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Abstract The performance of tungsten heavy alloys (WHAs) is related to the characteristic of matrix/W interfaces, which depends directly on the wettability of the matrix materials on W. This work designs a novel WHA that selects an AlCrFeNiV-system high entropy alloy (HEA) as matrix based on its wetting behavior on polycrystalline W. The wetting experiments show that this W/HEA system exhibits low contact angles at the temperatures for liquid phase sintering (LPS), and dissolutive wetting with a moderate W solubility in the HEA. This favorable wetting behavior benefits the densification process during LPS, leading to clean matrix/W interfaces with high bonding strength and hence a high ultimate tensile strength of 1132 MPa in the resulting W/HEA composite. These results indicate that the AlCrFeNiV-system HEA is a promising matrix material for WHAs. Graphical abstract Image 1 Highlights • A novel tungsten heavy alloy using high entropy alloy as matrix (W/HEA composite) is prepared by liquid phase sintering. • Dissolutive wetting of W by HEA melt with low contact angles is investigated. • W/HEA composite has fine W particle size of 13.15 μm and strong interfacial bonding. • W/HEA composite has a high yield strength of 705 MPa and high ultimate tensile strength of 1132 MPa. [ABSTRACT FROM AUTHOR]

Every strengthening/hardening method has its own limit. However, it is difficult to couple multiple extreme hardening in a bulk material, especially for highly strengthened ones. Here we demonstrate a strategy to further harden an ultrastrong precipitation-hardened high entropy alloy (HEA) with ultrafine-grain (UFG)/nanograin (NG) bands. These UFG/NG bands with nanoprecipitates were obtained by combining local severe plastic deformation (SPD) from cryogenic rolling and the pinning effect of precipitates during recrystallization. We found that the bands, with combined hardening of NGs and nanoprecipitates, provide an amazing yield strength of ~2.8 GPa and an ultrahigh hardness of ~9.7 GPa. Such nanoprecipitation-hardened UFG/NG bands in the bulk HEA contribute to an extra strengthening close to 300 MPa and an extremely high tensile strength of more than 2.2 GPa. This research presents a possibility for obtaining NG structure in bulk metals which will open new avenues for developing stronger alloys. [ABSTRACT FROM AUTHOR]

The susceptibility to adiabatic shear banding (ASB) of tungsten heavy alloys (WHAs) is a key factor to determine their penetration performance for kinetic energy penetrators (KEPs). This work reports a novel WHA with strong susceptibility to ASB that uses a precipitation-hardening high-entropy alloy (HEA) as the binding phase of W particles. The results find that nanoscale L1 2 precipitates and high dislocation density in the matrix contribute a high dynamic yield strength of ∼2300 MPa. Also, a narrow ASB with a width of ∼12 μm forms in the novel WHA, which is only 6% of the width of ASB in traditional WHAs like W-NiFe, exhibiting a great susceptibility to ASB. The redissolution of precipitates into the matrix because of temperature rise during shearing could sharply soften the shearing location, which is suggested to be a very important factor of destabilizing mechanism to promote the development of ASB. • The novel W-HEA alloy exhibits a peak compressive dynamic strength of ∼2300 MPa. • High susceptibility to adiabatic shear band (ASB) is observed in the W-HEA alloy. • ASB in W-HEA alloy has a narrow width of ∼12 μm and melting traces. [ABSTRACT FROM AUTHOR]

Deformed alloys commonly soften after annealing because of the decrease in defects. This work reports an annealing hardening that occurs in a cryo-rolled CoCrFeNi high-entropy alloy. This abnormal behavior is related to continuous twinning in nanoscale, which would have occurred in cryo-rolling but was belated until annealing was performed. This is because the stress accumulated in cryo-rolling was not enough to activate the reaction between dislocations and stacking faults, so as to require additional thermal activation (by annealing) for supplying the energy requirement for twinning. Due to the extra strengthening from stable twin boundaries, the annealed samples exhibit an ultrahigh yield strength close to 1.4 GPa (~6 times higher than the solid-solution counterpart), even after annealing for 24 h. These results confirm a possibility for introducing numerous stable nanotwins in bulk FCC metals to improve their mechanical properties. [ABSTRACT FROM AUTHOR]

Preparing bulk WNiFe alloys with high strengths and low W content (<80 wt%) is challenging. Here, we present a strategy, powder-fed laser melting deposition (LMD), to solve this problem. The LMD-prepared WNiFe (LMD WNiFe) samples show high mechanical strengths and low W contents of 50 and 75 wt%. The W particles in the LMD WNiFe samples uniformly distribute in the matrix (γ), exhibiting fine particle sizes of approximately one-fifth of those of conventional 93WNiFe alloys prepared by liquid phase sintering (LPS). The ultimate tensile strengths of the 50 and 75 wt% samples are 1120 and 1316 MPa, respectively, which are 24.44 and 59.33% higher than those of the LPS-prepared 93WNiFe alloy (LPS 93WNiFe). These results suggest a useful strategy for preparing low-W-content, high-strength WNiFe alloys with fine, uniformly distributed W particles. This finding offers new potential applications of WNiFe alloys in additive manufacturing. Unlabelled Image • WNiFe with W particle size of 5.5 μm is prepared by laser melting deposition (LMD). • WHAs with low W content (no W skeleton to keep shape) can be achieved by LMD. • W particles in LMD WHAs distribute uniformly in γ matrix. • The yield strength of LMD WHAs is 59.3% higher than that of LPS WHAs. [ABSTRACT FROM AUTHOR]

Tungsten heavy alloys with a L1 2 precipitation-hardening high-entropy alloy matrix exhibit high susceptibility to adiabatic shear, but the relationship between the size and morphology of L1 2 precipitates and the adiabatic shear behavior is not well understood. This work systematically studies the effect of different size and morphology L1 2 precipitates on the mechanical properties and susceptibility to adiabatic shear of the tungsten heavy alloy with an AlCrFeNiV-system high-entropy alloy matrix (W-HEA). The results show that the W-HEA with square L1 2 precipitates has tensile strength of 1300 MPa and dynamic compression strength of 2100 MPa at a stain rate of 6000 s−1. The higher interfacial energy of square L1 2 precipitates leads to the faster re-dissolution of square L1 2 precipitates into the matrix than ultrafine and lath-like L1 2 precipitates under temperature rise during shearing, which can sharply soften the shearing location and contribute to the narrowest adiabatic shear band (ASB) with width of 15 μm. [Display omitted] • The matrix of 3D printed fine-grained tungsten heavy alloy with high-entropy alloy matrix (W-HEA) contains different morphology L1 2 precipitates. • Effects of the morphology and size of the L1 2 precipitates on the adiabatic shear sensitivity of the W-HEA was revealed. • Large interfacial energy of the square L1 2 precipitates is the main reason for the formation of adiabatic shear band. [ABSTRACT FROM AUTHOR]

Coherent ordered nanoprecipitation (CON) hardening is an efficient strategy for breaking the strength-ductility trade-off. Revealing the precipitation mechanism and its influence on mechanical property is significant for further optimization of CON-strengthened alloys. In this work, we investigated the precipitation and mechanical behavior of the coherent FCC/L1 2 spinodal nanostructure and nano-lamellar BCC phase in a newly developed CON-strengthened Al 0.5 Cr 0.9 FeNi 2.5 V 0.2 high entropy alloy (HEA). We found that high-density defects induced by pre-deformation promoted the segregation of Cr, resulting in composition redistribution. The thermodynamics state of the matrix shifted into a spinodal regime and the ordering energy of L1 2 phase increased, facilitating the formation of coherent FCC/L1 2 spinodal nanostructure. Meanwhile, the Cr segregation promoted the precipitation of Cr-enriched nano-lamellar BCC phase. During tensile deformation, the FCC phase yielded first, followed by L1 2 and BCC phases in sequence. The L1 2 and BCC strengthening phases contributed to an ultrahigh macroscopic yield strength. Due to the low-misfit interconnected spinodal nanostructure, the differences in phase stress between FCC and L1 2 phases was insignificant, which could avoid the stress concentration and retain ductility. The nano-lamellar feature of the stiff BCC phase delayed the crack initiation and propagation. Our research revealed not only the significant effect of pre-deformation on CONs formation and refinement, but also the deformation mechanism of CONs, which shed new light on the microstructural optimization and mechanical property improvement of CON-strengthened alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

Including ductile solid-solution phases into NiAl intermetallic alloys can toughen these materials, but based on conventional alloying strategy, this approach either degenerates the strength or has no visible improvement in the room-temperature (RT) ductility. Here we show a feasible strategy to improve the RT ductility of NiAl alloys by replacing conventional dilute solid solutions with complex concentrated (i.e. , high-entropy) solid solutions as the ductilizing phases. The resulting alloy possesses a composite nanostructure, which combines B2-structured Ni(Al, Fe) phase with body-centered-cubic (BCC) and face-centered-cubic (FCC) structured high-entropy phases (HEPs) in different scales. We find that the applied stress is mainly partitioned to the B2 phase, contributing the alloy to high strength, while the ductile BCC and FCC HEPs, although bearing low loading, cooperate with the stress-induced martensitic transformation to accommodate the deformation, enhancing the sample ductility. Accordingly, our alloy presents superior tensile properties in a wide temperature range, including high strength (>1500 MPa at RT and >360 MPa at 700 °C) and good ductility (>9% at RT and ~8% at −50 °C), which achieves a simultaneous improvement in the ductility and strength compared with the conventional multiphase NiAl alloys. • Proposing a strategy to improve the ductility of multiphase NiAl alloys. • Revealing the distinctive ductilizing effect of high-entropy solid solutions. • Presenting the contribution of B2→L1 0 martensitic transformation to the ductility • Achieving a simultaneous improvement in the ductility and operating temperature. [ABSTRACT FROM AUTHOR]

• Fine-grained tungsten heavy alloy (FG-WHA) is prepared by liquid phase sintering. • Novel matrix that reduces W grain growth rate brings about FG-WHA. • Fine W grain in WHA contributes to a high ultimate tensile strength of 1267 MPa. • The FG-WHA exhibit a nearly full density and a good elongation of 10%. It is difficult to prepare fine-grain tungsten heavy alloys (WHAs), e.g. W-NiFe, by liquid phase sintering (LPS) mainly because of high solubility of W in the NiFe matrix. To obtain fine W grains, this work proposes to reduce W grain growth rate by selecting a high entropy alloy (HEA) with low diffusivity and solubility of W as the matrix of WHA. The results show that the LPS W-HEA has a fine W grain size of ~9.7 μm, which is about a third of the value in the conventional LPS W-NiFe. The fine W grains in the as-sintering W-HEA contribute to high yield strength and ultimate tensile strength of 840.8 MPa and 1267.3 MPa, respectively. These results suggest a new pathway for obtaining a fine-grain WHA by tailoring the matrix composition. [ABSTRACT FROM AUTHOR]