The elastic modulus of metallic glasses (MGs) is commonly considered to be "inherited" from their solvent (principal) element. However, this rule exhibits significant exceptions in Cu-based MG systems. To uncover the physical mechanism behind this anomalous inheritance, this study selected the Cu-Zr-Hf-Ti system as the research object. Based on first-principles calculations, a multi-scale analysis was conducted, including the macroscopic elastic modulus, atomic-scale bonding characteristics, and the electronic structure. The results show that the elastic modulus of this system is governed by low-stiffness interatomic interactions represented by Zr-Zr and Zr-Ti bonds, rather than by the principal element Cu. Electronic structure analysis further confirms that, although Cu dominates in composition, the electronic density of states (DOS) near the Fermi level is primarily contributed by the d-orbitals of the minor elements Zr and Hf. The introduction of Hf enhances the orbital hybridization between Cu-3d and Hf-5d, and reduces DOS near the Fermi level, thereby significantly increasing stiffness by promoting the directionality and covalency of bonding. Concurrently, the decrease in ratio of bulk modulus to shear modulus (B/G) and Poisson's ratio (n) values suggests a potential decline in toughness. This work clarifies that the inheritance of the elastic modulus in MGs is essentially determined by the key element that dominates the electronic DOS at the Fermi level. This finding provides a theoretical basis for the rational design of MGs with tailored mechanical properties from an electronic structure perspective.
High-performance noble metal electrocatalysts for water splitting face significant challenges including high cost, low atomic utilization, insufficient interface stability, and complex preparation processes, which severely limit their large-scale application. Therefore, developing lowcost, low-energy-consumption, and long-life electrocatalysts for water splitting is urgently needed. In this work, a carbon thermal shock strategy was used to rapidly synthesize ultrafine (10 nm) FeCoNiCrPt high-entropy alloy (HEA) nanoparticles on carbon fibers. Results show that in alkaline medium, the catalyst achieves current densities of 10 mA & centerdot;cm(-2) for the hydrogen evolution reaction (HER) and 100 mA & centerdot;cm(-2) for the oxygen evolution reaction (OER) with overpotential of only 34 and 264 mV, respectively. Furthermore, when FeCoNiCrPt samples are used as both anode and cathode in an alkaline electrolyzer for overall water splitting, a current density of 10 mA & centerdot;cm(-2) is achieved at only 1.53 V, with stable operation for more than 100 h. This carbon thermal shock strategy provides a simple and versatile approach for rapidly synthesizing well-dispersed HEA nanoparticles, offering a new pathway for developing low-cost, highly stable catalysts for overall water splitting.
In-situ ceramic phase-reinforced TaMoTiCr refractory high-entropy alloy (RHEA) composites were prepared by spark plasma sintering with the addition of 2.5wt% and 5.0wt% h-BN, separately. Results show that the h-BN promotes the uniform formation of (Ti, Ta)N, TaB2, and MoB ceramic phases within the body-centered cubic matrix, significantly increasing microhardness to 1136.95 HV. Tribological test results show that the composite with the addition of 2.5wt% h-BN presents great performance at room temperature with an ultra-low wear rate of 1.64 & times;10-7 mm3 N-1 m-1, while the composite with the addition of 5.0wt% h-BN shows optimal performance at 300 degrees C. Above 800 degrees C (elevated temperature condition), lubricious oxide tribolayers, rich in Cr2O3, TiO2, and B2O3, form on the material surface, effectively reducing friction and wear. At 1000 degrees C, the composite with the addition of 2.5wt% h-BN achieves a wear rate of 5.22 & times;10-7 mm3 N-1 m-1. This in situ ceramic reinforcement approach effectively enhances wear resistance of RHEAs across a wide temperature range, offering great potential for advanced aerospace applications.
Based on eutectic alloy design strategies combined with Pandat thermodynamic calculations, Zr-x(NiFe)(100-x) (x=75, 83, 90, wt%) alloy systems were designed and prepared. Furthermore, the intrinsic correlation mechanism between the microstructure and mechanical properties of the alloys was investigated. Results show that at Zr concentrations of 83wt% and above, the alloys exhibit a distinctive lamellar eutectic microstructure (tI12-Zr-2(Ni/Fe)/fcc-Zr) coexisting with hcp-Zr, featuring nanoscale FeZr3 interphase precipitates at eutectic interfaces. Notably, the liquidus formation temperature exhibits a substantial reduction to approximately 974 degrees C. The Zr-83(NiFe)17 and Zr-90(NiFe)(10) alloys exhibit compressive strengths of 1352 +/- 12 and 1263 +/- 10 MPa with corresponding fracture strains of 14.2%+/- 0.4% and 17.0%+/- 0.3%, respectively. These values represent a significant enhancement in fracture strain compared to conventional Zr-based amorphous alloys while maintaining comparable strength properties. Fractographic analysis reveals that dislocation pinning and shear band bifurcation phenomena induced by eutectic interfaces effectively impede crack propagation, facilitating a transition in fracture mode from brittle cleavage to 45 degrees shear-dominated failure with increasing Zr content. Under dynamic compression, both Zr-83(NiFe)(17) and Zr-90(NiFe)(10) alloys exhibit a strain rate hardening effect, and when the strain rate exceeds a critical value, the alloys undergo a ductile-to-brittle transition.
Ni-based superalloy coatings fabricated by laser melting deposition accumulate a large amount of residual stresses inside the coating, which adversely affects the microstructure and properties of the coating. The grade 4 Ni-based superalloy coatings reinforced with Nb and WC composite were prepared on 304NG stainless steel substrate by laser melting deposition technique, and the residual stresses inside the coatings were reduced by annealing treatment. The effects of annealing temperature and annealing time on the microstructure, microhardness, wear resistance, and tensile properties of the coatings were investigated. The results show that an increase in annealing temperature leads to an increase in the content of the softer matrix phase gamma-Ni of the coating, a decrease in hardness, and the transformation of the discretely-distributed eutectic structure into a continuously-distributed network structure. Comprehensive analysis indicates that the coating after 700 degrees C/1 h/furnace cooling treatment exhibits the most excellent wear resistance and tensile properties. This is because the fatigue cracks generated during friction and wear in this coating disappear, and the wear mechanism transitions from fatigue wear to abrasive wear. At the same time, while ensuring the wear resistance of the coating, the plasticity of the coating is enhanced, achieving a synergistic enhancement of strength and plasticity.
