Tensile Deformation Process Research Articles

Revealing the deformation mechanisms of the heterogeneous structured CrMnFeCoNi high entropy alloy with ameliorated mechanical and corrosion resistance properties

Developing high entropy alloy (HEA) with both high strength and ductility is a longstanding challenge as potential structural materials. The strength and ductility trade-off can achieve via tailoring heterogeneous structures. Herein, a gradient structure with grain size variation from surface to center was successfully introduced into the CrMnFeCoNi HEA by ultrasonic nanocrystal surface modification (UNSM) process. More importantly, the deformation mechanisms and strengthening mechanisms of the heterogeneous structured CrMnFeCoNi HEA during tension were also investigated. Experimental results demonstrated that the heterogeneous structured CrMnFeCoNi HEA shows excellent strength and ductility combination properties ascribed to the grain refinement strengthening, dislocation density strengthening, and twinning strengthening. Besides, the corrosion resistance properties are also simultaneously improved, resulting from the low surface roughness, small grain size, and large compressive residual stress value. During tensile deformation process, the deformation mode is the dislocation slip at low strain and the slip system of the alloy is mainly {111}〈110〉. With the increase of deformation amount, twin crossing occurs, and grain size gradually decreases. The deformation mode changes from dislocation slip to twinning at high strain. In conclusion, the UNSM process ameliorates the comprehensive mechanical and corrosion resistance properties of CrMnFeCoNi HEA.

The deformation behavior of the gradient nanostructured microstructure of low-carbon steel under the tensile stress

A microstructure within the gradient structure was successfully prepared using the ultrasonic impact treatment (UIT), achieving good strength to toughness synergy. Specifically, the diffraction peak on the surface of the gradient microstructure had a certain broadening effect. Furthermore, the grain size in the gradient deformation layer with a thickness of about ∼150 μm was coarsened from about 100 nm in the top layer (∼10 μm) to about 10 μm in the matrix layer (∼250 μm). Meanwhile, the tensile strength and yield strength of the sample after the UIT were increased by 12.1% and 60.0% respectively. This result was mainly attributed to the fact that the gradient structure could inhibit strain localization in tensile deformation, improving the mechanical properties through the synergistic effect of surface strengthening and bulk toughness. Digital image correlation (DIC) technology was used to observe the displacement characteristics of the sample during the tensile deformation process and the strain change near the fracture. The results showed that the gradient layer could disperse the stress and inhibit the strain localization. The geometrically necessary dislocation (GND) density of the GNS sample after tensile fracture was lower than that of the original sample.

Hot tensile deformation mechanism and microstructure evolution of Mg 2Nd alloy with heterostructure

The deformation mechanism and microstructure evolution of the extruded Mg2Nd alloy were investigated in the hot tensile deformation process at strain rate of 2.2 × 10−4 s−1 and deformation temperatures of 150 °C–300 °C. the results showed that the peak stress declines and the elongation to fracture increases with the increasing of deformation temperature. By observation of the microstructure, the fibrous extrusion zones (FEZs) and non-fibrous extrusion zones (non-FEZs) coexist in the alloy, and the microstructure deformation of the FEZs is more obvious than that of the non-FEZs. In the initial deformation stage, the grain deformation first occurs in the FEZs. In the later deformation stage, recrystallization occurs in both FEZs and non-FEZs. Moreover, the deformation mechanism of the FEZs is different from that of the non-FEZs. The deformation mechanism of the FEZs is dominated by intragranular slip, supplemented by grain boundary slip (GBS). The recrystallization mechanism in FEZs is continuous dynamic recrystallization (CDRX). On the contrary, the deformation of the non-FEZs is dominated by GBS, while the intragranular slip plays a coordinated role. The recrystallization mechanism in non-FEZs is discontinuous dynamic recrystallization (DDRX). Therefore, the dominated hot tensile deformation mechanisms of the alloys are alternated among intragranular slip, GBS and dynamic recrystallization (DRX)

Uniaxial tensile deformation and fracture process of structures forming by unsaturated intercalation of amine molecule into C-S-H gel.

The application of cement-based materials in engineering requires the understanding of their characteristics and subsequent deformation and fracture process of C-S-H gel in service. In this work, three types of amine molecules including tetraethylenepentamine (TEPA), polyacrylamide (PAM), and triethanolamine (TEA) were intercalated into C-S-H gel in an unsaturated statussuccessfully. Systematical analysis was performed on the structures and properties for both C-S-H gel and corresponding amine molecules/C-S-H gel. It was found that the unsaturated intercalation of amine molecules into C-S-H gel plays a key role in the geometry and therein density of nanocomposites. Subsequently, radial distribution function (RDF), time-correlated function (TCF), and mean square displacement (MSD) were applied to characterize the structure and dynamic information of the as-generated nanocomposites, demonstrating the occurrence of interaction between amine molecules with Ca-Si layer and acceleration of water diffusion by unsaturated intercalation of amine molecules into the interlayer region in C-S-H gel. Finally, the deformation and fracture process of C-S-H gel and amine molecules/C-S-H gel under uniaxial tensile loads were given by molecular dynamics simulation. It was indicated that the tangent modulus of nanocomposites demonstrates a strain-softening nature, indicating a visco-elastic behavior. The breakage of Ca-O bonds and hydrogen bonds dominates the fracture of C-S-H gel. Weak interaction for TEPA/C-S-H gel or TEA/C-S-H gel leads to a decreased tensile strength. Local stress concentration in other interlayer region governs the deformation and fracture process in spite of the formation of strong interaction between double bonded polar oxygen atoms in PAM molecules and Ca atoms in C-S-H gel.

Preparation and application of a stretchable, conductive and temperature-sensitive dual-network nanocomposite hydrogel

Conductive hydrogel has received extensive attention in the design and application of flexible electronic equipment, due to its flexibility, easy processing, good sensitivity and excellent electrochemical performance. In this study, we designed a stretchable conductive and temperature-sensitive dual-network nanocomposite hydrogel in a simple one-pot method. Fourier transform infrared (FTIR), scanning electron microscopy （SEM） and thermogravimetric analysis (TGA) were used to characterize the nanocomposite hydrogel. The formation of the double cross-linked network greatly improves the mechanical properties of the nanocomposite hydrogel, and continuous electron transport path formed by MWCNTs dispersed in a hydrogel network endows the nanocomposite hydrogel great conductive behavior and the hydrogel exhibited a stable relative resistance change during the tensile deformation process. The nanocomposite hydrogel displayed great application potential in wearable devices, smart robots, and flexible strain sensors.

Microstructural evolution of a polycrystalline cobalt during tensile deformation

The microstructural evolution of cobalt during tensile deformation was investigated via electron back scatter diffraction and transmission electron microscope. The undeformed sample has an almost pure hexagonal closed-packed structure, and there exist a large number of special boundaries with a 70.5°/<112‾0> misorientation. Twinning dominates the tensile deformation process, especially the {101‾2} twins. When the strain reaches 15%, the volume fraction of the twins reaches up to 61%. Meanwhile, {101‾2}−{101‾2} double twinning and even {101‾2}−{101‾2}−{101‾2} triple twinning are triggered, which work together with primary twins and martensite phase transformation to refine the grains. In addition, two different formation modes of special boundaries with misorientation of 39°/<112‾0> are observed. One is formed by partial dislocations slipping, and the other is formed by {101‾1}−{101‾2} double twinning.

Atomistic simulations of effects of Zr solute and loading mode on mechanical behavior of nanocrystalline Cu

The effects of Zr solute and loading mode on the structure, mechanics, and mechanical properties of nanocrystalline (NC)-Cu are studied using molecular dynamics simulations. Doping Zr atoms into NC-Cu systems stabilizes grain boundaries, suppresses dislocation nucleation and propagation, and increases the elastic deformation phase during tensile, compressive, and shear deformation processes. The tensile and shear strengths of NC-Cu/Zr systems are maximum at Zr concentrations of 5% and 3%, respectively. Young's modulus and mechanical strength of NC-Cu/Zr systems under compression both decrease with increasing Zr concentration. Grain boundary sliding dominates shear deformation and induces dislocation activity.

Investigation on thermo-mechanical processing and intergranular corrosion of TP347H stainless steel

The grain boundary character distributions of TP347H stainless steel after different thermo-mechanical processes in terms of grain boundary engineering (GBE) were investigated by EBSD. DL-EPR and electrolytic oxalic acid etch tests were carried out to evaluate the improvement of GBE treatment on intergranular corrosion. The low-Σ CSL grain boundary proportion of the TP347H can be increased to about 90% through a single-step thermo-mechanical treatment consisted of a slight tensile deformation (3%) and subsequent annealing process at 1150°C for 1 h. Compared with conventional TP347H, the optimum GBE microstructure suppressed intergranular corrosion due to the high proportion of low-Σ CSL grain boundaries, particularly the twin (Σ3) boundaries which is almost immune to intergranular corrosion.

Image-based numerical modeling of the tensile deformation behavior and mechanical properties of additive manufactured Ti–6Al–4V diamond lattice structures

This work concerns the numerical modeling of the deformation process and mechanical properties of structures obtained by the additive method laser power bed fusion (LPBF). The investigation uses diamond structures of Ti–6Al–4V titanium implantation alloy with various relative densities. To model the process of tensile deformation of the materials, geometric models were used, mapping the realistic shape of the examined structures. To recreate the geometry of the samples, computed tomography (CT) and microtomography (micro-CT) were used, which allowed to obtain two accuracy levels of the mapping details of the investigated structures shape. Taking into account the nonlinearity of the material in the computational model makes it possible to model the deformation process of cellular materials until the fracture initiation. On the basis of the performed calculations using the finite element method (FEM), the stress and strain distributions in deformed structures were obtained and analyzed. The relationship between the shape of cellular structures and their effective mechanical properties on a macroscopic scale was investigated. The influence of the accuracy of the structures shape mapping on their strength properties and stress and strain distributions was also described. On the basis of the conducted research, fracture initiation localizations in titanium cellular structures were indicated. Finally, the results of the numerical calculations were verified by experimental tests.

An atomistic simulation on the tensile and compressive deformation mechanisms of nano-polycrystalline Ti

In the present work, the molecular dynamics (MD) simulation is employed to investigate the tensile and compressive deformation behavior of nano-polycrystalline Ti with the mean grain size of 6.8 nm. The deformation behaviors reveal that the nano-polycrystalline Ti has different deformation mechanisms under the tension or compression. When the nano-polycrystalline Ti is applied tensile loading, the dislocation density quantification shows that there is no significant new dislocation appearing before the tensile strain reaches the failure strain (e = 0.12). Instead, a 25° difference in the grain boundary misorientation angle between two grains was observed, which indicates that the grain boundary rotation and sliding are appeared to dominate the tensile deformation process of nano-polycrystalline Ti. When the nano-polycrystalline Ti is applied compressive loading, the compressive stress increases linearly with the increase in compressive strain before the compressive strain arrives 0.075. Once the compressive strain exceeds 0.075, the nano-polycrystalline Ti enters the plastic deformation stage. In this case, the hcp-Ti atoms near the grain boundary were firstly transformed to the bcc-Ti atoms and then the hcp-Ti atoms within the grain transforms into the bcc-Ti atoms with the increase in compressive strain, which indicates that the plastic deformation of nano-polycrystalline Ti during the compression is dominated by the phase transformation from hcp-Ti to bcc-Ti. In addition, it is found that the deformation behaviors of nano-polycrystalline Ti are sensitive to strain rate and temperature. The present work could be beneficial for the design and fabrication of nano-polycrystalline Ti alloys with excellent mechanical properties.

A fast numerical method of introducing the strengthening effect of residual stress and strain to tensile behavior of metal matrix composites

Thermal residual stress and strain (TRSS) in particle reinforced metal matrix composites (PRMMCs) are believed to cause strengthening effects, according to previous studies. Here, the representative volume element (RVE) based computational homogenization technique was used to study the tensile deformation of PRMMCs with different particle aspect ratios (AR). The influence of TRSS was assessed quantitatively via comparing simulations with or without the cooling process. It was found that the strengthening effect of TRSS was affected by the particle AR. With the average strengthening effect of TRSS, a fast method of introducing the strengthening effect of TRSS to the tensile behavior of PRMMCs was developed. The new method has reduced the computational cost by a factor 2. The effect of TRSS on continuous fiber-reinforced metal matrix composite was found to have a softening-effect during the entire tensile deformation process because of the pre-yield effect caused by the cooling process.

Micro Plastic Deformation Behavior of Carbide-Free Bainitic Steel during Tensile Deformation Process.

The microstructure of carbide-free bainitic steel has been widely reported because of its excellent mechanical properties. However, no work has explored the deformation behavior of each phase in the microstructure, namely, retained austenite (RA) and bainitic ferrite (BF). In this paper, the deformation behavior of RA and BF during tension was investigated through the in situ electron backscatter diffusion method. The results showed that the RA surrounded by BF with a high Schmid factor (SF) was accelerated towards being transformed into martensite, but the surrounding BF with low SF value retarded the transformation. The kernel average misorientation (KAM) findings revealed that the strain of the RA and BF rapidly increased initially, slowed down after the critical points of 0.25 and 0.54, respectively, and then increased again. The calculated result for the KAM fraction indicated that the contribution of RA to the total plastic deformation gradually decreased throughout the total tensile process, whereas that of BF increased in the presence of RA.

Comparative study of tensile properties and magnetic properties for Nb-doped Fe-based wires

Herein, the comparative study of tensile and magnetic properties of Fe-based wires formed by rotated-dipping process before and after Nb-doping has been reported. In which, the phase composition, crystallization temperature, surface and fracture morphology, and magnetic performance are respectively investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscope (SEM) and Physical Property Measurement System (PPMS), respectively. Further, the experimental results indicate that the Nb-doped Fe-based wires show an amorphous state, uniform, and continuous, with excellent glass forming ability (GFA) and thermal stability. The saturation magnetization Ms and remanent magnetization Mr decrease owing to Nb-doping, while the coercivity Hc shows an increasing trend with the rising of Nb-doping, reaching 33.0 Oe. The tensile deformation process of Nb-doped Fe-based wires is mainly elastic deformation, reflecting the brittle fracture characteristics. While the Nb-doping can effectively enhance the tensile strength Rm of Fe-based wires, and the Rm of FeSiBNb3 wires exhibits the maximum value of 3.58 GPa. Moreover, the fracture morphology takes on the massive shear bands, and the fracture angles are about 45°, there are also some vein-shaped patterns and molten drops, even the fracture reliability analysis based on the statistical theory of Weibull mechanics indicates that the Nb-doped Fe-based wires possess an obviously improved fracture reliability. Therefore, it can be concluded that the Fe-based wires with improved tensile and magnetic properties as the candidates are adopted for potential electromagnetic and mechanical engineering applications.

Strain rate effects on tensile deformation behavior of Fe‐3.5Mn‐0.3C‐5Al ferritic based lightweight steel

AbstractTensile deformation behavior of Fe‐3.5Mn‐0.3C‐5Al ferritic based lightweight steel was studied in a large range of strain rate (0.001 s−1–1200 s−1). Microstructures of the steel before and after tension were observed. The results show that Fe‐3.5Mn‐0.3C‐5Al lightweight steel has a good strength (820 MPa) and plasticity (40 %) and exhibits excellent combinations of specific strength and ductility (&gt;32000 MPa %) at the strain‐rate of 0.001 s−1 after annealing at 850 °C for 5 minutes then directly quenching into water. The austenite in the steel tested was transformed into α′‐martensite during the tensile deformation process. With an increase in strain rate from 0.001 s−1 to 1200 s−1, tensile strength of the steel investigated increased from 820 MPa to 932 MPa, while its elongation first decreased from 40 % to 15 %, and then increased from 15 % to 29 %. At the strain rate of 1200 s−1, adiabatic heating resulted in temperature rising in matrix, suppressed the transformation of austenite to α′‐martensite. Comparing with transformation induced plasticity steel, the austenite in 3.5Mn lightweight steel is obviously unstable and cannot provide progressive phase transition.

Influence of manganese on deformation behavior of lightweight steel at different strain rate

Tensile deformation behavior of Fe–0.25C–3.5(10)Mn–5Al lightweight steel was studied in a large range of strain rate (0.001–1200 s−1) by using a universal material testing machine, intermediate strain rate tensile testing apparatus and rotation disk bar-bar tensile impact apparatus. Microstructures of the two steels before and after tension were observed by means of Optical Microscope (OM), Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). The results show that the two lightweight steels have a high strength and plasticity and exhibit excellent combinations of specific strength and ductility at the strain-rate of 0.001 s−1 after annealing at 850 °C for 5 min then directly quenching into water. During the tensile deformation process, the austenite in 3.5 Mn steel is transformed to α′-martensite. While in 10 Mn steel, the austenite is transformed to twinning. With an increase in strain rate from 0.001 to 1200 s−1, tensile strength of the two steels increase, whilst the elongation initially decrease, and then increase. At the strain-rate of 450 s−1, the elongation of the two lightweight steels are minimal, and the energy absorption capacity are the lowest. With the deformation progresses, the value of n increases from small to large, the strain hardening effect becomes high. Uniform deformation of 10 Mn lightweight steel was suppressed at high strain-rate. Comparing with 10 Mn lightweight steel, the austenite in 3.5 Mn lightweight steel is obviously unstable and cannot provide progressive phase transition.

Effect of dual-phase structure on the microstructure and deformation inhomogeneity of 2507 duplex stainless steel

ABSTRACT In this work, the microstructure and deformation mechanism, based on uniaxial tensile tests of 2507 super duplex stainless steel, is investigated using OM, XRD, EBSD, TEM and micro-Vickers. The experimental results indicate that the as-received sheet is not sensitive to strain rate at room temperature. The ferrite phase is softer than austenite phase during the tensile deformation process. In the initial stage of deformation, the strain is mainly accommodated in the ferrite phase. As the deformation increases, the strain continuously transmits to the austenite phase and the two phases coordinately deform. The strain is unevenly distributed in the two phases, and the strain is concentrated at the phase boundary.

Direct observation of microstructural fracture dynamics in carbon fiber reinforced plastics via in situ transmission electron microscopy

The tensile deformation process of carbon fiber reinforced plastics (CFRPs) was in situ observed by high-resolution transmission electron microscopy (TEM). CFRPs were prepared with sizing and unsizing treatment on the fiber surfaces. The microstructural evolution of crack propagation along fiber/resin interfaces and inside resin matrices was examined. Fine resin fragments remained on the fiber surfaces after fracture. From the differences in the shape of the residual resin fragments between the two types of CFRPs, the influence of the sizing treatment on fracture was quantitatively evaluated. We demonstrated a new method on the basis of in situ TEM to evaluate the microstructural fracture dynamics and the influence of the sizing treatment on fracture.

Structure, Reactivity, and Mechanical Properties of Sustainable Geopolymer Material: A Reactive Molecular Dynamics Study

Sodium aluminosilicate hydrate (NASH) gel, the primary binding phase in geopolymer, determines the mechanical properties and durability of environment-friendly construction materials. In this work, the models of NASH gel were obtained by two-step procedure: the temperature quenching method and Grand Canonical Monte Carlo water adsorption. The reactive force field molecular dynamics was utilized to investigate the structure, reactivity and mechanical performance of the NASH gel with Na/Al ratio ranging from 1 to 3. Q species, the connectivity factor, shows that the increase of sodium content in NASH gel leads to depolymerization of aluminosilicate network and more non-bridging oxygen atoms. The adsorbed water molecules dissociate near the non-bridging oxygen with high reactivity in defective aluminosilicate structure. The newly produced hydroxyls associate with the aluminate species, contributing to formation of pentahedron local structure. The sodium ions distributed in the cavity of the aluminosilicate skeleton have around 4 ~ 7 nearest neighbors. Furthermore, with increasing the amount of sodium, the molecular structure of the aluminosilicate skeleton is transformed from an integrity network to partial destroyed branch structures, which gradually decreases the stiffness and cohesive force of NASH gel characterized by the uniaxial tensile testing. During the large tensile deformation process, the reactive force field MD correlates the mechanical response with the chemical reaction pathway. The aluminosilicate skeleton is stretched broken to resist the tensile loading and the hydrolytic reaction of water molecules near the stretched Si-O and Al-O bond further accelerates the degradation of NASH gel. Hopefully, this work can shed light on material design for the high performance of sustainable geopolymer at nanoscale.

&lt;i&gt;In Situ&lt;/i&gt; Observation on the Deformation Behavior of Primary α-Ti in a Textured Ti-6Al-4V

The tensile deformation process and dislocation behavior of primary α-Ti of Ti-6Al-4V were studied by the in-situ tensile test combined with EBSD (electron backscatter diffraction). The initiation, evolution and distribution of dislocation slips at different strains were discussed. The results showed that the microtexture of the material had a significant influence on slip behavior. Typically, basal and prismatic &lt;a&gt; slips initiated first, but the dominant slip type was related to the local texture characteristics. Sometimes, the basal and prismatic &lt;a&gt; slips could still initiate when their Schmid factors were relatively low, while the pyramidal slips usually need a higher Schmid factor to initiate. With the increase of strain, the second slip system inside one grain was activated to accommodate the plastic deformation. When the deformation was localized in a specific microtextured region, basal &lt;a&gt; slips were dominant, but eventually the crack initiated from the &lt;c+a&gt; slip bands inside the grain.

Physical insights into stress–strain process of polymers under tensile deformation via machine learning

ABSTRACT Strain localization is a ubiquitous phenomenon of soft matters subjected to strain. Polymeric materials are a very important class of soft materials and widely used nowadays. Polymers have unique strain localization behavior such as crazing during tensile deformation. How to understand the mechanism at the molecular level of strain localization in polymeric materials has become an important topic in material science. In this work, tensile deformation process of polymers both under a melt state and a glassy state are investigated in MD simulations using a generic coarse-grained model. We use a machine learning technique, i.e., support vector machine (SVM) algorithm, to understand the local molecular structure and the dynamical properties during tensile deformation. By defining “softness” from the SVM model, we investigate the stress–strain behavior of both ductile polymer above glass transition temperature and brittle polymer glass during tensile deformation. We demonstrated that the softness can be used to predict physical properties efficiently; the softness provides deep physical insights into the non-equilibrium stress–strain process. We also find that the Hookean behavior of polymer glasses is mostly contributed by the hard regions of the system, and the elastic limit is quantitatively discussed as well.