Preparation of Cu-based Bulk Metallic Glass Matrix Composites

Cu47Ti34Zr11Ni8 bulk metallic glass （BMG） matrix composites containing in situ formed TiC particles and 5-TiCu dendrite phase were developed by copper mold cast. The thermal stability and microstructure of the composites are investigated. Room temperature compression tests reveal that the composite samples exhibit higher fracture strength and distinct plastic strain of 0.2%-0.5%, comparing with that of the corresponding Cu47Ti34Zr11Ni8 monolithic BMG.

A dispersion-based impact identification method:mechanical model and experimental verification

External transient impact loads widely exist in the service environment of various engineering structures,and urgent engineering and military application requirements call for research on the theory and method of impact identification.This manuscript proposes a method to identify the impact event.By employing the dispersive property of wave propagation through the waveguides,a dispersion-based average power spectral density(PSD)curve for quantitative representation of the dispersion is established,and its evolution law is investigated to apply the identification of impact events.The critical parameters of the average PSD curve are obtained by analyzing the response of the structure from the perspective of mechanics.The effectiveness of this method is verified through the development of the triple-successive-impact split Hopkinson bar and the triple-successive-impact experiment.Through the method proposed in this manuscript,a kind of impact identification under multiple impact loads,which is not convenient to measure directly by the sensor,is realized,especially in the case of highly transient external impact.

Microstructural evolution and energetic characteristics of TiZrHfTa_(0.7)W_(0.3)high-entropy alloy under high strain rates and its application in high-velocity penetration

Energetic structural materials(ESMs)integrated a high energy density and rapid energy release with the ability to serve as structural materials.Here,a novel triple-phase TiZrHfTa_(0.7)W_(0.3)high-entropy alloy(HEA)was fabricated and investigated as a potential ESM.A hierarchical microstructure was obtained with a main metastable body-centered-cubic(BCC)matrix with distributed Ta-W-rich BCC precipitates of various sizes and interwoven hexagonal close-packed(HCP)lamellar nano-plates.The compressive me-chanical properties were tested across a range of strain rates and demonstrated a brittle-to-ductile tran-sition as the strain rate increased while maintaining a high ultimate strength of approximately 2.5 GPa.This was due to the phase transformation from metastable matrix BCC to HCP structures.In addition,during the dynamic deformation,metal combustion originating from the failure surface was observed.Furthermore,the composition of the fragments was studied,and the results indicated that the addition of tungsten promoted combustion.Finally,the potential application of this HEA was evaluated by high-velocity penetration tests,and the results were compared to other typical structural materials for pene-trators and bullets.A comparison was conducted by assessing the geometries of the penetration channel employing two dimensionless parameters normalized by the projectile size,representing longitudinal and lateral damage,respectively.The normalized depth of the TiZrHfTa_(0.7)W_(0.3)HEA projectile was comparable to those of the other investigated materials,but the normalized diameter was the largest,showing an excellent ability to deliver lateral damage.

Phase transition and heterogeneous strengthening mechanism in CoCrFeNiMn high-entropy alloy fabricated by laser-engineered net shaping via annealing at intermediate-temperature

High-entropy alloys(HEAs)have attracted tremendous attention owing to their controllable mechanical properties,whereas additive manufacturing(AM)is an efficient and flexible processing route for novel materials design.However,a profound appraisal of the fundamental material physics behind the strengthening of AM-printed HEAs upon low/intermediate-temperature annealing is essential.In this work,Co CrFe Ni Mn HEAs have been prepared using laser-engineered net shaping(LENS)and subsequently annealed at different temperatures.The Co Cr Fe Ni Mn HEA annealed at intermediate-temperature(873 K)exhibits a strong strain hardening capability,resulting in ultimate strength of 725 MPa and plasticity of 22%.A ternary heterogeneous strengthening mechanism is proposed to explain this phenomenon,in which equiaxed grains,columnar grains,andσprecipitates play different roles during tensile deformation.The resultant excellent strength and ductility can be ascribed to the heterostructure-induced mismatch.The equiaxed grains provide adequate grain boundaries(GBs),which induce dislocation plugging-up and entanglement;the columnar grains induce the onset and arrest of the dislocations for plastic deformation;and theσprecipitates hinder the movement of slip dislocations.The results provide new insights into overcoming the strength-ductility trade-off of LENS-printed HEAs with complex geometries.