Hot Tensile Behavior Research Articles

A statistical assessment of the equivalence between creep and hot tensile behaviour of 2.25Cr-1Mo steel

A statistical assessment of the equivalence between creep and hot tensile behaviour of 2.25Cr-1Mo steel

Effect of Ti micro-addition on the hot tensile behaviour, microstructure and fractography of low-C high-manganese steels

The aim of the work was to determine the effect of Ti micro-addition on the hot tensile behaviour, microstructure and fractography of two low-C high-manganese steels with additions of Si and Al. The hot tensile tests were performed using the Gleeble 3800 thermomechanical simulator. Samples were stretched at a temperature range from 1050 ℃ to 1200 ℃ at a strain rate of 2.5·10 3 s−1. The microstructure of the tested high-manganese steels under conditions of hot deformation was influenced by strain hardening and simultaneous dynamic recrystallization, as well as precipitation processes-depending on the chemical composition of the alloy and plastic deformation parameters. The analysis of the curves registered in the hot tensile tests indicated that a decrease of strain hardening was the result of the dynamic recrystallization. Hot tensile curves of the Ti-micro-alloyed steel were characterized by higher yield stress compared to the Ti-free steel. The Ti micro-addition with a concentration of 0.075 wt.% guaranteeing stable TiN-type nitrides eliminated the possibility of precipitating AlN-type nitrides and complex MnS-AlN type non-metallic inclusions, which are harmful to hot ductility. Fracture modes of the Ti-free steel showed a mixed nature from 1050 ℃ to 1150 °C, i.e. ductile fracture and numerous cavities and voids were identified. As the deformation temperature increased to 1200 °C, the fracture character was brittle with numerous inter-crystalline cracks along austenite grain boundaries. The addition of Ti improved significantly the hot ductility behaviour characterized by higher values of flow stress and reduction in area as well as ductile fracture modes in the entire high deformation temperature range.

Experimental study on effect of deformation temperature on mechanical and biological activities of Ti-6Al-7Nb titanium alloy

Titanium alloy plays a crucial role in biomedical applications, particularly in the field of medical implants. One of the most significant advantages of titanium alloy is its excellent biocompatibility. Eventhough, it offered excellent behaviour, at elevated temperature, titanium alloys may experience softening, which limits their application in environment with higher operating temperatures. In this investigation, hot tensile and biological behaviour of the Ti-6Al-7Nb under different operating temperatures (300 °C, 400 °C, 500 °C and 600 °C) is studied. The biological behaviour of the deformed Ti-6Al-7Nb titanium alloy treated with simulated body fluid is studied. The microstructure and phase transformation of deformed titanium alloy is evaluated using scanning electron microscope (SEM) and x-ray diffraction (XRD) respectively. It was revealed that at temperature of 600 °C, the mobility of molecules at the interface between the solid and liquid phases increases. This enhanced mobility can lead to better wetting of the solid surface by the liquid, resulting in a decrease in the contact angle. The elevated temperature facilitates improved grain development, recrystallization and mobility. The coarser grains could result from deformation at temperature higher than 600 °C. It was concluded that the Ti-6Al-7Nb titanium alloy deformed with 600 °C showed the improvement in contact angle of 42 ± 2° and biocompatibility.

Analysis of Hot Tensile Fracture and Flow Behaviors of Inconel 625 Superalloy.

In this work, Inconel 625 alloy is explored regarding high-temperature tensile deformation and fracture behaviors at a strain rate of 0.005-0.01 s-1 under a deformation temperature ranging from 700-800 °C. The subsequent analysis focuses on the impact of deformation parameters on flow and fracture characteristics. The fractured surface reveals that ductile fracture is dominated by the nucleation, growth, and coalescence of microvoids as the primary failure mechanisms. The elevated deformation temperature and reduced strain rate stimulate the level of dynamically recrystallized (DRX) structures, resulting in intergranular fractures. The Arrhenius model and the particle swarm optimization-artificial neural network (PSO-ANN) model are developed to predict the hot tensile behavior of the superalloy. It indicates that the PSO-ANN model exhibits a correlation coefficient (R) as high as 0.9967, surpassing the corresponding coefficient of 0.9344 for the Arrhenius model. Furthermore, the relative absolute error of 9.13% (Arrhenius) and 1.85% (PSO-ANN model) are recorded. The developed PSO-ANN model accurately characterizes the flow features of the Inconel 625 superalloy with high precision and reliability.

Characterization of the microstructure, texture, and tensile behavior of additively manufactured Hastelloy X superalloy: Insights into heat treatment at 900 °C

This research aimed at the microstructural characterization and elucidation of room- and high-temperature tensile properties of additively manufactured Hastelloy X Ni-based superalloy heat-treated at 900 °C. The samples were fabricated via the laser powder bed fusion method utilizing two scan strategies known as island and meander types. The results indicated that the cellular structure embedded in the columnar grains of the as-built microstructure disappeared after applying the heat treatment, linking to the reduction in dislocation density while keeping the former morphology of the grains unchanged. However, the intensities of the Brass, Goss, Goss-Brass, and rotated Goss texture components were reduced, leading to the generation of more homogenous fibers in the heat-treated microstructure. Additionally, it caused the formation of a Mo-rich phase on the grain boundaries, which improved the room temperature's ultimate tensile strength. However, it was elucidated that the Mo-rich phase-induced void formation and intergranular cracking failure caused a slight decrease in hot ductility. Overall, the obtained results revealed that the heat-treated island samples showed superior hot tensile behavior than the meander sample due to having a larger grain size.

Tensile Behavior and Microstructure Evolution of an Extruded 6082 Aluminum Alloy Sheet at High Temperatures

The hot tensile behavior of an extruded 6082 alloy sheet at varying temperatures and strain rates was investigated by a Gleeble3500 thermal simulation testing machine. The optical microscope (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were applied to observe the microstructure evolution. It is found that the flow stress of the studied alloy declines with increasing deformation temperature. When deformed at high temperatures, the density of dislocation decreases obviously. In addition, precipitate coarsening occurs, resulting in a decrease in deformation resistance. The dimple number of the fracture samples increases with temperature and the size of the dimple becomes deeper, exhibiting an excellent plasticity. The 6082 sheet presents anisotropy of mechanical behavior at 300 °C, this can be attributed to the fibrous grain and the Brass component {011}<211>. The anisotropic behavior seems to be slighter with an increase in temperature. No obvious anisotropic behavior was found when tensiled at 400 °C. Because it is easier to activate the slip system at elevated temperatures, meanwhile, the recrystallization begins to occur at 400 °C.

Constitutive modeling hot tensile behavior of Ti6Al4V alloy by considering phase transformation and damage mechanisms

The hot tensile and fracture behavior, as well as damage mechanisms of Ti6Al4V alloy are investigated by the hot tension tests and microstructure observation experiments. For comprehensively characterizing the hot tensile behaviors, a developed dislocation density-based constitutive model was established by coupling the flow softening, phase transformation and damage mechanisms. The results show that the flow stresses under the relatively high strain rates (0.01–1 s−1) easily peak at low strains and then decrease with the further straining. However, under the low strain rate (0.001 s−1), the flow stress tends to a continuously increasing trend until fractured. After hot deformation, the fraction of β phase greatly increases compared to that under the initial state. Meanwhile, β-phase fraction increases with the strain rate decreasing or the deformation temperature increasing. The great input thermal energy by the high temperature and the long deformation period under low strain rates promote the α-β phase transformation. Furthermore, the necking diffusion caused by dislocation motion enhances the homogeneous deformation under low strain rate or high temperature. The cavitations preferentially nucleate at the α/β phase interface due to the inconsistent strain. The comparison of the measured and calculated results confirms the excellent prediction ability of the established model in reproducing the hot tensile behavior, β-phase fraction and damage evolution under different processing parameters.

Study of hot tensile deformation behavior and microstructure characteristics of Zn-22Al microtubes using direct resistance heating-assisted tensile tests

To explore the deformation behavior of Zn-22Al alloy microtubes during hot forming processes with rapid heating, direct resistance heating (RH)-assisted tensile tests using microtubes are introduced based on their quick and easy temperature control. Notably, the large temperature difference of the sample during the RH-assisted tensile tests affected the accuracy of the tensile test results. To perform the RH-assisted tensile tests of the microtubes correctly, the specimens were designed with optimized structures of effective and total lengths of 30 and 60 mm, respectively. Better ductility was observed in the microtube drawn at 200 °C owing to the highly activated grain boundary sliding (GBS) caused by its uniform finer grain structure, greater high-angle grain boundary (HAGB) densities in the close-to-fracture area, and intergranular ductile fracture mode. The primary deformation mechanism of the microtube during hot forming was built based on hot tensile behavior, microstructure, and fracture surface analysis. It was also demonstrated that there is an intrinsic relationship between the temperature distribution, change in the microstructure of different parts, and multiple necking phenomena of the microtube formation process.

Studies on flow stress behaviour prediction of AZ31B alloy: Microstructural evolution and fracture mechanism

The hot tensile flow behaviour of the AZ31B alloy is investigated at various varying deformation temperatures (200–350 °C) and strain rates (0.1s−1, 0.01s−1, and 0.001s−1). The deformation condition significantly influenced the mechanical properties and microstructural evolution. Observation from the tensile tests indicated a strong dependence of flow stress on deformation temperature and strain rates. At a constant strain rate, flow stress decreased as the temperature increased, while at a constant deformation temperature, flow stress decreased with decreasing strain rates. The strain rate sensitivity varies from 0.01 to 0.25, suggesting a diffusion-controlled dislocation climb mechanism. Dynamic recrystallization (DRX) initiation was observed at 250 °C and a strain rate of 0.001s−1, characterized by the formation of necklace-type grains with low pole intensity. Predominantly, the DRX softening mechanism, including continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX), was observed at 350 °C and 300 °C for a strain rate of 0.001s−1. Fracture morphology analysis of the tested samples indicated a micro-void coalescence mechanism. Equiaxed dimples were found at 350 °C and a strain rate of 0.001s−1, while oval-shaped dimples were observed at 300 °C and 0.1s−1. A strain-compensated Arrhenius model was incorporated to estimate the flow stress prediction for hardening and softening regions. Statistical parameters such as the average absolute relative error (AARE = 13.50) and coefficient of determination (R = 0.97) were calculated. Good agreement between experimental and prediction stresses was achieved at a 0.001s−1 strain rate for all deformation temperatures.

Microstructural features and hot tensile behaviour of tungsten inert gas welded TP321 nuclear tubes at elevated temperatures

Austenitic stainless steel (ASS) tubes, specifically TP321, are widely used in nuclear reactors and heat exchangers due to their excellent strength, toughness, and corrosion at ambient and elevated temperatures. The microstructure observed in the TP321 weldment reveals the existence of equiaxed dendrites, along with delta ferrite and TiC precipitates within the austenitic matrix. Electron backscatter diffraction (EBSD) scans confirm differences in texture, grain size, and grain misorientation distribution in the weld metal (WM), heat-affected zone (HAZ), and base metal (BM) regions of the weldment. The EBSD texture at the WM zone is strong in the 〈0 0 1〉 fiber direction, consistent with the face-centered cubic structure of the TP321. Hot tensile tests were conducted on BM and WM samples at 450 °C, 550 °C, 650 °C, 700 °C, 850 °C, and 900 °C using a Gleeble 3500 simulator. The yield strength (YS), ultimate tensile strength (UTS), and percentage elongation (EL) exhibited a decreasing trend with the rise in test temperature. The strain hardening capacity (Hc) of both BM and WM decreases with increasing test temperatures due to enhanced dislocation movement. The strain hardening exponent, ‘n’ was determined for BM and WM through suitable fitting of stress–strain curves using the Hollomon equation and depicted a decreasing trend with rising test temperatures. The fractured samples are subjected to scanning electron microscope (SEM) analysis to investigate the failure mechanism. Fractography of the fractured samples reveal the presence of micro voids and dimples, supporting the ductile nature of the rupture.

Effect of 316L Stainless Steel Fabrication on Oxidation Resistance, Surface Morphology, and Hot Tensile Behavior

Samples based on 316L stainless steel were prepared by conventional manufacturing process (CM) and laser powder bed fusion (L-PBF). Surface morphology changes under air oxidation in the temperature range 600-900 °C were carried out. Tensile tests were carried out in the temperature range of 700-900 °C for strain rates between 0.001 and 0.1 s−1. The materials showed good oxidation resistance up to 700 °C. The CM and L-PBF material had a high mass gain instability and similar microstructures developed under high temperatures were found in both alloys. Increased temperature increases Cr concertation in the L-PBF material up to 40 at.% at 800 °C and a rich Fe based oxide is formed at 900 °C. Slightly thicker oxide scales were formed in the CM than in the L-PBF material.The hot tensile tests reveal that a fast work hardening occurs for all hot tensile tested samples up to a strain of approximately 0.025. Low temperatures and high strain rates within the investigated range promote a second work hardening regime, while a plateau in the flow stress is observed at high temperatures and low strain rates. The highest yield stress and peak stress values are reached at 700 °C. The yield stress is nearly independent of the strain rate at 700 °C. It decreases with a decrease in strain rate for 800 and 900 °C, and it decreases with an increase in temperature. The elongation till fracture varies from 10 to 22%, and it is strongly influenced by defects inherent of the L-PBF process.

Hot tensile behavior of a 7046-aluminum alloy: Fracture mechanisms and constitutive models

Hot tensile behavior of a 7046-aluminum alloy: Fracture mechanisms and constitutive models

The influence of the LPSO on the deformation mechanisms and tensile properties at elevated temperatures of the Mg-Gd-Zn-Mn alloys

The introduction of long period stacking ordered (LPSO) phase is an effective way to improve the performance of the magnesium alloys at elevated temperatures. In this paper, the hot tensile behaviors of two Mg-4Gd-1Zn-0.5Mn (wt.%) alloys with different lamellar LPSO volume fractions under the strain rate of 2.2 × 10–4 s –1 and at varied temperatures (150 °C–250 °C) were investigated. With the increasing of the deformation temperatures, the peak stresses of the alloy with lower volume fraction of the LPSO decreased (denoted as LL alloy). The hot tensile mechanical properties of the alloy with higher volume fraction of the LPSO (denoted as HL alloy) are significantly higher than those of LL alloy. When the deformation temperature was 250 °C, the LL alloys significantly underwent dynamic recrystallization (DRX) and the DRX dominated by discontinuous dynamic recrystallization (DDRX). However, the HL alloys did not have obvious DRX due to the lamellar LPSO hindering the grain boundary migration. The basal fiber texture of the alloy was produced after hot tensile. The deformation of the LL alloys was dominated by prismatic <a> slip during the hot deformation while the deformation of the HL alloys was dominated by the prismatic <a> slip and pyramidal <c+a> slip. The pyramidal <c+a> slip was activated by the Young's moduli mismatch between the α-Mg matrix and LPSO. Lamellar LPSO has an positive effect on strengthening the mechanical properties of the alloy which is attributed to the hinder of LPSO to non-basal slip, the prick function of kink to basal slip and the inhibition of LPSO to DDRX.

Investigation on the fracture mechanism and constitutive relations of a typical Ni-based superalloy

The hot tensile behavior of a typical Ni-based superalloy is elucidated using a microcomputer-controlled electronic universal testing machine at various deformation temperatures (920–1010 °C) and strain rates (0.001–0.01 s−1). Further, the influence of deformation parameters on the fracture characteristics is clarified. The results reveal that the tensile stress speedily rises to a peak level, beyond which it continuously declines until the final rupture. Moreover, numerous dimples exist on the fracture surface, and tenacity nests appear between adjacent dimples, suggesting that micro-void coalescence is the primary failure mechanism. Meanwhile, almost completed dynamic recrystallization (DRX) at elevated deformation temperature and slow strain rate promotes the intergranular fracture of the tested superalloy. Besides, an Arrhenius-type (AT) constitutive model and an artificial neural network (ANN) combined with particle swarm optimization (PSO) algorithms are established and validated. The maximum value of the mean absolute relative error (MARE) for the AT model is 9.74%, while it decreases to 4.20% for the PSO-ANN model. The correlation coefficient (R) increases from 0.9050 for the AT model to 0.9737 for the PSO-ANN model. Overall, it is demonstrated that the established PSO-ANN model has a high prediction performance and is an effective model for reproducing the hot tensile behavior of the tested superalloy.

Microstructure and hot tensile behavior of Hastelloy X superalloy laser powder-bed fusion-fabricated through different scanning patterns

Tailoring the microstructure of the additively manufactured metal parts through adjusting process parameters is a useful pathway to reduce the necessity of post-treatments, leading to a reduction in cost and production steps. This work deals with the effects of scanning patterns on microstructures and hot tensile behavior of the laser powder-bed-processed Hastelloy X Ni-based superalloy at the as-built condition. Two scanning patterns of meander and island were used to build fully-dense specimens. The scanning transmission electron microscopy observations revealed the generation of dislocation-cell structure within the columnar austenitic grains. Dense-dislocation tangles and some Cr- and Mo-rich precipitates decorated the cell walls. Both meander and island specimens had almost the same crystallographic texture, average local misorientation, and average geometrically necessary dislocations density. However, the specimen employing the island scanning pattern had a larger grain size and cell size than the meander one. It was due to a lower cooling rate in the island specimens than in the meander one. It was found that although the room-temperature tensile properties of both specimens were not significantly different, the island specimen had superior tensile properties at high temperatures. However, the meander and island tensile specimens both underwent intergranular brittle fractures at 760 °C and 860 °C, leading to ductility loss at elevated temperatures. The fractography observations illustrated that combined influences of the weakening of the grain boundaries with an increase in temperature and the accumulation of dislocations resulted in intergranular cracking, leading to brittle fracture and ductility loss at high temperatures.

Hot Tensile Deformation Behavior and Constitutive Models of GH3230 Superalloy Double-Sheet.

In this paper, the hot tensile deformation of a GH3230 superalloy double-sheet was conducted under deformation temperatures ranging from 1123~1273 K and strain rates ranging from 0.001~0.2 s-1. The flow behavior of the GH3230 superalloy double-sheet was analyzed in detail. The hot tensile deformation process of the GH3230 superalloy double-sheet includes four stages of elastic deformation, strain hardening, steady state and fracture. The true stress decreases with the increasing deformation temperature and decreasing strain rate. The variation of the strain rate sensitivity index and strain hardening index with processing parameters were discussed. The average apparent activation energy for hot tensile deformation is 408.53 ± 46.96 kJ·mol-1. A combined Johnson-Cook and Hensel-Spittle model considering the couple effect of strain hardening, strain rate hardening and thermal softening was established to describe the hot tensile behavior of the GH3230 alloy double-sheet. Compared to Johnson-Cook model and Hensel-Spittle model, this model has the highest predicting accuracy. The average absolute relative error of true stress between the experimental and the predicted is only 2.35%.

Hot tensile behavior of SiC-, NbC-, and MgO-reinforced LM25 metal matrix composites for high-temperature applications

Hot tensile behavior of SiC-, NbC-, and MgO-reinforced LM25 metal matrix composites for high-temperature applications

Analysis of hot tensile behaviour and prediction of thermal stresses during processing of AZ31 magnesium alloy

The use of magnesium alloys is rapidly increasing in automotive and aerospace industries. Accurate constitutive modelling of material at high temperature is a key input for numerical simulation of manufacturing processes. In the present work, hot tensile deformation behaviour of AZ31 alloy was studied by performing uniaxial tensile tests in the temperature range of 250°C–450°C and strain rates ranging from 0.1 to 0.001 s−1. The flow stress behaviour of AZ31 alloy was modelled using two rate-dependent inelastic models, viz. Garafalo law and extended Ludwik law. Various constants in these models were predicted as a function of strain rate and temperature. These rate dependent laws were integrated using Finite Element (FE) based algorithms for thermo-mechanical simulation. Evolution of thermal stresses in solid state quenching and static casting of AZ31 alloys were studied. Results reveal that both material models accurately predict the evolution of thermal stresses for high temperature quenching and casting processes.

Hot tensile deformation behaviour and microstructure evolution of Al3La phase reinforced Mg-5Li-3Al-2Zn alloy formed in-situ by La2O3 particle

In this study, LAZ532 alloy reinforced with Al 3 La phase in-situ precipitated by adding La 2 O 3 particle was fabricated by melting casting. The hot tensile deformation behaviour of the composite was investigated at deformation temperatures of 423 K ~ 573 K and strain rates of 8.3 × 10 −5 s −1 –1.7 × 10 −3 s −1 . The results indicated that the peak stress and elongation at fracture of the composite gradually decreased and increased respectively, with the deformation temperature increased or the strain rate decreased. In particular, the composite exhibited outstanding quasi-superplasticity with elongation to fracture up to 213% at 573 K and 8.3 × 10 −5 s −1 . Based on the results of theoretical calculation, the activation energy Q of the composite was 97.8 kJ/mol. In addition, by the observation and analysis of microstructure at different strains, the strain induced the precipitation of pearlite-like Al 3 La phase in the grains during hot tensile deformation. The deformation behaviour of the composite was a synergetic deformation mechanism dominated by GBS, supplemented by DDRX and intragranular slip, and the intragranular slip was dominated by prismatic and pyramidal I <c+a> slips. • The Mg Li composite exhibits excellent performance with tensile strength of 229 MPa at 423 K and 1.7 × 10 −3 s −1 . • The Mg Li composite exhibits excellent superplastic deformation ability with elongation of 213% at 573 K and 8.3 × 10 −5 s −1 . • Strain induced precipitation of pearlite-like Al 3 La particles in the grain during the thermal deformation. • The deformation behaviour is a synergetic mechanism dominated by GBS, supplemented by DDRX and intragranular slip.

Strain Rate Dependence of Hot Tensile Behavior, Microstructure Evolution, and Fracture Mechanism of Lean Duplex Stainless Steel 2101

To improve the hot workability of lean duplex stainless steel 2101 (LDX 2101), the effects of strain rate on the hot tensile behavior, microstructure evolution, and fracture mechanism of LDX 2101 are systematically studied. Results indicate that ferrite is softened by continuous dynamic recrystallization (CDRX) and austenite may start through a mechanism analogous to CDRX at the low strain rate of 0.1 s−1. A softening mechanism similar to the discontinuous dynamic recrystallization (DDRX) is observed both in ferrite and in austenite at the strain rate of 5 s−1. The main fracture mechanism is a void accumulation fracture mode. Cracks form and propagate into the ferrite due to the low softening degree of austenite at the strain rate of 0.1 s−1. As the strain rate increases to 5 s−1, the dynamic recrystallization behavior of austenite increases due to the accelerated accumulation of dislocations and the high storage energy. The microhardness and strain distribution difference between ferrite and austenite decreases, and the crack propagation trend weakens, thus improving the thermoplasticity. The findings are of great significance for understanding the thermoplasticity of LDX 2101 and other two‐phase alloys.