Tensile Deformation Process Research Articles

Mechanically robust and thermal-insulated polyimide aerogel films by polymerization-regulated strategy for flexible thermal protection

The development of flexible and foldable aerogels for thermal protection in harsh environments has been a long-term challenge as high porosity and weak interface connection can result in typical brittleness. Herein, a remarkable polymerization-regulated strategy was proposed to prepare polyimide (PI) aerogel films with high flexibility and efficient thermal insulation in extreme temperatures by using a facile phase-separation (PS-PI films) method. The polymerization degree of monomers was innovatively used to regulate the flexibility and mechanical properties of PS-PI films by slightly regulating the proportion of monomers. The results showed that the PI aerogel film realized the transition from brittleness to high flexibility, and the tensile strength and fracture strain of PS-PI films were increased by 3 times (11.7 MPa) and 4 times (18.7 %), respectively. Besides, a finite element model was established to analyze the tensile deformation process, revealing the destruction mechanism of aerogel film. The prepared PS-PI film also exhibited robust mechanical properties and efficient thermal insulation properties at extreme temperatures (−130 to 300 °C). The developed PS-PI film possessed high flexibility and efficient thermal-insulated performance at extreme temperatures, which could be a potential candidate for thermal protection in aerospace, energy, and buildings.

Effect of friction stir welding with different heat input on microstructure evolution, mechanical properties and deformation behavior of twin-induced plasticity steel

The effect of friction stir welding (FSW) with different heat input on microstructure evolution, mechanical properties and deformation behavior of twin-induced plasticity steel was investigated in this paper. The results show that compared to the basal material (BM), the grain size in the stir zone (SZ) of FSW joint with low heat input was refined, and a large amount of deformation twins was formed. The grain was refined and numerous dislocations were formed in the stir zone-heat affected zone (SZ-HAZ) interface. In the FSW joint with high heat input, the grain size in SZ increased, while no deformation twins were observed. A large number of fine equiaxed grains were formed in the SZ-HAZ interface, while the grains in HAZ coarsened. Compared to the BM, the tensile strength and yield strength of low heat input joint increased to 1108 MPa and 597 MPa, respectively, while the elongation decreased to 50.4%, resulting in a strength-elongation product of 92% of BM. The joint with high heat input experienced a decrease in tensile strength, yield strength, and elongation to 806 MPa, 465 MPa, and 22.8%, respectively, with a strength-elongation product of only 30% of BM. During the tensile deformation process, the plastic deformation in the low heat input joint was mainly concentrated in BM, followed by HAZ, while SZ exhibited minimum plastic deformation, and the tensile fracture occurred at zone between SZ and HAZ. In the high heat input joint, the maximum plastic deformation occurred in the SZ, with lower plastic deformation in BM and HAZ, and finally fractured at the SZ. The constrain effect of different micro-zones and hindrance effect of dislocations and fine grains were main responsible for the deformation behavior of low and high heat input joints.

The strength contribution via heterostructure in a Mg-Gd-Zn-Mn alloy

Deformation by extrusion is an effective means to enhance the performance of magnesium alloys. However, the resulting microstructure heterogeneity always lead to poor plasticity. Therefore, it is crucial to explicit the impact of heterogeneous structure on the deformation mechanism of the alloys. In this work, the microstructures evolution, mechanical properties, and fracture mechanism of Mg-xGd-1Zn-0.5Mn (x = 0, 2, 4, and 6) alloys were investigated. The elongation reached its maximum (40%) when the Gd content was 2%, which was attributed to the formation of the RE-texture and grain refinement. As the Gd content was further increased, the alloy developed a heterostructure consisting of both undynamic recrystallization (UDRX) grains and dynamic recrystallization grains (DRX). The exist of the heterostructures resulted in an increased strength which was attributed to the influences of texture strengthening derived from UDRX grains, the lamellar LPSO fiber strengthening and fine grain strengthening of DRX grains. At the initial stage of deformation in the heterostructure, the basal slip of DRX grains play a dominant role, while the UDRX grains strengthens the alloy effectively. The lamellar LPSO precipitated in the UDRX grains suppressed twinning effectively. As the concentrated stresses were enough to break through the barrier for twining of LPSO, numerous twins nucleated in the deformed grain thus resulting in the nucleation of cracks. During the process of tensile deformation, twins experienced greater basal slip resolved shear stress than that of the parent grains, resulting in significant basal slip activated due to twin. Consequently, there was a high stress concentration at the twin boundaries, leading to the nucleation of cracks. The varied deformation amount also resulted in the crack initiating at the interface of DRX grain and UDRX grain. This investigation provides valuable insights into the influence of a heterostructure on the deformation mechanism of Mg-Gd-Zn-Mn alloys.

FABRICATION AND PROPERTIES OF HIGH-CHROMIUM CAST IRON DISPERSED STEEL MATRIX COMPOSITE

Composites with high-chromium cast iron (HCCI) dispersed in a steel matrix were prepared using the multilayer rolling-forming method. The macroscopic morphology, microstructure and tensile properties of the bimetal composites were analyzed. The experimental results showed that brittle HCCI layers were necked and broken into uneven blocks or granules after hot-rolling forming. The fractured HCCI was encased in carbon steel completely, and the two metals achieved good metallurgical bonding. The Fe, Cr, Mn and C elements were diffused at the interface. The tensile strength of the composite was better than that of the as-cast iron. During the process of tensile deformation, the composite displayed a complex crack propagation rather than a fracture caused directly by brittleness. The damage tolerance and energy absorption capacity of the bimetallic composite were improved with a decentralized structure.

An atomistic simulation study on ductility of amorphous aluminum oxide

Aluminum oxide is a widely recognized structural ceramic material known for electrical insulation and wear/corrosion resistance. Recent studies have challenged the conventional perception of brittleness by uncovering remarkable plasticity in amorphous aluminum oxides. To further enhance the fracture toughness of aluminum oxides and expand their applications in fields requiring resistance, it is crucial to analyze the factors influencing the tensile deformation process and investigate the underlying origins of ductility. In this study, molecular dynamics simulations were employed to compare the ductility of amorphous aluminum oxides with crystalline aluminum oxides and other amorphous ceramic oxides. Our findings indicate that the degree of crystallinity significantly influences ductility. Moreover, the simulations revealed that amorphous aluminum oxides exhibit the highest total elongation among binary structural ceramic oxides such as TiO2 and SiO2, underscoring the intrinsic plasticity of aluminum oxide. Furthermore, we discovered that aluminum oxides possess a low bond-dissociation energy (EBD) compared to other structural ceramic oxides, leading to a higher occurrence frequency of plastic deformation mechanisms. Based on these observations, low EBD could be proposed as the probable indicator that enables the estimation of ductility of structural amorphous oxides without resorting to complex atomistic simulations. This quantitative criterion, based on an easily accessible material property, provides valuable guidance for predicting the ductility of newly-designed structural ceramic materials.

Microstructure-Sensitive Deformation Modeling and Materials Design with Physics-Informed Neural Networks

Microstructure-sensitive materials design has become popular among materials engineering researchers in the last decade because it allows the control of material performance through the design of microstructures. In this study, the microstructure is defined by an orientation distribution function. A physics-informed machine learning approach is integrated into microstructure design to improve the accuracy, computational efficiency, and explainability of microstructure-sensitive design. When data generation is costly and numerical models need to follow certain physical laws, machine learning models that are domain-aware perform more efficiently than conventional machine learning models. Therefore, a new paradigm called the physics-informed neural network (PINN) is introduced in the literature. This study applies the PINN to microstructure-sensitive modeling and inverse design to explore the material behavior under deformation processing. In particular, we demonstrate the application of PINN to small-data problems driven by a crystal plasticity model that needs to satisfy the physics-based design constraints of the microstructural orientation space. For the first problem, we predict the microstructural texture evolution of copper during a tensile deformation process as a function of initial texturing and strain rate. The second problem aims to calibrate the crystal plasticity parameters of the Ti-7Al alloy by solving an inverse design problem to match the PINN-predicted final texture prediction and the experimental data.

Tailoring phase transformation and precipitation features in a Al21Co19.5Fe9.5Ni50 eutectic high-entropy alloy to achieve different strength-ductility combinations

Eutectic high-entropy alloys (EHEAs) that combine the advantages of HEAs and eutectic alloys are promising materials for high-temperature environments. However, the mechanical properties of currently developed EHEAs still cannot meet the servicing requirements. Here, we propose a strategy to optimize the tensile properties in a Al21Co19.5Fe9.5Ni50 EHEA by regulating the phase transformation and precipitation features. The results showed that the as-cast Al21Co19.5Fe9.5Ni50 EHEA mainly consists of face-centered cubic (FCC) and B2 phases showing a lamellar morphology, and the FCC and B2 phases keep a stable K-S orientation relationship. Solution treatment at 900 and 1100 °C followed by furnace cooling to room temperature leads to a significant precipitation of L12 phases within the FCC phases. In the subsequent tensile deformation process, dispersed L12 phases and the transformation from B2 to L10 phases can significantly enhance the yield strength of the designed EHEA. Furthermore, solution treatment at the same temperature, followed by rapid water quenching, results in the appearance of numerous L10 phases within the B2 phases. The transformation from L10 to B2 phases during subsequent tensile deformation can make the B2 and FCC phases return to a K-S orientation relationship. This, in turn, reduces the tendency for dislocation pile-ups at the phase interfaces and improves the ductility. We believe that this work will provide some new references for designing EHEAs with excellent mechanical properties.

Role of cluster structure on the deformation behavior of Zr58Cu36Al6 metallic glass

Molecular dynamics simulations were used to simulate the process of tensile and compressive deformation of Zr58Cu36Al6 metallic glass (MG), and the variations of various cluster structures during the deformation were analyzed by the Voronoi tessellation method. The prepared Zr58Cu36Al6 alloy was found to be amorphous and the glass transition temperature obtained was about 753 K. In the deformation processes, the icosahedral-like clusters with the biggest quantity percentage decreased significantly and eventually, the damaged icosahedral-like clusters tended to be destroyed into "fragmented" clusters. Icosahedral-like clusters were more stable due to their lower average strain and shear stress compared to other clusters. The higher strain and shear stress of the clusters led to an earlier stress drop of Zr58Cu36Al6 MG during compression. However, the higher connectivity of the icosahedral network remained in Zr58Cu36Al6 MG making the overshoot stress and flow stress larger but lower plasticity in compression than those in tension.

Effect of hydrogen embrittlement on the safety assessment of low-strength hydrogen transmission pipeline

Currently, no systematic approach exists for the safety assessment method of hydrogen transmission low-strength pipeline, it is necessary to study the effect of hydrogen embrittlement (HE) on the method of failure assessment diagram (FAD) for the defective pipe. The hydrogen charging experiments of tensile and Charpy impact specimens for the L245 pipe steel were carried out with charging time of 0, 30, 90, and 120 h, and then the tensile and Charpy impact tests were immediately conducted. The HE indexes of tensile and Charpy impact properties were presented to quantitatively analyze the effect of HE under tensile and impact deformation processes. Subsequently, the FAD method coupled with the effect of HE was investigated to analyze the difference in the safety assessment method between hydrogen and non-hydrogen environments. Finally, the fracture morphology of tensile and Charpy impact specimens was observed to analyze the responses of microscopic fracture modes between hydrogen and non-hydrogen environments. The results show that the effect of HE on the tensile properties of the base material is more sensitive than that of the weld joint. The FAC with the effect of HE for safety assessment of defective pipes shrinks by reducing the safe zone. The decrease ratio of safety factors affected by HE presents an increasing tendency as the increase of crack depth while showing a decreasing tendency as the increase of internal pressure.

Effect of Plastic Deformation and Acidic Solution on the Corrosion Behavior of Ti-6Al-4V ELI Titanium Alloy

This study investigated the tensile deformation of Ti-6Al-4V ELI titanium alloy and its effect on corrosion performance. The results showed that the structural morphology of the samples’ strain levels of 0%, 5%, and 10% had minimal changes under an optical microscope. Further investigation of grain orientation information was conducted using electron backscatter diffraction (EBSD), revealing that tensile deformation induced grain rotation, resulting in the diversity of originally preferred orientation grains and a decrease in texture strength. A small amount of {10–12}<−1011> extension twinning formed during the tensile deformation process. The electrochemical properties of Ti-6Al-4V ELI samples with different strain levels were evaluated in 3.5% NaCl solution with pH values of 7 and 1.5. The results indicated that both plastic deformation and acidic environments were detrimental to the passivation film on the titanium alloy surface, leading to reduced corrosion resistance.

Significant improvement of mechanical properties of cold-spray-additive manufactured FeCoNiCrMn high-entropy alloy via post-annealing

In this work, equimolar FeCoNiCrMn high-entropy alloy (HEA) was fabricated by solid-state cold spray additive manufacturing (CSAM) technique and post-annealed. The microstructure evolution and mechanical properties of the deposits before and after annealing were systematically evaluated. The tensile test results revealed that the deposit annealed at 1000 °C for 2 h exhibited an excellent combination of tensile strength and ductility, with a doubled ultimate tensile strength of 455 MPa compared with the as-sprayed and significantly improved elongation (28%). The improved strength can be attributed to the healing of micropores and interparticle interfaces in the deposit due to the interface diffusion induced by high temperature. The recovery of ductility is the result of a significantly decreased dislocation density and enhanced metallurgical bonding at interfacial regions. For the first time, the current work demonstrated that the combination of CSAM and post-annealing strategy could achieve the strength-ductility synergy of HEA deposits. The results of in-situ analysis show that the mechanism of tensile deformation process includes particle separation, and it can be inferred that the preparation of dense sediments combined with post-treatment is the direction of further optimization.

Enhanced strength and ductility in friction stir processed Cu–Mn alloys

In this study, the ultrafine-grained (UFG) Cu–5Mn alloys were prepared by friction stir processing (FSP) to investigate the influence of short-range ordering (SRO) on the tensile deformation behavior. Due to the dynamic recrystallization, the uniform and equiaxed UFG microstructures were obtained in FSP Cu–5Mn alloys with low density of dislocations, high fraction of high-angle grain boundaries, high Taylor factor and high degree of recrystallization. The introduction of Mn atoms into the Cu matrix cannot change the stacking fault energy apparently but increase the SRO degree. Although the dominant mechanism was still the wavy slip of dislocation, the planar slip of dislocations was motivated and many twin layers were observed in the ultrafine grains of FSP Cu–5Mn alloy. The change of SRO degree can significantly improve the dislocation storage capacity during the tensile deformation process, and promote the improvement of the strain-hardening rate, resulting in an excellent strength-ductility match in FSP UFG Cu–5Mn alloy.

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%.

Study on quasi-in-situ tensile microstructure evolution law of 5052-O aluminum alloy based on EBSD

SHIMADZU AGS-100KN universal testing machine was used to carry out tensile experiments of 2.2%, 5%, 10%, 15%, 20% and 25% of different tensile elongations on 5052-O aluminum alloy. The surface DIC morphology characteristics and the evolution law of the microstructure of samples under different elongation rates were studied by the DIC (digital image correlation) and the EBSD (electron backscatter diffraction). The results show that the tensile strength of the 5052-O aluminum alloy reaches the maximum value of 205.632 MPa and the elongation at failure is 28.8%. When the tensile deformation is 2.2%, there is an obvious slip band at 45° to the direction of the tensile axis. At 10% deformation, the slip band is obviously narrowed, with darker interior color and large deformation. With the gradual increase of the deformation, the proportion of the microstructure recrystallization area and the substructure area decreases, and the proportion of the deformation area increases. The plastic deformation mechanism is mainly the dislocation slip. The low angle grain boundary gradually increases and the high angle grain boundary decreases as the increase of deformation. When the deformation is above 15%, the changing trend of low-angle and high-angle grain boundaries also slows down. During the tensile deformation process, the corresponding KAM (Kernel Average Misorientation) value distribution curve value is constantly moving to the right and expanding. The R-type texture {124}< 211 > always exists, the Brass texture {110}< 112 > and the S-type texture {123}< 634 > keep increasing. • During the quasi-in-situ tensile test of the 5052-O aluminum alloy sample, the change of the sample morphology was continuously recorded by DIC. It can dynamically observe the microstructure changes of the specimen during the tensile process. • EBSD was used to study the evolution of grain orientation, the change of recrystallization region and the statistics of crystallographic orientation difference of specimens under different deformations during tensile deformation. It reveals the stress concentration mechanism in the deformation region and discusses the evolution of texture after tensile deformation. It provides some theoretical basis for the process optimization in industrial production. • Through the analysis of the texture evolution, the R-type texture {124}< 211 > existed during the deformation process. The Brass texture {110}< 112 > and S-type texture {123}< 634 > continued to increase with the tensile deformation increased.

Enhancing the strength–ductility synergy of medium-Mn steel by introducing multiple gradient structures

In this study, novel multiple gradient structures with various distributions of austenite/martensite phase, grain sizes, and dislocation densities were fabricated in medium-Mn steel by using torsion treatment, and the corresponding tensile properties and deformation mechanisms were investigated. The results showed that the yield strength and the total elongation of the multiple-gradient-structured samples increased by 27% and 25%, respectively, compared with their homogeneous counterparts. A distinct phase transformation behavior was observed in the present gradient medium-Mn steel. That is, the strain-induced martensitic transformation was promoted in the center during the entire tensile deformation process; however, it was suppressed at the surface during the initial deformation stage and then significantly triggered during the remaining deformation process. Moreover, active strain partitioning at the macroscale and microscale occurred during plastic deformation, which led to a higher hetero-deformation induced (HDI) stress in the multiple-gradient samples. A combination of a strong and persistent transformation-induced plasticity effect, active HDI strengthening and HDI hardening, and dislocation strengthening contributed to the superior strength–ductility synergy of the gradient-structured medium-Mn steel.

A rolled Mg−8Al−0.5Zn−0.8Ce alloy with high strength-ductility synergy via engineering high-density low angle boundaries

Developing low-cost rolled Mg alloys with both high strength and ductility is desirable, while the improved strength is generally accompanied with decreased ductility. Here, by using rotated hard-plate rolling (RHPR) with a total thickness reduction of ∼85%, we obtained a Mg−8Al−0.5Zn−0.8Ce (wt.%, AZ80−0.8Ce) alloy with a high strength-ductility synergy, i.e., the yield strength (YS), ultimate tensile strength (UTS) and elongation-to-failure (EF) are ∼308 MPa, ∼360 MPa and ∼13.8%, respectively. It reveals that the high YS is mainly originated from grain boundary strengthening (∼212 MPa), followed by dislocation strengthening (∼43 MPa) and precipitation hardening (∼25 MPa). It is found that a relatively homogeneous fine grain structure containing a large fraction (∼62%) of low angle boundaries (LABs) is achieved in the RHPRed alloy, which is benefit for the high tensile EF value. It demonstrates that LABs have important contributions to strengthening and homogenizing tensile deformation process, leading to the simultaneous high strength and high EF. Our work provides a new insight for fabrication of low-cost high performance Mg alloys with an excellent strength-ductility synergy.

DIC/DSI based studies on the local mechanical behaviors of HR3C/T92 dissimilar welded joint during plastic deformation

In this study, both the digital image correlation (DIC) and depth-sensing indentation (DSI) measurements were performed to investigate the non-uniform local mechanical behaviors of HR3C/T92 dissimilar welded joint during plastic deformation. The macro-scale DIC experiments showed the uneven distribution and transfer phenomena of the plastic deformation in the welded samples. The grain-scale DIC measurements further revealed that the strain localization was closely related to the local microstructures. To understand the correlation of the non-uniform deformation behavior with the local microstructure in the welded samples, the electron backscatter diffraction (EBSD) tests in the as-received state and ex-situ optical microscope (OM) observations during the tensile deformation process were conducted. The slip morphologies were found to be different across the welded joint, and the grain-scale strain localizations were proved to be closely related with the behaviors of the slip bands. Moreover, ex-situ DSI tests were also carried out to determine the local mechanical properties of the HR3C/T92 dissimilar welded joint during the tensile deformation process. The basic elasto-plastic properties (elastic modulus, yield strength, and hardening parameters) in particular zones of the welded joint were estimated by using the multi-fidelity deep neural network method combined with indentation characteristic parameters. The non-uniform deformation behavior of the HR3C/T92 welded joint during tensile loading was further simulated by using the finite element method based on the estimated elasto-plastic properties of the welded joint, and a general agreement between the simulated result and experimental tensile curve has been obtained.

Acoustic and thermal energy evolution of AZ31B magnesium alloy under static tensile deformation

Based on the complexity of material damage and fracture behavior, the tensile deformation process of AZ31B magnesium alloy is characterized by infrared thermography (IR) and acoustic emission (AE) these two non-destructive technologies, and using in-situ EBSD technology to explore microstructure evolution under different tensile strains simultaneously. The results show that in the process of tensile deformation, the degree of strain hardening increases continuously with the deformation, and the deformation mechanism of the material changes from basal slip to pyramidal slip and {10–12} tensile twinning. The tensile deformation stage presents different signal characteristics. Using fracture mechanics and the energy release law of materials, combined with temperature and AE signal fluctuations, the transformation of the deformation mechanism, the degree of work hardening, and the dangerous zone during the entire tensile process can be effectively captured.

Real‐time observation of microcrack growth in thin film microtomed from rubber/nanocellulose composite sheets, during tensile deformation

AbstractRubber/nanocellulose composite sheets improve tensile properties compared with neat rubber sheets, when nanocellulose materials are suitably compounded with rubber matrices. First, two oven‐dried nanocellulose materials containing different additive components were prepared from nanocellulose/water dispersions, and the oven‐dried nanocellulose‐containing materials were compounded with rubber sheets under high shear forces by using a two‐roll mill. The tensile moduli and strength of the rubber/nanocellulose composite sheets were clearly better than those of the rubber sheet prepared without nanocellulose, while the elongations at break were similar. Thin films were cut from the rubber/nanocellulose composite sheets, and their real‐time tensile deformation processes were observed by transmission electron microscopy (TEM) to understand the time‐dependent patterns of crack propagation, void formations, and fusion between cracks and voids in the composites during tensile deformation. TEM observations showed that the composite sheets consisted of individual rubber/nanocellulose clusters. Voids initially formed inside the rubber/nanocellulose clusters, propagated to form cracks, fused with other voids or secondary cracks. There were slight differences between the crack‐propagation patterns of the two rubber composites, probably because of differences in the morphologies, sizes, distributions, and structures of the rubber/nanocellulose clusters, and surface chemical structures of individual nanocellulose elements between the composites.

In Situ Tensile Deformation and Mechanical Properties of α Platelets TC21 Alloy.

The present study was focused on the relationship between an α platelet microstructure and the properties of TC21 alloy, and the tensile deformation process was revealed by in situ observation. To obtain the α platelet microstructures, the samples were administered a solution treatment (1000 °C for 15 min) and then cooled to room temperature by different cooling methods (furnace cooling (FC), open-door furnace cooling (OFC), air cooling (AC), and water quench (WQ), corresponding to an increased cooling rate). It is found that α platelets become thinner and colonies become narrower with the increase in cooling rate. The formation of the platelet microstructure is based on the preferred Burgers orientation relationship of {110}β//{0001}α and <111>β//<110>α. The α platelets orientation changes with the cooling rate. These differences in α platelets thickness and orientation result in the excellent ductility of the sample with thick platelets and the high strength of the samples with thin platelets. During the in situ tensile deformation process, the crack propagation path is deflected in the presence of grain boundaries, α platelets, and α colonies with different orientations. The fracture of the sample with thick α platelets shows better ductility compared to those with thin α platelets.