Formation Of Deformation Bands Research Articles

Spontaneous emergence of deformation bands in single-crystal plasticity simulations at small strain

AbstractIn metal single crystals, the observed formation of deformation banding pattern has been explained by greater latent hardening of slip systems than their self-hardening, which promotes spatial segregation of plastic slips and lamination towards single-slip domains. Numerical studies focusing on the formation of deformation bands usually involved initial imperfections, boundary-induced heterogeneity, or the postulate of minimal global energy expenditure which additionally promoted non-uniformity of deformation. This article analyses the case when no such mechanism enforcing locally non-uniform deformation is implemented in the finite element (FE) method, while the global system of equations of incremental equilibrium is solved in a standard way. The new finding in this paper is that the deformation banding pattern can appear spontaneously in FE simulations of homogeneous single crystals even in the absence of any mechanism favouring deformation banding in the numerical code. This has been demonstrated in several examples in the small strain formalism using a plane-strain model in which the twelve fcc slip systems are reduced to three effective plastic slip mechanisms. Incremental slips are determined at the Gauss-point level either by incremental work minimization in the rate-independent case or by rate-dependent regularization. In the rate-independent approach, the trust-region algorithm is developed for the selection of active slip systems with the help of the augmented Lagrangian method. Conditions under which a banding pattern appears spontaneously or is suppressed are discussed. In particular, a critical rate sensitivity exponent is identified.

Excellent specific strength-ductility synergy in novel complex concentrated alloy after suction casting

Lightweight alloys are known to improve the fuel efficiency of the structural components due to high strength-to-weight ratio, however, they lack formability at room temperature. This major limitation of poor formability is most of the time overcome by post-fabrication processing and treatments thereby increasing their cost exponentially. We present a novel Ti50V16Zr16Nb10Al5Mo3 (all in at. %) complex concentrated alloy (Ti-CCA) designed based on the combination of valence electron concentration theory and the high entropy approach. The optimal selection of constituent elements has led to a density of 5.63 gm/cc for Ti-CCA after suction casting (SC). SC Ti-CCA displayed exceptional room temperature strength (UTS ∼ 1.25 GPa) and ductility (ε ∼ 35 %) with a yield strength (YS) of ∼ 1.1 GPa (Specific YS = 191 MPa/gm/cc) without any post-processing treatments. The exceptional YS in Ti-CCA is attributed to hetero grain size microstructure, whereas enormous strength-ductility synergy is due to the concurrent occurrence of slip and deformation band formation in the early stages of deformation followed by prolonged necking event due to delayed void nucleation and growth. The proposed philosophy of Ti-CCA design overcomes the conventional notion of strength-ductility trade-off in such alloy systems by retaining their inherent characteristics.

On the microstructure, texture and electrochemical properties of severely deformed and artificially aged lightweight AA2050 Al–Cu–Li alloy

Lightweight 3rd generation Al–Cu–Li alloy AA2050 was severely deformed via Multi Axial Forging (MAF) at 170 °C followed by artificial aging at 150 °C. Effect of MAF and post MAF aging on microstructure and precipitation was investigated using transmission electron microscopy (TEM). Formation of deformation bands and large dislocation cells were evident on MAF processed samples. Post MAF peak aging resulted in the distribution of fine T1 precipitates in grain interiors with reduction in grain boundary precipitation. Bulk texture studies reveal the formation of strong Goss and S texture components upon MAF processing. Further, low temperature artificial aging doesn’t exhibit significant changes in texture characteristics, either in terms of texture intensities or texture components. Polarization studies showed that peak aged samples exhibited better corrosion resistance compared to un-aged samples. Overall, 12 pass MAF processed and peak aged samples showed higher corrosion resistance. Further, corrosion surface morphologies examination revealed the change in corrosion mechanisms with thermomechanical treatments. Improved corrosion resistance after MAF and peak aging widens the requirements in aerospace and aircraft applications for such engineering alloys.

Phase transformation and deformation behavior under isothermal compression in β-quenched metastable Ti-10V-2Fe-3Al alloy

Comprehensive knowledge on the hot deformation behavior and microstructure evolution of metastable titanium alloys is critical for process optimization and microstructure regulation. The isothermal compression of β-quenched metastable titanium alloys (Ti-10 V-2Fe-3Al) was experimented at different temperatures (600 ℃−800 ℃) with the strain rate of 10−3 s−1 in present work. The stress-strain curves show that the flow stress reduces with increasing temperature, and the characteristics of the stress-strain curve at low temperature (600 ℃) are clearly distinct from those at other high temperatures. During the isothermal compression process at 600 °C, the deformation went through four stages: initial linear hardening (stage Ⅰ), Discontinuous yielding phenomenon (DYP, stage Ⅱ) followed by work hardening (stage Ⅲ) and final flow softening (stage Ⅳ). Further observations of the microstructure throughout each deformation stage revealed that the precipitation of αGB and the proliferation of dislocation lead to initial linear hardening behavior. The softening of deformation behavior during the discontinuous yield stage is originated from the fragmentation of αGB and the generation of a large amount of moving dislocations. Almost all β phase transformed into lamellar α phase as the deformation degree increased, which is the main cause of work hardening after discontinuous yield. The major causes of final flow softening are the formation of deformation bands and spheroidization of α phase. The present work analyses the correlation between the deformation behavior and microstructure features on the deformation mechanisms of metastable β titanium alloys and reveals the potential mechanism of metastable β alloy under thermal deformation and provides more comprehensive information for the optimization of the process parameters of hot deformation.

A comparative analysis of a unique DRX process in achieving a homogeneous distribution of β grains in the single phase region of as-cast Ti644321 alloy

This study aims to investigate the distinctive characteristics of a specialized dynamic recrystallization (DRX) process, which results in a fine and uniform distribution of β grains within the single phase region of as-cast Ti644321 alloy. The formation of deformation bands (DB) and flow localization (FL) is a result of the instability region. On the other hand, the stability region exhibits significant dynamic recrystallization (DRX). The phenomenon of DRX encompasses continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX), and the coupling mechanism of DDRX and CDRX, which was discovered in this study. The occurrence of DDRX is attributed to grain boundary bulging, while CDRX is a result of the progressive rotation of subgrains. A strain rate of 0.1 s−1 was found to form a fine and uniform distribution of β grains. The formation of this microstructure is facilitated by a coupling mechanism that combines CDRX and DDRX, which involves the grain boundary strain concentration effect that triggers DDRX and the subgrain rotational nucleation process of CDRX. The deformation mechanism of the alloy during hot deformation varies depending on the η value. In the high η region, the primary deformation mechanism is mainly DDRX+CDRX, while in the medium η region, it transitions to CDRX+DRV. Ultimately, in the low η region, the primary deformation mechanism is DB + FL. The presence of a high proportion of DBs hinders DRX. This study provides novel insights into the mechanisms of DRX in β titanium alloys and emphasizes the significance of considering different forms of DRX.

Prediction of Macroscopic Deformation Bands in Porous Metals with Unidirectional Through‐Pores

The formation of macroscopic deformation bands constitutes undesired stress fluctuations in the compression of porous metals. This research is aimed at revealing the predictability of the formation of deformation bands in porous metals with unidirectional through‐pores. Finite element analyses of compression tests of such porous metals are conducted with the commercial code Abaqus/Standard and Explicit 2018. Three cubic specimens with different L/d (specimen edge length L, pore diameter d) but with the almost same porosity are prepared, and quasi‐static compression is simulated. The results suggest that the formation of horizontally propagated deformation bands is suppressed as L/d increases. A path search is performed to predict the location of deformation bands on a graph that represents equivalent plastic strain (PEEQ) distribution in the specimens. It is revealed that horizontally propagated deformation bands at compressive strain e = 10.0 pct can be predicted as the path with the largest mean of PEEQ at e = 1.0 pct when the following two conditions are met; the minimum PEEQ in the path has to be larger than zero, and the standard deviation of the PEEQ mean in candidate paths has to be sufficiently large.

In situ EBSD study of formation and propagation of deformation bands in a single-crystal superalloy during tensile deformation

In situ EBSD study of formation and propagation of deformation bands in a single-crystal superalloy during tensile deformation

Energy approach to the selection of deformation pattern and active slip systems in single crystals

The recently introduced quasi-extremal energy principle for incremental non-potential problems in rate-independent plasticity is applied to select the deformation pattern and active slip systems in single crystals. The standard crystal plasticity framework with a non-symmetric slip-system interaction matrix at finite deformation is used. The incremental work criterion for the formation of deformation bands is combined with the quasi-extremal energy principle for determining the active slip systems and slip increments in the bands. In this way, the incremental energy minimization approach has been extended to the non-potential problem of deformation banding in metal single crystals. It is shown that fulfilment of the mathematical criterion for incipient deformation banding in a homogeneous crystal in the multiple-slip case under certain conditions requires non-positive determinant of the hardening moduli matrix. Numerical examples of energetically preferable patterns of deformation bands are presented for Cu and Ni single crystals.

Formation of Deformation Bands during Impact Indentation of an Al–6Mg Alloy

Formation of Deformation Bands during Impact Indentation of an Al–6Mg Alloy

Formation of Deformation Bands during Impact Indentation of an Al–6Mg Alloy

The nucleation and growth of macrolocalized deformation bands initiated by impact indentation in deformed aluminum-magnesium alloy samples have been investigated by acoustic emission and highspeed video recording with a time resolution to 50 μs. The indenter impact has been found to trigger the developmentof a ~1–3% amplitude plastic deformation macroscopic jump due to the nucleation and propagation of about ten deformation bands on an alloy surface, thus demonstrating the Portevin–Le Chatelier effect. Macrolocalized deformation bands are shown to be a dangerous type of erosion damage that can cause thesudden fracture of an alloy.

Quantitative investigation of strain partitioning and failure mechanism in ultrafine grained medium Mn steel through high resolution digital image correlation

Ultrafine grained medium Mn steel exhibits simultaneous high strength and ductility, however, often showing Lüders deformation and discontinuous yielding phenomena. The connections between martensite transformation and Lüders deformation as well as the localized failure behavior are quantitatively investigated through high resolution digital image correlation, enabled by nanoscale strain distribution and microstructural alignment. At a low global tensile strain level, strain localization happens in austenite domain resulted from a sequential slip deformation and martensite transformation, which then triggers the yielding of ferrite by generating thin strain channels to connect adjacent hotspots. This microscopic deformation mode promotes the formation of macroscopic deformation bands, resulting in Lüders band initiation and propagation. When increasing the applied load, the externally imposed strain is accommodated by ferrite instead, resulting in pronounced strain partitioning. The triple grains boundary having no further strain hardening capacity is favorable for void initiation and propagation.

Atomistic analysis of plastic deformation and shear band formation in FCC/FCC metallic nanolayered composites

Atomistic analysis of plastic deformation and shear band formation in FCC/FCC metallic nanolayered composites

Hot deformation behavior of Mg-5Li-3Al-2Zn-0.2Zr alloy based on constitutive analysis, processing map, and microstructure evolution

The hot deformation behavior of Mg-5Li-3Al-2Zn-0.2Zr alloy was investigated via hot compression tests at 573–673 K/0.001–1 s−1. True stress-strain curves exhibit typical dynamic recrystallization characteristic, the proposed strain-compensated Zener-Hollomon model shows high accuracy in predicting flow stress, and the average activation energy of the alloy is calculated as 164.2196 kJ·mol−1. The instability region spans all temperatures at higher strain rates and the cause is the formation of local deformation bands composed of ultrafine recrystallized grains. The optimum deformation processing for Mg-5Li-3Al-2Zn-0.2Zr alloy is determined as 673 K/0.001 s−1. The microstructure evolution reveals that the alloy compressed at 573–623 K mainly undergoes continuous dynamic recrystallization controlled by dislocation cross-slip, and the alloy compressed at 673 K mainly undergoes discontinuous dynamic recrystallization controlled by dislocation climb.

Dynamic hardness and formation of Portevin-Le Chatelier bands during impact indentation

The effect of shock indentation on the formation and propagation of the Portevin-Le Chatelier deformation bands in an aluminum-magnesium alloy was studied experimentally using acoustic emission and high-speed video recording methods. Dynamic and nonlinear responses to shock indentation are revealed: the first include high values of dynamic hardness and local strain and loading rates, and the second - threshold and multiple nature of force and acoustic responses. It is shown that the bands of macrolocalized deformation represent a latent bulk type of erosion damage, which reduces the mechanical stability and durability of the alloy. Keywords: contact shock, Portevin-Le Chatelier effect, deformation bands, fracture, aluminum-magnesium alloy.

Динамическая твердость и образование полос Портевена-Ле Шателье при ударном индентировании

The effect of shock indentation on the formation and propagation of the Portevin-Le Chatelier deformation bands in an aluminum-magnesium alloy was studied experimentally using acoustic emission and high-speed video recording methods. Dynamic and nonlinear responses to shock indentation are revealed: the first include high values of dynamic hardness and local strain and loading rates, and the second - threshold and multiple nature of force and acoustic responses. It is shown that the bands of macrolocalized deformation represent a latent volumetric type of erosion damage, which reduces the mechanical stability and durability of the alloy.

Understanding deformation band formation across a range of length scales in the Paradox Basin, Utah

In evaporite basins, salt flow can drive complex deformation of high porosity sedimentary units adjacent to salt and this has been demonstrated by recent numerical modeling studies, however field evidence of this deformation has remained elusive. Detailed analysis of high-porosity wall and cover rocks adjacent to a large salt-cored anticline in Salt Valley, UT yields three observable deformation band gradients. A long-wavelength gradient of steeply dipping normal/shear bands is recognized along structural transects up to 5 km away from the Salt Valley anticline axis. A shorter-wavelength (5–60 m) deformation band gradient shows band density increasing toward similarly-oriented brittle normal faults. A third gradient of intense compactional deformation banding is recognized adjacent to the salt diapir. Importantly, cement phases are undamaged in these bands, indicating that they likely experienced plastic critical-state deformation prior to cementation. The steeply-dipping deformation bands and normal faults are interpreted to be broadly contemporaneous and result from outer arc extension of the Salt Valley anticline; the dense compactional band network adjacent to salt likely accommodated compression during diapiric rise contemporaneous with folding. This integration of field and petrologic studies with forward modeling makes a critical step toward developing predictive models for deformation band formation in hydrocarbon systems.

Determining the thermoplastic deformation mechanism of titanium reduction reactors and recommendations to increase the reactor service life

The object of research reported in this paper is the stressed-strained state of reactors when producing titanium sponge by the magnesium thermal method, taking into consideration the conditions of their operation and the physical and mechanical properties of the materials. The problem considered is the plastic deformation of the reactor in the process of reducing titanium tetrachloride. To solve this task, an axisymmetric geometric model of the reactor was built using a CAD module of the Comsol Multiphysics software package. For the calculation, the Nonlinear Structural Materials module was used. Owing to the method of finite elements, the critical parameters for the formation of the plastic deformation band of the reactor were determined. Modeling the process of thermoplastic deformation of the reactor under the conditions of obtaining titanium sponge has made it possible to determine the temperature gradient in the upper part of the reactor wall, which leads to local plastic deformation of the wall. The solution to the problem of continuing the reactor service would be to prevent overheating (overcooling) of the reactor wall within the resulting temperature. The physical and mechanical parameters of the material of the reactor wall, necessary to prevent the occurrence of an annular band of plastic deformation, have also been determined. It was shown that at ∆T˃∆Tcrit=60 °C, the walls of a 10-ton reactor during the reduction of titanium tetrachloride with magnesium perceive plastic deformation whose maximum value can reach Deformation mechanisms that lead to a change in the shape of the side wall of reactors of magnesium-thermal production of sponge titanium under the action of a heterogeneous temperature field have been determined. The proposed technological solutions are to eliminate local changes in diameter in the upper part of the reactor wall. This will make it possible not only to increase the life of the reactors but will reduce the flow of alloy components into the titanium sponge of nickel, chromium, and iron

Enhancement of ballistic performance enabled by boron-doping in subzero-treated (ferrite+austenite+martensite) triplex lightweight steel

Investigations of dynamic deformation and ballistic performance of ultra-high-strength lightweight steels for steel armor applications have not been conducted to date. In this study, effects of boron(B)-doping on ballistic performance were explored in subzero-treated Fe-0.3C-9Mn-5Al and Fe-0.3C-9Mn-5Al-0.005B (wt%) lightweight steels in relation to band structures and B segregation. The dynamic deformation and adiabatic shear band (ASB) formation behaviors were examined by a Hopkinson pressure bar (SHPB). The band structure is critical in inhibiting ASB propagation, as it is continuously blocked at tempered-martensite/ferrite boundaries. The crack propagates along the embrittled ASB and penetrates into tempered-martensite/ferrite boundaries, producing delamination of elongated grains in the undoped steel. On the other hand, the delamination does not occur in the B-doped steel because the segregation of solute B at prior austenite grain boundaries enhances the grain-boundary cohesion. Thus, the B-doped steel outperforms conventional rolled homogeneous armor steels and the undoped steel as well, providing a significant deal of potential for developing excellent ballistic-performance lightweight steel armors.

Island-Matrix Inhomogeneous Deformation Behavior, Formation of Deformation Band, and BUT Forming of DP Steel

Islands-Matrix-Dual-phase (I-M-DP) steel is received a great deal attention for better concern with the emissivity, fuel consumption and passengers safety. A number of deformation plasticity issues are yet to be fully understood. Complex deformation stages for various stain is predicted as the natural outfall of the plastic strain localization caused by the ill-assorted deformation between the martensite-island phase and the ferritic-matrix phase. Modeling is carried out both in macro level by bending under tension (BUT) for different roller radius/sheet thickness ratios to acquire strain and stress state deformation and micro scale by Representative Volume Element (RVE) according to element position. It can relate both the 2D, 3D micro and macro scale finite element based BUT model’s result of flow behavior. Systematically strain based severe deformation pattern arises from outfall of plastic strain localization and von Mises stress distribution in island-matrix steels are investigated on the microstructure by finite element method for ill-assorted deformation between phases.

Heterogeneous deformation and damage mechanisms in multi-phase TA15 Ti-alloy: Insights from experiments informed damage-crystal plasticity modelling

Understanding the mesoscale heterogeneous deformation and its induced material damage is significant to enhance the mechanical properties of polycrystalline aggregates. In this work, a damage-coupled crystal plasticity finite element (DC-CPFE) model based on high-fidelity microstructure was developed to investigate the heterogeneous deformation and damage behavior of TA15 Ti-alloy with tri-modal microstructure composed of globular alpha (αp), lamellar alpha (αl) and transformed beta (βt). A three-step procedure combining the nanoindentation test, stress relaxation test, and uniaxial tensile test was proposed to determine the material parameters in the crystal plasticity constitutive and damage models of the three constituent phases. Based on the developed DC-CPFE model, the heterogeneous slip modes and traces of tri-modal microstructure were predicted and analyzed. The heterogeneous deformation of tri-modal microstructure was found to be mainly caused by the heterogeneous deformation in α phases, which was featured by the deformation bands and local shear bands. Deformation bands occurred in both of the deformation-preferential and -lagged αp grains and the hard-to-deform αl grains. Local shear bands only produced in αl grains, which were related to both of the soft geometry orientation and the activation of prismatic slip systems. Meanwhile, the formation of deformation bands and local shear bands could be promoted by the local lattice rotation. The above heterogeneous deformation led to four types of damage, which were caused by the slip band intersection, the slip transfer impedance, the local shear band, and the property and orientation mismatches among the adjacent grains, respectively.