The interactions between chemical phase fields and structural defects play a key role in the properties of alloys. We illustrate the importance of these interactions in driven alloys, where defects are continuously being created, with particular focus on systems where radiation-induced segregation occurs. Specifically, we compare the microstructural evolution in undersaturated Ni-Si and Ni-Ge alloys during both 100 keV He and 2 MeV Ti irradiations. While the equilibrium phase diagrams of these systems are similar, and both systems show strong radiation-induced segregation, the evolving defect structures are remarkably different. Ni-Si reveals a high density of Frank loops, while Ni-Ge shows a complex array of dislocations. Moreover, a Ni3Ge precipitate shell is observed to coat He bubbles, while no segregation of Si is observed at such bubbles. We explain these differences in behaviors to solute drag by interstitial fluxes in Ni-Si vs solute drag by vacancy fluxes in Ni-Ge.
Developing an external-template-free route for synthesizing nanoporous covalent ceramics remains challenging because their strong covalent bonding typically necessitates high-temperature processing, which can limit nanoscale architectural control. Here, we report the fabrication of three-dimensional nanoscale bicontinuous porous β-SiC (3Dnbp-β-SiC) at 1073 K through a top-down metallurgical route based on liquid metal dealloying. During this process, a Mn5SiC precursor with a layered crystal structure was immersed in molten Bi, where Mn was selectively dissolved while the residual Si–C framework self-organized into crystalline β-SiC. Unlike the nearly isotropic ligament networks commonly observed in conventional dealloying systems, the product comprises a bicontinuous porous architecture constructed from interconnected nanoplates and exhibits a mesoporous structure with a BET surface area of 56.9 m2 g−1. These results highlight liquid metal dealloying as a viable metallurgical strategy for fabricating nanoporous covalent ceramics at a relatively low temperature.
Serrated flow in transformation-induced plasticity (TRIP) steels is commonly attributed to dynamic strain aging (DSA), whereas deformation-induced martensitic transformation (DIMT) may simultaneously influence deformation behavior. To clarify their respective roles, Fe–24Ni–0.3C steel and carbon-free Fe–30Ni alloy were investigated. Only Fe–24Ni–0.3C exhibited serrated flow and Portevin–Le Chatelier (PLC) bands despite active DIMT in both alloys, demonstrating that serration originates from carbon-induced DSA rather than DIMT. Notably, with increasing strain, serration transitioned from Type A, characterized by continuous PLC-band propagation, to Type B, characterized by discontinuous hopping propagation in the Fe–24Ni–0.3C specimen. Quantitative DIC analysis revealed a decrease in band velocity and an increase in the inter-band nucleation interval across the transition, which coincided with active DIMT. At 100°C, suppression of DIMT eliminated this transition. These results demonstrate that DSA triggers serrated flow, whereas DIMT modifies PLC-band dynamics and promotes the Type A-to-Type B transition.
Severe-plastic deformation (SPD) is a key approach to prepare high-performance Cu-Ni-Mn alloys by promoting θ-MnNi precipitation and inducing α-Cu grain refinement, but this is not practical to produce components with complex geometries. Here, Cu-20wt.%Ni-20wt.%Mn alloy with high strength up to 1345 MPa and 3.6% tensile ductility was fabricated by ultrasonic solidification and subsequent heat treatment without any deformation procedures, whose comprehensive mechanical property was even better than those after SPD. Ultrasound transformed coarse α-Cu dendrites to tiny equiaxed grains, with homogenized solutes and high dislocation density after solidification. These further provided abundant nucleation sites and reduced solute concentration gradient during subsequent heat treatment, facilitating the precipitation of θ-MnNi phase with small size and increased volume fraction. The effective precipitation and grain refinement enhanced alloy strength, while dense slipping dislocations and deformation twins improved its plasticity, which both contributed to the strength-ductility synergy.
A long-standing puzzle in glass science is why critical cooling rates for vitrification span approximately eleven orders of magnitude while atomic diffusivities at the glass transition temperature Tg converge within a narrow window. This observation demonstrates explicitly that atomic mobility alone does not govern glass-forming ability. We propose that the controlling factor could instead be the mobility and spatial localisation of configurons — broken-bond excitations that mediate structural rearrangement in disordered networks. In first-order transformations such as crystallisation, configurons are mobile and delocalised, enabling percolation and long-range ordering. In vitrification — a second-order-like transition — configurons are slow and Anderson-localised within the disordered network, suppressing percolation and preserving the amorphous state despite comparable atomic mobility.
Surface protective nitride layers are crucial for enhancing corrosion resistance of uranium (U) alloys, but the protective efficiency is influenced by its thickness discontinuity. Herein, the asynchronous nitridation behavior of constituent α and γ phases in duplex U-2.0 wt.% Nb alloys is investigated via experimental microstructure characterizations and theoretical analysis. Following plasma nitriding, a UN2-x surface layer is formed on the alloy substrate, yet exhibiting a distinct phase-dependent discontinuity of thickness: thick in the α phase but thin in the γ phase. The density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations reveal the intrinsic mechanism underlying this phenomenon: the Nb element thermodynamically suppresses nitride formation while kinetically facilitating nitrogen diffusion along the γ phase, collectively leading to UN2-x thickness discontinuity. This work clarifies the phase-related asynchronous growth mechanism of surface nitride layers in duplex U-2.0Nb alloys, which enriches the fundamental understanding of plasma nitriding in multi-phase U alloys.
Due to the high thermal conductivity inherent in ternary half-Heusler (HH) thermoelectric materials, their thermoelectric figure-of-merit (ZT) is significantly constrained. In this work, we propose the equivalent valence electron principle for designing high-entropy HH materials. High-quality ZrHfCoNiSnSb alloys were successfully synthesized, exhibiting significantly reduced lattice thermal conductivity in comparison to conventional ternary HH materials. High-resolution transmission electron microscopy analyses revealed the presence of abundant dislocations and nanoscale clusters within the ZrHfCoNiSnSb matrix. The multi-scale scattering centers generated by these microstructural features effectively scatter phonons across the full frequency spectrum, leading to an exceptionally low thermal conductivity of approximately 2.6 W/m·K at near-room-temperatures. First-principles calculations further reveal that ZrHfCoNiSnSb HH materials exhibit a moderate band gap and low formation energy. The equivalent valence electron principle proposed in this study not only offers guidance for expanding high-performance HH systems but also provides new insights into the design of high-entropy alloys.
In the present study, Ni-free (TiZrHf)–Mo–Sn multi-principal element alloys exhibiting low magnetic susceptibility together with shape memory effect and superelasticity were developed. The (TiZrHf)–2.50Mo–2Sn and (TiZrHf)–2.25Mo–3Sn alloys exhibited both shape memory effect and superelasticity, while the deformation behavior gradually changed toward superelasticity with increasing Mo and Sn contents. The (TiZrHf)–2.50Mo–3Sn alloy annealed at 1223 K for 1.8 ks exhibited a β single phase with preferred ⟨101⟩ orientation parallel to the rolling direction and a superelastic recovery strain of 3.2%. The developed alloy showed a low magnetic susceptibility of 1.43 × 10⁻⁶ cm³ g⁻¹, indicating its potential for MRI-compatible biomedical applications.
The microstructural evolution of a W-36.5wt.%Cr (W-67at.%Cr) alloy aged within the W-Cr miscibility gap was investigated after varied 1250°C heat treatment durations, leading to a discontinuous transformation of the parent bcc matrix into a two-phase bcc-1 Cr(W) + bcc-2 W(Cr) lamellar structure, with a high lattice misfit of +6.4% ±0.2%. Intriguingly, this precipitation was accompanied by significant recrystallisation and grain refinement, with a reduction in the mean grain size from 146 µm in the homogenised condition to 61 µm after 100h ageing, with no externally applied strain (i.e. no thermomechanical processing). Further analysis of the electron backscatter diffraction data indicated that the high misfit between the two bcc phases led to strain building up in the lattice during precipitation, which in turn drives recrystallisation during ageing. This Precipitation Induced Recrystallisation termed “PIX” provides a new alternative means to achieve grain refinement in engineering alloys.
As a magnetic Weyl semimetal with broken time-reversal symmetry, Co3Sn2S2 is considered an exceptionally important platform for exploring spintronics and correlated quantum phenomena. In this work, Co2.8X0.2Sn2S2 (X = Fe, Ni, Mn) samples were synthesized to investigate the effects of dopants at specific concentrations on magnetic and transport properties. Magnetic measurements revealed that the selected dopants induce significant changes in the Curie temperature, magnetic moment, and coercive field stemming from differences in the strength and type of exchange interactions within the kagome lattice. Benefiting from the interplay between magnetism, electronic correlations, and nontrivial band topology, the amplitude, shape, and temperature characteristics of the anomalous Hall effect exhibit pronounced dopant dependence. Qualitative and quantitative analyses based on scaling laws clearly demonstrate that the anomalous Hall effect is determined by both intrinsic and extrinsic mechanisms. These findings deepen our understanding of the transport properties of novel magnetic topological phases.
The present work demonstrates the selective synthesis of bicontinuous nanoporous Mo–Ni intermetallic compounds via partial liquid metal dealloying (PLMD). This innovative technique exploits a phase equilibrium between a liquid bath and solid ligaments to realize a self-limiting leaching process such that Ni dissolution is spontaneously terminated at a desired composition. Using this approach, bicontinuous porous architectures were produced for all binary intermetallic compounds in the Mo–Ni phase diagram. Electrochemical evaluations revealed that porous Mo7Ni7 exhibited the highest activity when employed as a catalyst for the hydrogen evolution reaction. A novel two-step PLMD process was used to construct a hierarchically porous Mo7Ni7 structure showing significantly enhanced catalytic performance as a result of ligament refinement.
The MAX phases constitute a large family of atomically layered ternary carbides/nitrides with hexagonal structure (space group P63/mmc) applauded for their compositional versatility, which is demonstrated by the easy formation of solid solutions with varying chemical complexity. This work presents a generalised steric stability framework to quantify the lattice distortions of Mn+1AXn MAX phases. The derived framework was consequently used to evaluate the steric stability of 13 ternary MAX phases in the (Ti,V,Cr,Zr,Nb,Hf,Ta)-Al-C system and correlate their lattice distortions to their experimental synthesisability by spark plasma sintering. The comparative synthesisability of these Mn+1AlCn phases relates well to the magnitude of their lattice distortions, unit cell crystallography, and the Goldschmidt radius of their constituent elements. Finally, this work addresses the limitations and sensitivity of the lattice distortion calculations based on Rietveld refined X-ray diffraction data.
