Uniform Plastic Deformation Research Articles

Corrosion fatigue behavior of Fe-16Mn-0.6C-1.68Al twinning-induced plasticity steel in simulated seawater

The nature of corrosion fatigue of twinning-induced plasticity (TWIP) steel in a simulated seawater environment was investigated through various tests. Results indicated that TWIP steel has high corrosion fatigue susceptibility, which is mainly caused by anodic dissolution at grain boundaries and twin boundaries. However, uniform plastic deformation tends to inhibit corrosion fatigue. The influence of plastic deformation on corrosion fatigue of TWIP steel was clarified through the aspects of microstructure evolution, mechano-electrochemical effect, fatigue damage, etc. Findings reveal that plastic deformation or metallurgical design for high grain boundary strength will improve the resistance of corrosion fatigue for TWIP steel.

Tailoring twist extrusion process; the better strain behavior at the lower required loads

This study dealt with discovering the optimal conditions of the twist extrusion parameters for producing materials possess enhanced strain behavior with the least amount of extrusion load. It was found that the twist angle has a dominant influence on the strain behavior of the deformed sample with the contribution percentage of 56%, while the effect of friction coefficient would be the most noticeable if the required extrusion load is considered. Based on above, pure copper with the square cross-section was subjected to the process with the large twist angle at the best lubricant state. The results showed that the strength and hardness of the deformed copper were considerably enhanced compared to the initial condition due to the substantial grain refinement. The uniform plastic deformation zone of the deformed sample is limited which causes the reduction of strain-hardening exponent and ductility. Moreover, the lateral region of the sample’s cross-section endures larger plastic strain compared to the central one, leading to owning higher hardness. A combined microstructure consisting of low angle dislocation walls and high angle grain boundaries was also determined for the deformed copper.

Method of Predicting Necking True Stress in a Thin-Walled Tube Under a Complex Stress State

Abstract Method of predicting the strength of thin-walled tubes under a complex stress state, taking into account changes in the initial dimensions, is proposed. Uniform plastic deformation of a thin-walled tube under short-term static load by internal pressure and axial tension is considered. The tube material is considered to be homogeneous, isotropic and incompressible. The principle of maximum load is used to derive analytical dependences. The main decisions and conclusions were made using the Considere scheme.

Influence of composition on the mechanical properties of metallic nanoglasses: Insights from molecular dynamics simulation

The introduction of a glass–glass interface is an effective way to improve the plasticity of metallic glass. However, the strength–plasticity trade-off has not still been effectively overcome. Here, the effect of the composition on the mechanical properties and deformation behavior of the CuZr nanoglass (NG) is investigated under tensile loading by a molecular dynamics simulation. The results indicate that high-performance NGs can be obtained by adjusting the percentage of Cu atoms. There is a critical Cu content (i.e., 75%), which makes the NGs have both high strength and high plasticity. The results show that with the increase in the Cu content, the deformation mechanism of the NGs changes from necking to uniform plastic deformation and then to the nucleation and the growth of the main shear band. Our results underscore the importance of the composition in the design and preparation of high-performance metallic glass.

Pressure-induced maximum shear strength and transition from shear banding to uniform plasticity in metallic glass

The effect of pressure on the mechanical and physical properties of metallic glasses (MGs) has been widely reported. In experiments, it remains challenging to mechanically loading the materials under extreme hydrostatic pressures and carrying out the corresponding measurements. Here, we investigate the pressure dependence of shear response of a typical brittle FeP MG by using molecular dynamics (MD) simulations. We show that the plastic deformation of this MG loaded at a pressure below 10 GPa is highly localized in the form of a dominant shear band. The plastic flow stress during shear banding is measured to increase with the applied pressure, leading to a pressure-induced strengthening behavior at pressures in the range of 0–10 GPa. As the pressure is increased to a critical pressure of approximately 15 GPa, there occurs a transition in the deformation mechanism from localized shear banding to a delocalized shear deformation mechanism governed by the uniform activation of individual shearing events in the material. At this critical pressure, both the yield strength and the average flow stress are maximized. Further increasing the pressure lowers the strength of the material. The pressure effect on the evolution of different types of atomic clusters is analyzed, revealing that the pressure-sensitivity of atomic clusters in MGs is related to their structural symmetry. Under high hydrostatic pressures, low-symmetry clusters become sluggish due to their larger pressure sensitivity. In such circumstances, high-symmetry clusters with lower pressure sensitivity are relatively more active during shear deformation and evenly distributed in the whole sample, leading to the uniform plastic deformation at high pressures. Our findings calls for further experimental investigations of the effect of pressure on mechanical properties and deformation mechanisms of MGs.

Influence of Severe Plastic Deformation on Static Recrystallization Microstructure of Pure Iron

In recent years, ultrafine-grained steel has been gaining increasing attention as a high-performance material. Accordingly, it is necessary to develop an efficient production method for ultrafine-grained steel. Severe plastic deformation is a critical factor that causes grain subdivision into ultrafine grains less than 1 µm in diameter. In this study, the effects of plastic deformation on the microstructure and static recrystallization of pure iron were studied by comparing orthogonal cutting and rolling. Orthogonal cutting yielded ultrafine grains with a diameter of 0.2 µm. It was found that a high strain rate in the thin shear plane generated during the cutting process caused a uniform subdivision of grains, and this uniform plastic deformation resulted in the uniform recrystallization of grains. In addition, a theoretical model was developed, and it was revealed that the number of recrystallized grains depended on the fraction of a large-misorientation area constructed with geometrically necessary boundaries (GNBs). It was suggested that the cutting process was more advantageous than rolling in producing ultrafine recrystallized grains because cutting could apply severe plastic strain uniformly on a work material, effectively generating GNBs.

Influence of Cryogenic Treatment on Microstructure and Mechanical Properties of Ti6Al4V Alloy

Cryogenic treatment is an emerging application that can make significant changes in many materials. In this study, shallow (− 80 °C) and deep (− 196 °C) cryogenic treatment was applied to Ti6Al4V alloy. Additionally, aging treatment and supplementary deep cryogenic treatment were also performed. Tensile tests were done to observe the effects of cryogenic treatment on the mechanical properties and formability of Ti6Al4 alloy. According to the results of these tests, it was observed that the cryogenic treatment had a positive influence on the plasticity properties of Ti6Al4V alloy. For the 24-h and 36-h deep cryo-treated samples, the uniform plastic deformation region (UPDR) was extended 5 and 8.3% compared to untreated sample, respectively. However, this improvement in plasticity observed in samples treated with cryogenic treatment for 36 h led to a decrease in yield strength by 2%. Microstructural and XRD analysis was performed to characterize the microstructural changes that happened with the effect of applied heat treatments. The characterization study shows that with the application of cryogenic treatment internal structure of the material changed, the β phase ratio of the alloy decreased from 8.1 to 5.6% with 36-h deep cryogenic treatment. The unstable β phase was transformed into α phase and stable β phase. The experimental study shows that cryogenic treatment improves the plasticity and toughness of Ti6Al4V alloy at room temperature and regulates the microstructure and reduces the residual stress.

Enhancement of uniform plastic deformation for pure titanium foils by applying pre-strain combining with resistance heating method for microforming

Pure titanium (Ti) is usually deformed at elevated temperatures due to its poor formability at room temperature (RT), resulting in its strength reduction after deformation. Applying pre-strain combining with resistance heating (RH) method, which can be conducted at one procedure, was proposed to enhance its plasticity in this work. The influence of the proposed process on tensile deformation of pure Ti foils with 50μm thick was investigated using a RH assisted tensile testing system. Full strain field was measured by a digital image correlation (DIC) system with laser speckles. Uniaxial tensile pre-strain ranging from 1% to 2% was applied at a low temperature of 160°C with relatively high nominal strain rates of 10−2 and 10−1s−1. Then tensile tests were conducted at RT with a nominal strain rate of 10−3s−1. As results, although the ultimate tensile strength (UTS) slightly decreased with increasing pre-strain, the maximum decreasing rate was within 4%, indicating that the effect of pre-strain on UTS is negligible. The strain distribution analyzed from DIC was relatively uniform at UTS. Uniform elongation increased with increasing pre-strain. The maximum increasing rate achieved 36%. It is confirmed that the heating rate using RH for heating Ti foils with 50μm thick is about 340 times larger than that for heating Ti sheets with 1mm thick. The quick response of RH makes it possible for the application of the proposed process to mass production for manufacturing microparts.

Application of the method of current functions in stationary plastic deformation processes

A method of determining the components of the strain rate tensor based on the method of current functions is developed. It is assumed that, with an axisymmetric plastic deformation of the metal in a channel with curvilinear borders, the kinematics of the process are similar to a flat flow. Using the incompressibility equation and the differential equation of the current lines, it is established that the current function maintains a constant value along the current lines. Two infinitely close current lines are considered in the flow plane to explain the kinematic content of the current function. The expression for flow through the finite transverse-sized tube was obtained. In the absence of radial velocity components at the boundaries, we obtain the restrictions imposed on derivatives of the current functions at these boundaries. The method of calculation of kinematic deformation characteristics for established axisymmetric processes will allow to simplify the mathematical processing of the obtained results. Real processes of metal processing are always accompanied by uneven plastic molding, which affects the power and kinematic parameters, the quality of finished products. The main technological factors affecting the appearance of the inhomogeneity and the nature of its distribution are the form factor (geometric parameters of the original workpiece) and the coefficient of contact friction. The study of technological parameters affecting the distribution of non-uniformity of plastic molding will allow to create practical recommendations for reducing the influence of the above mentioned parameters to ensure more uniform plastic deformation. Due to elastic-plastic deformation and local heating, which occur during surface-plastic deformation processing, the stress-strain and physical state of the surface layer is formed. This changes the microgeometry of the surface, the physical and mechanical properties of the surface layer of the workpiece. The surface treated by methods of surface-plastic deformation, has high hardness, residual compression stresses in the surface layer, smoothed out the micro-roughness. Accordingly, increases wear resistance, fatigue strength, resistance to corrosion and more.

Evaluation of interface structure and high-temperature tensile behavior in Cu/Al8011/Al5052 trilayered composite

This paper dealt with the combined processing of roll-casting and hot-rolling to fabricate high-performance Cu/Al8011/Al5052 composite with ultrathin copper thickness. It was shown that the intermetallic compounds formed at the Cu/Al interface include Al4Cu9, AlCu, and Al2Cu from the copper side, respectively, in which the CuAl phase has the lowest thickness due to its the high diffusion activation energy. Also, Al2Cu, due to having the lowest amount of Gibbs free energy, was initially formed at the interface, followed by the Al4Cu9 and AlCu phases. Although the room-temperature tensile strength of the trilayered composite is close to each other in both directions, the elongation to failure in the rolling direction is about 37% better than that of the transversal direction. Furthermore, no clear slip bands were observed in the uniform plastic deformation zone of the stress-strain curve during the high-temperature tensile tests compared to the room-temperature counterparts. Despite the decrease in tensile strength with increasing test temperature, this composite shows good tensile behavior at temperatures below 200 °C due to the pure shear fracture mode.

Heterogeneous microstructure and voids dependence of tensile deformation in a selective laser melted AlSi10Mg alloy

Microstructure and voids evolution of a selective laser melted (SLM) AlSi10Mg alloy during tension were systematically investigated. The SLM AlSi10Mg sample is featured with a multi-level heterogeneous microstructure that is composed of melt pools (MPs), columnar Al grains and sub-cells. According to the Si morphologies and thermal history, the MP could be divided into three regions, including the fine structure zone (FSZ), remelted zone (RMZ) and heat-affected zone (HAZ), respectively. The Si segregation phenomenon on sub-cells boundaries is observed and may attributed to the constitutional supercooling. The tensile deformation behaviors of the vertical sample (V-sample) vary from the horizontal sample (H-sample) for that heterogeneous microstructure arises strain localization in V-sample. In addition, the voids have no obvious effect on the uniform plastic deformation, while they may affect the non-uniform deformation during tension. The combined effects of strain localization and void contribute to the earlier break in V-samples than in H-samples.

Enhanced mechanical properties and corrosion resistance of a fine-grained Mg-9Al-1Zn alloy: the role of bimodal grain structure and β-Mg17Al12 precipitates

ABSTRACT A good combination of mechanical properties and corrosion performance is desired when employing Mg alloys in engineering applications. Therefore, it is essential to investigate both the mechanical properties and corrosion resistance of processed Mg alloys to determine the optimum combinations of materials properties. This study investigates the microstructure, mechanical properties, and corrosion resistance of AZ91 (Mg–9Al–1Zn, wt.%) alloys in chloride-containing environments under different processing conditions. The findings revealed that the AZ91 alloy exhibits good mechanical properties combined with high corrosion resistance after microstructure modification through equal channel angular pressing (ECAP). This microstructure was characterized by a bimodal grain structure with the formation of a high volume fraction of well dispersed β-Mg17Al12 precipitates. The superior mechanical properties of the AZ91 alloy after ECAP process were mainly attributed to the combined effect of significant grain refinement and high volume fraction of fine β-Mg17Al12 precipitates that provided grain boundary and precipitation strengthening and promoted a more uniform plastic deformation. The enhanced corrosion resistance of the fine-grained AZ91 alloy was related to the presence of a highly protective oxide layer, the formation of a highly adherent and compact layer of corrosion products, and the development of uniform corrosion with shallow corrosion pits. This simultaneous improvement in strength, ductility, and corrosion resistance of fine-grained AZ91 alloys can serve as a guide for future alloy design and represents a promising alternative for industrial applications.

Effect of original microstructure on wear property of ER9 wheel steel

ABSTRACT In this work, the influence of original microstructure on wear property of ER9 wheel steel is studied by GPM-40 rolling wear tester. The pearlite + proeutectoid ferrite (P+F) sample exhibits the lower wear loss than the tempered sorbite (TS) sample at different cycles. However, the TS sample has better fatigue wear resistance than the P+F sample. High wear loss and more uniform plastic deformation of the TS sample can inhibit the formation of fatigue wear cracks. During rolling-sliding wear process, for the P+F sample, the high surface hardness and the pearlite colonies/proeutectoid ferrite are the main reasons to cause the initiation of fatigue cracks. The formation of an interface of hardening layer causes the propagation of cracks easily. These factors lead to a large amount of fatigue wear cracks be formed at the P+F sample surface.

Prediction of the Boundary States for Thin-Walled Axisymmetric Shells Under Internal Pressure and Tension Loads

Abstract A method for calculating the ultimate true stresses arising in the walls of shells of revolution in the area of uniform plastic deformation is developed in the research. In order to derive the stability loss for the plastic deformation process the criterion of maximum load is taken as the basis, simple differential equations were solved. It has been shown analytically that the level of the boundary true stresses is much lower when the values of the principal stress ratios approach to 2 or 1/2 compared to the adjacent stress states.

Investigation on microstructure and mechanical properties of multiphase ZrSn1.5Alx alloy with simultaneous enhance of strength and plasticity

Abstract There are many means and mechanisms to strengthen alloys, but often at the cost of plasticity. Strength or plasticity? In practice, the two often appear as contradictory relationships. In the current work, the ZrSn1.5Alx (x = 6, 8, 10, 12, 14 at. %) alloy obtained by controlling the Al content was smelted and hot-rolled at 890 °C, and then immediately quenched to obtain an alloy containing α + β + AlZr3 multiphase structure. Compared with ZrSn1.5Al6 alloy, ZrSn1.5Al14 alloy reaches a high ultimate tensile strength (1080.84 MPa) and a large elongation at fracture (28.59%) at room temperature, an increase of 27.6% and 86.3%, respectively. The formation of AlZr3 particles pins dislocations, promotes cross-sliding of dislocations, and improves the dislocation nucleation rate by changing the dislocation sliding mode, which increases the dislocation density and promotes uniform plastic deformation, enhance the strain-hardening ability of the alloys, thereby improve its plasticity and strength simultaneously. Optical microscopy (OM) and scanning electron microscope (SEM) were used to observe the metallographic structure and tensile fracture morphology. The transmission electron microscope bright field (TEM-BF) image and scanning transmission electron microscope high-angle annular dark field (STEM-HAADF) image of the sample were observed for detailed analysis. The samples were taken in the rolling direction and the mechanical properties were evaluated by uniaxial tensile tests at room temperature. In summary, the machining process is simple, the cost is low, and it is suitable for large-scale industrial-grade applications. It may have reference significance to other alloy systems.

Dynamic Mechanical Behavior and Adiabatic Shear Bands of Ultrafine Grained Pure Zirconium

Dynamic compression tests were carried out to investigate dynamic mechanical behavior and adiabatic shear bands in ultrafine grained (UFG) pure zirconium prepared by equal channel angular pressing (ECAP) and rotary swaying. The cylindrical specimens were deformed dynamically on the split Hopkinson pressure bar (SHPB) at different strain rates of 800 to 4 000 s-1 at room temperature. The temperature distribution of the shear bands was estimated on the basis of temperature rise of uniform plastic deformation stage and thermal diffusion effect. The results show that the true stress-true strain curves of UFG pure zirconium are concave upward trend of strain in range of 0.02-0.16 due to the effects of strain hardening, strain rate hardening and thermal softening. The formation of the adiabatic shear bands is the main reason of UFG pure zirconium failure. A large number of micro-voids are observed in the adiabatic shear bands, and the macroscopic cracks develop from the micro-voids coalescence. The fracture surface of UFG pure zirconium exhibits quasi cleavage fracture with the characteristic features of shear dimples and river pattern. The highest temperature within the shear bands of UFG pure zirconium is about 592 K.

Investigation of the effect of low temperature on the mechanical behavior of an ultrafine-grained metastable steel using a physically based analytical model

A duplex steel consisting of an ultrafine-grained austenite (γ) matrix and a residual strain-induced α′-martensite (SIMα′), i.e., ultrafine-grained (γ + SIMα′) steel, was fabricated by the cryogenic-rolling of a 304 austenitic stainless steel followed by annealing. Tensile tests of the ultrafine-grained (γ + SIMα′) steel were carried out at 77–298 K, the corresponding mechanical properties, austenite stability and kinetics of SIMα′ were investigated, and a physically-based analytical model was established to explore its temperature-dependent mechanical behavior. The results showed that the increase in the tensile strength caused by the decrease in temperature was significantly greater than that of the yield strength and was accompanied by a slight decrease in elongation. In addition, the strength-ductility synergy increased with reducing temperature. The work-hardening of the ultrafine-grained (γ + SIMα′) steel changed from continuous reduction in the work-hardening rate to the three-stage work-hardening behavior with a hardening peak as the temperature decreased from 298 K to 77 K. The analytical model revealed that the contribution of austenite to the work-hardening rate (Θγ) had a positive effect during the early uniform plastic deformation (UPD) stage and then a negative effect during the middle-late UPD stage. Both the positive and negative effects were enhanced with decreasing temperature. However, the contribution of SIMα′ to the work-hardening rate (Θα′) had only a positive impact throughout the whole UPD stage and was also improved with decreasing temperature. The work-hardening rate of ultrafine-grained (γ + SIMα′) steel was initially attributed mainly to the austenite during the early UPD stage and then was governed by the SIMα′ during the middle-late UPD stage. Moreover, the enhanced growth rate of Θγ and Θα′, resulting from the temperature decrease, led to the change from the continuous reduction of work-hardening between 298 K and 253 K to a three-stage work-hardening behavior between 173 K and 77 K.

Microstructures and mechanical properties of Zr–Al binary alloys processed by hot-rolling

The microstructures and mechanical properties of Zr–xAl alloys (x = 0, 3, 6, 9 and 12 at.%) that underwent the hot-rolling at 1143 K and the subsequent water-quenching were investigated. Microstructural analyses show that the pure Zr, Zr–3Al and Zr–6Al alloys mainly consisted of the α and α′ phases and exhibited bimodal microstructures. The Zr–9Al and Zr–12Al alloys consisted of the α, β, Zr2Al and Zr3Al phases and exhibited equiaxed microstructures. Tensile tests show that, with the increase in Al content, the yield and ultimate strength of the alloys increased from 324.9 MPa and 443.8 MPa (pure Zr) to 665.2 MPa and 787.6 MPa (Zr–12Al), respectively. Meanwhile, the elongation to failure initially decreased from 17.3% (pure Zr) to 10.3% (Zr–6Al) and subsequently increased to 19.5% (Zr–12Al). Analyses show that the significant enhancement of yield strength resulted from the solid solution strengthening by Al. In addition, dynamic precipitation occurred in the Zr–9Al and Zr–12Al alloys. The precipitated Zr3Al particles resulted in the obvious strain hardening behavior of the Zr–9Al and Zr–12Al alloys. The high strain hardening rate and elongation at the uniform plastic deformation stage of the Zr–12Al alloy resulted in the simultaneous enhancement of the ultimate strength and ductility.

Effect of solution temperature on static recrystallization and ductility of Inconel 625 superalloy fabricated by directed energy deposition

Solution treatment is a very important method to modify the microstructure and mechanical properties of additive-manufactured nickel-based superalloy. This study mainly investigated the effect of solution temperature on static recrystallization and ductility of Inconel 625 superalloy fabricated by directed energy deposition (DED). The microstructural results showed that static recrystallization occurred after solution treatment, and as the solution temperature increased, the recrystallization volume fraction in the alloy gradually increased. When the solution temperature reached 1200 °C, static recrystallization occurred more completely. The tensile results indicated that the elongation and strain hardening exponent of Inconel 625 improved with the solution temperature increased, while the yield strength decreased. The deformation behaviors during the tensile process of different samples were obtained by digital image correlation (DIC), and the results showed that the uniform plastic deformation ability was strengthened with the solution temperature increased. In addition, due to the decrease of dislocation density, the yield strength decreased, too. Besides, the increase of strain hardening exponent delayed the appearance of the necking and the dissolution of the Laves phase caused the ductility increasing.

Grain Morphology and Orientation Effect on the High-Temperature Tensile Behavior of Directionally Solidified Magnesium Alloy

Columnar-structured Mg97.27Zn2.54Y0.19 alloy with the preferred growth direction of 〈22$$\bar{4}$$5〉 and 〈12$$\bar{3}$$3〉, and Mg98.01Zn1.84Y0.13Zr0.03 alloy with the preferred growth direction of 〈11$$\bar{2}$$0〉 were prepared using the directional solidification technique and then tensile tested at 250–300 °C. The results showed that the Mg97.27Zn2.54Y0.19 alloy with columnar dendritic structure experienced a significant deformation strengthening period when stretched at 250 °C, and a typical dynamic recrystallization stage at 300 °C, which were mainly accounted for its well-developed secondary dendrites, a large number of branch-shaped second phases distributed in the longitudinal grain boundary, and less granular second phases existing in the crystal. While in the whole test temperature range (250–300 °C), the stress–strain curves of Mg98.01Zn1.84Y0.13Zr0.03 alloys with cellular dendritic crystals showed a steady deformation state because of the second phases with strip distributing in the longitudinal grain boundary, which was induced by a balance between the deformation strengthening and the dynamic recrystallization. Especially at 300 °C, this steady deformation state existed in the strain of 5.6%–36%. The good uniform plastic deformation was closely related to the small misorientations between columnar grains, the associated movement of grains by grain boundary slipping, and the less percentage of dynamically recrystallized grains which could do harm to the orientation continuity of the columnar crystals. The directionally solidified Mg98.01Zn1.84Y0.13Zr0.03 and Mg97.27Zn2.54Y0.19 alloys with different orientation and grain morphology show different high temperature mechanical properties at 250 °C and 300 °C.