Properties of Cu–Cr–Zr alloy with ultrafine-grained (UFG) structure produced by equal-channel angular pressing (ECAP) via different routes have been investigated. Special attention was paid to the ...optimization of multi-functional structural, thermal, electrical and mechanical properties of the alloy by aging of UFG one. Multi-pass ECAP via different routes gives rise to the formation of a deformation-induced submicrocrystalline structure with the grain (subgrain) sizes in the range of 200–300nm depending on applied routes which leads to high hardness and strength in the Cu–Cr–Zr alloy with reduced ductility. Amongst the applied routes, route-Bc was found to be the best processing path for achieving the lowest grain size, the highest hardness and strength. Aging of 8Bc-processed UFG samples increases the hardness and strength of Cu–Cr–Zr alloy while retaining an electrical conductivity comparable to that of aged coarse-grained (CG) one. A satisfactory electrical conductivity of 71%IACS without considerable loss of peak hardness was achieved after aging of 8Bc-processed UFG alloy at 425°C for 240min. The precipitation strengthened UFG alloy remains its stable behavior at elevated temperatures up to 450°C.
•A significant grain refinement of alloy Mg-1.0%Zn-0.3%Ca by ECAP was demonstrated.•A sharp inclined basal texture was formed by ECAP processing.•ECAP slightly increase the strength characteristic ...and fatigue life of the alloy.•Doubling of ductility due to the activation of prismatic slip was achieved by ECAP.•ECAP did not impair the chemical corrosion resistance of the alloy.
Magnesium alloy Mg-1.0%Zn-0.3%Ca was processed by equal channel angular pressing (ECAP) with the aim to refine its microstructure. ECAP was found to reduce the average grain size from 106.0 ± 2.05 μm in the initial state to 4.0 ± 0.19 μm and 8.0 ± 0.18 μm in the transverse and longitudinal sections, respectively. This resulted in a slight strengthening (the yield strength and the ultimate tensile strength rose from 92 and 194 MPa in the initial stat to 106 and 215 MPa after processing, respectively). The main advantage of ECAP is the concurrent increase of tensile elongation from 12.8% to 23.9%. The absence of pronounced strengthening and a significant increase in ductility are associated with the formation of an inclined basal texture, along with activation of prismatic slip during ECAP. It was also shown that ECAP leads to an increase in the fatigue limit of the alloy from 100 MPa to 110 MPa and does not impair its resistance to chemical corrosion.
Microstructure (including its uniformity), texture, and mechanical properties of Mg-Al-Zn-Mn alloy billets after radial-shear rolling (RSR) were investigated. RSR with the temperature in the interval ...420–140 °C and true strain up to 2.63 was shown to lead to grain refinement down to 1.5–3.5 μm (as determined by optical microscopy). The microstructure was found to be reasonably uniform over the transversal cross-sections of the billets. The transmission electron microscopy analysis also revealed submicron sized grains and the formation of two types of particles: Mg17Al12 particles 300–500 nm in size and MgAl nanoparticles of different shapes 20–40 nm in size. Increments in strain and step-wise decrease in deformation temperature with the number of RSR passes was found to lead to a transformation of the initial basal texture to the prismatic texture. The RSR of the Mg-Al-Zn-Mn magnesium alloy was demonstrated to result in significant strength and good ductility owing to a fortunate interplay between fine grain structure and favorable texture promoting activity of non-basal slip systems.
•Radial-shear rolling of alloy Mg-Al-Zn leads to grain refinement (1.5–3.5 μm).•Fine grain structure is reasonably uniform over a billet cross-section.•RSR leads to a transformation of the initial basal texture to the prismatic one.•RSR of the alloy studied results in superior strength combined with good ductility.
An analysis of phases precipitation during the supersaturated solid solution (SSSS) decomposition in binary Cu–Cr, Cu-Hf and ternary Cu–Cr–Hf alloys after equal-channel angular pressing (ECAP) was ...carried out. ECAP affects the ageing kinetics by changing the sequence of phase precipitation, and accelerates the decomposition of SSSS.
The age-hardenable Mg-4.7%Y-4.6%Gd-0.3%Zr (wt%) alloy has been studied after high pressure torsion (HPT) at room temperature, 200°C and 300°C. The formation of partially nanocrystalline structure ...upon HPT results in substantial strengthening relative to the undeformed state of the alloy. The research showed that the strength of the HPT processed alloy could be further improved by aging.
An age-hardenable Mg-Y-Nd-Zr alloy (WE43) was severely deformed using high-pressure torsion (HPT) at room temperature, 200°C or 300°C to refine the microstructure and improve its mechanical ...properties. Thermal stability of microstructure of HPT processed alloy was studied by monitoring its microhardness and age behavior. The deformation by HPT in the temperature range of 20–300°C was accompanied by twinning with the twin size of 0.4–8.1µm. A very fine grain structure with the average grain size of 30–100nm was formed, predominantly within the twins, during and after HPT. Severe deformation by HPT resulted in substantial strengthening of the WE43 alloy, especially after processing at room temperature. The strength of the HPT processed WE43 alloy was additionally improved by subsequent aging. It was found that thermal stability of strengthening induced by HPT did not depend on the deformation temperature and sustained to 250°C.
•HPT at 20–300°C results in significant strengthening of magnesium alloy WE43.•The strength of the HPT processed WE43 alloy is additionally improved by aging.•Thermal stability of HPT induced hardening does not depend on the HPT temperature.•HPT accelerates the precipitation during aging irrespective of the HPT temperature.•Nano-scale grains with the size of 30–100nm are formed within the twins during HPT.
The effect of cold rotary swaging (RS) and subsequent aging on the structure, electrical conductivity, mechanical characteristics and fracture toughness of the Cu-0.77%Cr-0.86%Hf alloy was studied. ...RS leads to the formation of a microstructure elongated along the direction of deformation with grains width of 8.0 ± 0.2 μm. An ultrafine-grained structure with shear bands of 370 ± 10 nm in width and subgrains of 500 ± 13 nm in size is formed inside these elongated grains. The refinement of the microstructure after RS leads to an increase in ultimate tensile strength (UTS) from 300 ± 5 to 505 ± 12 MPa and a decrease in ductility from 54.0 ± 2.4 to 12.9 ± 0.3%. A subsequent aging of the alloy leads to the precipitation of fine particles of Cr and Cu
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Hf phases. The precipitation of these particles leads to an additional increase in UTS of RS-treated alloy up to 558 ± 11 MPa and ductility up to 15.4 ± 2.4%. In this case, the decomposition of the supersaturated solid solution, which accompanies the particles precipitation, leads to an increase in the electrical conductivity of the deformed alloy up to 77.7 ± 1.6%IACS. The combination of RS and subsequent aging at a temperature of 450 °C for 4 h leads to an increase in the fatigue limit from 220 to 393 MPa. In addition, this treatment allows to increase the fracture toughness coefficient by 6 times.
Effects of ultrafine grain formation via high pressure torsion (HPT) and precipitation during aging on the microstructure, mechanical and tribological properties of a Cu-Cr-Zr alloy have been ...investigated systematically. HPT results in the formation of ultrafine-grained (UFG) structure in the alloy with an average grain/subgrain size of 155 nm which leads to remarkable improvement in its hardness and strength along with a reduction in elongation to failure. Aging of UFG alloy brings about further strengthening due to the precipitation. UFG formation by HPT increases substantially the wear resistance of Cu-Cr-Zr alloy and reduces the friction coefficient. The highest wear resistance and the lowest friction coefficient are obtained on the sample processed by HPT and subsequent aging. The dominant wear mechanism of the alloy varies depending on the applied processes. Adhesion with smearing is the predominant wear mechanism for the initial (warm extruded) samples having coarse-grained (CG) structure. UFG samples show less adhesional effect with less smearing, and a higher tendency to the formation of cracks, abrasion and delamination seem to be dominant in those samples. Oxidative wear mechanism is also operative in both CG and UFG alloy samples. It may be concluded from this study that a combined process including UFG formation by HPT and subsequent precipitation by artificial aging provides a simple and effective processing procedure for improving the strength, hardness and wear resistance of Cu–Cr–Zr alloys without modification of the chemical composition.
•Cu-Cr-Zr alloy with ultrahigh strength achieved by HPT and aging.•Aged UFG alloy leads to a remarkable improvement in its wear resistance.•Adhesion is the dominant wear mechanism in coarse-grained (CG) Cu-Cr-Zr alloy.•Delamination with less adhesion becomes the main wear mechanism for aged UFG alloy.
The present research establishes a possibility of producing nano- and submicrocrystalline structure in fully austenitic state of the metastable Cr–Ni–Ti steel after high pressure torsion (HPT) by ...raising the temperature of severe plastic deformation above the treshold value for strain-induced martensite transformation, and at room temperature by reducing the temperature of strain-induced martensite transformation with the grain size decreases during step-by-step decreasing HPT temperature.
•Decreasing of the grain size reduces the temperature of martensite transformation.•HPT with step-by-step decreasing temperature produces an austenite nanostructure.•Fully austenite state is achieved by reducing the martensite threshold value.•The microstructure was refined by HPT down to a mean grain size of 60–120nm.•HPT increases the strength of Cr–Ni–Ti steel by 3–6 times with a loss in ductility.
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