Stages Of Work Hardening Research Articles

Achieving exceptional strain-hardening ability in nanocrystalline Ni–W coatings through compositionally modulated multilayer approach

Nanocrystalline Ni–W coatings show exceptional strength; however, they exhibit poor toughness due to limited ductility and high residual stresses which impede their use in practical applications as a potential hard chrome replacement. In the present study, compositionally modulated multilayer (CMM) coatings with alternate layers of Ni-1 at% W (soft) and Ni-15 at% W (hard) of three different layer thicknesses of 1, 0.5, and 0.1 μm are developed by pulse reverse electrodeposition to achieve the strength-ductility synergy, thereby enhanced wear resistance. Microcompression test results reveal that all the CMM coatings exhibit remarkably higher strain-hardening ability than the homogenous coatings. Significant fluctuations in the strain-hardening rate and a positive shift in the onset stress for the work-hardening stages were observed with the layer thickness. This suggests a strong interplay between the hard and soft layers on the deformation characteristics of multilayer coatings. Detailed electron microscopy of the cross-section of the deformed micropillars shows substantial evidence of co-deformation of both layers. A mechanism is proposed to explain the enhanced strain-hardening in multilayers involving the strength incompatibility arising in the layers leading to lateral constraints, resulting in strain gradient plasticity, stabilizing of local shear by the soft layers, and the barrier effect of the interfaces.

Effect of strain path and short-term post-annealing on the microstructure, texture, and mechanical anisotropy of low-carbon steel

In this research, the effect of strain path and short-term post-annealing on the microstructure, texture, and mechanical anisotropy of low-carbon steel was investigated. Asymmetric unidirectional rolling (AUR) and asymmetric cross rolling (ACR) were applied on Fe-0.072C steel. The ACR-processed sheet revealed a very limited number of new grains compared to the AUR-processed sheet, which was due to the dynamic recovery induced by strain path change. The average ferrite grain size of the post-annealed AUR- and ACR-processed samples was 11.5 and 14.1 μm, respectively. The dominant recrystallization in the annealed AUR-processed sheet was discontinuous static recrystallization, while that in the annealed ACR-processed sheet was continuous static recrystallization. The weak typical rolling textures (γ-fiber and α-fiber) at the midthickness of both rolled sheets demonstrated that the shear deformation effectively contributed to the formation of the shear textures during asymmetric cold rolling. The ACR decreased the intensity of the overall texture more than the AUR process due to the changes in the reference frame of deformation after each pass, which destabilized ideal texture components. The results showed that Goss and {111}〈112〉 components were continuous and discontinuous static recrystallization textures in the asymmetrically cold-rolled low-carbon steel sheet during the annealing treatment, respectively. The annealed AUR-processed sheet revealed a weaker texture as compared to the annealed ACR-processed sheet. The significant changes in the preferred orientations of the annealed AUR-processed sample led to weaker texture intensity compared to the annealed ACR-processed sheet. The hardness of the annealed AUR-processed sheet (183.8 HV) was higher than that of the annealed ACR-processed steel (156.9 HV), which was owing to the larger grain size and also the elimination of the γ-fiber texture in the annealed ACR-processed sheet. The strength along the rolling direction was lower than that along the transverse direction in the AUR-processed sheet. However, in the ACR-processed sheet, the values of strength were similar along three different tensile directions. As an important conclusion, if both high-strength and low-anisotropy are needed in the low-carbon steel sheets, it's better to apply ACR rather than AUR. In addition, if both high toughness and low anisotropy are essential, it's better to use AUR followed by post-annealing rather than ACR + post-annealing. The length of the intermediate stage of work hardening in the annealed ACR-processed sample was much less than the annealed AUR-processed sheet due to the presence of harder orientations (〈111〉 and 〈110〉) along rolling and transverse directions in the annealed ACR-processed sample. Finally, the fracture behavior of deformed and post-annealed steel sheets for both strain paths was ductile and shear ductile.

On the Onset of Plasticity: Determination of Strength and Ductility

The analysis of the work hardening variation with stress reveals insight to operative stress-strain mechanisms in material systems. The onset of plasticity can be assessed and related to ensuing plastic deformation up to the structural instability using one constitutive relationship that incorporates both behaviors of rapid work hardening (Stage 3) and the asymptotic leveling of stress (Stage 4). Results are presented for the mechanical behavior analysis of Ti-6Al-4V wherein the work hardening variation of Stages 3 and 4 are found to: be dependent through a constitutive relationship; be useful in a Hall-Petch formulation of yield strength; and provide the basis for a two point-slope fit method to model the experimental work hardening and stress-strain behavior.

Achieving excellent strength and ductility synergy by δ phase strengthening in low-density high-manganese steel

ABSTRACT In this study, we developed a novel lightweight Fe-Mn-Al dual-phase with high strength, excellent ductility, and considerable toughness. The study involved a thorough exploration of heat treatment processes and mechanical behaviour. The microstructure of the Fe-Mn-Al dual-phase steel consists of austenite and δ-ferrite. In the early stages of plastic deformation, austenite undergoes primary deformation, leading to a faster increase in dislocation density and microhardness. In later stages, strain is transferred from austenite to δ-ferrite through high-density dislocation walls, resulting in coordinated deformation of the two-phase structure. The excellent strength-ductility combination of Fe-Mn-Al dual-phase steel is attributed to multiple stages of continuous work hardening. Initially, dislocation nodes in δ-ferrite contribute to work hardening. Subsequently, high-density dislocation structures and the strengthening effect of hard δ-ferrite enhance work hardening. Finally, deformation twins in austenite, along with the TWIP effect, further increase work hardening, emphasizing the importance of these interactions in improving mechanical performance.

Study on the work-hardening behavior and tissue property analysis of high-strength magnesium alloy

Abstract Magnesium alloys show great superiority for modern applications due to their good biocompatibility, degradability, and excellent mechanical properties. In this paper, the strengthening effects and mechanisms of composite precipitation phases, microalloying regulated recrystallization behavior, composite grain organization, and new strain aging methods in magnesium alloys are investigated in terms of five stages of work hardening, heat treatment, and strengthening properties. The use of rare earth elements can effectively enhance the aging strengthening properties of magnesium alloy through the use of gadolinium (Gd) and yttrium (Y) in rare earth elements for the development of high-strength magnesium alloy. The results show that the solubility of aluminum in magnesium reaches the maximum of 12.6mmass.% at the eutectic temperature of 436℃and then gradually decreases with the decrease of temperature, and when the temperature decreases to room temperature, the solubility decreases to 2mass.%. The elongation of alloy 0.5Al alloy 0.5Zr alloy on the basis of the aging state was 6.7% and 4.8%, respectively. This paper provides theoretical and experimental guidance for the development of high-strength magnesium alloys through an in-depth study of strengthening mechanisms such as composite precipitation strengthening, crystal strengthening and strain aging strengthening.

Machine learning-assisted constitutive modeling of a novel powder metallurgy superalloy

The flow behavior and microstructure evolution during thermomechanical processing (TMP) of powder metallurgy superalloys are very important for their service behavior. In this contribution, a machine learning-assisted physical model was proposed to predict the flow stress, dynamic recrystallization (DRX) kinetic, and grain size evolution of a novel FGH4113A superalloy during the TMP. The work hardening and dynamic softening stages were modeled separately to predict the flow stress. The novel aspect of the proposed model is that the strong coupled effects of deformation temperature, strain rate, true stain, and primary γ' precipitates on the DRX kinetic were quantitatively described by the genetic algorithm-based artificial neural network (GA-ANN). Besides, the grain size modeling considered the pinning effect by primary γ' precipitates and the deformation-induced DRXed grain growth. Comparing the experimental and predicted flow curves, DRX fraction, and average grain size reveals that the proposed model has a preferable prediction accuracy than the conventional model. Then the specific DRX kinetic and grain size evolution characteristics were revealed. The promoting effect of strain rate on the DRX degree was gradually increased with the deformation temperature. Finally, the 3D processing map based on the developed model was established to guide TMP's optimized design and microstructure control. Three domains were divided and discussed: grain refinement, constant, and growth. The optimal processing window is defined as 1000–1050 °C/0.001–0.006 s−1 and 1075–1100 °C/0.008–0.01 s−1.

The Macroscopic Phenomena in Plasticity

In this paper, the fundamental principles of plastic flow localization are briefly outlined. During the development of plastic flow, there is a changeover in the localization patterns conforming to the corresponding stage of work hardening based on the autowave nature of plastic flow localization. In particular, the evolution of plastic flow from yield point to fracture involves the following four stages of autowave generation: switching autowave → phase autowave → stationary dissipative structure → collapse of autowave. The most intriguing localization pattern is attributed to a phase autowave, which forms at the stage of linear work hardening. The characteristics of the phase autowave (propagation velocity, dispersion, and grain size dependence of the wavelength) have been determined experimentally. Moreover, an elastic-plastic strain invariant is introduced to describe the elastic and plastic properties of the deforming medium, as well as to establish the above characteristics of autowaves. A hypothetic quasi-particle, corresponding to the autowave of localized plasticity, is considered and its potential properties are estimated to interpret the localization process characteristics.

Heterogeneity of deformation, shear band formation and work hardening behavior of as-printed AlSi10Mg via laser powder bed fusion

The deformation heterogeneities and micro-to macro-structural evolution of shear bands were thoroughly characterized and assessed in correlation with the work hardening behavior of laser powder bed fused as-built AlSi10Mg using compression testing at 78 and 293 K in a wide range of constant strain rates. Using the Kocks-Mecking model, work hardening behavior was correlated with the evolved microstructure and rate-controlling deformation mechanisms. It was found that initial work hardening (athermal hardening rate) is dependent on the strain rate at both 78 and 293 K, where it increases by a transition from shearing to looping of nano-precipitates in the 10−2-10−1 s−1 strain rate range. Stages II (hardening stage) and Stage III (dynamic recovery stage) of work hardening were also observed and their dependence on temperature and strain rate was assessed. The former includes the dislocation-obstacle interactions resulting in work hardening, whereas the latter consists of recovery processes where density of dislocations decreases. Shear banding was reported for higher strain rates manifesting in micro- and then evolving into macro-shear bands with deformation, which led to the increase in the dislocation recovery rate in Stage III of work hardening. Compressive work hardening mechanisms were discussed for both 78 and 293 K temperatures.

Скоростная чувствительность механических свойств сплава ZK60 с высокой степенью коррозионных повреждений

According to the stable opinion, hydrogen absorbed by magnesium alloys during corrosion can cause their stress corrosion cracking. One of the characteristic markers indicating the involvement of diffusible hydrogen into the fracture mechanism of metals is the negative strain rate dependence of the embrittlement degree. Recent studies show that the loss of ductility of the ZK60 alloy specimens subjected to a short-term (1.5 h) pre-exposure in a corrosive medium actually decreases with the increasing strain rate. However, after the removal of corrosion products from the surface of specimens, the strain rate dependence of the ductility loss becomes positive, which indicates the absence of hydrogen in the bulk of a metal. At a short-term exposure in a corrosive environment, the deep penetration of hydrogen into a metal could be limited due to the insufficient time for hydrogen diffusion. The paper studies the mechanical behavior of the ZK60 alloy subjected to a longer (12 h) pre-exposure in a corrosive medium followed by tensile testing in air at various strain rates. The authors consider the effect of strain rate, long-term pre-exposure in a corrosive medium, and subsequent removal of corrosion products on the strength, ductility, stages of work hardening, and localized deformation, as well as on the state of the side and fracture surfaces of specimens. The study identified that the ductility loss of specimens pre-exposed in a corrosive medium for 12 h decreases with the increasing strain rate, regardless of whether the corrosion products have been removed from their surface or not. It is shown that in this case, the negative strain rate dependence of the ductility loss is associated not with hydrogen dissolved in the bulk of a metal but with the presence of severe corrosion damage of the specimens’ surface. The authors proposed an explanation for the effect of corrosion damage on the mechanical properties and their strain rate sensitivity.

Elastic Moduli and Mechanical Properties of Mo5SiB2 Single Crystals in the Mo-Si-B System

With outstanding high-temperature properties, the intermetallic Mo5SiB2 alloy is regarded as an extremely competitive ultra-temperature structural material. The maximum Young’s modulus of 398.0 GPa for single Mo5SiB2 crystals was found to be at the vertex of the [010] direction, while the minimum value of 264.0 GPa was found in the [001] direction. For hardness, the maximum value was 451.7 HV after compression at 1200 °C in the radial direction, while the maximum hardness was 437.2 HV at 1300 °C in the axial direction of {111}<110>, showing obvious anisotropy. Under compression, the flow stresses rapidly increased and then decreased with the increase in strain, corresponding to the two different stages of work hardening and softening. An EBSD test showed that the grain orientation remained the same at different rates, but the texture was different. After high-temperature compression, the crystal underwent plastic deformation, dislocations slipped along the slip plane, and the grain rotated, so the grain texture changed from {111}<110> to {001}<110>.

An innovative constitutive material model for predicting high temperature flow behaviour of inconel 625 alloy

Inconel 625 nickel alloy with its attractive high-temperature strength, excellent corrosion and oxidation resistance is mainly used for critical applications in demanding environments, in both as-cast and wrought conditions. Hot processing of this alloy is crucial for achieving its tailored mechanical properties due to the significant variation in microstructural changes with varying process parameters like temperature, strain, and strain rate. In this study, isothermal hot compression tests were carried out at temperatures ranging from 900 to 1100 °C, and under strain rates ranging from 0.01 to 1 s−1. The flow curves revealed three stages of deformation, including a substantial work-hardening stage followed by dynamic recovery and flow softening. Microstructural observations showed the occurrence of discontinuous dynamic recrystallisation (DDRX) as the dominant recrystallisation mechanism during the flow softening. Microstructural analysis suggested that the DRX was more sensitive to the test temperature as compared to the strain rate. An innovative material's constitutive model was developed, by combining Johnson–Cook (JC) and Avrami approaches, to predict work-hardening, dynamic recovery, and flow softening stages of deformation. The predicted flow behavior was in a good agreement with the experimentally measured data. The developed material model was integrated into DEFORM® 3D finite element (FE) simulation software as a user subroutine for the prediction of deformation behaviour in a double truncated cone (DTC) sample. Comparison between the experimentally measured data and the results of FE simulation on the DTC sample showed a very good convergence, indicating the suitability of the proposed material’s constitutive model for large scale simulations.Graphical

Constitutive relationship of (Ti5Si3 +TiBw)/TC11 composites based on BP neural network

The Gleeble3500 thermal simulator was used to (2vol%Ti5Si3 +5vol%TiBw)/TC11 composites with network reinforcement structure at a deformation temperature of 1183–1363 K and a strain rate of 0.01–10 s-1 to perform a deformation of 60% constant temperature compression experiment. The thermal deformation behavior of composites and the stress-strain curve of thermal compression deformation were studied through the results of constant temperature compression experiments. In addition, based on the Arrhenius equation and the BP neural network model, the constitutive equations of flow stress σ, strain rate ε ̇, and deformation temperature T were established. The results show that as the strain rate increases and the deformation temperature decreases, the flow stress of the composites increases, and the stress-strain curve shows three stages of work hardening, rheological softening and stable rheology. Based on the Arrhenius model, a constitutive equation was established to fit and predict the true flow stress. The average relative error, the correlation coefficient and, the root mean square error are 7.4%,0.99526,14.5, successively. The prediction has a rough generalization ability and has deviation errors. On the other hand, based on BP Neural network model, a constitutive equation was established to fit and predict the true flow stress. The average relative error, the correlation coefficient and, the root mean square error are 2.5%, 0.99675, 3.7 in sequence. The prediction accuracy is high, and the generalization ability is strong. Thus, It is suitable for the establishment of nonlinear constitutive equations of materials.

The Microstructure Evolution of Mg-RE Alloy Produced by Reciprocating Upsetting Extrusion during Hot Compression

Mg-13Gd-4Y-2Zn-0.4Zr (wt. %) alloy bar produced by three passes reciprocating upsetting extrusion (named as RUE-ed bar) exhibited fine grain with the average grain size of 3.02 μm. Hot compression tests of the RUE-ed bar were carried out on Gleeble-3800 compression unit at different deformation temperatures (653, 683, 713, and 743 K) and strain rates (0.001–1 s, 0.01–1 s, 0.1–1 s, and 0.5–1 s). This alloy showed work hardening and softening stages in hot compression, the thermal activation energy of the RUE-ed bar was 150 ± 1 kJ/mol and the constitutive equation was: ε˙=1.80×109[sinh(0.0174σ)]2.47exp[−150×1038.314×T]. Numerous Mg5 (Gd, Y, Zn) phase re-dissolved in α-Mg matrix appeared in the RUE-ed samples during hot compression deformation. The movement of the dislocation stimulated the re-dissolution of the Mg5 (Gd, Y, Zn) phase. The re-dissolution of Mg5 (Gd, Y, Zn) phase promoted texture strengthening and DRX grains growth in this experiment. In addition, the transformation and kinking of LPSO phase played an important coordinating role in the process of hot compression; 18R-LPSO was changed to 14H-LPSO phase at low strain rate while the LPSO phase kinked dominant to coordinated deformation at high strain rate.

Effect of High Strain Rates on Adiabatic Shear Bands Evolution and Mechanical Performance of Dual-Phase Ti Alloy

In the present work, the adiabatic shear characteristics of our recently designed α + β dual-phase Ti alloy at different strain rates have been investigated by hat shaped specimen. The deformation process is divided into three stages: work hardening stage, steady stage, and unstable thermal softening stage. Along or near the shear deformation paths, the microvoids and the cracks can be captured at the strain rate of 1.8 × 104 s−1, 2.0 × 104 s−1, and 2.3 × 104 s−1, both of which contribute to the stable and unstable softening. It is found that dynamic stored energy of cold work will be significantly improved by the enhanced high strain rate. In the view of coupling analysis of inverse pole figure and grain boundary map, it seems that low angle grain boundaries present a good resistance to the formation of cracks and thermal softening. On the contrary, high angles grain boundaries are typically located in ASBs and their affecting regions, which is in line with the reported results. While the geometrical necessary dislocation (GND) density of adiabatic shear band (ASB) and its surroundings increased significantly, the width of the ASB becomes wider as the strain rate increases, which is consistent with the theory of sub-grain rotation dynamic recrystallization model. The formation of multiple ASBs in the corner position is schematically illustrated and the average elastic modulus and hardness of the ASB region are lower than the α and β phases, combined with the GND analysis, which proves that the ASB is a thermal softening zone in this experiment.

Studying Deformation Behaviors in Austenitic Stainless Steels within a Temperature Range of 143 K < T < 420 K

This work deals with studying staging and macroscopic strain localization in austenitic stainless steel 12Kh18N9T within a temperature range of 143 K < T < 420 K. The visualization and evolution of macroscopic localized plastic deformation bands at different stages of work hardening were carried out by the method of the double-exposure speckle photography (DESP), which allows registering displacement fields with a high accuracy by tracing changes on the surface of the material under study and then comparing the specklograms recorded during uniaxial tension. The shape of the tensile curves σ(ε) undergoes a significant change with a decreasing temperature due to the γ-α'-phase transformation induced by plastic deformation. The processing of the deformation curves of the steel samples made it possible to distinguish the following stages of strain hardening, i.e. the stage of linear hardening and jerky flow stage. A comparative analysis of the design diagrams (with the introduction of additional parameters of the Ludwigson equation) and experimental diagrams of tension of steel 12Kh18N9T for different temperatures is carried out. The analysis of local strains distributions showed that at the stage of linear work hardening, a mobile system of plastic strain localization centers is observed. The temperature dependence of the parameters of plastic deformation localization at the stages of linear work hardening has been established. Unlike the linear hardening, the jerky flow possesses the propagation of single plastic strain fronts that occur one after another through the sample due to the γ-α' phase transition and the Portevin-Le Chatelier effect. It was found that at the jerky flow stage, which is the final stage before the destruction of the sample, the centers of deformation localization do not merge, leading to the neck formation.

High temperature mechanical properties and strain hardening mechanism of directionally solidified Mg-Gd-Y alloy

The Mg-6.0Gd-0.5Y alloy, with straight grain boundaries and preferred growth orientation [224(_)3], was prepared by directional solidification. The microstructure evolution during tensile tests at 150–350 °C was investigated using Electron Back-Scattered Diffraction (EBSD) and High-Resolution Transmission Electron Microscopy (HRTEM). Subsequently, the relationship between the deformation mechanism and mechanical properties was discussed. The results show that there are obvious uniform plastic deformation stage and work hardening stage after yield for the tensile stress-strain curves of the Mg-6.0Gd-0.5Y samples tested at 150°C–250 °C, while evident dynamic recrystallization characteristic can be observed for the curve of the sample tested at 350 °C. It is found that the stable high-temperature strength of the Mg-6.0Gd-0.5Y alloy can be attributed to the delayed dynamic recrystallization, the formation of compression twins and I1-type stacking faults. In addition, the superior plasticity of the alloy is related to the high concentration of crystal orientation, the activation of tensile twins, and non-basal slip which can provide more than 5 independent systems.

Unveiling the microstructure evolution based on deformation mechanisms and dynamic recrystallization in as-extruded AZ31 Mg alloys during uniaxial compression

A series of uniaxial compression experiments were carried out on the as-extruded AZ31 Mg alloy with<10–10>-<11–20>//ED (extrusion direction) double fiber texture at 200–350 ℃. The microstructure evolution during the work hardening and dynamic softening stages were systematically investigated based on deformation mechanisms and dynamic recrystallization (DRX), respectively. Experimental and simulation results demonstrated that in the work hardening stage, the dominant deformation mechanisms were the basal<a>slip and {10−12} twinning at 250 ℃, while the basal<a>slip and prismatic<a>slip 350 ℃. The appearance of profuse {10−12} twins at 250 ℃ not only effectively refined the microstructure but also quickly promoted the formation of strong<0001>//CD (compression direction) texture. Moreover, the activation of twin variants was mainly dependent on their own Schmid factor that was higher in<10–10>//CD grains, resulting in the earlier disappearance of the<10–10>//ED texture component than the<11–20>//ED texture component. In contrast, owing to the limited of {10−12} twins, the samples at 350 ℃ exhibited a weak fiber texture with diffusely distributed of basal plane along the CD. In the dynamic softening stage, high temperature increased both the grain size and proportion of DRXed grains, resulting in a more homogeneous microstructure. More importantly, the continuous DRX (CDRX) transformed into discontinuous DRX (DDRX) as the temperature increased from 250 °C to 350 °C. The similar orientation between the new CDRXed grains and parent grains at 250 ℃ preserved the strong<0001>//CD texture, while at 350 ℃ the basal texture was significantly weakened due to the random orientation DDRXed grains and higher activation of pyramidal<c + a>slip. These findings are beneficial for the optimization of the temperature range of the MDF process.

Hot deformation constitutive model and processing maps of homogenized Al–5Mg–3Zn–1Cu alloy

Isothermal uniaxial compression experiments were performed in the range of 300–450 °C and 0.001 to 10 s −1 to clarify the hot deformation behavior of homogenized Al–5Mg–3Zn–1Cu alloy. The results revealed that the flow curves exhibited typical characteristics of DRV/DRX accompanied by the work-hardening, and the existence of three distinct stages of work-hardening, transition, and steady-state in each flow curve. A strain-compensated constitutive model for determining flow stress in this alloy was established with highly acceptable predictability. The dominant deformation mechanism of the alloy is dislocation climbing. Also, dynamic-material-model-based processing maps at various strains were constructed, and the unstable and workable domains were distinguished. Instability generally occurred in high strain rates and low temperatures zone with prevalent instability forms such as cracking and flow localization. The workable domain was 375–450 °C and 0.001–0.1 s −1 , in which the microstructure of the deformed alloy was characterized by dynamic recovery and multiple types of dynamic recrystallization. The dynamic precipitates were labeled as T-Mg 32 (AlZnCu) 49 phase. These intermittently distributed precipitates along the grain boundaries were stable in all temperature ranges, while the intragranular precipitates were inhibited at 300 °C. Temperature increment to 400 °C led to a large number of dispersed intragranular precipitates which redissolved into the matrix as temperature exceeded 450 °C.

Analysis of Tensile Deformation Behaviour of Dual Phase -590 Steel at Different Temperatures and Strain Rates

ABSTRACT An accurate uniaxial constitutive model is necessary to analyse the plastic deformation behaviour of metal and for reliable finite element simulations in sheet metal forming operations. In the present study, the hot uniaxial tensile flow stress analysis of dual phase (DP590) steel thin sheet has been carried out under a quasi-static strain rates of 0.1–0.001/s at the temperature range of 723–1073 K. The flow stress behaviour is significantly affected by test temperatures, strain rates and sheet orientations. Further, the Fields–Backofen constitutive flow relationship has been used to investigate the flow stress behaviour. This predicted flow stress curves shows a good fit to the experimentally measured stress at the work-hardening stage. Furthermore, a modified Fields–Backofen constitutive equation with a softening term has been considered to predict the flow behaviour. The capability of models has been evaluated based on the correlation coefficient (R), average absolute error AAE (Δavg) and root mean square error (RMSE). A better prediction of flow stress behaviour is observed by modified modified Fields–Backofen model with R = 0.9552, Δ = 0.034 and s = 0.0564.

Influence of Cold Rotary Swaging on Microstructure and Uniaxial Mechanical Behavior in Alloy 718

In this study, the influence of cold rotary swaging on microstructure and mechanical properties of the precipitation-strengthened nickel-based superalloy 718 (Alloy 718) was investigated. The initial stages of work-hardening were characterized by means of microhardness, electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) analyses. Furthermore, attention was devoted to the mechanical behavior at ambient and elevated temperature (550 °C) in uniaxial tension and compression. Rotary swaging to different true strains of maximum varphi = 0.91 caused a moderate increase of microhardness and enhanced markedly the load-bearing capacity in tension, giving rise to yield strength beyond 2000 MPa. The mechanical strength R_{p0.2} in tension subsequent to rotary swaging perfectly correlates with increasing dislocation density rho estimated from XRD in the form of a Taylor-like relationship R_{p0.2} propto sqrt{rho }. In compression, transient stress–strain evolution without the occurrence of a clear elastic range and distinct yield phenomenon was observed. Restoration of the elastic range, accompanied by a pronounced increase of microhardness, was obtained by a post-swaging tempering treatment at 600 °C.