Effects Of Deformation Parameters Research Articles

Dependence of α-phase size on flow stress during dynamic recrystallization steady state in Ti60 alloy

The dependence of α-phase size on flow stress was characterized by a proposed kinetic model during dynamic recrystallization (DRX) steady state in Ti60 alloy. According to the isothermal compression tests, the influence of deformation parameters on the steady-state flow stress was analyzed and the constitutive equation was established to predict the steady-state flow stress under different deformation temperatures and strain rates. A power-law relationship between the DRX average grain size and steady-state flow stress with an exponent of −2 is obtained from the dynamic balance during DRX steady state. The effect of deformation parameters on α-phase size was observed through the microstructure after deformation, and the applicability of the model for Ti60 alloy was verified by the comparison between predicted and experimental data.

Determination of no-recrystallization temperature for a Nb-bearing steel

The recrystallization behavior of a Nb-bearing steel was investigated during multipass deformation under continuous cooling conditions. By a series of six-pass compression tests conducted on a thermomechanical simulator, the effect of deformation parameters, including strain, strain rate and interpass time, on the no-recrystallization temperature (Tnr) was determined. The results show that Tnr decreases with increasing strain and also decreases slightly with increasing strain rate. The strain has more appreciable influence on the Tnr compared with strain rate. When the interpass time is less than 10 s, the Tnr decreases with increasing interpass time. The mathematical model of Tnr was established considering the effect of pass strain, strain rate and interpass time. The calculated results agreed well with the actual experimental value.

Static Recrystallization Behavior of SA508-III Steel during Hot Deformation

The static recrystallization behavior of SA508-III steel was investigated by isothermal double-hit hot compression tests at the deformation temperature of 950–1250 °C, the strain rate of 0. 01–1 s−1, and the inter-pass time of 1–300 s. The effects of deformation parameters, including forming temperature, strain rate, degree of deformation (pre-strain) and initial austenite grain size, on the softening kinetics were analyzed. Experimental results show that static recrystallization kinetics is strongly dependent on deformation temperature and degree of deformation, while less affected by the strain rate and initial grain size. The kinetics and microstructural evolution equations of static recrystallization for SA508-III steel were developed to predict the softening behavior and the statically recrystallized grain size, respectively. Based on the comparison between the experimental and predicted results, it is found that the established equations can give a reasonable estimate of the static softening behavior for SA508-III steel.

Nucleation mechanisms of dynamic recrystallization for G3 alloy during hot compression

Dynamic recrystallization (DRX) mechanisms of a nickel-based corrosion-resistant alloy, G3, were investigated by hot compression tests with temperatures from 1050 to 1200 °C and strain rates from 0.1 to 5.0 s−1. Deformation microstructure was observed at the strain from 0.05 to 0.75 by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). Work hardening rate curves were calculated to analyze the effect of deformation parameters on the nucleation process. Results indicate that strain-induced grain boundary migration is the principal mechanism of DRX. Large annealing twins promote nucleation by accumulating dislocations and fragmenting into cell blocks. Continuous dynamic recrystallization is also detected to be an effective supplement mechanism, especially at low temperature and high strain rate.

Modified constitutive analysis and activation energy evolution of a low-density steel considering the effects of deformation parameters

In the present study, typical hyperbolic sine equation was found inappropriate to model the flow behavior of a Fe-18Mn-8Al-0.8C low-density steel in warm to hot deformation regime. This is related to the fact that the materials constants do not actually remain constant during deformation. Considering the effects of deformation parameters, a modified model was derived and used to accurately predict the flow behavior of the steel. The 3D activation energy map showed that the activation energy would decrease at high temperature due to the thermally activated nature of dislocation motion. However, the calculated activation energies are higher than those for conventional austenitic steels since the present highly alloyed steel is considered to be strongly strengthened by solid solution. The solute drag effect of alloying elements is found to be the main reason for obtaining higher activation energy values at relatively low strain rates. The subsequent calculations showed that the activation energy would decrease by about 50 kJ.mol−1 by increasing the strain due to the occurrence of dynamic recrystallization at above 1073 K. In contrast, the accumulation of deformation energy in the absence of dynamic recrystallization (below 1073 K) would lead to activation energy increase by increasing the amount of deformation.

Constitutive analysis of hot deformation behavior of a Ti6Al4V alloy using physical based model

The effect of deformation parameters on the flow behavior of a Ti6Al4V alloy has been studied to understand the deformation mechanisms during hot compression. Cylindrical samples with partially equiaxed grains were deformed in the α+β phase region at different thermo-mechanical conditions. To develop components with tailored properties, the physically based Estrin and Mecking (EM) model for the work hardening/dynamic recovery combined with the Avrami equation for dynamic recrystallization was used to predict the flow stress at varying process conditions. The EM model revealed good predictability up to the peak strain, however, at strain rates below 0.01s−1, a higher B value was observed due to the reduced density of dislocation tangles. In contrast, the flow softening model revealed higher value of constants a and b at high strain rates due to the reduction in the volume fraction of dynamic recrystallization and larger peak strain. The predicted flow stress using the combined EM+Avrami model revealed good agreement with the measured flow stress resulted in very low average absolute relative error value. The microstructural analysis of the samples suggests the formation of coarse equiaxed grains together with the increased β phase fraction at low strain rate leads to a higher flow softening.

Grain boundary engineering of powder processed Ni-base superalloy RR1000: Influence of the deformation parameters

Traditional processing routes for Grain Boundary Engineering (GBE) often require multiple iterations of cold work followed by short annealing cycles. Since each iteration of deformation and annealing imparts a modest increase in the fraction of twin and special grain boundaries, multiple iterations are required to achieve a sufficiently high fraction (~50%) of special grain boundaries that result in the improved properties. This GBE approach therefore is not suitable for the fabrication of large, complex shaped structures and leads to added manufacturing lead time and cost. In this investigation, the effect of deformation parameters on powder processed Ni-base superalloy RR1000 was investigated. By systematically quantifying the effects of deformation temperature (1100–1020°C), strain rate (0.05–0.001/s) and the post deformation annealing temperature (1115°C and 1145°C), a set of optimized processing parameters were identified such that the length fraction of Σ3 boundaries increased from 35% to 52% following a single deformation anneal cycle. Deformation parameters (T>1060°C and ε̇<0.01/s) that resulted in strain accommodation via superplastic flow or grain boundary sliding/rotations did not enhance the formation of Σ3 boundaries upon annealing. Whereas deformation parameters that resulted in a transition in the dominant deformation mechanism from superplastic flow to dislocation plasticity (T<1060°C and ε̇>0.001/s) promoted the formation of annealing twins, which are key for grain boundary engineering and stimulating the formation of Σ3 boundaries during annealing.

Static Recrystallization Kinetics of a Twin-roll Cast AZ31 alloy

The static recrystallization (SRX) behaviour of twin-roll cast and annealed magnesium AZ31 strip during hot deformation was determined under deformation conditions corresponding to the hot strip rolling process used in the production of twin-roll cast magnesium coils. Plane strain compression tests were performed using double-hit schedules at temperatures of 250°°C°–°400°°C, strain rates of 1°s-1°–°10°s-1, and inter-pass times of 1°s°−°400°s, whereby the first deformation step had a logarithmic strain below the critical logarithmic strain necessary for the beginning of dynamic recrystallization. Based on the experimental results, the kinetic equations and grain size model were established. Results show the effects of deformation parameters, including forming temperature and strain rate, on static softening fractions and grain size in the two-pass hot-deformed AZ31 alloy. Deformation-induced precipitations do not hinder the softening processes.

Study of Static Recrystallization Behaviors of GCr15 Steel Under Two-Pass Hot Compression Deformation

In order to study the static recrystallization behavior of GCr15 steel during hot deformation process, twopass hot compression experiments were conducted on Gleeble-3500 thermo-simulation system at the test temperatures from 850 to 1150 C strain rate from 0.01 to 1 s 21 , strain from 0.05 to 0.15 and inter-stage delay time from 1 to 100 s, respectively. The effects of temperature, strain rate and strain on static recrystallization of GCr15 steel were discussed in details. And the kinetic equations, in which the tensiontime index n was 0.35 and the activation energy Q was 225.86 kJ/mol, were proposed. The comparison between the experimental results and predicted results was performed and the research results indicated that the effects of deformation parameters on the static recrystallization in multi-stage hot deformation are significant. The predicted results are in good agreement with the experimental ones, which indicates that the proposed kinetic equations can give an accurate estimate of the static recrystallization behaviors and microstructural evolutions for GCr15 steel.

Higher dimensional non-Kerr black hole and energy extraction

We investigate the properties of the horizons and ergosphere in a rotating higher dimensional (HD) deformed Kerr-like black hole. We also explicitly bring out the effect of deformation parameter $\epsilon$ and the extra dimension on the efficiency of the Penrose process of energy extraction from a black hole. It is interesting to see that the ergosphere size is sensitive to the deformation parameter $\epsilon$ as well as spacetime dimensions $D$. This gives rise to a much richer structure of the ergosphere in a HD non-Kerr black hole, thereby making the Penrose process more efficient compared with that of the four-dimensional Kerr black hole.

Hot tensile deformation behaviors and fracture characteristics of a typical Ni-based superalloy

The hot tensile deformation behaviors and fracture characteristics of a typical Ni-based superalloy are studied by uniaxial tensile tests under the deformation temperature range of 920–1040°C and strain rate range of 0.01–0.001s−1. Effects of deformation parameters on the flow behavior, microstructural evolution and fracture characteristics are discussed in detail. The results show that the flow behaviors are significantly affected by the deformation temperature, strain and strain rate. Under relatively low deformation temperatures (920, 950 and 980°C), the flow curves are composed of three distinct stages, i.e., work hardening, steady stress and flow softening stages. The flow curves show the typical DRX characteristics under relatively high deformation temperatures (1010 and 1040°C). With the increase of deformation temperature or the decrease of strain rate, the fraction of recrystallized grains increases. The synthetical effects of localized necking and microvoid coalescence cause the fracture of the studied superalloy under all the deformation conditions. δ phase (Ni3 Nb) and carbides are the nucleus for the formation of microvoids. Also, δ phase plays an important role in the coalescence of microvoids.

Hot deformation mechanism and microstructure evolution of a new near β titanium alloy

Transmission Electron Microscope (TEM) and Electron Backscattered Diffraction (EBSD) are employed to explore the influence of deformation conditions on microstructure and the deformation mechanism of a new near β titanium alloy Ti-7333 after hot compression tests which at temperatures ranging from 770 to 970°C and strain rates ranging from 0.001 to 10s−1. The results showed that the effect of deformation parameters on microstructure evolution is significantly. Both increasing the temperature and decreasing the strain rate seem to promote the dynamic recrystallization process. The mechanism is dominated by dynamic recovery, globularization and dynamic recrystallization. The globularization trend of α phase is more remarkable deformed at higher temperature and lower strain rate. And reverse, the lower temperature and higher strain rate are more favorable to α phase refinement. The fraction of low-angle grain boundaries in the deformation microstructure decreases with the increasing of temperature and decreasing of strain rate. It illustrates the low-angle grain boundaries would turn to high-angle grain boundaries during deformation. The expression of the size of recrystallized grains Dr and parameter Z is obtained by regression analysis as lnDr=8.79964−0.33663lnZ. All the deformed samples present strong 〈001〉 and weak 〈111〉 fiber texture. With the increasing of temperature and decreasing of strain rate, the 〈001〉 texture strengthens gradually and 〈111〉 texture weakens gradually until extinction.

Hot tensile deformation and fracture behaviors of AZ31 magnesium alloy

The hot tensile deformation and fracture behaviors of the hot-rolled AZ31 magnesium alloy were studied by uniaxial tensile tests with the temperature range of 523–723K and strain rate range of 0.05–0.0005s−1. Effects of deformation parameters on the strain hardening rate, strain rate sensitivity, microstructural evolution and fracture morphology were discussed. The results show that: (1) The flow curves show a considerable strain hardening stage and no obvious diffuse necking stage under the relatively low temperatures (523 and 573K). (2) The elongation to fracture increases with the increase of the deformation temperature. But, the sharp drop of the elongation to fracture under 723K and 0.0005s−1 results from the synthetical effects of the grain growth, inverse eutectic melting reaction (α+β=L) and the incipient melting of α matrix. (3) For the case with the deformation temperature of 623K and relatively low strain rates, the fracture mechanism is the combination of the void coalescence and intergranular fracture. (4) Under the deformation temperature of 723K, the fine recrystallized grains experienced a rapid growth and the deformation mechanism is the dislocation creep with the help of inverse eutectic liquid phase. (5) The presence of proper amount of liquid phase on the grain boundary changes the deformation mechanisms, and makes great contribution to the high ductility. However, it will deteriorate the material ductility if the amount of liquid phase is too much.

Recrystallization of 30Cr2Ni4MoV ultra-super-critical rotor steel during hot deformation. Part Ш: Metadynamic recrystallization

► The kinetic equations of metadynamic recrystallization were developed. ► The grain size model for metadynamic recrystallization was proposed. ► The effects of forming parameters on the microstructural evolution were studied. The metadynamic recrystallization (MDRX) behavior of 30Cr2Ni4MoV ultra-super-critical (USC) rotor steel during hot deformation was investigated based on the first part of this study, in which the evolution of the dynamically recrystallized structure was studied in detail. Compression tests were performed using double hit schedules at temperatures of 970–1250 °C, strain rates of 0.001–0.1 s −1 and inter-pass time of 1–100 s. Based on the experimental results, the kinetic equations and grain size model were established. Results show that the effects of deformation parameters, including forming temperature and strain rate, on MDRX softening fractions and austenite grain size in the two-pass hot deformed 30Cr2Ni4MoV steel are significant. Results also reveal that the pre-strain (beyond the peak strain) has little influence on the MDRX behaviors in 30Cr2Ni4MoV steel. Comparisons between the experimental and the predicted results were carried out. A good agreement between the experimental and the predicted results was obtained, which verified the developed models.

Plastic flow behavior of a high-strength magnesium alloy NZ30K

Abstract The plastic flow behavior of a newly developed high strength magnesium alloy, Mg–3Nd–0.2Zn–0.4Zr (NZ30K, wt.%), was investigated by tensile testing in the temperature range of 25–400 °C and a strain rate range of 1 × 10 −4 –1 × 10 −2 . The constitutive relationship for this alloy deformed at elevated temperatures was determined by plotting the experimental data according to the Arrhenius and hyperbolic sine models. The results show that both equations fit the experimental data reasonably well. The effect of deformation parameters on the microstructure and deformation mechanisms of the alloy was also examined using optical metallography and electron backscattered diffraction (EBSD) techniques. The results suggest that basal slip and twinning are the main deformation mechanisms at temperatures up to 200 °C; and that recrystallization occurs at deformation temperatures above 200 °C. Dynamic recrystallization (DRX) was shown to be the main softening mechanism at temperatures above 400 °C.

Relationship between microstructure and deformation behaviour during dynamic compression in Ti–3Al–5Mo–5V alloy

The relationship between microstructure and deformation and damage behaviour during dynamic compression in Ti–3Al–5Mo–5V alloy has been studied using several experimental techniques, including optical microscopy, scanning electron microscopy and microhardness measurements. It was found that the deformation behaviour during dynamic compression was closely related to deformation parameters. After dynamic deformation, the deformation shear band that formed in the titanium alloy had microhardness similar to that of the matrix. However, the microhardness of the white shear band was much higher than the matrix microhardness. The effects of deformation parameters, including deformation rate and deformation degree, on deformation localisation were investigated. Based on the results from the present work, the microstructure and deformation processing parameters can be optimised. In addition, treatment methods after dynamic compression were explored to restore alloy properties. Using post-deformation heat treatment, the microstructure and property inhomogeneity caused by shear bands could be largely removed.

Effect of processing parameters on the hot deformation behavior of as-cast TC21 titanium alloy

Isothermal compression tests of as-cast Ti–6A1–2Zr–2Sn–3Mo–1Cr–2Nb (TC21) titanium alloy are conducted in the deformation temperature ranging from 1000 to 1150 °C with an interval of 50 °C, strain rate ranging from 0.01 to 10.0 s −1 and height reductions of 30%, 45%, 60% and 75% on a computer controlled Gleeble 3500 simulator. The true stress–strain curves under different deformation conditions are obtained. Based on the experimental data, the effects of deformation parameters on the hot deformation behavior of as-cast TC21 alloy were studied. The deformation mechanisms of the alloy in the whole regimes are predicted by the power dissipation efficiency and instability parameter and further investigated through the microstructure observation. It is found that at the height reductions of 30%, 45% and 60%, the softening of stress–strain curves at high strain rate (>1.0 s −1) is mainly associated with flow localization, which is caused by local temperature rise, whereas at low strain rate, the softening is associated with dynamic recrystallization (DRX). However, the instability showed in flow localization occurs at low strain rate of 0.01 s −1 when the height reduction reaches 75%. In addition, the effects of strain rate, deformation temperature and height reduction on microstructure evolution are discussed in detail, respectively.

A new method to predict the metadynamic recrystallization behavior in 2124 aluminum alloy

The metadynamic recrystallization behaviors in deformed 2124 aluminum alloy were investigated by isothermal interrupted hot compressive tests, which were carried out at the deformation temperatures of (653–743) K, strain rates of (0.01–10) s−1 and inter-stage delay time of (30–180) s. A new approach, “peak stress method”, is proposed to calculate the softening fractions induced by the rapid metadynamic recrystallization. The kinetic equations were developed to predict the metadynamic recrystallization behaviors in hot compressed 2124 aluminum alloy. Both the experimental and predicted results show that the effects of deformation parameters, including strain rate, deformation degree and temperature, on the softening behaviors in the two-pass hot compressed 2124 aluminum alloy are significant. A good consistency between the experimental and predicted results indicates that the proposed kinetic equations can precisely estimate the softening behaviors and metadynamic recrystallization kinetics of the hot compressed 2124 aluminum alloy.

Effect of deformation parameters on the precipitation mechanism of secondary α phase under high temperature isothermal compression of Ti–6Al–4V alloy

Isothermal compression tests were conducted for Ti–6Al–4V alloy in the α + β two-phase field, and the effect of deformation parameters on the precipitation of secondary α phase in the subsequent air cooling process following isothermal compression was investigated. The experimental results show that the morphology of secondary α phase transforms gradually from lamellar colony to equiaxed morphology with the increase of strain rate and height reduction and with the decrease of deformation temperature. And the precipitation mechanisms of the secondary α phase under different isothermal compression conditions are explored by noting the effect of the crystal defect (i.e., dislocation, grain boundary and subgrain boundary) density in the β matrix.

Microstructure-based Simulation of Plastic Deformation Behavior of SiC Particle Reinforced Al Matrix Composites

This article, in order to unearth the deformation mechanism of particle reinforced metal matrix composites, establishes a finite element model (FEM) based on the actual microstructures. It finds out and analyzes the distribution of von Mises effective stress, strain and the maximum principal stress in the matrix and particles. Moreover, the overall stress and strain in the matrix and composites are calculated. By comparison, a tiny discrepancy exists between the experimental results and the simulation with respect to flow stresses. The effects of deformation parameters, such as temperature and strain rate, on the strengthening mechanism are explored and proved to be weak.