The superplastic behavior of ultrafine-grained (UFG) alloys Al-6% Mg-0.12% Sc-0.10% Zr-0.1% X, where X = Yb (alloy 1 (Yb)), Er (alloy 2 (Er)), and Hf (alloy 3 (Hf)), was studied. The objects of comparison were alloys Al-6% Mg-0.12% Sc-0.20% Zr (alloy 4 (Zr)) and Al-6% Mg-0.22% Sc-0.10% Zr (alloy 5 (Sc)). The effect of a simultaneous increase in the flow stress and elongation to failure in the superplasticity mode has been found. The maximum elongation to fracture in UFG alloys 1 (Yb) and 2 (Er) is observed at lower deformation temperatures than in alloys 4 (Zr) and 5 (Sc). The superplastic characteristics of alloy 3 (Hf) exceed those of alloys 4 (Zr) and 5 (Sc) with an increased content of alloying elements (in at %). UFG alloy 1 (Yb) at low temperature (400 degrees C) has good ductility (delta = 910%). The effect of the type and concentration of alloying elements on the deformation behavior and grain growth in UFG alloys Al-6% Mg is analyzed. With the superplasticity of UFG alloys, there is competition between strain-induced grain growth and dynamic recrystallization. It is shown that the fracture of UFG alloys under superplasticity is caused by the formation of pores on large Al3X particles.

A hot salt corrosion (HSC) test was performed on the fine-grained titanium alpha-alloy Ti-2.5Al-2.6Zr (Russian industrial alloy PT-7M). The ultrafine-grained (UFG) microstructure in the titanium alpha-alloy was formed via cold Rotary Swaging. The grain size and volume fraction of the recrystallized microstructure in the alloy were varied by choosing appropriate annealing temperatures and times. The microstructure and corrosion resistance of UFG alloys were studied after 30 min of annealing at 500-700C and after 1000 h of annealing at 250C. Metallographic studies were carried out to investigate the effects of annealing on the nature and extent of corrosive damage in the titanium alpha-alloy Ti-2.5Al-2.6Zr. After HSC tests, surface analyses of the titanium alpha-alloy samples were conducted using X-ray diffraction and electron microscopy. During the HSC testing of the titanium alpha-alloy Ti-2.5Al-2.6Zr, a competitive interaction between intergranular corrosion (IGC) and pitting corrosion was observed. To the best of our knowledge, it was shown for the first time that annealing affects the relationship among the IGC, pitting corrosion and uniform corrosion rates of the titanium alloy. Prolonged low-temperature annealing at 250C resulted in a more pronounced increase in the uniform corrosion rate than short-term high-temperature annealing for 30 min at 500-700C. An in-depth analysis of the effect of the structure and phase composition of the grain boundaries on the susceptibility of the alpha-alloy Ti-2.5Al-2.6Zr to HSC was conducted.

Al-6%Mg-Sc-Zr alloys with the total ratio of Sc + Zr = 0.32 wt.% make up the target of this research. The content of scandium and zirconium varied with an increment of 0.02%. The alloys were produced by induction casting. Their ultrafine-grained (UFG) microstructure was formed with Equal Channel Angular Pressing (ECAP). Such cast alloys have a homogeneous macrostructure formed by small equiaxed grains in the central part of the ingot and columnar crystals along the edges of the cross section. After ECAP, the average grain size in the alloy specimens is 0.5–1 µm. The average grain size does not depend on the ratio of Sc and Zr in these alloys. Superplasticity tests were performed at temperatures ranging from 300 to 500 °C and at a strain rate varying between 3.3·10-3 and 3.3·10-1 s-1. UFG Al-6%Mg-0.20%Sc-0.12%Zr and Al-6%Mg-0.18%Sc-0.14%Zr alloys exhibit the highest superplasticity. It was suggested that changes in Sc:Zr ratio affect spatial distribution and composition of the following precipitating particles: Al3Sc, Al3Zr, Al3(ScxZr1-x). An increase in Zr concentration is shown to reduce the susceptibility of UFG alloys to cavitation fracture.

The thermal stability of a bimetallic wire made of three novel aluminum alloys Al–0.25 wt

The microstructure and mechanical properties at room and elevated temperatures of ultrafine-grained steel 08H18N10Т, obtained by the equal-channel angular pressing method (ECAP) at temperatures of 150 and 450 °C have been studied. It has been established that UFG steel has an increased content of α`-martensite and when it is heated, nanoparticles of the σ-phase are released. It has been shown that ultrafine-grained steel has high tensile strength and good ductility. A decrease in the Hall-Petch coefficient of ultrafine-grained steel was noted, which is due to the fragmentation of δ-ferrite particles during ECAP.

Results of investigations of the kinetics of solid solution decomposition during annealing of fine-grained (FG) Al–0.5

This paper reported the results of research into the effect of Equal Channel Angular Pressing (ECAP) temperature and 1-h annealing temperature on mechanical properties, stress-relaxation resistance, and corrosion resistance of austenitic steel AISI 321L with strongly elongated thin δ-ferrite particles in its microstructure. The formation of α′-martensite and fragmentation of austenite grains takes place during ECAP. Ultrafine-grained (UFG) steels demonstrate increased strength. However, we observed a reduced Hall–Petch coefficient as compared with coarse-grained (CG) steels due to the fragmentation of δ-ferrite particles. UFG steel specimens were found to have 2–3 times higher stress-relaxation resistance as compared with CG steels. For the first time, the high stress-relaxation resistance of UFG steels was shown to stem from a internal stress-relaxation mechanism, i.e., the interaction of lattice dislocations with non-equilibrium grain boundaries. Short-time 1-h annealing of UFG steel specimens at 600–800 °C was found to result in the nucleation of σ-phase nanoparticles. These nanoparticles affect the grain boundary migration, raise strength, and stress-relaxation resistance of steel but reduce the corrosion resistance of UFG steel. Lower corrosion resistance of UFG steel was shown to be related to the formation of α′-martensite during ECAP and the nucleation of σ-phase particles during annealing.

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.

A solid-phase diffusion welding of coarse-grained and ultrafine-grained (UFG) specimens of titanium near-α alloy Ti-5Al-2V used in nuclear power engineering was made by Spark Plasma Sintering. The failure of the welded specimens in the conditions of hot salt corrosion and electrochemical corrosion was shown to have a preferentially intercrystalline character. In the case of the presence of macrodefects, crevice corrosion of the welded joints was observed. The resistance of the alloys against the intercrystalline corrosion was found to be determined by the concentration of vanadium at the titanium grain boundaries, by the size and volume fraction of the β-phase particles, and by the presence of micro- and macropores in the welded joints. The specimens of the welded joints of the UFG alloy are harder and have a higher resistance to hot salt corrosion and electrochemical corrosion.

Superplastic behavior of ultrafine-grained (UFG) Al-6Mg-0.12Sc-0.10Zr-0.1X alloys, where X = Yb (Alloy #1-Yb), Er (Alloy #2-Er), and Hf (Alloy #3-Hf), has been studied. The total content of Sc, Zr, Yb, Er, Hf in the alloys was 0.32 wt. Al-6Mg-0.12Sc-0.20Zr (Alloy #4-Zr) and Al-6Mg-0.22Sc-0.10Zr (Alloy #5-Sc). Their UFG microstructure was formed with ECAP. Two different types of deformation behavior during superplasticity were demonstrated. A simultaneous increase in yield stress and elongation to failure during superplastic deformation was discovered. High deformation temperatures were shown to cause a competition between dynamic (strain-induced) grain growth and dynamic recrystallization, leading to a finer grain microstructure. The values of strain hardening factor (n), strain rate sensitivity factor (m), and superplastic deformation threshold stress (Sp) were determined. The impact of the type and concentration of alloying elements on the deformation behavior and dynamic grain growth of Al-6 that the maximum elongation to failure in Alloy #1-Yb and Alloy #2-Er is observed at lower deformation temperatures than in Alloy #4-Zr and Alloy #5-Sc. The superplastic properties of Alloy #3-Hf are superior to those of Alloy #4-Zr and Alloy #5-Sc with high content of alloying elements (in at. manifests good elongation to failure (910 satisfiability of Hart's criterion for calculating uniform deformation value under superplastic conditions was verified. It was demonstrated that cavitation when pores are formed in large Al3X particles at high temperatures causes early failure of aluminum alloys.

Relaxation resistance and corrosion resistance of samples of ultrafine-grained steel 08H18N10T obtained by the method of equal-channel angular pressing at temperatures of 150 and 450 °C are investigated. For ultrafine-grained steel with high values of the limit of macroelasticity and yield strength, a decrease in the Hall—Petch coefficient due to fragmentation of δ-ferrite particles at the method of equal-channel angular pressing is shown. It is established that the samples of ultrafine-grained steel have 2-3 times higher relaxation resistance compared to coarse-grained steel. It is noted that the method of equal-channel angular pressing leads to an increase in the rate of general corrosion. At the same time, despite the decrease in corrosion resistance, samples of ultrafine-grained steels have high resistance to intercrystalline corrosion. It is established that the decrease in corrosion resistance of ultrafine-grained steel is due to an increase in the volume fraction of martensite deformation at the method of equal-channel angular pressing.

The conductor aluminum alloys of Al-0.25wt.%Zr alloyed additionally with X = Er, Si, Hf and Nb were the objects of our investigations. The fine-grained microstructure in the alloys was formed via equal channel angular pressing and rotary swaging. The thermal stability of the microstructure, specific electrical resistivity and microhardness of the novel conductor aluminum alloys were investigated. The mechanisms of nucleation of the Al3(Zr, X) secondary particles during annealing the fine-grained aluminum alloys were determined using the Jones–Mehl–Avrami–Kolmogorov equation. Using the Zener equation, the dependencies of the average secondary particle sizes on the annealing time were obtained on the base of the analysis of the data on the grain growth in the aluminum alloys. The secondary particle nucleation during long-time low-temperature annealing (300 °C, 1000 h) was shown to go preferentially at the cores of the lattice dislocations. The Al-0.25%Zr-0.25%Er-0.20%Hf-0.15%Si alloy subjected to long-time annealing at 300 °C has the optimal combination of microhardness and electrical conductivity (59.8%IACS, Hv = 480 ± 15 MPa).

The relaxation resistance and corrosion resistance of ultrafine-grained (UFG) steel 08Kh18N10T samples fabricated by equal-channel angular pressing (ECAP) at temperatures of 150 and 450°C are investigated. The UFG steel has a high macroelasticity limit and yield strength and exhibits a decrease in the Hall–Petch coefficient due to the fragmentation of δ-ferrite particles during ECAP. UFG steel samples are found to have 2–3 times higher relaxation resistance as compared to coarse-grained steel samples. ECAP is shown to increase the rate of general corrosion. Despite a decrease in the corrosion resistance, the UFG steel samples have high intergranular corrosion resistance. The decrease in the corrosion resistance of the UFG steel is found to be caused by an increase in the volume fraction of strain-induced martensite during ECAP.

Hot rolled commercial metastable austenitic steel 321 with strongly elongated thin delta-ferrite particles in its microstructure was the object of investigations. Ultrafine-grained (UFG) microstructure in steel 321 was formed by Equal Channel Angular Pressing (ECAP) at 150 oC and 450 oC. When heating the UFG steel specimens, the nucleation of sigma-phase particles blocking the grain boundary migration was observed. The maximum elongation to failure (~250%) was achieved at the deformation temperature 750 oC. The process of superplastic deformation of the UFG steel 321 is controlled by simultaneous grain boundary sliding and power-law creep. The contribution of each process depends on the grain growth rate in the superplasticity regime as well as on defect accumulation on the grain boundaries. The fracture of the UFG steel 321 specimens has a cavitational character - an intensive formation of large elongated pores at the non-metallic particles as well as of the submicron pores at the sigma-phase particles in the course of superplastic deformation were observed.

This research was undertaken to study the way deformation behaves in ultrafine-grained (UFG)-conducting Al-Zr alloys doped with Sc, Hf, and Yb. All in all, eight alloys were studied with zirconium partially replaced by Sc, Hf, and/or Yb. Doping elements (X = Zr, Sc, Hf, Yb) in the alloys totaled 0.4 wt.%. The choice of doping elements was conditioned by the possible precipitation of Al3X particles with L12 structure in the course of annealing these alloys. Such particles provide higher thermal stability of a nonequilibrium UFG microstructure. Initial coarse-grained samples were obtained by induction casting. A UFG microstructure in the alloys was formed by equal-channel angular pressing (ECAP) at 225 °C. Superplasticity tests were carried out at temperatures ranging from 300 to 500 °C and strain rates varying between 3.3 × 10−4 and 3.3 × 10−1 s−1. The highest values of elongation to failure are observed in Sc-doped alloys. A UFG Al-0.2%Zr-0.1%Sc-0.1%Hf alloy has maximum ductility: at 450 °C and a strain rate of 3.3 × 10−3 s−1, relative elongation to failure reaches 765%. At the onset of superplasticity, stress (σ)–strain (ε) curves are characterized by a stage of homogeneous (uniform) strain and a long stage of localized plastic flow. The dependence of homogeneous (uniform) strain (εeq) on test temperature in UFG Sc-doped alloys is increasing uniformly, which is not the case for other UFG alloys, with εeq(T) dependence peaking at 350–400 °C. The strain rate sensitivity coefficient of flow stress m is small and does not exceed 0.26–0.3 at 400–500 °C. In UFG alloys containing no Sc, the m coefficient is observed to go down to 0.12–0.18 at 500 °C. It has been suggested that lower m values are driven by intensive grain growth and pore formation in large Al3X particles, which develop specifically at an ingot crystallization stage.

The thermal stability of a bimetallic wire made of four novel aluminum alloys Al – 0.25 % Zr with different Sc and Hf contents has been investigated. A wire made of pure aluminum A99 was studied as an object of comparison. Alloys were obtained by injection molding in vacuum. Cast samples were subjected to severe plastic deformation and annealing, which ensured the formation of a uniform microstructure and the release of stabilizing Al3(Zr,Sc,Hf) nanoparticles. The wire ∅ 0.26 mm was obtained by joint deformation of an aluminum alloy with a copper shell by rolling in rolls. The effect of 30-minute annealing in the temperature range from 200 to 500 °C on the parameters of the microstructure and physical and mechanical properties (microhardness, strength, plasticity, specific electrical resistivity) of the wire was studied. The wire has high strength and increased thermal stability. After annealing at a temperature of 500 °C, a homogeneous fine-grained structure with a grain size of 3 – 5 µm was formed in the wire, increased hardness and strength of the samples was observed due to the separation of Al3(Zr,Sc,Hf) particles. There is an intense diffusion of copper from the shell into the surface layers of the aluminum alloy, which can lead to embrittlement of the wire.

The thermal stability of a composite wire made of microalloyed aluminum alloys Al–Zr–(Sc, Hf) is investigated. The wire is produced by the combined drawing of a copper-coated aluminum alloy. The effect of annealing on the mechanical properties of the composite conductive aluminum wire is studied. It is shown that the process of decomposition of the solid solution upon the annealing of composite wires occurs in two stages, due to the separate precipitation of Al3Zr particles at “low” temperatures and the precipitation of Al3(Sc, Hf) particles at “high” annealing temperatures. Mechanical tensile tests show that annealing at 500°C for 30 minutes reduces the strength and increases the ductility of the wire by up to 10%. After annealing, a homogeneous fine-grained structure is formed in the wire, and increased hardness and strength of the samples is observed due to the release of Al3(Sc, Hf) particles.

Mechanical properties of fine grained Al-(1, 2, 3 )%Zn alloys obtained by Equal Channel Angle Pressing were studied. The recrystallization activation energy was found to decrease with increasing Zn content. The Hall-Petch coefficient for the Al-Zn alloys was found to change nonmonotonously during annealing. An increased Zn concentration at the grain boundaries was shown to result in altering the creep and superplasticity mechanisms of the Al-Zn alloys. The corrosion rate of the Al-Zn alloys was found to depend on the annealing temperature nonmonotonously. The corrosion rate in the Al-( 2,3)%Zn alloy was shown to decreasing down to 8-9 mm/year with increasing the annealing temperature up to 200 degrees C. The increasing of the annealing temperature up to 300 degrees C leads to the increasing of the corrosion rate up to 11.4-11.9 mm/year. The obtained results were analyzed on the base of a concept of solid phase wetting of the grain boundaries in the Al by Zn. The effect of solid state wetting of the grains boundaries was shown to allow explaining majority of anomalia observed in the Al-Zn alloys: (i) the effect of the reduction of the recrystallization activation energy; (ii) the effect of a non-monotonous variation of the Hall-Petch coefficient during annealing; (iii) an increasing of plasticity of the Al-Zn alloys in the creep regime, etc. In order to describe the anomalia in the corrosion resistance of the Al-Zn alloys, one should also take into account a nonuniform Zn distribution in the specimens. (C) 2021 Elsevier B.V. All rights reserved.