Plastic Deformation Capability Research Articles

Design of non-heat-treatable Al-Fe-Ni alloys with high electrical conductivity and high strength via CALPHAD approach

Electrical conductivity and strength are two critical properties concerned for rotors materials in electric vehicles. However, the two properties are often mutually exclusive in cast Al alloys. The present work proposes a novel non-heat-treatable Al-Fe-Ni alloy by considering the intermetallic compound’s content and morphology. With the modification of Ni and Fe content, the solidification path of designed alloy were calculated to predict the phase composition, which would greatly impact their performance. The as-cast Al-2Fe-1Ni (wt%) alloy exhibits comprehensive properties with an ultimate tensile strength of 131.2±2.5 MPa, an elongation of 20.2±3.6 % and an electrical conductivity up to 52.0±0.1 %IACS. The eutectic microstructure of Al13(Fe,Ni)4+α-Al in Al-2Fe-1Ni alloy accounts for over 90 %, much larger than the eutectic content in Al-0.4Fe-3.4Ni and Al-1Fe-1Ni alloys. The fine eutectics in Al-2Fe-1Ni alloy improve the second-phase strengthening effects and plastic deformation capability. In addition, the fibrous rod-like intermetallic reduces the electron scattering during the propagation process and leaves more space for free electron movement. The dominant second phase transforms from Al3Ni phase to Al9FeNi phase, further enhancing the thermal stability of the alloy. After aging treatment at 180 °C for 100 h, it shows no noticeable change in electrical conductivity and mechanical properties. It is hoped that this work can provide a new design approach for high-strength and high-conductivity Al alloys.

Interfacial microstructure and synergistic enhancement mechanism of symmetric gradient SiCp-reinforced aluminum matrix sandwich structure

Inspired by the biological sandwich structure to achieve excellent mechanical properties with both high strength and high ductility, the symmetric gradient silicon carbide particles (SiCp) reinforced aluminum (Al) composites, consisting of 10% SiCp/Al-3% SiCp/Al-Al-3% SiCp/Al-10% SiCp/Al, was fabricated using spark plasma sintering technology. The flat interface was achieved through hot rolling, significantly improving the bonding of interlayers. The differences in SiCp content among layers led to distinct evolution patterns in microstructure. In the pure Al layer, a notable continuous recrystallization mechanism was observed, while in the 3% SiCp/Al and 10% SiCp/Al layers, the recrystallization mechanism was nucleation-growth. The transmission electron microscope results indicated that the hindrance of dislocation motion at the interlayer interface and SiCp-Al interface enhanced the dislocation density, thereby improving its plastic deformation capability. On the other hand, the deflection and passivation of cracks at the interlayer interface significantly improves toughness. The differences intragranular strain among layers were most pronounced at the interlayer interfaces, leading to them becoming the stress concentration zone. Uncoordinated plastic deformation leads to sequential failure of layers, vertical cracks first occurred in the 10% SiCp/Al layer, then propagated towards the interlayer interface and the 3% SiCp/Al layer, respectively.

The deformation mechanism of low symmetric Ti–Pt intermetallic compounds containing high density of planar defects

Intermetallic compounds typically exhibit limited plastic deformation capacity due to challenges in activating dislocation slip and deformation twinning, coupled with a lack of alternative deformation mechanisms. Ti–Pt alloys are a prevalent type of intermetallic compound utilized in high-temperature shape memory alloys and as materials for energy applications in electric fields. However, they often exhibit poor deformation capability. Here, we prepared a low-symmetry intermetallic phase, Ti4Pt3, which demonstrates significant plastic deformation capability. This phase features a high density of parallel planar defects, resulting in an exceptionally large lattice periodicity perpendicular to these defects. Through in-situ scanning electron microscope compression tests, we observed substantial plastic deformation in this new phase. Analysis of the deformed Ti4Pt3 phase revealed that the dense planar defects create uniformly distributed sites of internal stress concentration, enabling a rapid increase in back stress within crystals. This phenomenon leads to notable lattice rotation and localized order-disorder transitions, both crucial mechanisms facilitating plastic deformation and enhancing deformation capacity. Our research underscores the potential of leveraging structural asymmetry to enable unconventional deformation mechanisms, thereby enhancing the plasticity of intermetallic materials.

Enhancing fatigue crack propagation resistance of heterostructured Al composites and multistage crack mechanisms

High tensile strength and low fatigue crack propagation (FCP) rate are hard to achieve simultaneously in aluminium (Al) based materials, which has been a long-lasting topic. It is because the traditional strengthening mechanisms may lead to the increase in FCP rate. In this work, we developed dual-level heterostructures by incorporating the in-situ synthesized TiB2 particles into Al matrix, to create particle-lean zones (PLZs) and particle-rich zones (PRZs) by extrusion. Fine grains were introduced by particle-associated local recrystallization in PRZs. By means of particle and grain size distribution, a heterostructured Al composite featuring with the coarse grains in PLZs and fine grains in PRZs was fabricated. It was found that simultaneous enhancement of both the strength and FCP resistance of Al composite was achieved through the development of heterostructures. During FCP, the PRZs can retard the growth of slip bands and increase crack deflection frequency while the PLZs increase the crack deflection distance and plastic deformation capability at crack tip. The fracture behavior of composite during FCP depended on grain characteristics, particles and stress intensity range. The detailed cracking behavior for typical <100>Al and <111>Al grains in different FCP stages was identified. The associated models were developed for different FCP behaviors. Particularly, the quantitative relationship between Pairs parameters and microstructure features was established, which was critical to understand fatigue properties of Al composite reinforced by small particles. These findings can provide a strategy to design metal materials with an excellent combination of both static and dynamic mechanical properties.

Realizing the outstanding strength-toughness combination of API X65 steel by constructing lamellar grain structure

The development of pipeline steels with exceptional cryogenic toughness is deemed imperative for their applications in various engineering fields. In this work, API X65 steel with lamellar grain (LG) structure is constructed through warm deformation techniques. Comparative analysis with raw API X65 steel revealed notable enhancements in both yield strength (YS) and ultimate strength (UTS), exhibiting increments of 315 MPa and 164 MPa, respectively, while retaining substantial fracture toughness (KIc = 251.14 MPa m0.5). Remarkably, the LG steel exhibits a distinct absence of a ductile-brittle transition behavior over a wide temperature range, maintaining an exceptionally high impact energy from room temperature (RT) to liquid nitrogen temperature (LNT), and the Charpy impact energy exceeding 330 J at LNT, nearly 16 times higher than the raw API X65 steel. This performance can be primarily attributed to the superior plastic deformation capability, coupled with the delamination toughening mechanism. The resultant tortuous path of crack propagation effectively facilitates the absorption of substantial energy, decreases notch tip sensitivity depending on the temperature, stress triaxiality, and strain rate, thereby fostering excellent cryogenic toughness.

Controllable stress-adsorbed layers in Ti/TiN/TiAlN coatings: Mechanical performance and micropillar compression

Solid particle erosion often compromises the durability of turbine engine blades, particularly those used in offshore and desert environments. Surface protective coatings have emerged as a promising solution to significantly enhance the erosion resistance of compressor blades. In this study, TiAlN multilayer coatings were deposited onto Ti-6Al-4V substrates using a vacuum arc deposition technique. The article explored the strategic incorporation of TiN-Ti-TiN stress-adsorbed layers (SALs) within TiAlN-based coatings. It also investigated the microscale mechanisms leading to coating failure under conditions of micropillar compression. The findings revealed that the presence of metal/ceramic interfaces significantly improved the adhesion strength, crack resistance, erosion resistance and fracture toughness of the coatings. The multilayer deformation behavior of the coatings was primarily determined by the plastic flow of the softer metal layers. The SALs played a crucial role in reducing the elastic strain energy by generating nanotwins, coherent interfaces, and high-density dislocations during deformation, thereby improving the coatings' plastic deformation capability. Moreover, the implementation of dual-cycle SALs successfully reduced radial crack propagation, facilitating a transition from brittle fracture to a combined brittle-ductile fracture mechanism. This study highlights the critical role of metal/ceramic interfaces and SALs in improving the erosion resistance and co-deformability of TiAlN-based hard coatings.

Synergistic effect of Al2O3-decorated reduced graphene oxide on microstructure and mechanical properties of 6061 aluminium alloy

In this study, Al6061 alloy matrix composites reinforced Al2O3-decorated reduced graphene oxide (Al2O3/RGO) with 0.1, 0.3 and 0.5 weight present (wt%) were successfully fabricated using high energy ball milling and hot extrusion techniques. The microstructures of these Al2O3/RGO/Al6061 aluminum matrix composites (Al MMCs) were characterized. The results showed that Al2O3/RGO were uniformly distributed within the Al6061 matrix and tightly bonded to the matrix. Al2O3 encapsulation on RGO surface would prevent the formation of Al4C3 brittle phase in matrix, ensuring that there was no reaction between the reinforcement and the matrix Al6061. Tensile strength and Vickers hardness tests demonstrated that the mechanical properties of Al MMCs significantly increased with addition of Al2O3/RGOs. Remarkably, Al MMCs with 0.1 wt% reinforcement showed tensile yield and tensile strengths of 270 MPa and 286 MPa, respectively, which were 49% and 43% higher than those of pure Al6061 prepared using the same process. Furthermore, the 0.1 wt% Al2O3/RGO composite also showed the best plastic deformation capability in considering of the strength.

Magnetic-assisted ultrasonic nanocrystal surface modification induced microstructures of titanium alloy

Surface nanocrystallization together with compressive residual stresses can significantly improve the mechanical properties of metallic materials. An innovative surface process called magnetic-assisted ultrasonic nanocrystal surface modification (MA-UNSM) is reported here. By coupling integrates magnetoplasticity and shocking-induced plasticity, the MA-UNSM can enhance the plastic deformation capability of materials without significantly increasing the USNM processing temperature, thus realizing more effective grain refinement, deeper plastic-affected depth and higher-magnitude residual stresses, as evidenced by microscopic characterization and mechanical measurements. Our results demonstrated that the magnetic field improves the plasticity of the material by reducing the resistance between dislocations and pinning obstacles and thus enhances the effectiveness of ultrasonic peening treatment. Magnetic field with two intensities (0.25 T and 0.6 T) were used to assist UNSM, and the results showed that 0.6 T was the better condition.

Improvement of plastic deformation property and current carrying capacity of Bi2212 wires through low oxygen partial pressure post-annealing of precursor

The performance of superconducting magnets is greatly dependent on the size and uniformity of the superconducting filaments within the wire. However, in the fabrication of Bi2Sr2CaCu2Ox (Bi2212) wires using ceramic oxide as the superconducting filaments, we face multiple challenges including filament fragility, poor uniformity, and non-smooth Ag/superconductor interfaces. These challenges primarily stem from the significantly lower plastic deformation capability of ceramic oxide powder filaments compared to metal matrices. To address these challenges, this study focuses on the modification of ceramic oxide precursor powders. Through the utilization of low-temperature, low oxygen partial pressure (pO2) heat treatment, we have observed significant changes in the Cu chemical states and lattice parameters within the Bi2212 grains. These alterations have proven to be highly effective in reducing the energy required for grain sliding and, in turn, enhancing the plastic deformation properties of the Bi2212 oxide filament. Furthermore, post-annealing the oxide powder under low pO2 conditions narrows the gap in plastic deformability between the Ag sheath and the oxide filaments, resulting in improved filament uniformity and a smoother Ag/oxide interface in Bi2212 wires. Notably, the Bi2212 grains exhibit an orderly arrangement within the wires. As a result of these improvements, the critical current density (Jc) of the final wires increases by an impressive 70 %. The outcomes of this study are not only crucial for producing Bi2212 magnets with higher magnetic field strength, improved magnetic field uniformity, and enhanced operational stability, but also offer fresh insights and methodologies for advancing the field of superconducting materials.

Short-range-order degree dominated physical and mechanical properties of refractory multi-principal element alloys: a first-principles study

The degree of short-range order (SRO) can influence the physical and mechanical properties of refractory multi-principal element alloys (RMPEAs). Here, the effect of SRO degree on the atomic configuration and properties of the equiatomic TiTaZr RMPEA is investigated using the first-principles calculations. Their key roles on the lattice parameters, binding energy, elastic properties, electronic structure, and stacking fault energy (SFE) are analyzed. The results show the degree of SRO has a significant effect on the physical and mechanical properties of TiTaZr. During the SRO degree increasing in TiTaZr lattice, the low SRO degree exacerbates the lattice distortion and the high SRO degree reduces the lattice distortion. The high degree of SRO improves the binding energy and elastic stiffness of the TiTaZr. By analyzing the change in charge density, this change is caused by the atomic bias generated during the formation of the SRO, which leading to a change in charge-density thereby affecting the metal bond polarity and inter-atomic forces. The high SRO degree also reduces SFE, which means the capability of plastic deformation of the TiTaZr is enhanced.

Study on the Compressive and Flexural Properties of Coconut Fiber Magnesium Phosphate Cement Curing at Different Low Temperatures.

The incorporation of coconut fiber (CF) into magnesium phosphate cement (MPC) can effectively improve upon its high brittleness and ease of cracking. In practical engineering, coconut fiber-reinforced magnesium phosphate cement (CF-MPC) will likely work in cold environments. Therefore, it is essential to understand the effects of various types of low-temperature curing on CF-MPC performances, but there are very few studies in this area. In this study, the static compression and three-point bending test were utilized to examine the compressive and flexural characteristics of CF-MPC with various CF contents and different negative curing temperatures. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were conducted to observe the impact of low-temperature maintenance on the structure and hydration reaction of the specimens. The results indicate that CF-MPC curing at low temperatures was more prone to cracks during compression and bending, while the appropriate amount of CF could enhance its plastic deformation capability. The CF-MPC's compressive and flexural strength declined as the curing temperature dropped. Moreover, with the rise in CF content, the samples' compressive strength also tended to fall, and there was a critical point for the change in flexural strength. In addition, MPC's primary hydration product (MgKPO4·6H2O) decreased with a drop in curing temperature, and more holes and fractures appeared in CF-MPC.

Research progress and prospects of plastic thermoelectric materials

In recent years, significant progress has been made in the research of plastic thermoelectric materials, for example, Ag&lt;sub&gt;2&lt;/sub&gt;S-based alloys. These materials exhibit excellent room-temperature plasticity due to their low slipping barrier energy and high cleavage energy, with synergistic enhancements in plasticity and thermoelectric properties achievable through alloying and doping strategies. The latest study on Mg&lt;sub&gt;3&lt;/sub&gt;Bi&lt;sub&gt;2&lt;/sub&gt;-based single crystals demonstrated superior performance in terms of plastic deformation capability and room-temperature thermoelectric properties. Microstructural characterization and theoretical calculation have revealed the crucial role of dislocation glide in the plastic deformation process of Mg&lt;sub&gt;3&lt;/sub&gt;Bi&lt;sub&gt;2&lt;/sub&gt; single crystals, especially, the low slipping barrier energy observed in multiple slip systems. Importantly, the Te-doped single-crystalline Mg&lt;sub&gt;3&lt;/sub&gt;Bi&lt;sub&gt;2&lt;/sub&gt; shows a power factor of ~55 μW cm&lt;sup&gt;–1&lt;/sup&gt; K&lt;sup&gt;–2&lt;/sup&gt; and &lt;i&gt;ZT&lt;/i&gt; of ~0.65 at room temperature along the &lt;i&gt;ab&lt;/i&gt; plane, which exceed those of the existing ductile thermoelectric materials. These findings not only deepen the understanding of microscopic deformation mechanisms in plastic thermoelectric materials but also establish an important foundation for optimizing material properties and developing novel flexible thermoelectric devices. Future applications of these materials in practical devices still face challenges in thermal stability, chemical stability, and interfacial contact. Addressing these issues will promote the application of plastic thermoelectric materials in the field of flexible electronics.

The Microstructures, Mechanical Properties, and Deformation Mechanism of B2-Hardened NbTiAlZr-Based Refractory High-Entropy Alloys.

The NbTiAlZrHfTaMoW refractory high-entropy alloy (RHEA) system with the structure of the B2 matrix (antiphase domains) and antiphase domain boundaries was firstly developed. We conducted the mechanical properties of the RHEAs at 298 K, 1023 K, 1123 K, and 1223 K, as well as typical deformation characteristics. The RHEAs with low density (7.41~7.51 g/cm3) have excellent compressive-specific yield strength (σYS/ρ) at 1023 K (~131 MPa·cm3/g) and 1123 K (~104.2 MPa·cm3/g), respectively, which are far superior to most typical RHEAs. And, they still keep appropriate plastic deformability at room temperature (ε > 0.35). The superior specific yield strengths are mainly attributed to the solid solution strengthening induced by the Zr element. The formation of the dislocation slip bands with [111](101_) and [111](112_) directions and their interaction provide considerable plastic deformation capability. Meanwhile, dynamic recrystallization and dislocation annihilation accelerate the continuous softening after yielding at 1123 K.

Plastic deformation capacity obtained by the process of strain delocalization in Hf0.5Nb0.5Ta0.5Ti1.5Zr multi-principal-element alloy

Multi-principal element alloys (MPEAs) with body-centered-cubic (BCC) structures composed of elements of IVB, VB, and VIB usually exhibit high compressive strength and superior high-temperature performance. However, premature necking under tensile loading at ambient temperature limits their applications. Herein, we report the Hf0.5Nb0.5Ta0.5Ti1.5Zr MPEA with a single BCC phase, which performs considerable tensile plasticity by the process of strain delocalization. The formation of dispersed slip bands and two major strain localized regions suppress premature necking. The strain-localized region with a larger strain gradient realized strain delocalization during non-uniform deformation, resulting in considerable tensile plasticity (∼20%) with a yield strength of 922 MPa. Two dominated work hardening mechanisms were revealed. One is the geometrically necessary dislocations (GNDs) produced by non-uniform deformation which can coordinate deformation incompatibility, thus enhancing plastic deformation capability. The other is the lattice distortion which can provide an easy path for the cross slip of dislocations and realize strain delocalization. These two kinds of work-hardening mechanisms jointly contribute to the significant plastic deformation capacity of the Hf0.5Nb0.5Ta0.5Ti1.5Zr MPEA.

High compression strength pure tungsten fabricated by plasma arc additive manufacturing

Pure W were fabricated by wire plasma arc additive manufacturing technology (WPAAM) and systematically investigated in terms of the microstructure and mechanical property. The as-fabricated W exhibits large-size columnar grains along the deposition direction, and it has extremely few microcracks, compared with that fabricated by laser powder bed fusion (LPBF). The compression strength and compressive plastic deformation capability of WPAAM W are significantly improved compared to the widely studied LPBF W and the fine grained W fabricated by other processes. In particular, the strength of WPAAM W is comparable to that of ultrafine grained W. A microstructure-based predictive model of compressive strength is developed to understand the strength performance of AM W. The proposed model correlates the manufacturing process, microstructure and mechanical property of additive manufactured W. This study is expected to shed light in the development of additive manufacturing technology of refractory metals.

Microstructure and tensile properties of high-entropy alloy Al0.5CoCrFeNi particles reinforced Ti/Al laminated composite

ABSTRACT Novel Ti/Al laminated composite embedded with particles of the high entropy alloy Al0.5CoCrFeNi were produced by vacuum hot press sintering at 650°C. The microstructure of the laminated composite was investigated using XRD, SEM, EDS, TEM and EBSD techniques. It was found that a thin layer of Al3Ti was formed at the Ti/Al interface. There were no obvious defects between the Al0.5CoCrFeNi particles and Al matrix, achieving a good interfacial bond. The tensile properties of the material were tested at room temperature. The results of the tensile test indicated that the material exhibited an elongation to failure of 59% and an average tensile strength of 240 MPa, demonstrating excellent plastic deformation capability. During the tensile process, the expansion of fractures and cracks in Al0.5CoCrFeNi particles can consume energy, which helps to improve the material’s ability to undergo plastic deformation. Based on the morphologies of tensile fracture, it has been observed that the fracture surface of high entropy alloys exhibits a mixed fracture mode consisting of both brittle and plastic fracture. The brittle BCC phase has been identified as the main cause of cracking in HEA. Ultimately, the material fractures due to necking.

The effect of WC-Co substrates on TiN/TiCN/Al2O3/TiCNO multilayer coatings

ABSTRACT In order to determine optimum substrate, TiN/TiCN/Al2O3/TiCNO coatings were deposited on WC-7Co substrate and WC-6Co substrate (named as Coating-7Co and Coating-6Co, respectively), and then the effect of WC-Co substrates on TiN/TiCN/Al2O3/TiCNO multilayer coatings was investigated by comparing the microstructure, hardness, adhesion strength, oxidation resistance and wear resistance of Coating-7Co and Coating-6Co. Results show that WC grain size of WC-6Co substrate is smaller, correspondingly the grain size of each layer in Coating-6Co is smaller, and the surface roughness is lower. Compared with Coating-7Co, Coating-6Co exhibits higher hardness, better plastic deformation capability, better oxidation resistance, lower friction coefficient and better short-period wear resistance. However, because of higher residual tensile stress and lower adhesion strength, the long-period wear resistance of Coating-6Co is worse than Coating-7Co conversely. To make good use of Coating-6Co, some post-deposition treatment techniques that can reduce residual tensile stress and improve adhesion strength should be considered.

Superior strength-plasticity synergy in a heterogeneous lamellar Ti2AlC/TiAl composite with unique interfacial microstructure

Improving the plasticity of TiAl alloys at room temperature has been a longstanding challenge for the development of next-generation aerospace engines. By adopting the nacre-like architecture design strategy, we have obtained a novel heterogeneous lamellar Ti2AlC/TiAl composite with superior strength-plasticity synergy, i.e., compressive strength of ∼2065 MPa and fracture strain of ∼27%. A combination of micropillar compression and large-scale atomistic simulation has revealed that the superior strength-plasticity synergy is attributed to the collaboration of Ti2AlC reinforcement, lamellar architecture and heterogeneous interface. More specifically, multiple deformation modes in Ti2AlC, i.e., basal-plane dislocations, atomic-scale ripples and kink bands, could be activated during the compression, thus promoting the plastic deformation capability of composite. Meanwhile, the lamellar architecture could not only induce significant stress redistribution and crack deflection between Ti2AlC and TiAl, but also generate high-density SFs and DTs interactions in TiAl, leading to an improved strength and strain hardening ability. In addition, profuse unique Ti2AlC(11¯03¯)/TiAl(111) interfaces in the composite could dramatically contribute to the strength and plasticity due to the interface-mediated dislocation nucleation and obstruction mechanisms. These findings offer a promising paradigm for tailoring microstructure of TiAl matrix composites with extraordinary strength and plasticity at ambient temperature.

Study of the microstructure and mechanical property relationships of gas metal arc welded dissimilar Hardox 450 and S355J2C+N steel joints

This research reports the investigation of the dissimilar welding of Hardox 450 and S355J2C+N steels, which have two different superior properties, by the gas metal arc welding (GMAW) method in terms of microstructure and mechanical properties. Experiments were performed using mechanical tests such as Vickers microhardness (HV 0.1), bending, Charpy V-Notch impact, wear, and tensile test. Optical microscopy (OM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analyzes have been implemented. A variation in the welded joint microstructure was observed, which affect the mechanical properties. Grain size distribution in area fraction was determined from the EBSD maps of S355J2C+N steel, welded zone, heat affected zone (HAZ) and Hardox 450 steel. The hardness value was measured 311 ± 8 HV for Hardox 450 base material. While the hardness of the S355J2C+N base metal was ∼187 ± 8 HV, the hardness of the weld center was measured as 249 ± 8 HV. Mechanical strength analysis revealed that the yield strengths of base metals were 513 ± 8 MPa and 1464 ± 8 MPa for S355J2C+N and Hardox 450, respectively. The highest tensile strength of the sample extracted from the longitudinal direction of the welded joint is 899 ± 8 MPa. The highest tensile strength of the transverse sample, which was subjected to the tensile tests, was determined as 699 ± 7 MPa and it fractured from the S355J2C+N steel which has less strength. The joint efficiency was determined as ∼133%. The weld zone has sufficient toughness and the change in toughness values in the HAZ is small. The grain size increased from martensitic Hardox 450 steel region to S355J2C+N region, in addition to this, the hardness decreased with the effect of transition from martensitic structure region to ferritic structure region. The welding zone is compatible with two different materials and has a high plastic deformation capability. With the welding procedure followed in the study, Hardox 450 and S355J2C+N dissimilar materials were successfully combined, and it was determined that this welded joint was scientifically and industrially applicable.

Shock compression and spallation of a medium-entropy alloy Fe40Mn20Cr20Ni20

Shock compression and spallation of a low-cost cobalt-free medium-entropy alloy (MEA), Fe40Mn20Cr20Ni20 (at%), with a face-centered-cubic structure are investigated via plate impact experiments, to reveal its dynamic mechanical properties and corresponding microscopic deformation/damage mechanisms. The Hugoniot equation of state, yield strength, spall strength and pullback rate are obtained from free-surface velocity histories. Post-deformation samples are characterized with transmission electron microscopy, scanning electron microscopy and electron backscatter diffraction. The Fe40Mn20Cr20Ni20 MEA exhibits a good balance in spall strength and ductility (low pullback rate) at a relatively low cost, compared to several other types of medium/high entropy alloys and steels. At sufficiently high impact velocity (e.g., 500 ms−1 here), nanoscale deformation twinning becomes a key deformation mechanism for Fe40Mn20Cr20Ni20 MEA in addition to dislocation slip. During spallation, voids (i.e., damage) nucleate preferentially at grain boundary triple junctions, and grow isotropically with increasing loading. Owing to fine grains and strong plastic deformation capability of the Fe40Mn20Cr20Ni20 MEA, void coalescence is accomplished by intragranular shear deformation bands and cracks, which contributes to its high ductility.