Activation Energy for Grain Growth of the Isochronally Annealed Ultrafine Grained Magnesium Alloy after Hot Extrusion and Equal-Channel Angular Pressing (EX-ECAP)

Stráská, Jitka; Stráský, Josef; Janeček, Miloš

doi:10.12693/aphyspola.128.578

Cited by 10 publications

(4 citation statements)

References 21 publications

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“…Thus, it is concluded that lattice self‐diffusion is the dominant mechanism for grain growth in the severely deformed Mg–1.43Nd alloy in the high temperature range. This is in good agreement with the assumption that lattice self‐diffusion is the dominant process of grain growth when the alloy consists of large grains which is correct for the present alloy after annealing at 350 and 450 °C. In fact, a strong basal texture was reported as also responsible for an increase in the activation energy for grain growth and, as shown in Figure , the texture of the present alloy starts to change after annealing at 250 °C where a basal texture is well developed.…”

Section: Discussionsupporting

confidence: 90%

Thermal Stability of an Mg–Nd Alloy Processed by High‐Pressure Torsion

et al. 2019

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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.

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Section: Discussionsupporting

confidence: 90%

Thermal Stability of an Mg–Nd Alloy Processed by High‐Pressure Torsion

et al. 2019

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“…The corrosion behaviour is affected by structural change due to solution treatment and high deformation level. The hot rolling and highpressure torsion process can also confirm these results, which mentioned lower corrosion resistance due to high deformation levels [39]-[41]. It can be concluded that the ECAP process of solution treated ZK60 can improve the mechanical properties and modify the corrosion behaviour for biodegradable materials.…”

Section: Discussionmentioning

confidence: 75%

The Effect of Precipitation on Microstructure and Corrosion Behaviour of Zk60 Subjected to Severe Plastic Deformation as Biodegradable Material

Rifai¹

2022

metal.

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Microstructure and corrosion behaviour of ZK60 subjected to severe plastic deformation (SPD) as biodegradable material has been investigated in terms of grain refinement process and precipitation formation. Equal channel angular pressing (ECAP) was one of the well-known SPD techniques due to their advantages to promote dislocation and grain fragmentation. ZK60 billet was cut to a 10 mm diameter cylindrical shape for biodegradable material application. ECAP process was carried out up to two passes by Route Bc at 423 K temperature process. Microhardness test was performed at ECAP processed sample, and the structure observation was carried by optical microscope and transmission electron microscope. The corrosion behaviour of the material was investigated by an anodic polarization curve. The ECAP process promotes dislocation accumulation efficiently and ultrafine-grained structure formation. It may improve the formability characteristic of ZK60. The hardness also showed significant increment during the ECAP process due to the high level of deformation. Corrosion behaviours and microstructure observation during the ECAP process showed a correlation that concluded that grain refinement and precipitation formation influenced the electrochemical properties. The alloying element such as Zn and Zr promoted the protective film for corrosion due to their ability for pitting protection. ECAP improved the precipitation formation for corrosion resistance, microstructure uniformity and material formability.

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“…This unusual behavior can be attributed to recovery and recrystallization processes at elevated temperatures. Diffusion of atoms, which facilitates superplastic behavior, is enhanced by fast diffusion paths like pipe diffusion along dislocations or grain boundaries, which was found as the dominant diffusion processes in severely deformed UFG microstructure [30,58,65]. Note also that the activation energy of grain boundary diffusion in pure Mg (92 kJ/mol [52]) is much lower than the activation energy of self-diffusion (135 kJ/mol [53]).…”

Section: Superplastic Behaviormentioning

confidence: 96%

“…[58] shows that if true activation energy of the process responsible for the grain growth continuously rises from the activation energy of grain boundary diffusion (115 kJ/mol) to the activation energy of lattice self-diffusion (164 kJ/mol), then the (wrong) fitting by a single Arrhenius equation indeed results in very low (and physically meaningless) estimate of apparent activation energy (33 kJ/mol). Based on a simple model assuming continuous increase of activation energy [58], it can be concluded that the dominant diffusion process is the grain boundary diffusion up to 210°C, while the lattice self-diffusion is dominant from 400°C. In the intermediate region, the effect of grain boundary diffusion decreases due to undergoing grain growth.…”

Section: (A) the Activation Energy Of Grain Growthmentioning

confidence: 99%

Thermal Stability of Ultra-Fine Grained Microstructure in Mg and Ti Alloys

Stráská¹,

Zháňal²,

Václavová³

et al. 2017

Severe Plastic Deformation Techniques

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This chapter reviews the thermal stability of ultra-fine grained (UFG) microstructure in selected magnesium and titanium-based materials prepared by severe plastic deformation (SPD). The focus is on the wide palette of experimental methods applicable for investigation of microstructural stability. These methods include scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), microhardness measurement, positron annihilation spectroscopy (PAS), and electrical resistance measurement. Microstructural stability of UFG commercially pure (CP) Ti and Ti-6Al-7Nb alloy produced by equalchannel angular pressing (ECAP) is studied ex situ after annealing by SEM, by microhardness measurements, and in situ during heating, by high precision electrical resistance measurements. Both materials show stable UFG structure up to 440°C. Further annealing causes recovery and recrystallization of the microstructure. At 650°C, the microstructure is completely recrystallized. Magnesium alloy AZ31 is prepared by hot extrusion followed by ECAP. UFG microstructure recovers and continuously recrystallizes during annealing. The microstructure of UFG AZ31 alloy is stable up to 170°C and subsequent grain growth is analyzed. Special attention is paid to interpret the activation energy of the grain growth. The superplastic properties of UFG AZ31 alloy are investigated in the temperature range of 170-250°C.

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Activation Energy for Grain Growth of the Isochronally Annealed Ultrafine Grained Magnesium Alloy after Hot Extrusion and Equal-Channel Angular Pressing (EX-ECAP)

Cited by 10 publications

References 21 publications

Thermal Stability of an Mg–Nd Alloy Processed by High‐Pressure Torsion

Thermal Stability of an Mg–Nd Alloy Processed by High‐Pressure Torsion

The Effect of Precipitation on Microstructure and Corrosion Behaviour of Zk60 Subjected to Severe Plastic Deformation as Biodegradable Material

Thermal Stability of Ultra-Fine Grained Microstructure in Mg and Ti Alloys

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