corrosion–fatigue fracture of an ultrafine-grained Ti–2.2Al–2.5Zr pseudo-α titanium alloy (PT-7M alloy), which is used in atomic power engineering, is studied. The formation of an ultrafine-grained structure by rotary forging is found to increase the corrosion–fatigue strength. The parameters in Basquin’s equation are determined, and the slope of the σa–log N fatigue curve is shown to nonmonotonically depend on the temperature of annealing of the ultrafine-grained alloy.