Dynamic Plastic Deformation Research Articles

Effect of microstructure on dynamic response of ferrite matrixed steel at high strain rates

Dynamic response of steels at high strain rates are of great practical significance for understanding mechanical structures under extreme load conditions. To explore the relationship between structure and stress during dynamic deformation at high strain rates, steel specimens were prepared with varied microstructures of ferrite, ferrite and pearlite, and ferrite and spherical carbide. It is revealed that different microstructured steels exhibit drastically different characteristic of waves excited by the instantaneous impact of a servo-hydraulic tensile testing. It is also observed that a beat frequency response exists under dynamic deformation at certain high strain rates. It is therefore proposed that dynamic plastic deformation starts with stress fluctuation with a dislocation damped vibration model, and two successively excited waves are superimposed to form the beat frequency response.

Phase reversion mediated the dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium-entropy alloy

An ultra-high strain rate (104 s-1) dynamic plastic deformation treatment at liquid nitrogen temperature (LNT-DPD) followed by annealing is carried out to obtain dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium entropy alloy (MEA). Such extreme loading conditions resulted in extensive phase transformation in this MEA. Subsequent annealing at 650°C for 1 h further induced reverse phase transformation and partial recrystallization, forming a complex heterogeneous microstructure characterized by nested trimodal grain sizes and partitioned dislocation density. A superior yield strength of ∼800MPa and a good ductility of ∼40% were simultaneously achieved in this heterogeneous alloy. In order to reveal the effects of grain size and dislocation density distributions on the mechanical property improvements, the underlying deformation mechanisms were systematically discussed. High density of geometrically necessary dislocations (GNDs) would be induced in complex heterogeneous structures during tensile deformation due to strain gradients or partitioning between different regions, which would lead to additional strengthening and work hardening. These results provide a novel approach to overcome the strength-ductility trade-off dilemma for FCC-structured MEAs.

Macro-micro deformation mechanism of tantalum‑tungsten alloy flyer under explosive loading

This study investigates the macro-micro deformation mechanism of tantalum and tantalum‑tungsten alloys under extreme rate loading. Flyers with varying tungsten contents (0 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%) and different texture were subjected to explosive loading tests. Molding and penetration capabilities of the flyers were comprehensively assessed by the mild-steel witness plate, recovered penetrator and plug. Tantalum‑tungsten alloys with 10 wt% tungsten were crushed, forming discrete holes on witness plate, while those flyers with 0 wt%, 2.5 wt%, 5 wt%, and 7.5 wt% tungsten content formed complete circular perforations on the witness plate. Recovered penetrators and plugs indicated partial fracture of pure tantalum. The increased tungsten content in the alloy enhances the penetration stability and recovery integrity of the penetrator, while simultaneously reducing dynamic plastic deformation. Microstructural analysis via Electron Back Scatter Diffraction (EBSD) revealed a robust {111}//Z axial texture at impact side of the penetrator, which weakened with increasing tungsten content; While un-impacted side showed a {110}//Z axial texture. And uniform equiaxial crystalline structures outperformed long strip grain structures subjected. Therefore, the alloys' molding abilities and penetration stabilities ranked as Ta2.5 W > Ta5W > Ta&Ta7.5 W > Ta10W. These findings provide a foundation for the application of tantalum and tantalum‑tungsten alloys under explosive loading.

Dynamic plastic deformation at liquid nitrogen temperature and aging effects on microstructure and properties of Cu-0.3Zr-0.15Cr alloys

The 9R phase is rarely formed in copper alloys because of its high stacking fault energy. In this study, we generated a large amount of 9R phase in Cu-0.3Zr-0.15Cr alloys by dynamic plastic deformation (DPD) at liquid nitrogen temperature for the first time, and revealed the transformation mechanism of 9R to nanotwins. The process of DPD + aging treatment enables the alloy to obtain excellent comprehensive properties (strength of 657 MPa, electrical conductivity of 75.2 % IACS, and elongation of 14.6 %), which are derived from the heterogeneous microstructure composed of ultrafine structures, coarse grains, and nano precipitated phases. In addition, we have evaluated the phase transformation kinetics after DPD at liquid nitrogen temperature. This work provides a new way to better understanding the microstructure transition and precipitation kinetics under dynamic plastic deformation with aging treatment at liquid nitrogen temperature.

Overcoming strength-ductility trade-off in bimodal metal matrix composite with 3D graphene-strengthened hetero-interface

Strength-ductility synergy has long been a challenge in the development of advanced metallic materials. In this study, we fabricated a novel bimodal-structured nickel matrix composite, which features in-situ synthesized three-dimensional graphene networks (3DGN) strengthening the hetero-interfaces between coarse-grained and fine-grained zones (CGZ and FGZ). Compared to the bimodal matrix, this 3DGN-reinforced composite exhibits remarkable enhancements of 30 % in yield strength, 40 % in ultimate tensile strength, and 40 % in uniform elongation, respectively, representing the highest comprehensive performance among nickel matrix composites and pure nickel obtained through cold rolling, severe plastic deformation, and dynamic plastic deformation as reported in the previous literature. The superior strength-ductility combination originates from the incorporation of 3DGN, which enables multiple strengthening and toughening mechanisms. Specially, the strength and strain hardening capability have been enhanced through improved dislocation storage capacity, a stronger hetero-deformation induced (HDI) hardening effect, and the activation of numerous stacking fault ribbons. Moreover, high-density dispersed microcracks in the FGZ relieve strain/stress concentrations while being constrained within the CGZ, further enhancing tensile ductility. This study provides new insights into addressing the inherent strength-ductility paradox in metal matrix composites.

Twinning behavior and variant selection mechanism of b.c.c tantalum during dynamic plastic deformation

In this paper, the microstructure and twinning behavior of tantalum (Ta) during dynamic plastic deformation (DPD) were jointly analyzed in combination with impact experiments and molecular dynamics simulations, with a focus on the mechanism of variant selection for twinning. The results indicated that twins nucleate at grain boundaries and gradually grows with increasing deformation until it penetrates the entire grain. Due to the difference of grain boundary dislocation density, strain rate and deformation temperature have significant impacts on the quantity and distribution of twins. In addition, at room temperature, nearly half of the twin variants in DPD samples do not conform to Schmid law, and almost all the twin variants in liquid nitrogen samples do not follow to Schmid law. The activation of these non-Schmid variants is mainly affected by the strain coordination. Through this study, we have deepened our understanding of the dynamic microstructural response of Ta under high-speed deformation conditions.

High-Strain-Rate Deformation Behavior of Co0.96Cr0.76Fe0.85Ni1.01Hf0.40 Eutectic High-Entropy Alloy at Room and Cryogenic Temperatures.

The deformation behaviors of Co0.96Cr0.76Fe0.85Ni1.01Hf0.40 eutectic high-entropy alloy (EHEA) under high strain rates have been investigated at both room temperature (RT, 298 K) and liquid nitrogen temperature (LNT, 77 K). The current Co0.96Cr0.76Fe0.85Ni1.01Hf0.40 EHEA exhibits a high yield strength of 740 MPa along with a high fracture strain of 35% under quasi-static loading. A remarkable positive strain rate effect can be observed, and its yield strength increased to 1060 MPa when the strain rate increased to 3000/s. Decreasing temperature will further enhance the yield strength significantly. The yield strength of this alloy at a strain rate of 3000/s increases to 1240 MPa under the LNT condition. Moreover, the current EHEA exhibits a notable increased strain-hardening ability with either an increasing strain rate or a decreasing temperature. Transmission electron microscopy (TEM) characterization uncovered that the dynamic plastic deformation of this EHEA at RT is dominated by dislocation slip. However, under severe conditions of high strain rate in conjunction with LNT, dislocation dissociation is promoted, resulting in a higher density of nanoscale deformation twins, stacking faults (SFs) as well as immobile Lomer-Cottrell (L-C) dislocation locks. These deformation twins, SFs and immobile dislocation locks function effectively as dislocation barriers, contributing notably to the elevated strain-hardening rate observed during dynamic deformation at LNT.

Shock compression of single-crystal stainless steel

We studied the orientation-dependent dynamic properties and plastic deformation mechanisms in single-crystal austenitic FeCr18Ni12.5 stainless steel shocked to peak stresses ranging 3.8-12.0 GPa. The 〈110〉 and 〈111〉 principal Hugoniots generally match that of polycrystalline 304L stainless steel, but the 〈100〉 Hugoniot exhibits lower shock velocities and comprises two distinct regions. The Hugoniot elastic limits (HELs) and spallation strengths range 0.5-1.2 GPa and 2.2-3.8 GPa, respectively, and exhibit trends previously observed in polycrystalline steels. We generally observed the largest HELs along 〈100〉 and the largest spallation strengths along 〈111〉. Microscopy revealed larger twin and martensite fractions in the 〈100〉 samples, correlations in twinning and martensite prevalence with dynamic response, and orientation-dependent differences in dislocation behavior near the spallation plane.

A comparison study of high purity nickel fabricated by laser powder bed fusion and subjected to dynamic plastic deformation

High density additively manufactured (AM) pure Ni samples were fabricated by laser powder bed fusion with 46 sets of processing parameters. The microstructure, thermal stability, and tensile properties of the sample with the optimized set of parameters were evaluated. To compare the inherent size effects related to dislocation cells and grain boundaries on thermal stability and strengthening, ultrafine-grained Ni samples with an identical chemical composition were also prepared by dynamic plastic deformation (DPD) with strain levels ranging from 0.2 to 2.2. The dislocation cells in AM Ni tended to coarsen between 400 and 600 °C, and partially disentangled and recovered at 700 °C−1200 °C but were reluctant to fully recrystallize even at 1200 °C due to the existence of oxide particles. These oxides were unexpected in high purity Ni. Consequentially, the yield strength of AM Ni continuously decreased with the increase of annealing temperature but remained higher than that of the fully recrystallized samples. The DPD Ni samples exhibited a higher strength level than AM Ni but with a poor uniform elongation. Meanwhile, their full recrystallization occurred at 500 °C for all strain levels, indicating inferior thermal stability compared to AM Ni. Fitting the inherent feature size with strength in the Hall-Petch relationship indicated that dislocation cell boundaries were weaker barriers to glissile dislocations compared to grain boundaries. The Taylor's hardening equation also correlated well with the dislocation cell strengthening in AM Ni. The AM Ni filled in a spot on the strength-ductility map that coarse-grained Ni and DPD Ni were unable to access.

A structural-thermal coupled modeling approach on the formation of adiabatic shear bands in steel sheet blanking process

Adiabatic shear banding reflects an unstable and dynamic plastic deformation mechanism occurring at high strain and strain rates which is strongly conjugated to fracture. Current work carries out a numerical study on the initiation and development of adiabatic shear bands (ASBs) in blanking process of AISI 4340 steel sheet. A structural-thermal coupled finite element analysis is developed in LS-DYNA software by implementing a thermo-viscoplastic flow rule for material plasticity and a damage criterion considering dynamic failure. The numerical simulations are focused on capturing ASB genesis through intense shear localization by evincing strain instability. Also, the evolution of ASB mechanism is investigated, aiming to contribute a stage-by-stage propagation and highlight its connection to dynamic failure. Further, the effect of ASB temperature and strain field on fracture is analysed, while the influence of strain/strain rate hardening and thermal softening on strain instability, peak force and the blanked surface is studied. The results revealed an S-shaped ASB due to severe shear localization and significant temperature increase, leading to dynamic recrystallization around punch-die corners and reacting to strain instability and dynamic. Finally, high magnitude thermal softening during ASB development resulted in earlier ASB generation and reduction of the peak blanking force, while further it decreased shear zone expansion and increased fractured length in the blanked surface.

Largely enhanced compressive strength and plastic deformation of Fe-doped all-d-metal heusler alloy Cr2CoV

The structure dynamic stability, magnetic property, strength, and plastic deformation of all-d-metal Heusler alloys Cr2Co1-xFexV (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) have been investigated in this study. It is found that Cr2Co1-xFexV alloys tend to crystalize in the XA-type Heusler phase. The atomic radius becomes the decisive factor in determining the lattice size. With the increase of Fe concentration, the interaction between Cr(B)-Fe atoms increases, resulting in the increase of Curie temperature. The magnetic moments of the Cr2CoV and Cr2FeV are analyzed in conjunction with the theoretical calculations. The ductility and compressive strength of the materials gradually increase with the increase of Fe content. Especially in Cr2FeV alloy, a high compressive strength of up to 3050 MPa and a large ductility of up to 61% are achieved, and no fracture occurs, showing excellent mechanical properties. The electron localization function diagram shows that d-d orbital hybridization is formed and weak in Cr2CoV and Cr2FeV alloys, which helps to form metal bonds. Consequently, the ductility of the all-d-metal Heusler alloys was improved, which increased the fatigue life in practical application.

Microstructural mechanisms imparting high strength-ductility synergy in heterogeneous structured as-cast AlCoCrFeNi2.1 eutectic high-entropy alloy

The dual-phase AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) presents a promising solution to the strength-ductility trade-off dilemma, making it a highly desirable option for structural materials with vast potential applications. However, the relationship between the mechanical properties and the unique as-cast heterostructures needs to be further revealed. Here, we conducted in-situ tensile experiments of the as-cast EHEA to unveil the mesoscopic/microscopic microstructural mechanisms of strength-ductility synergy via investigating the dynamic real-time plastic deformation behaviors and crystallographic information evolution, as well as characterizing the deformed microstructures via transmission electron microscopy. The results indicate that the sequential dominant heterogeneous deformation induced hardening resulting from the incompatible plastic deformation between different types of heterogeneous microstructures is the primary source of its remarkable strength-ductility synergy. Moreover, the unique elongated lamellar microstructures of the as-cast EHEA offer numerous phase boundaries, and the growth twins in the face-centered cubic (FCC) phase generate abundant twin boundaries, all of which contribute to boundary strengthening and further enhance the strength and ductility of the as-cast EHEA. Furthermore, abundant cross-slip and dislocation substructures in the FCC phase provide strain hardening for as-cast EHEA, while body-centered cubic phase contributes to the high strength through precipitation hardening. Consequently, the heterostructure induced multiple strengthening mechanisms are responsible for the high strength-ductility synergy in the as-cast EHEA. The present work provides a new perspective to explain the strength-ductility synergy of similar heterogeneous structured alloys.

Impact response of metastable dual-phase high-entropy alloy Cr10Mn30Fe50Co10

Plate impact experiments are conducted on a metastable dual-phase high-entropy alloy (HEA) Cr10Mn30Fe50Co10 with different matrix grain sizes and phase fractions. Free surface velocity histories are obtained along with microstructure characterizations. Postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. Multiple deformation mechanisms are observed, including dislocation slip and stacking fault in the face-center cubic (FCC) phase, dislocation slip and deformation twinning in the hexagonal close-packed (HCP) phase, and the FCC to HCP transformation. For spallation, damage is ductile in nature. Despite different microstructures, micro-voids prefer to nucleate at high-angle grain boundaries within the FCC phase, leading to similar spall strength. Upon shock loading, a dynamic plastic deformation partitioning behavior among the two phases is observed; at high shock stress, denser dislocations in the HCP phase result in increased fractions of voids around the FCC/HCP phase interface and within the HCP phase during spallation damage.

INCREASING THE CORROSION RESISTANCE OF HOT-ROLLED STEEL PIPES BY DYNAMIC DEFORMATION OF THE SURFACE COMBINED WITH INHIBITORY TREATMENT

The results of experimental studies of the surface corrosion resistance and metallographic structure of 139x5 mm pipes made of steel grade 20 using three types of inhibitors and various modes of dynamic plastic deformation are presented.. It has been esta

Microstructure and twinning behavior of b.c.c tantalum under dynamic plastic deformation

In this paper, dynamic plastic deformation (DPD) of tantalum (Ta) was achieved by split Hopkinson pressure bar and a variety of DPD conditions were set to systematically investigate the microstructure of the deformed samples, focusing on the twinning behavior. Results showed that the deformation conditions have a significant effect on the number and distribution of {112}<111>twins. Compared with {100} and {111} grains, {110} grains are more prone to twinning due to the fewer slip systems. As the strain rate increases or the deformation temperature decreases, the number of twins increases dramatically. In addition, the texture of Ta samples gradually changes from {110} to mixed {100} and {111} textures with the increasing deformation, and the number of twins first increases and then decreases. After calculation, it is found that the selection of twin variants in Ta under DPD not only follows Schmid law but is also influenced by strain coordination. The research in this paper deepens the understanding of tantalum as a material for armour-piercing projectile.

Improving the strength and SCC resistance of an Al-5Mg-3Zn alloy with low-angle grain boundary structure

The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening. Adding a third component to form precipitation can improve their strength, but it usually leads to high-stress corrosion cracking (SCC) sensitivity due to the formation of high-density precipitates at grain boundaries (GBs). So far, it is still challenging to improve the strength of Al-Mg alloys without reducing SCC resistance. Herein, a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced. By dynamic plastic deformation and appropriate annealing treatment, near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion (71%) of the low-angle grain boundary. TEM statistical investigations show that the precipitation of active T' phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions, and the area fraction of GB precipitates is reduced from 72% to 21%, which significantly decreases the SCC susceptibility. This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.

Retracted: “Fabrication and Characterization of Magnesium-Based WE43/TiC Nanocomposite Material Developed Via Friction Stir Processing and Study of Significant Parameters” [ASME Journal of Engineering Materials and Technology, 2023, 145(3), p. 031007; DOI: 10.1115/1.4062321

Abstract Magnesium metal matrix composites (MMMCs) have exceptional mechanical and metallurgical characteristics, which have drawn the interest of researchers across the world. In the present research study, an attempt has been made to fabricate WE43 magnesium (Mg) based nanocomposites using friction stir processing (FSP) after incorporating nano-titanium carbide (TiC) as a reinforcement. Further, the impact of different FSP variables such as transverse speeds (40 mm/min and 80 mm/min), and tool rotation speeds (900 rpm and 1800 rpm) over the metallurgical, wear, and mechanical performance has been studied. The large thermal energy generated by the rotating FSP tool gives rise to the mechanism of dynamic recrystallization and plastic deformation. This contributes to refining the microstructure and improvement in microhardness as per Hall–Patch relation—contributing to prominent grain size refinement and Orowan mechanism strengthening, due to the dispersion of reinforcement particulates. The outcome of the results depicts that the nanocomposite fabricated at a tool rotation speed of 1800 rpm and 80 mm/min transverse shows better mechanical and tribological characteristics than other developed composites and the base alloy. More specifically, the grain size was reduced nearly 12 times, microhardness was 2.58 times higher, and ultimate tensile strength (UTS) was 2.08 times higher when contrasted to the base alloy. Moreover, the unprocessed base material was characterized by an adhesive wear mechanism whereas the presence of scratches depicts the abrasive wear mechanism was dominant for WE43/TiC nanocomposite.

Microstructural evolution and high-temperature deformation mechanism of 4Cr5MoSiV1Ti steel

Hot-working die steel usually withstands complex loading conditions and higher service temperatures, and its mechanical properties will inevitably deteriorate because of dynamic recovery, recrystallization, and plastic deformation of tempered martensite during service. A systematic study was carried out on a newly developed 4Cr5MoSiV1Ti hot working die steel to clarify the related microstructure evolution and deformation mechanism by stretching deformation at different temperatures ranging from room temperature to 640 °C. Results obtained show that the ultimate and yield tensile strength values at room temperature are about 1904 MPa and 1691 MPa, respectively. With increasing testing temperature, the strength decreases, the plasticity increases, and the fracture mode changes from brittle to ductile. All of these are closely related to a combined effect of tempered martensitic dynamic recovery, recrystallization, and secondary phase re-dissolution. Deformation mechanisms change from dislocation slip to rotation or sliding of ferrite with increasing stretching temperature.

Evolution of zinc coatings during drawing process of steel wires

The paper shows a significant influence of the multi-stage wire drawing technology on deformability and phase transformations in the zinc coating. SEM tests proved that the coating after hot-dip galvanizing consists of a number of thin layers, ranging from 1 to 5 µm, and differing in thickness, chemical composition and properties. When pulled through the drawing die the zinc coating heats up (as a result of friction between the material and the tool) and its dynamic plastic deformation. It resulted in the fracture and partial crushing of the hard-intermetallic phases. It has been proven that as the wire passes through successive drawing dies, the coating is thinned and diffusion as well as phase remodelling of individual structural components occurs; in the place of phase ζ, the intermetallic phase δ1 develops, increasing its share in the diffusion layer. The crystals of intermetallic phases located on the border of the diffusion and outer layers break up and remain dispersed in the zinc. An analysis of the microhardness of the coating has proven that the level of the increase in the microhardness of the zinc coating is contingent on percentage of iron in particular layers of coating.

Study on deformation behavior of tantalum under cryogenic temperature dynamic plastic deformation

Tantalum samples were dynamically deformed at liquid nitrogen (LN) temperature to obtain one pass (LN-DPD-1pass) and three pass LN-dynamic plastic deformation (LN-DPD-3pass) samples, and Ta was also dynamically loaded at room temperature (RT-DPD) for comparison. Results showed that although all the three DPD samples are essentially formed by {100} and {111} grains, the LN-DPD-3pass sample is significantly more severely fragmented. The low-angle grain boundaries are fairly uniformly distributed indicating a high homogeneity of the deformed microstructure. Meanwhile, the proportion of random texture in LN-DPD-3pass sample is higher as compared to the other two samples due to the rotation of dynamic recrystallization grains during DPD. Uniform deformation structure and similar stored energy of the deformed grains lead to the formation of excellent microstructure in the annealed LN-DPD-3pass samples.