Heterogeneous Deformation Research Articles

Strong and ductile CrCoNi medium-entropy alloy via dispersed heterostructure

Here we advocate the strategic design of dispersed heterostructure to retain ductility and toughness in high-strength metals, using the equiatomic CrCoNi alloy as an example. Dispersed heterostructure, with nanograins and/or ultrafine grains (the hard zone) dispersed around micrometer-sized grain (the soft zone), is fabricated by cold-rolling followed by sequential flash-annealing at increasing temperatures. It displays a decent uniform elongation of ∼ 20 % and an exceptional strain energy density limit up to ∼ 240 mJ/mm3 at the strength level of ∼ 1.2 GPa, which is unattainable by its homogeneous as well as clustered heterogeneous counterparts. Grain size-dependent heterogeneous deformation evokes inter-zone interactions, which induce strain partitioning, activate additional mechanical twinning and promote developments of dislocation gradient and long-range internal stress near zone boundary sequentially, imparting a multistage work hardening with extraordinary strain hardening rate up-turn followed by slow attenuation. Dispersed heterostructure provides a higher density of zone boundary, ensuring more extensive inter-zone interaction and thus maximizing the extraordinary strain hardening to improve ductility.

Data-driven design of eutectic high entropy alloys

Eutectic high entropy alloys (EHEAs) have attracted tremendous research interest over the past decade due to their superior physical and mechanical properties. Given the compositional complexity, there are no well-established phase diagrams for EHEAs. Therefore, the compositional design of EHEAs has been following a trial-and-error empirical approach, which is time-consuming, costly, and ineffective. To accelerate the search for EHEAs, data-driven approaches, particularly machine learning (ML) based modeling, have recently been utilized in lieu of the traditional empirical approach. In this article, we provide a critical overview of the recent efforts in the design and development of EHEAs, which covers the various empirical methods and the state-of-the-art machine learning models developed for EHEAs. In addition, we also briefly discuss the mechanical properties and plasticity strengthening mechanisms in EHEAs which are related to their heterogeneous microstructure, such as heterogeneous deformation induced strengthening, twinning induced strengthening, and phase transformation induced strengthening.

Investigation of accelerated recrystallization behavior via electropulsing treatment in CoCrFeMnNi high-entropy alloy

In this work, the effects of annealed temperatures (700 °C, 800 °C) and heating rates (low heating rate (LR) of 0.17 °C/s, medium heating rate (MR) of 500 °C/s and high heating rate (HR) of 4000 °C/s) on recrystallization behavior in equiatomic CoCrFeMnNi high-entropy alloy (HEA) were investigated. The mechanism of accelerated recrystallization behavior induced by electropulsing treatment (EPT) was elucidated through the evolution analysis of microstructure and geometrically necessary dislocations (GNDs). The results showed that the average GNDs density and grain size of the recrystallized region decreased with increasing annealed heating rate. At 700 °C, the average recrystallized grain size decreased from 6.1 μm to 2.2 μm with increasing annealed heating rate. At 800 °C, the HR material exhibited a higher recrystallization percentage and the corresponding decrease in average grain size from 12.5 μm for LR to 4.7 μm for HR. EPT promoted the recrystallization nucleation rate by reducing the recrystallization nucleation barrier. The better combination of grain refinement and dislocation strengthening due to heterogeneous deformation led to the yield strength (772 MPa) and fracture elongation (0.30) of the MR sample increased by ∼31% and ∼25% respectively compared with LR after annealing at 700 °C. This work provides essential insights into accelerating the recrystallization behavior and further improving the degree of grain refinement of CoCrFeMnNi HEA via EPT under the lower rolling amounts.

Syn‐depositional halokinesis in the Zechstein Supergroup (Lopingian) controls Triassic minibasin genesis and location

AbstractSalt tectonics is typically caused by the flow of mobile evaporites in response to post‐depositional gravity gliding and/or differential loading by overburden sediments. This situation is considerably more complex near the margins of salt basins, where carbonate and clastic rocks may be deposited at the same time as and be interbedded with more mobile, evaporitic strata. In these cases, syn‐depositional salt flow may occur due to density differences in the deposited lithologies, although our understanding of this and related processes is relatively poor. We here use 3D seismic reflection and borehole data from the Devil's Hole Horst, West Central Shelf, offshore UK to understand the genesis, geometry, and kinematic evolution of intra‐Zechstein Supergroup (Lopingian) minibasins and their effect on post‐depositional salt deformation. We show that immobile, pinnacle‐to‐barrier‐like, carbonate build‐ups and anhydrite are largely restricted to intra‐basin highs, whereas mobile halite, which flowed to form large diapirs, dominates in the deep basin. At the transition between the intra‐basin highs and the deep basin, a belt of intra‐Zechstein minibasins occurs, forming due to the subsidence of relatively dense anhydrite into underlying halite. Depending on primary halite thickness, these intra‐Zechstein minibasins created topographic lows, dictating where Triassic minibasins subsequently nucleated and down‐built. Our study refines the original depositional model for the Zechstein Supergroup in the Central North Sea, with the results also helping us better understand the style and distribution of syn‐depositional salt flow within other layered evaporitic sequences and the role intra‐salt heterogeneity and related deformation may have in the associated petroleum plays.

The effect of grain size on deformation modes and deformation heterogeneity in a rolled Mg–Zn–Ca alloy

Grain refinement could promote the activation of non-basal slip and enhance the strength and ductility of Mg alloy simultaneously. In this work, the grain size effect on deformation modes and deformation heterogeneity and its relations to crystallographic orientation in a rolled Mg–1.58Zn–0.1Ca alloy sheet with a weakened transverse direction (TD) spread texture were investigated via intragranular misorientation axis (IGMA) and high resolution-digital image correlation (HR-DIC) measurement. The results indicate that a decrease of the grain size from 55 to 13 μm increased the yield strength (YS) by 56.9%, from 72 MPa to 113 MPa, for the TD samples, but only by 8% for the rolling direction (RD) samples, from 125.7 to 135.7 MPa. Moreover, grain refinement enhanced the elongation by 76.4% for the TD samples, from 11% to 19.1%, and merely by 26.5% for the RD samples, from 16.6% to 21%. The transition in dominant deformation modes due to grain size decreasing can be summarized as: for the RD samples: basal slip → prismatic slip; for the TD samples: basal slip + tension twinning → prismatic slip. The enhanced activity of prismatic slip in the fine-grained (FG)-TD and FG-RD samples can be ascribed to the reduced ratio of critical resolved shear stress (CRSS)prismatic/CRSSbasal. For both the RD and TD samples, grain refinement facilitated deformation homogeneity, which could be related to the enhanced activity of basal slip and non-basal slip, as well as the resulting improved deformation compatibility across grain boundary.

Simulation of the inelastic deformation of porous reservoirs under cyclic loading relevant for underground hydrogen storage

Subsurface geological formations can be utilized to safely store large-scale (TWh) renewable energy in the form of green gases such as hydrogen. Successful implementation of this technology involves estimating feasible storage sites, including rigorous mechanical safety analyses. Geological formations are often highly heterogeneous and entail complex nonlinear inelastic rock deformation physics when utilized for cyclic energy storage. In this work, we present a novel scalable computational framework to analyse the impact of nonlinear deformation of porous reservoirs under cyclic loading. The proposed methodology includes three different time-dependent nonlinear constitutive models to appropriately describe the behavior of sandstone, shale rock and salt rock. These constitutive models are studied and benchmarked against both numerical and experimental results in the literature. An implicit time-integration scheme is developed to preserve the stability of the simulation. In order to ensure its scalability, the numerical strategy adopts a multiscale finite element formulation, in which coarse scale systems with locally-computed basis functions are constructed and solved. Further, the effect of heterogeneity on the results and estimation of deformation is analyzed. Lastly, the Bergermeer test case-an active Dutch natural gas storage field-is studied to investigate the influence of inelastic deformation on the uplift caused by cyclic injection and production of gas. The present study shows acceptable subsidence predictions in this field-scale test, once the properties of the finite element representative elementary volumes are tuned with the experimental data.

Microstructure and Mechanical Properties of Severely Deformed Polypropylene in ECAE (Equal Channel Angular Extrusion) via Routes A and C

Equal channel angular extrusion (ECAE) is a solid-state extrusion process for modifying microstructures via severe plastic deformation without modifying the specimen cross section. In this study, changes in the microstructure and mechanical properties of polypropylene resulting from extrusion orientation route A (no rotation between extrusions) and extrusion orientation route C (a rotation of 180° between extrusions) are investigated using a 90° die-angle tooling outfitted with back pressure. Important differences are reported for the ECAE-induced deformation behavior between the two processing routes. A focus is made on the occurrence of heterogeneous plastic deformations (periodic shear banding and warping) for both routes and the control and inhibition of the plastic instabilities via regulated back pressure and ram velocity. Wide-angle X-ray scattering is carried out to characterize the structural evolution as a function of the processing conditions including route, extrusion velocity and BP application. The mechanical properties of the specimens machined from the ECAE pieces are examined under different loading paths including uniaxial tension/compression and simple shear. Full-field displacements converted to volumetric strains revealed the profound impacts of the processing route on the deformation mechanisms during tensile deformation.

Graphene nanoplatelets induced laminated heterogeneous structural titanium matrix composites with superior mechanical properties

In this study, a novel laminated heterogeneous structural titanium matrix composites (TMCs) were fabricated by the incorporation of graphene nanoplatelets (GNPs) via the flake powder metallurgy route. The heterogeneous deformation between soft and hard regions produced significant back stress hardening. Results showed that dramatically higher ultimate tensile strength of 858 MPa could be achieved in 0.1wt% GNPs/Ti(R1) composite, which exhibited the enhanced strength (+166 MPa compared with that of pure Ti(R1)) while maintained a good ductility of 18%.

Tensile properties and deformation behavior of an extra-low interstitial fine-grained powder metallurgy near alpha titanium alloy by recycling coarse pre-alloyed powder

An extra-low interstitial near alpha alloy Ti−3Al−2Zr−2Mo (wt%) was fabricated by hydrogenation and thermomechanical consolidation (TMC) of the coarse and spherical pre-alloyed powder with particle sizes of 60 to 270 μm. The coarse powder is a byproduct of pre-alloyed powder produced for selective laser and electron beam additive manufacturing. The TMC process involves powder compaction, fast sintering, in-situ dehydrogenation and an immediate hot extrusion to form a fully dense and fine-grained martensitic microstructure. Further dehydrogenation in vaccum at 700 °C converted the martensitic microstructure into an interwoven α/β microstructure which exhibited an improved yield strength, apparent necking and premature cracking at grain boundary α (αGB) ribbons. A further annealing of 880 °C/1 h/AC led to the formation of a fine-grained α/βt composite structure, which achieved an enhance ultimate tensile strength of 835 MPa and excellent tensile ductility of 16.0%. Analysis of the deformation behavior of the alloy in different states revealed that the α/βt composite structures brought about an enhanced strain hardening capability by heterogeneous deformation effect of hard βt and soft α-laths, which inhibited the formation of microcracks and consequently improved the coordinated deformation.

Multi-scale modelling of deformation heterogeneities in explosively welded layered sheets

A multi-scale numerical investigation of local heterogeneities in the strain and stress fields occurring during forming of explosively welded layered metallic sheets is the main goal of the research. Explosive welding is a complex process involving various phenomena occurring in materials during an impact at high velocities and pressures, especially at the interfaces of colliding metals. As a result, the interface of the layered metallic sheets is often highly heterogeneous at the microscale level, what directly affects the sheet behaviour under subsequent forming conditions. To investigate this issue, the mesh-free numerical model of the explosive welding process is used first to recreate the characteristic features of the interface morphology. Various detonation velocities are used to provide diversified morphological features at the interface. Obtained results are then used as input data to develop the concurrent multi-scale finite element model of material behaviour under deformation conditions. The multi-scale modelling concept with explicit representation of the interface region is used. The highly refined heterogeneous FE mesh was generated in the interface region to capture local heterogeneities occurring at the microscale. Particular attention is put on numerical investigation of an influence of interface morphology in the welding zone on the development of the stress localisation that may directly lead to fracture initiation during forming.

Defect-associated microstructure evolution and deformation heterogeneities in additively manufactured 316L stainless steel

Previous research mainly focused on heterogenous microstructure modification to improve mechanical properties, but how the microstructure evolves during deformation has not been clarified yet when metallurgical defects are involved. In this work, austenitic 316L stainless steel was additively manufactured using selective laser melting (SLM), exhibiting typical heterogeneous microstructure with variation in grain structure, texture and metallurgical defects. Besides, the quasi-in-situ microstructural observation was conducted to reveal three competitive plastic deformation mechanisms to accommodate the deformation heterogeneities, i.e., lack-of-fusion pores, twinning and deformation bands. With presence of large lack-of-fusion pores (>1%), they accommodated the main strain and acted as preferential crack initiation sites, contributing to the pre-mature failure. In terms of near-full dense materials, microstructure and texture became significant with prevalent twinning and deformation bands. Twinning was activated in grains with <111> and <101> orientations parallel to the tensile direction, which promotes twin-dislocation and dislocation-cellular wall interactions and thus stabilizes the strain hardening. Deformation bands occurred along the columnar grain bands due to the deformation heterogeneities, which are likely to give rise to the initiation of micro-cracks with continuous strain. These findings offer insight into the microstructure modification and heterogeneous deformation behavior and provide key guidance for additively manufacturing stainless steels with high strength and ductility.

Direct observation of three-dimensional short fatigue crack closure behavior in Ti-6Al-4V alloy using ultra-high-resolution X-ray microtomography

Local 3D short fatigue crack closure behavior was investigated in Ti-6Al-4V alloy using ultra-high-resolution X-ray microtomography (XMT). The results show that the inhomogeneous distribution of plasticity-induced and roughness-induced crack closure is caused by the variation of crack path morphologies. These crack path morphologies exhibited heterogeneous plastic deformation at the crack-tips due to the anisotropic nature of α grains and varying extents of crack tilting and twisting caused by the interaction of the crack front with α/α boundary or α/α + β interface. It was revealed via surrogate-based statistical analysis that the Schmid factor has the strongest effect on crack growth rate.

Dynamic behavior and microstructural evolution of TiAl alloys tailored via phase and grain size

As a kind of promising aerospace material, TiAl alloys need to withstand extreme conditions such as high-rate impact loads and high temperatures. The mechanism on the failure and fracture of TiAl alloys under extreme conditions is related with the microstructure, including phase and grain size. In the present research, two kinds of TiAl alloys tailored with different microstructures, near lamellar (NL) and near gamma (NG), were fabricated by thermo-mechanical treatment. Microstructural characterization was analyzed by XRD and EBSD. The dynamic behavior of the TiAl alloys under different temperatures ranging from 293 K–873 K was investigated by a split Hopkinson pressure bar. The strain rate sensitivity and temperature sensitivity was analyzed. The microstructural evolution was concerned to understand the failure mechanism of the two kinds of the TiAl alloys. The NG-TiAl had the homogeneous deformation with synergy effect between homogeneous equiaxed grain and lamellar structure, and no failure occurred in NG-TiAl. However, the NL-TiAl showed heterogeneous deformation with both “orange peel effect” and cracks, which was attributed to large equiaxed grain and brittle γ-lamellae with similar orientation. Further, the cracks were easily nucleated and propagated from the interface between γ-lamellae structures, especially in the γ-lamellae structures parallel with the loading direction. Finally, the modified Johnson–Cook constitutive model was proposed to describe the deformation behavior, in which both strain rate hardening and temperature softening terms were expressed as a function of strain and strain rate.

Effect of carbide precipitation on Coffin–Manson relationship of a polycrystalline nickel‐based superalloy

AbstractThis study explores the dual‐slope Coffin–Manson (C–M) behavior of a polycrystalline nickel‐based superalloy, EA, used in turbine engine applications with an emphasis on discerning the micro‐mechanisms responsible for it. The motivation for distinguishing the micro‐mechanisms responsible for bi‐linear C–M behavior stemmed from the earlier evolved comprehensions that state that the fatigue life estimation based on the extrapolation of any single line gives inaccurate results. Transmission electron microscopy (TEM) investigations of fatigue fractured specimens at low strain amplitudes, Δε/2, revealed that dislocations are homogeneously distributed in the γ‐channels and occasionally form networks at γ/γ′ interface. Whereas deformation is heterogeneous at high Δε/2 owing to the complex dislocation reactions. Cr23C6 carbides are precipitated during the high Δε/2 fatigue tests, which act as obstacles for dislocations. The deformation heterogeneity resulting from the dislocation–γ′ precipitate interactions and the dislocation–M23C6 carbide interactions accounts for the dual‐slope C–M behavior.

Revealing the Origin of Heterogeneous Phase Transition and Deformation Behavior in Au-Ag-Cu-Based Multicomponent Alloys

Local chemical heterogeneity of highly-concentrated multicomponent alloys has drawn much attention as it can produce novel material behaviors and remarkable properties. In Au-Ag-Cu-based multicomponent alloys, phase separation and ordering have long been recognized to correlate with grain boundaries (GBs), but there is still a lack of atomic-scale understanding of the heterogeneous phase transition and how the microstructures respond to deformation. In this paper, a joint experimental and theoretical study was conducted on a medium-entropy polycrystalline model alloy, which is a representative Au-Ag-Cu-based multicomponent alloy with important applications in fields such as photocatalyst and micro-/nano-electromechanical systems. The GB regions are observed to preferentially nucleate two-phase lamellar structures, which are softer than grain interiors featuring short-range-order and modulated morphologies. First-principles calculations suggest the GB segregation of Ag and depletion of Cu are energetically favorable, consequently creating compositions that facilitate phase separation and impede ordering. Calculations of elasticity-based mechanical properties, stacking fault and surface energies reveal the GB lamellar structures are intrinsically soft with heterogeneous deformation capabilities. Furthermore, design strategies based on GB segregation engineering and tuning the dual-phase compositions are proposed to control heterogeneities. The results provide new insights into GB segregation, phase nucleation precursor and mechanical properties of noble-metal multicomponent alloys.

Strain hardening and stored energy in high-Mn austenitic based low-density steel

In the present study an attempt has been made to understand the high strain hardening in austenitic low-density steel using two full field measurements of temperature and strain on the sample during tensile deformation. Based on these measurements’ evolution of energy storage during deformation was calculated. High energy storage has been attributed to the interaction between dislocation groups belonging to different slip bands and destruction of short-range order (SRO) clusters. This in turn, dictates the range of the elastic stress field of slip bands. Furthermore, weak deformation heterogeneity ensued just after yield and continued with a fixed strain pattern up to facture. This did not result in macroscopic instability but manifested as microstructural heterogeneity in the form of micro-band and nano twins at later stages of deformation. A mathematical model of energy storage based on dislocation entrapment is discussed.

Metamafic dyke and sill swarms in the Dom Feliciano Belt: Insights for post-collisional strike-slip tectonics and fluid-assisted metamorphism

The oblique collision of the Congo, Kalahari, and Rio de la Plata cratons resulted in the formation of the Dom Feliciano Belt that evolved from rifting, drifting, and amalgamation between ca. 1.0 and 0.5 Ga. The post-collisional stage of the orogenic event (ca. 600 – 530 Ma) is marked by lithospheric scale shear-zones, voluminous magmatism, and volcano-sedimentary sequences. However, the tectonic regimes, metamorphism and the development of space-forming structures are still debated. We present a comprehensive petrographic, mineralogical, and geochemical study of Ediacaran metamafic dyke and sill swarms from the easternmost portion of the São Gabriel Terrane (central Dom Feliciano Belt, southern Brazil). Mafic swarms and lamprophyres from two different areas in the syntectonic Caçapava do Sul aureole show heterogeneous microstructures, metamorphic degree and whole-rock composition due to heterogeneous metamorphism, deformation, and metasomatism. We aimed at deciphering the origin of the sheeted intrusions and the metamorphic processes that led to such heterogeneities. Trace-element composition indicates that the melts were formed at high depths and went through significant crustal assimilation during the ascent through the crust either in a continental arc or an island arc setting. Greenschist facies metamorphism and upper-crust brittle deformation partially preserved subvolcanic textures in metamafic dykes at the outer portion of the aureole. In opposition, amphibolite facies metamorphism with a significant fluid flow component resulted in highly modified and heterogeneous metamafic sills at the inner portion of the aureole and at high strain domains of the Caçapava do Sul Shear Zone. Heterogeneities in different areas are caused by the distance to batholith and to high-strain domains of the shear zone while variations within the same area result from heterogeneous and localized fluid flow during metamorphism. We suggest that the mafic swarms represent markers of the initial stage of the development of the shear zone and were metamorphosed due the subsequent syntectonic emplacement of Caçapava do Sul Granitic Complex. Remarkably, we note that heterogeneities in coeval units that often hinder the understanding of the Precambrian stratigraphy can be explained by heterogeneous fluid-assisted metamorphism, especially near shear zones and syntectonic intrusions.

Urban hazards caused by ground deformation and building subsidence over fossil lake beds: a study from Taipei City

Widespread land subsidence has become an increasing problem in urban areas worldwide and is caused by a combination of effects, of which in particular climate change, growing urbanization trends, and unbalanced groundwater extraction are considered to be the primary ones. While groundwater extraction can be a dominant reason for inland subsidence, other factors comprise excessive surface load of buildings or unsuitable substrate for foundations. In this study, a closer look is taken at Taipei City, which has been facing challenges of ground subsidence, and whose ground movement has been investigated using time series of Sentinel-1 remote sensing data. The results indicate that a specific region of the city experiences significant surface subsidence in local areas of former (dormant) river and lake beds with rates of up to 60 mm between 2017 and 2020. Furthermore, a precise spatio-temporal heterogeneity of deformation was identified upon combination of precipitation and groundwater level data. It can be shown that widespread monitoring using remote-sensing data is a feasible tool to identify and track locations exposed to subsidence hazards for urban planning and urban development phases in the future.

ERRATUM: Spatiotemporally heterogeneous deformation, indirect tectonomagmatic links, and lithospheric evolution during orogenic activity coeval with an arc flare-up

ERRATUM: Spatiotemporally heterogeneous deformation, indirect tectonomagmatic links, and lithospheric evolution during orogenic activity coeval with an arc flare-up

High-resolution mapping of the strain heterogeneity in heterogeneous and homogeneous structured Mg 13Gd alloy

The hetero-deformation induced (HDI) stress can effectively promote extra strengthening and strain hardening behavior, which originates from the heterogenous deformation between soft and hard domains. How to quantitatively evaluate the strain heterogeneity at the micron and sub-micron scales remains a great challenge during deformation incompatibility. In this study, the strain evolution at grain level of heterogeneous (HES) and homogeneous-structured (HOS) Mg 13Gd (wt%) alloy was characterized by high-resolution digital image correlation. Both HES and HOS samples show strain heterogeneity related to the physical slip bands inside grains, and the magnitude of local deformation in grain level is much higher than the macroscopic strain, especially at grain boundaries. The HOS sample can also generate HDI stress due to the remarkable difference in Schmid factor and lower geometrical compatibility factor between adjacent grains. The formation of dispersed strain bands in the coarse grains with hard orientation of the HES sample contributes to strain delocalization behavior and the improvement of strain hardening capacity. These results provide us with a new insight for heterostructured design of Mg alloys on a more microscopic scale. • The strain evolution at grain level of heterogeneous and homogeneous-structured Mg 13Gd (wt%) alloy was characterized by high-resolution digital image correlation. • The heterogeneous and homogeneous-structured sample showed strain heterogeneity, and the magnitude of local deformation in grain level was much higher than the macroscopic strain, especially at grain boundaries. • The homogeneous-structured sample can also generate the hetero-deformation induced stress due to the remarkable difference in Schmid factor and lower geometrical compatibility factor between adjacent grains. • The formation of dispersed strain bands in the coarse grains of the heterogeneous-structured sample contributed to strain delocalization behavior as well as the improvement of strain hardening capacity.