Effect Of Stacking Fault Energy Research Articles

Effect of stacking-fault energy on dynamic recrystallization, textural evolution, and strengthening mechanism of Fe−Mn based twinning-induced plasticity (TWIP) steels during friction-stir welding

This study aims to elucidate the effect of stacking fault energy (SFE) on the microstructural evolution and related hardening mechanisms of Fe−18Mn−0.6C−(0 and 1.5)Al and Fe−30Mn−3Al−3Si (wt.%) twinning−induced plasticity (TWIP) steels during friction stir welding (FSW) using a high−resolution electron backscattered diffractometer. With increasing SFE, the intensities of the Goss, CuT, and Brass components increased via active dynamic recrystallization (DRX) accompanied by twinning. The 30Mn weld, which had the highest SFE, exhibited the highest recrystallization fraction (94.8 %) and an increasing rate of hardness (40.9 %). This is because a higher SFE can enhance dislocation mobility, leading to an active rate of continuous DRX as well as discontinuous DRX. Consequently, the refinement of the recrystallized grains effectively assisted the hardening of the 30Mn weld after FSW. Hence, we concluded that SFE should be considered to improve the properties of TWIP steels after FSW.

Effect of Stacking Fault Energy on Cryo Deformation Behavior of Austenitic Stainless Steels

Effect of Stacking Fault Energy on Cryo Deformation Behavior of Austenitic Stainless Steels

Effect of Texture and Temperature on Strain‐Induced Martensitic Transformation in 304 Austenitic Stainless Steel

The austenitic stainless steel's remarkable mechanical properties are caused by twinning‐induced plasticity and transformation‐induced plasticity mechanisms. Numerous studies focus on stacking fault energy's effect, which is affected by various factors, to interpret and control these mechanisms. However, crystallographic orientation is also an important parameter for mechanical properties in metals. This study compares the mechanical properties and microstructural features of 304 austenitic stainless steel, focusing on the effect of initial texture and deformation temperature. Microstructural characterization is identified by an interrupted tensile test based on strain, tensile direction, and temperature conditions, and X‐ray diffraction and electron back‐scattered diffraction analysis are performed. The results show that the mechanical features and strain‐induced martensitic transformation rate depend on the tensile directions. In addition, this trend is maintained irrespective of the temperature conditions. The attribute reason is that the difference in the Taylor factor and the formation rate of the deformed band structure is induced by the initial crystallographic orientations. Moreover, a decrease in temperature significantly increases the dislocation densities and abundant twins and transformed martensites formation. Furthermore, the yield and tensile strengths are enhanced while the elongation decreased with the tensile strains.

Effects of short-range ordering and stacking fault energy on tensile behavior of nitrogen-containing austenitic stainless steels

The tensile behavior of austenitic stainless steels with different concentration of nitrogen was studied by analyzing deformation microstructure and calculating short-range ordering (SRO) as well as stacking fault energy (SFE). Increasing nitrogen concentration increased SFE and SRO, which affected the tensile behavior. From the early to intermediate deformation stages, the nitrogen addition induced slip planarity and the delay of dynamic recovery, which were brought by the increase of SRO. As a result, work hardening rate (WHR) rose with the nitrogen content at the end of the intermediate deformation stage. On the other hand, the SFE effect was noticeable at higher strain levels. With increasing nitrogen concentration, the formation of slip lines was suppressed and dynamic recovery was promoted. Hence, the reduction in WHR was accelerated with the nitrogen addition. When the overall dynamic recovery behavior was assessed with dislocation-density based constitutive modeling, it was found to depend mainly on SRO rather than on SFE. Therefore, the alloy with higher nitrogen content could achieve higher dislocation density and flow stress.

Effects of Stacking Fault Energy and Temperature on Grain Boundary Strengthening, Intrinsic Lattice Strength and Deformation Mechanisms in CrMnFeCoNi High-Entropy Alloys with Different Cr/Ni Ratios

Effects of Stacking Fault Energy and Temperature on Grain Boundary Strengthening, Intrinsic Lattice Strength and Deformation Mechanisms in CrMnFeCoNi High-Entropy Alloys with Different Cr/Ni Ratios

Effect of SFE on the evolution of crystallographic texture in Cu-Zn alloys subjected to severe plastic deformation

Within the framework of experimental investigations and computer modeling using the viscoplastic self-consistent (VPSC) model of a material plastic flow, the regularities of preferential orientations formation were established, the proportion of certain texture components was estimated, and existing slip systems (SS) and twinning systems (TS) were identified for equal-channel angular pressing (ECAP) of copper alloys depending on the stacking fault energy (SFE).

Effect of Stacking Fault Energy and Solute Atoms on Microstructural Evolutions of FCC Metals Processed by Severe Plastic Deformation

Pure copper, pure silver, Cu-6.8at%Al, Cu-1at%Mn and Cu-5at%Ni (stacking fault energies (SFEs) are about 41, 22, 23, 43 and 105mJ/m2, respectively) were processed by equal channel angular pressing (ECAP) at the same homologous temperatures to investigate the effect of SFE and solute atoms on microstructural evolutions. The final grain size of Cu-6.8at%Al after eight passes of ECAP was the smallest followed by that of Cu-1at%Mn with little difference. The former alloy reaches saturation for grain size and grain boundary misorientation in early passes of ECAP while the latter continues decreasing even after eight passes. The role of shear bands and deformation twins is predominant for grain fragmentation in the early stage for Cu-6.8at%Al and Ag with low SFE while evolution from cell walls to grain boundaries is main mechanism for Cu, Cu-1at%Mn and Cu-5at%Ni with medium or high SFE. Solute Mn atom of Cu-Mn with high atomic size misfit and may suppress the dynamic recovery which transforms cell walls to grain boundaries, and allow accumulation of higher dislocations and reduction of cell size to smaller scales.

Effects of Stacking Fault Energy and Solute Atoms on Microstructures of Ultrafine Grained Copper Alloys Processed by Severe Plastic Deformation

Effects of Stacking Fault Energy and Solute Atoms on Microstructures of Ultrafine Grained Copper Alloys Processed by Severe Plastic Deformation

Effect of Stacking-Fault Energy on the Deformed Structures and Work Hardening of Ag and Ni after Scratching during Early Loading Stage

Friction wear are accompanied by the formation of refined structures and shear bands in the surface layers of metals and alloys. The propensity for refinement and shear band formation is mainly determined by the stacking-fault energy (SFE). Despite the fact that significant studies have been dedicated to plastic deformation during friction, little effort has been directed toward elucidating the early stages of deformation hardening that is accompanied by the effects of SFE. The research results presented herein focused on the initiation of twin and lamellar shear bands, transformation of nano-grained structures during shear banding, and the deformation hardening of surface layers during the scratching of metals with low and high SFE. Flat samples of low (Ag) and high (Ni) SFE were scratched with a diamond indenter for one to ten friction cycles. The friction surfaces were examined with a field-emission scanning electron microscope. It was shown that the scratch track sizes and amounts of pile-up material were lower for Ag than those for Ni. High deformation hardening of Ag relative to Ni was confirmed by the inhibition of cross-slip and the formation of ultra-fine structures. The deformed structure of Ag after ten scratch cycles was characterized by the formation of core shear bands that were bent in the depth of the deformed layers. It was shown that the balance between deformation hardening and softening was crucial in preserving a steady friction state and forming wear particles.

Effect of Stacking Fault Energy on Microstructure and Texture Evolution during the Rolling of Non-Equiatomic CrMnFeCoNi High-Entropy Alloys

The evolution of microstructure and texture in three non-equiatomic CrMnFeCoNi high-entropy alloys (HEAs) with varying stacking fault energy (SFE) has been studied in up to 90% rolling reductions at both room and cryogenic temperature. All the HEAs deform by dislocation slip and additional mechanical twinning at intermediate and shear banding at high rolling strains. The microstructure is quite heterogeneous and, with strain, becomes highly fragmented. During rolling, a characteristic brass-type texture develops. Its strength increases with a decreasing SFE and the lowering of the rolling temperature. The texture evolution is discussed with regard to planar slip, mechanical twinning, and shear banding.

Effect of Stacking Fault Energy on the Grain Structure Evolution of FCC Metals During Friction Stir Welding

The effect of stacking fault energy (SFE) on the grain structure evolution of face-centered cubic metals during friction stir welding was investigated by using pure aluminum, pure copper and Cu–30Zn alloy as experiment materials. Tool “stop action” and rapid cooling were employed to “freeze” the microstructure of the flowing materials around the tool. Marker materials were used to show the streamline of the material flow. The microstructures of the three materials at different welding stages were contrastively studied by the electron backscatter diffraction technique. The results show that at the material flow stage, as the SFE decreases, the grain structure evolution changes from the continuous dynamic recrystallization to discontinuous dynamic recrystallization, and further to the dynamic equilibrium between the annealing twinning due to thermally activated grain boundary migration and the twin destruction during the plastic deformation. Owing to different grain structure evolution mechanisms, the grain structure at the end of the material flow is greatly different. Especially in copper, a lot of dislocations remain, which gives rise to the static recrystallization occurring during the subsequent cooling stage.

Atomistic simulation of the stacking fault energy and grain shape on strain hardening behaviours of FCC nanocrystalline metals

ABSTRACTUltra-fine grained copper with nanotwins is found to be both strong and ductile. It is expected that nanocrystalline metals with lamella grains will have strain hardening behaviour. The main unsolved issues on strain hardening behaviour of nanocrystalline metals include the effect of stacking fault energy, grain shape, temperature, strain rate, second phase particles, alloy elements, etc. Strain hardening makes strong nanocrystalline metals ductile. The stacking fault energy effects on the strain hardening behaviour are studied by molecular dynamics simulation to investigate the uniaxial tensile deformation of the layer-grained and equiaxed models for metallic materials at 300 K. The results show that the strain hardening is observed during the plastic deformation of the layer-grained models, while strain softening is found in the equiaxed models. The strain hardening index values of the layer-grained models decrease with the decrease of stacking fault energy, which is attributed to the distinct stacking fault width and dislocation density. Forest dislocations are observed in the layer-grained models due to the high dislocation density. The formation of sessile dislocations, such as Lomer–Cottrell dislocation locks and stair-rod dislocations, causes the strain hardening behaviour. The dislocation density in layer-grained models is higher than that in the equiaxed models. Grain morphology affects dislocation density by influencing the dislocation motion distance in grain interior.

Effects of Stacking Fault Energy on Deformation Mechanisms in Al-Added Medium Mn TWIP Steel

In this study, the effect of aluminum (Al) addition to a manganese (Mn) steel Fe-12Mn-0.5C in regard to the change in stacking fault energy (SFE) and the consequent evolution of deformation microstructure and texture were investigated during cold rolling. An analysis of the texture and microstructure was performed to understand the deformation micro-mechanisms. Deformation micro-mechanisms were substantiated by the estimation of dislocation density and the arrangement of dislocations in the deformed microstructure by X-ray line profile analysis, which revealed significant changes in the dislocation structure with the addition of Al. Three stages of deformation mechanism were observed in all Al-added compositions. In the early stages of deformation, slip as well as twinning prevailed. In the intermediate stage, twinning took over completely and at large strains, macroscopic shear bands became the dominant deformation mode. An increase in the propensity of nanometer-sized deformation twins was observed with rolling strain. However, the addition of Al decreased the overall twin fraction in the deformed microstructure. The theoretical twinning stress was calculated to explain the crucial role of SFE on the occurrence of deformation twins in these steels. The deformation texture was predominantly of the brass type for all the Al-added compositions; however, appreciable differences were seen with Al content. The 〈111〉//ND γ-fiber, which develops in Al-free Fe-12Mn-0.5C, completely disappeared in 3 wt pct Al-containing material.

Effects of stacking fault energies on formation of irradiation-induced defects at various temperatures in face-centred cubic metals

ABSTRACTBy using the six sets of interatomic potentials for face-centred cubic metals that differ in the stacking fault energy (SFE) while most of the other material parameters are kept almost identical, we conducted molecular dynamics simulations to evaluate the effects of SFE on the defect formation process through collision cascades. The simulations were performed at 100, 300 and 600 K, with a primary knock-on atom energy of 50 keV. The number of residual defects is not dependent on the SFE at all the temperatures. For clusters of self-interstitial atoms (SIAs), their clustering behaviour does not depend on the SFE, either. However, the ratio of glissile SIA clusters tends to decrease with increasing SFE. This is because perfect loops, the edges of which split into two partial dislocations with stacking fault structures between them in most cases, prefer to form at lower SFEs. The enhanced formation of glissile SIA clusters at lower SFEs can also be observed even at increased temperature. Because most large vacancy clusters have stacking fault structures, they preferentially form at lower SFE; however, it is observed only at the lowest temperature, where the mean size increases with decreasing SFE. At higher temperatures, because of their extremely low number density, the vacancy clustering behaviour does not depend on the SFEs.

Plastic deformation of FCC alloys at cryogenic temperature: the effect of stacking-fault energy on microstructure and tensile behaviour

The deformation behaviour of metals and alloys is significantly affected by both stacking-fault energy and processing temperature. By lowering the former, deformation twinning is favoured over dislocation slip, whilst cryogenic processing partially suppresses dynamic recovery. Three materials having different stacking-fault energies, that is, Al AA1050 (high), pure Cu (medium) and Cu–15Zn alloy (low) were rolled at room (RTR) and at cryogenic (CR) temperatures up to a true strain equal to 1.5. Annealed coarse-grained samples were tested in tension at room and cryogenic temperatures. The processed samples were characterized by optical and transmission electron microscopy, hardness measurements and room-temperature tensile tests. CR increases the tensile strength with respect to RTR for the three materials; elongation to failure is decreased for AA1050, whilst for Cu and Cu–15Zn the CR effectively increases the ductility. Cu–15Zn sample after CR exhibits a microstructure relatively heterogeneous, suggesting static recrystallization events in the temperature excursion from 77 to 298 K. Finally, it was concluded that cryogenic deformation increases strength, whilst low SFE increases the ability to absorb plastic deformation, an effect strongly increased at cryogenic temperatures. The present investigation gives some basis for the development of cryogenic severe plastic deformation processes.

A continuum model for dislocation pile-up problems

A 2-d dislocation pile-up model is developed to solve problems with arrays of edge dislocations on one or multiple slip planes. The model developed in this work has four unique features: 1) As a continuum mechanics model, it captures the discrete behaviors of dislocations including the region near pile-up boundaries. 2) It allows for a general distribution of dislocations and applied boundary conditions. 3) The computational complexity does not quadratically scale with increased number of dislocations. 4) The effect of anisotropy and stacking fault energy can be naturally modeled. Pile-ups against a lock under shear load are extensively investigated, which shows the dependence of near-lock piles distribution on the total number of dislocations. The stacking fault energy effect is found to be positively correlated to the length of an equilibrated pile-up. The stress intensity near a bi-metallic interface is studied for both isotropic material and anisotropic materials. The model is validated by reproducing the solutions of problems for which analytical solutions are available. More complicated phenomena such as interlacing and randomly distributed dislocations are also simulated.

Влияние энергии дефекта упаковки на накопление дислокаций при пластической деформации поликристаллических сплавов на основе меди

Влияние энергии дефекта упаковки на накопление дислокаций при пластической деформации поликристаллических сплавов на основе меди

Effects of stable and unstable stacking fault energy on dislocation nucleation in nano-crystalline metals

Dislocation nucleation from grain boundaries (GB) can control plastic deformation in nano-crystalline metals under certain conditions, but little is known about what controls dislocation nucleation, because when data from different materials are compared, the variations of many interacting properties tend to obscure the effects of any single property. In this study, we seek clarification by applying a unique capability of semi-empirical potentials in molecular dynamics simulations: the potentials can be modified such that all significant material properties but one, are kept constant. Using a set of potentials developed to isolate the effects of stacking fault energy, we show that for a given grain boundary, loading orientation and strain rate, the yield stress depends linearly on both the stable and unstable stacking fault energies. The coefficients of proportionality depend on the GB structure and the value of the yield stress is related to the density of the E structural units in the GB. While the impact of the stable stacking fault energy is easy to understand, the unstable stacking fault energy requires more elucidation and we provide a framework for understanding how it affects the nucleation and propagation process.

Influence of stacking fault energies on the size distribution and character of defect clusters formed by collision cascades in face-centered cubic metals

Molecular dynamics simulations are performed to evaluate the influence of the stacking fault energy (SFE) as a single variable parameter on defect formation by collision cascades in face-centered cubic metals. The simulations are performed for energies of a primary knock-on atom (EPKA) up to 50keV at 100K by using six sets of the recently developed embedded atom method–type potentials. Neither the number of residual defects nor their clustering behavior is found to be affected by the SFE, except for the mean size of the vacancy clusters at EPKA=50keV. The mean size increases as the SFE decreases because of the enhanced formation of large vacancy clusters, which prefer to have stacking faults inside them. On the other hand, the ratio of glissile self-interstitial atom (SIA) clusters decreases as the SFE increases. At higher SFEs, both the number of Frank loops and number of perfect loops tend to decrease; instead, three-dimensional irregular clusters with higher densities appear, most of which are sessile. The effect of SFE on the number of Frank loops becomes apparent only at a high EPKA of 50keV, where comparably large SIA clusters can be formed with a higher density.

Microstructure and tensile properties of Cu[sbnd]Al alloys processed by ECAP and rolling at cryogenic temperature

CuAl alloys with different stacking fault energy (SFE) were processed by equal channel angular pressing and rolling (ECAP + R) at cryogenic temperature with liquid nitrogen cooling. The effect of SFE on microstructure, effective grain size, dislocation density and tensile properties has been investigated. With decreasing of SFE during cryogenic ECAP, shear bands were developed to be step-shaped by cutting through high density of deformation twins, effective grain size reduces and dislocation density increases. Subsequently imposed to cryorolling, the lamellar thickness of twins and grain size is further reduced. Tensile strength increases with a decrease of SFE, and further enhanced after the additional rolling. The improvement of strength in CuAl alloys is attributed to the finer grains/twin thickness and the higher dislocations density. The maximum tensile strength of 871 MPa and uniform elongation of 4.3% in Cu7%Al is simultaneously achieved.