For the first time, a giant shape memory effect of 15.7 ± 0.2% was obtained in [1¯44]-oriented single crystals of the Cr20Mn20Fe20Co34.5Ni5.5 at.% high-entropy alloy undergoing FCC↔HCP martensitic transformation, under a tensile stress of 160 MPa. This value amounted to 90% of the theoretical value of the lattice deformation 17.5% for the FCC–HCP martensitic transformation in [1¯44] orientation under tension and is currently the highest for this transformation in iron-based alloys. The physical reason of the giant shape memory effect in the [1¯44]-oriented single crystals of the Cr20Mn20Fe20Co34.5Ni5.5 at.% high-entropy alloy is related to the combination of the high yield strength of the initial FCC-phase with the development of thin HCP-martensite predominantly in one system.

The mechanism of phase transformation from hexagonal close-packed (hcp) to body-centered-cubic (bcc) structure in Mg single crystal under high pressure is studied by molecular dynamics (MD) simulations. The hcp-bcc phase transformation is achieved by a shear-shuffle mechanism, through the formation of bcc nanotwinned structure and the subsequent detwinning. The nanotwinned structure can effectively accommodate the shear caused by the hcp-bcc phase transformation, which facilities the growth of bcc phase under hydrostatic pressure. The detwinning turns the bcc nanotwinned structure into bcc nano-polycrystalline. Two twinning modes with the opposite twinning shear occur during the detwinning, which can accommodate the shear in different directions. The mechanism of hcp-bcc phase transformation revealed in this work brings out a comprehensive understanding of the plastic mechanism under high pressure, which is helpful for the further materials design under high pressure.

The mechanical response of {12¯11} and {12¯12} coherency twin boundaries (CTB) under external loading was investigated with molecular dynamics simulations in titanium and magnesium. Mutual transformation between {12¯11} and {12¯12} CTB was revealed, i.e., {12¯12} CTB can transform into two co-zone {12¯11} CTBs, forming a twin junction, while reversibly {12¯11} CTB can transform into {12¯12} CTB and the other co-zone {12¯11} CTB, forming another twin junction. The simulation result thus well explains the experimental observation of twin junctions. Moreover, owing to the geometric compatibility and mobility of the two junctions, the mutual transformation between {12¯11} CTB and {12¯12} CTB produces {12¯12}/{12¯11} twin networks with perceivable plastic strain accommodation.

CoCrMo (CCM) alloys fabricated by laser powder bed fusion (LPBF) normally exhibit low ductility. In the present study, a new plastic deformation mode of residual stress tailored high stacking fault (SF) is proposed for LPBF fabricated CCM alloy, delivering an excellent ductility (∼14.5%) in the as-fabricated state. Elaborate microstructural characterization elucidated that low level of initial residual stress contributes to a high stacking fault probability, generating extensive amounts of SFs to sustain the plastic deformation. Such massive deformation faulting activities mitigated the strain localization between FCC/HCP phase of CCM alloy with high residual stress level. Further low temperature annealing treatment validated the above theory, and increased the ductility to ∼21.4% with a high tensile strength of ∼1181 MPa. The present study demonstrated that the ductility of LPBF fabricated CCM alloy can be significantly enhanced by tuning the internal residual stress and the associated stacking fault probability.

Both MXenes and high-entropy ceramics are booming material families. The rich surface functional groups and elemental controllability of MXenes, as well as the rich composition space of high-entropy ceramics provide these materials unexpected chemical properties, and thus they have great potential in energy storage. Herein, we successfully synthesized a novel high-entropy MXene (HE-MXene), Ti1.1V1.2Cr0.8Nb1.0Mo0.9C4Tx for the first time. The aberration-corrected scanning transmission electron microscopy, density functional theory calculation, and super energy-dispersive X-ray spectroscopy together demonstrate that the five transition metals are uniformly dispersed in one MX slab in the form of solid solutions. The Ti1.1V1.2Cr0.8Nb1.0Mo0.9C4Tx exhibits high capacity as a supercapacitor electrode with a gravimetric capacitance of 284.6 F g−1 at a current density of 1 A g−1 and also shows outstanding stability. This work proves the existence of M5X4Tx HE-MXene and further adds a new member to the MXene family, providing support for its application in other fields.

Together with void nucleation, growth, and coalescence, void collapse is a crucial component in ductile spallation. This work reports single void collapse behaviors in perfect Al under isothermal and adiabatic conditions based on molecular dynamics simulations. Two typical void collapse mechanisms, spontaneous collapse and compressive collapse, are clearly revealed. At the initial stage of void collapse, the former may be primarily attributed to the surface tension and the viscosity effects, and the latter is due to the expanding compression of a big void to a small one. The inertia effect predominates the void collapse, especially at the late stage of collapse; the temperature softening effect also conduces to the collapse under adiabatic circumstances. The average radius of the void follows an exponent decrease, and void collapse behavior is unaffected by the spallation sequence. Lastly, it is phenomenologically discovered that isothermal tension and adiabatic shock are pretty similar in void evolution.

Synchro-Shockley dislocations, as zonal dislocation, are the major carrier of plasticity in Laves phases at high temperatures. The motion of synchro-Shockley dislocations is composed of localized transition events, such as kink-pair nucleation and propagation, which possess small activation volumes, presumably leading to sensitive temperature and strain rate dependence on the Peierls stress. However, the thermally activated nature of synchro-Shockley dislocation motion is not fully understood so far. In this study, the transition mechanisms of the motion of synchro-Shockley dislocations at different shear and normal strain levels are studied. The transition processes of dislocation motion can be divided into shear-sensitive and -insensitive events. The external shear strain lowers the energy barriers of shear-sensitive events. Thermal assistance is indispensable in activating shear-insensitive events, implying that the motion of synchro-Shockley dislocations is prohibited at low temperatures.

Powder bed fusion experiments were conducted to investigate the microstructure of Scalmalloy® utilizing standard circular and Adjustable Ring-Mode (ARM) laser beams. The ARM laser beam produced an almost fully equiaxed grain structure, characterized by a significantly thicker Fine Grain (FG) band, compared to the circular laser beam with the same overall volumetric energy density. The discussion explored the mechanisms underlying this remarkable advancement, with a particular focus on the nucleation role of the L12 Al3(ScxZr1-x) phase. Among various theories explaining the inhomogeneous distribution of L12 particles, the findings were found to be more consistent with the primary precipitation at low cooling rates. The research indicates the potential for achieving a fully equiaxed microstructure through heat source modulation without compromising productivity.

Dwell fatigue crack growth in nickel-based superalloys is influenced by a complex interplay between mechanical and chemical phenomena. The stress distribution at the crack tip is closely related to these phenomena and to the local microstructure. In this study we evaluate experimentally the microscale residual stress distribution ahead of crack tips in RR1000 alloy samples after interrupted high temperature dwell fatigue testing. In the crack opening direction the results show a compressive residual stress zone, the extent of which is linked to the plastic zone size and crack growth retardation behaviour. In the direction of crack propagation the residual stress is also influenced by crystallographic grain orientation. The results demonstrate a novel approach of experimentally evaluating crack tip stress distribution via focused ion beam – digital image correlation (FIB-DIC) ring-core measurements at the grain-level. This provides new insights into fatigue crack growth in microstructurally heterogeneous materials.

The impacts of solute segregation and chemical order on grain boundary (GB) migration are investigated by atomistic simulations in the NbMoTaW multi-principal element alloy (MPEA). Assisted by a contrived Nb-rich model, it is found that solute segregation and chemical order synergistically inhibit GB migration. Nb segregation increases the critical stress for GB migration, and the presence of chemical order further enhances the resistance of GB to plastic deformation. The destruction of local ordering structures is responsible for the difficult GB migration. Transition pathway analyses show that GB modified with both Nb segregation and chemical order requires high migration barrier, and the prior migration of GB sites tends to avoid regions with heavier chemical order. These results provide new insight into how chemical complexity affects elementary GB motion and contribute to manipulating the stability of MPEAs.

A strategy bypassing “rolling+annealing” while involving merely ultrasonic vibration-modulated static compressive loading was established to enhance the strength-ductility synergy in a C-doped CoCrNi medium entropy alloy. Specifically, by superimposing ultrasonic vibration of 20 KHz in frequency and 20 μm in amplitude onto a compressive load of ∼180 MPa (∼60% of yield strength) applied on a coarse grain CoCrNiC0.1 alloy for 25 min, yield strength, ultimate tensile strength, and total elongation of the alloy were largely improved to 530 MPa, 950 MPa, and 36.5%, showing respectively an increment of 77%, 28%, and 53% from the original state (300 MPa, 740 MPa, and 23.8%). Structure analysis on the ultrasonically processed CoCrNiC0.1 alloy indicates that intragrain precipitation of Cr7C3 networks of a characteristic size ∼20 μm provoked by ultrasonic vibration was the main cause for the strength-ductility synergy. Our work provides a promising path to engineer the strength-ductility synergy in precipitation-strengthened alloys.

Simulation of diffusion-controlled phase growth has long been practiced by strictly following Fick-Onsager-Darken law for diffusion under the assumptions of local equilibrium and sharp interface. However, a major pain point is the difficulty of finding operating tie-lines at the interface for multi-component alloys. In the present work, a new scheme is presented to deal with this difficulty by extending from Larsson and Reed scheme (Larsson and Reed, Acta Mater. 56 (2008) 3754–3760). The flux balance equations are rewritten to enhance the accuracy and fulfilled from the very beginning of simulations. The simulation results of the Fe-Mn-Mo and Fe-C-Mn ternary systems, as well as high-order systems, demonstrate the applicability and robustness of the new scheme. The simulation of the Fe-C-Mn system reveals the details of the early stages of the bcc phase growth, showing a shrink of bcc before its growth with two growth modes smoothly switched.

Reduced activation ferritic/martensitic (RAFM) steel emerging as the promising structural material of fusion reactors, has attracted considerable attention to improve its high-temperature performance. In the present study, a new-type RAFM steel (Fe-8.9Cr-0.82W-0.23Mn-0.086Si-0.27Ti-0.075C-0.032O) enhanced by in-situ nanoparticle constituents containing high-density and dispersed TiC, TiO and TiO@TiC (with core (TiO)-shell (TiC) structure) was manufactured using selective laser melting (SLM) with imposed oxygen atmosphere in the printing chamber. The novel TiO@TiC with core-shell structure is reported for the first time in RAFM steels. In addition, the high-temperature mechanical properties achieved in the present study are superior to those of other additive manufactured RAFM or oxide dispersion strengthened RAFM (ODS-RAFM) steels, which is attributed to the high-density and dispersed nanoparticles introduced by additional oxygen addition during SLM. The proposed idea for taking the reactive atmosphere into consideration for alloy design in this study could be extended to other alloys.

Iron impurities frequently observed in BaxK1-xFe2As2 wires and tapes not only cause local suppression of superconductivity but also act as macro-obstacles to transport current. We find that the agglomerated iron particles are not introduced by external sources or caused by incomplete reactions but result from the chemical environments determined by nominal compositions. The excess K added to the raw materials for compensating the evaporated K consumes the stoichiometric arsenic and induces unreacted iron. Decreasing the K content indeed removes the redundant Fe but also deteriorates superconductivity. Instead, slightly excessive addition of As is proved to be a twin-track approach in fabricating high-performance superconductors. Through modulation of the nominal composition Ba0.6K0.5-βFe2As2+δ, we effectively eliminate the iron impurities and improve the transport critical current density of the tape to Jc(4.2 K, 10 T)=9.59×104 A/cm2. A reaction model is proposed to explain the formation mechanism of the iron particles.

A novel Fe-rich medium entropy alloy (MEA) space with a γ+γ’-only phase field at 800 °C is proposed where the volume fraction and dissolution temperature of γ’-phase can be tuned by substituting Fe for Ni/Co and Cr. The γ+γ’-structured Fe-35.5Ni-4Cr-6.3Al-3.2Ti alloy (Fe-content of 51 at.%; γ’-volume fraction of 24%) after a recrystallisation and ageing treatment displays a yield strength of 902 MPa, ultimate strength of 1370 MPa and a tensile ductility of 24%. The presented alloy space progresses towards the development of Fe-rich MEAs with good strength retention (>600 °C) for heat-resistant structural applications.

The transformation of compression twins (CT) to double twins (DT) is studied in a dual-textured Mg-6.5%Zn(wt.) alloy during deformation along the extrusion axis. After 7.3% compression, 85% of CT are transformed to DT. This ratio drops to 22% and 36% during tension although the applied stresses and strains in tension were much higher. The Schmid factor of the actual DT variants was very low (and often negative) in tension and compression and could not explain the differences in DT activity. It is shown that the suppressed CT→DT transformation during tension is accompanied by the activation of 〈a〉 non-basal slip -rather than 〈a〉 basal slip- which presumably hinder the transformation because the dissociation of 〈a〉 basal dislocations is necessary to nucleate and grow extension twins in primary CT. These findings point out an effective strategy to suppress DT by activating 〈a〉 non-basal slip, which may be useful to design Mg alloys with high ductility.

MAX phases gain increasing attention as protective coatings due to superior anti-corrosion and oxidation resistance for harsh high-temperature applications. However, the lower strength and strength-ductility trade-off in bulk MAX phases still pose an enormous challenge arising from the large ratio of c/a lattice parameters and less activated slips. Here, nanocrystalline Cr2AlC coating with high-purity was fabricated using a hybrid arc/sputtering technique with subsequent thermal annealing. Cylindrical micropillar compression test was conducted by FIB milling to identify the mechanical properties of the coating under deformation. The stress-strain curves demonstrated that an ultrahigh compressive strength of 5.3 GPa with strain beyond 12.5% was surprisingly achieved for Cr2AlC coating, which was 5 times larger than all the reported bulk MAX phases before. Specifically, the extraordinary ductility at RT is ascribed to the synergy of the fundamental basal slip, additional non-basal slip and deformation twinning stimulated by ultra-refinement effect of nano-crystalline Cr2AlC coating.

High entropy alloy (HEA) nanoparticles have wide application prospects in electrocatalysis due to their unique structure. However, the surface of HEA nanoparticles has strong chemical activity due to numerous suspended and unsaturated bonds, which poses serious challenges to storage and transportation. To solve this problem, we used a double pulse carbothermal shock process to coat the surface of HEA nanoparticles with graphene. The formation mechanism of HEA nanoparticles and the graphene coating mechanism were discussed. The results showed that the HEA thin films were curled into nanoparticles by the change of orientation of twin structure under the thermal stress of carbothermal shock. After the complete HEA nanoparticles were formed, the carbon dissolved in the HEA nanoparticles will gradually precipitate out during a second carbothermal shock and form multiple layers of graphene on the surface, and forming a structure of graphene-coated HEA nanoparticles.

Using high angle annular dark-field scanning transmission electron microscopy, we report the formation of a five-fold symmetry structure at the (1¯100)η//(110)Al edge interface of otherwise defect-free η2 precipitates in Al-Zn-Mg-Cu alloys. This quasicrystal entity has a demonstrated ability to hinder growth at the interface where it resides. Assisted by calculations based on density functional theory, the five-fold symmetry structure is shown to form easily at Zn-rich conditions due to favorable interfacial energies at all stages of evolution. These findings offer an enhanced perspective of precipitate stabilization in an alloy of widespread industrial interest, presenting a potential alternative path to alloy design.

First principles calculations in the NiCoCr medium-entropy alloy predict a negative stacking fault energy (SFE) at T=0 K, implying an infinite Shockley partial dissociation distance. Many experiments at room temperature (RT) show however a finite dissociation. This discrepancy has been suggested due to solute strengthening that prevents the partial separation. Here, atomistic simulations in a model NiCoCr alloy having a negative SFE show that solute strengthening can limit partial separation at T=0 K but, the solute-induced barriers are easily overcome at RT and time scales of only 1 ns. Under experimental conditions (time scales of hundreds of seconds and longer), solute pinning is therefore insufficient to limit dissociation. Finite partial separations are thus presumably due to a positive stacking fault free energy at RT or short-range-order effects. It is argued here that the former is more likely than the latter.