Search

• E a of recrystallization of hybrid AZ31/Mg-0.6Gd was estimated as 112 ± 10 kJ/mol. • Mg 17 Al 12 and Mg 2 Zn phases in the AZ31 region obstructs the grain growth process. • The effect of Mg 5 Gd and Mg 12 Gd phases in the mg-0.6gd region is less evident. The recrystallization and grain growth activation energies of the hybrid AZ31/Mg-0.6Gd (wt.%) alloy were calculated using differential scanning calorimetry analyses and scanning electron microscopy, respectively, after fabricating by high-pressure torsion up to 20 turns and then subjecting to an isochronal annealing treatment from 423 to 723 K for 1 h. The DSC results show one exothermic peak belonging to the static recrystallization of the AZ31 region with an activation energy of 112 ± 10 kJ/mol. The grain growth kinetics for the AZ31 and Mg-0.6Gd regions were described by the Arrhenius equation. The calculation with a grain growth exponent equal to 4 gave values for the activation energies in both the AZ31 (146.2 ± 8.4 kJ/mol) and Mg-0.6Gd (90.9 ± 13.5 kJ/mol) regions. The present results reveal the heterogeneity of the thermal stability of the AZ31/Mg-0.6Gd hybrid material. [Display omitted] [ABSTRACT FROM AUTHOR]

The stored energy and activation energy for recrystallization were investigated for a Cu-Ni-Si alloy after high-pressure torsion processing for N = ½, 1, 5 and 10 turns at room temperature. The contributions of geometrically necessary dislocations (GNDs), statistically stored dislocations (SSDs) and vacancies to the stored energy were calculated through the Vickers microhardness measurements, kernel average misorientation (KAM) measurements and an analysis by differential scanning calorimetry (DSC). The results show that the total stored energy decreases rapidly after equivalent strain of εeq ∼ 9 and then saturates through εeq ∼ 86 at ∼70 J/mol. Concurrently, the local stored energy in GNDs and SSDs was found to depend strongly on the radial distance from the centre of the disc and increase with increasing equivalent strain at εeq ∼ 16 and saturate with further straining. Accordingly, the results indicate that the GNDs and vacancies are responsible for the high stored energy in the initial stage of deformation at equivalent strain range of εeq = 8.6–16 and thereafter their contribution decreases slightly due to the occurrence of dynamic recrystallization and the formation of fine grains. At the same time, the contribution of the SSDs is similar to that of the GNDs only in high strain deformation as at εeq = 49.3 to accommodate the deformation process. An activation energy for recrystallization was estimated in the range of ∼ 89.7–98.7 kJ/mol, thereby suggesting poor thermal stability. [ABSTRACT FROM AUTHOR]

An Mg-0.41Dy (wt%) alloy was successfully processed by high-pressure tension (HPT) through 5 turns at room temperature. The evolution of the recrystallization microstructure and the texture and mechanical properties of the deformed alloy were investigated after annealing at 200 and 400 °C for 1 h using Electron Backscatter Diffraction (EBSD) and Vickers measurements. The recrystallization temperature and activation energy were evaluated using Differential Scanning Calorimetry (DSC). Processing by HPT led to significant grain refinement with an average grain size of ~0.5 ± 0.1 μm which increased to ~1.2 ± 0.8 μm after annealing at 400 °C. This slow increase in grain size at a high temperature demonstrates a good thermal stability of the microstructure. The alloy exhibited two main fiber textures after HPT processing: firstly a typical basal fiber (φ 1 = 0–360°, Φ = 0° and φ 2 = 0–60°) and secondly a fiber localized at φ 1 = 180°, Φ = 60° and φ 2 = 0–90°. These textures were retained after annealing at 400 °C. There was no change in the microhardness value after annealing at 200 °C (41 ± 1 Hv) and only a minor decrease after annealing at 400 °C (38.4 ± 0.5 Hv). The DSC results showed that the temperature associated with the recrystallization process increased with increasing heating rate and the activation energy for recrystallization was measured as ~25 kJ mol−1. • Processing by HPT up 5 turns produces a significant refinement in grain size. • The recrystallization temperature was measured in the range of ~120–200 °C. • The activation energy for recrystallization was ~25 kJ mol−1. • The texture was retained after subsequent annealing at 400 °C for 1 h. • A good thermal stability was demonstrated after annealing at 400 °C for 1 h. [ABSTRACT FROM AUTHOR]

Thermal stability of a Cu-Cr-Zr alloy processed by equal-channel angular pressing up to16 passes was investigated using isochronal annealing ranging from 250 to 850 °C for 1 h. The microstructure, crystallographic texture and micro hardness of samples were characterized through electron back scatter diffraction and Vickers micro hardness measurements. The recrystallized grain size was stable between 250 °C and 500 °C then increased quickly. The achieved mean grain size, after 1, 4 and 16 ECAP passes, was around 5.5 μm. A discontinuous mode of recrystallization was found to occur and a Particle Simulated Nucleation mechanism was evidenced. The evolution of the high angle grain boundary fraction increased notably after annealing above 550 °C. The crystallographic texture after isochronal annealing was similar to that of ECAP simple shear, no change of the texture during annealing was observed but only slight intensity variations. Micro hardness of all Cu–Cr–Zr samples showed a hardening with two peaks at 400 and 500 °C associated with precipitation of Cu cluster and Cu 5 Zr phase respectively, followed by a subsequent softening upon increasing the annealing temperature due to recrystallization. [ABSTRACT FROM AUTHOR]

Among the severe plastic deformation processing (SPD) of materials, high-pressure torsion (HPT) is known to induce considerable amounts of plastic strain and crucial grain refinement up to the nanometer scale. There have been several reviews on the mechanical properties and/or microstructure correlations of SPD-processed materials published during the last two decades. By contrast, a review on the crystallographic texture evolution during HPT processing is not at present available. Consequently, this work was undertaken to review the texture evolution in Face-Centered Cubic (FCC), Body-Centered Cubic (BCC) and Hexagonal Close-Packed (HCP) crystal structure materials processed exclusively by HPT with a special emphasis on the influence of many intrinsic and extrinsic factors such as the imposed strain, the deformation temperature and the alloying elements. [ABSTRACT FROM AUTHOR]

The evolution of microstructure, texture, and mechanical properties of an Mg–1.43Nd (wt%) alloy is investigated after processing by high‐pressure torsion at room temperature through five turns and isochronal annealing for 1 h at 150, 250, 350, and 450 °C using electron backscatter diffraction and Vickers microhardness. The alloy exhibits a good thermal stability up to annealing at 250 °C, with mean grain size of ≈0.65 μm. The microhardness shows an initial hardening after annealing at 150 °C and then a subsequent softening. The deformation texture, a basal texture shifted 60° away from the shear direction (SD), is retained during annealing up to 250 °C. In contrast, a basal texture with symmetrical splitting toward SD is developed after annealing at 350 °C. The precipitation sequence and their pinning effects are responsible for the age‐hardening, stabilization of grain size, and the texture modification. The kinetics of grain growth in the Mg–1.43Nd alloy follows two stages depending on the temperature annealing range, with an activation energy of ≈26 kJ mol−1 in the low temperature range of 150–250 °C and ≈147 kJ mol−1 in the high temperature range of 250–450 °C. [ABSTRACT FROM AUTHOR]

• The peak temperature of recrystallization was in the range of 441.9 ± 2.0–497.8 ± 4.0 K. • The recrystallized fraction increased with increasing heating rate. • The peak temperature decreased with the thickness reduction. • The activation energy of recrystallization ranged from 93.3 ± 2.1–116.6 ± 2.6 kJ mol−1. • The Avrami exponent n of recrystallization was found close to 0.6. In the present study the kinetics of recrystallization phenomenon of hot-rolled Mg-1.33La (wt.%) alloy was investigated using differential scanning calorimetry (DSC) analysis. The alloy was hot-rolled at 693 K to 20 and 50 % of thickness reduction. The DSC experiments results showed that the peak of recrystallization process ranged from 441.9 ± 2.0–497.8 ± 4.0 K and increased with increasing heating rate. The activation energy evaluated through the non-isothermal DSC treatment ranged from 93.3 ± 2.1–116.6 ± 2.6 kJ mol−1 and correlates well with the increase of stored energy during the deformation processing. The Avrami exponent of recrystallization was found close to 0.6 which indicates that the recrystallization preferentially occurred along grain boundaries and within deformation features such as twins. [ABSTRACT FROM AUTHOR]