A new dynamic recrystallization kinetics model for a Nb containing Ni-Fe-Cr-base superalloy considering influences of initial δ phase

Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy were calculated to characterize the deformation mechanism. Then, the effects of hot deformation parameters on deformation mechanism, microstructure evolution and hot workability of AZ31 alloy were discussed. With increasing deformation temperature, the operation of non-basal slip systems and full development of dynamic recrystallization (DRX) contribute to effective improvement in hot workability of AZ31 alloy. The influences of strain rate and strain are complex. When temperature exceeds 350°C, the deformation mechanism is slightly dependent of the strain rate or strain. The dominant mechanism is dislocation cross-slip, which favors DRX nucleation and grain growth and thus leads to good plasticity. At low temperature (below 350°C), the deformation mechanism is sensitive to strain and strain rate. Both the dominant deformation mechanism and inadequate development of DRX deteriorate the ductility of AZ31 alloy. The flow instability mainly occurs in the vicinity of 250°C and 1 s -1 .

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“…Similar results are also given in Ref. [36,37]. The microstructure observation is in agreement with the prediction from processing map.…”

Section: Effect Of Temperature On Deformation Mechanism and Workabilitysupporting

confidence: 91%

Deformation Mechanism and Hot Workability of Extruded Magnesium Alloy AZ31

Jin

Yan

et al. 2017

Acta Metall. Sin. (Engl. Lett.)

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“…The Avrami Equation has been widely used to describe the kinetics of DRX . The volume fraction of DRX can be expressed as:

X_{drx} = 1 - exp true(- k_{d r x} {((ϵ - ϵ_{c}) / ϵ_{p})}^{n_{drx}} true), true(ϵ \geq ϵ_{c} true)

where X drx is the DRX volume fraction, K drx is the Avrami constant, and n drx is the material constant.…”

Section: Resultsmentioning

confidence: 99%

Hot Deformation Behavior and Microstructural Evolution of SA508‐IV Steel

Dai

Yang

2018

steel research int.

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The hot deformation behavior and microstructural evolution of SA508-ІV steel are studied through hot compressive tests in the temperature range of 950-1250 C, and in the strain rate range of 0.001-1 s À1 . The hot deformation activation energy and the stress exponent are calculated to be 328.73 KJ mol À1 and 3.29 by the regression analysis of sine hyperbolic function. On this basis, the constitutive Equations are developed. Moreover, the relationship between work hardening and dynamic softening is explained, and a two-stage constitutive model is established to predict the flow stress of SA508-ІV steel. The predicted and experimental values show a good consistency. Based on the conventional dynamic recrystallization kinetics model, the volume fraction of the dynamic recrystallization is also estimated, and the results show that the maximum fraction is close to 100% under the higher temperature and lower strain rate. Furthermore, the microstructural evolutions at different deformation conditions are also analyzed, and the DRX grain size has an exponential increase with increasing deformation temperature and decreasing strain rate.

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“…The heterogeneous development of ultrafine DRX grains should lead to specific variation of the fraction recrystallized, which commonly exhibits sigmoid‐type function of strain . Taking the grains with sizes below 3 μm as DRX grains (Figure ), the fraction recrystallized ( F DRX ) is shown in Figure b as the area fraction of DRX grains.…”

Section: Resultsmentioning

confidence: 99%

“…The development of discontinuous DRX results generally in characteristic strain softening . Thus, the fractional softening on the stress‐strain curve has also been used to evaluate the DRX progress . The envelope stress‐strain curve plotted over 10 forging passes in Figure can be used to evaluate the fractional softening during the studied multiple forging.…”

Section: Resultsmentioning

confidence: 99%

On Kinetics of Grain Refinement and Strengthening by Dynamic Recrystallization

et al. 2018

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The grain refinement and strengthening of an austenitic stainless steel are studied under multiple multidirectional forging at 1073 K up to strains of 4. The structural changes are characterized by the development of discontinuous and continuous dynamic recrystallization (DRX) leading to the grain refinement down to submicrometer level. The new ultrafine grains develop primarily along original grain boundaries and deformation microbands, leading to heterogeneous necklace-like microstructures at intermediate strains followed by rapid expansion of the DRX grains occupying the whole worked sample at large strains. The change in the fraction of ultrafine grains is commonly characterized by a sigmoid-type dependence on strain and can be expressed by a modified Jonson-Mehl-Avrami-Kolmogorov equation. The DRX development is accompanied by a stepwise decrease in the flow stress at reloading in each subsequent forging pass especially in intermediate strains. This stepwise softening results from rapid growth of freshly nucleated grains. In contrast, after forging, both the yield strength and ultimate tensile strength at room temperature increase progressively with an increase in the number of forging passes. The strengthening during DRX development can be attributed to concurrent contribution of work-hardening and grain refinement and can be expressed by a summation of recovered and recrystallized fractions.

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A new dynamic recrystallization kinetics model for a Nb containing Ni-Fe-Cr-base superalloy considering influences of initial δ phase

Cited by 116 publications

References 60 publications

Deformation Mechanism and Hot Workability of Extruded Magnesium Alloy AZ31

Deformation Mechanism and Hot Workability of Extruded Magnesium Alloy AZ31

Hot Deformation Behavior and Microstructural Evolution of SA508‐IV Steel

On Kinetics of Grain Refinement and Strengthening by Dynamic Recrystallization

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