WC-15Al0.5CuMnMoTi cemented carbides with a homogeneous microstructure and superior properties were successfully fabricated via spark plasma sintering (SPS). The effects of NbC and TaC additions on the microstructure and mechanical properties of the WC-HEA cemented carbides were systematically investigated. The results demonstrate that with increasing NbC and TaC contents, the WC grain size first decreases and then increases. TaC exhibits a more pronounced effect on inhibiting grain growth than NbC, as its higher solubility in the HEA reduces the solubility of WC, thereby effectively suppressing grain growth. An appropriate amount of TaC is more effective in enhancing the Vickers hardness and transverse rupture strength (TRS) of the WC-HEA cemented carbides, while a suitable amount of NbC is more beneficial for improving their fracture toughness. The WC-HEA cemented carbide containing 0.5 wt% TaC exhibits the most uniform microstructure, with an average WC grain size of 256 nm and a relative density of 98.88%, and demonstrates optimal mechanical properties, including a Vickers hardness of 2375 kgf & sdot;mm-2, a fracture toughness of 10.2 MPa & sdot;m1/2, and a TRS of 1317 MPa. The mechanism of action of grain growth inhibitors is as follows: at the high-temperature stage, Nb or Ta atoms dissolved in the HEA hinder grain boundary migration through the solute drag effect; during the cooling stage, the precipitated (Nb, W) C or (Ta, W) C second phases stabilize and refine the microstructure via the Zener pinning effect.

High-entropy borides (HEBs), as an emerging branch of high-entropy materials, have become a prominent research frontier in the field of ultra-high-temperature ceramics (UHTCs). The high configuration entropy effect is used to stabilize single-phase solid solution structures, which exhibit comprehensive properties that are difficult to achieve by traditional binary borides. This review aims to systematically summarize the research progress on HEBs, first covering their theoretical predictions and component design based on first-principles methods. Then, some typical systems are described and the main preparation techniques such as arc melting and spark plasma sintering are summarized. The core of this paper is to comprehensively evaluate the outstanding performance characteristics of HEBs, which not only include their exceptional mechanical properties such as ultra-high hardness and excellent fracture toughness, but also delve into their high-temperature friction and wear behavior, as well as their oxidation resistance. Finally, based on their unique performance advantages, the application prospects in extreme working conditions such as aerospace and cutting tools are prospected, and the challenges in this field are pointed out.

Developing high-performance Ti(C, N) cermets without relying on toxic and expensive Co or Ni binders remains a formidable challenge, primarily due to the notorious hardness-toughness trade-off. In this study, we successfully overcome this bottleneck by integrating a physics-informed machine learning framework with rigorous experimental validation to engineer a novel Co/Ni-free Ti(C,N)-FeCrMoMnCu cermet. Bypassing traditional empirical trial-and-error, we deployed a Divide-and-Conquer Gaussian Process Regression (DC-GPR) model. By mapping raw compositions into a thermodynamic descriptor space, the algorithm efficiently identified the FeCrMoMnCu high-entropy alloy (HEA) as the optimal "green" binder candidate. Subsequent experimental synthesis via spark plasma sintering (SPS) confirmed that this designed binder naturally crystallizes into a highly desirable "ductile FCC + strong BCC" dual-phase network. We found that the inherent sluggish diffusion of the HEA severely restricts the Ostwald ripening of ceramic grains, enabling the cermet to achieve near-full densification (97.0%) and a robust interfacial architecture at an optimal sintering temperature of 1450 degrees C. Mechanistically, this profound interfacial bonding forces propagating cracks into extensive energy-dissipating pathways, including transgranular cleavage and severe crack deflection. Consequently, the optimized cermet exhibits a superior hardnesstoughness synergy, achieving an ultra-high Vickers hardness of 1924.5 HV alongside an outstanding fracture toughness of 10.75 MPa & sdot;m1/2. Ultimately, this work not only presents a transformative Co/Ni-free HEA bonded cermet but also establishes a highly reliable, data-driven paradigm for designing next-generation, environmentally sustainable cutting-tool materials.

High-entropy diboride (HEB) ceramics have exhibited versatile properties. Yet, single-phase HEBs are supposedly rare; consequently, robust prediction of such HEB formation is rather challenging owing to the vast element combinations. Herein, the Automatic FLOW partial occupation methodology was employed to construct 56 quinary metal HEBs. Potential single-phase HEBs were identified through the evaluation of entropy forming ability (EFA), computed via high-throughput density functional theory calculations. EFA, derived from the energy distribution spectrum obtained through randomized calculations, effectively characterizes the accessibility of states that are equally sampled in proximity to the ground state. Furthermore, it provides a quantitative measure of configurational disorder that can contribute to the stabilization of high-entropy homogeneous phases. To achieve this, a total of 4 256 distinct configurations within the compositional space were computed. Correlating these computational findings with experimental data obtained from samples synthesized by spark plasma sintering revealed that systems exhibiting an EFA value greater than 80 (eV per atom) demonstrate a higher propensity to form single-phase HEBs.

High-entropy diborides (HEBs) are promising ultra-high-temperature ceramics but suffer from challenges in densification and low fracture toughness. In this study, (Hf0.2Zr0.2Ti0.2Ta0.2Mo0.2)B2 HEB-based composites were prepared via spark plasma sintering using hybrid Ni and Al2O3 additives. The effects of additive ratios and sintering temperatures on microstructure and mechanical properties were investigated. XRD and EDS confirmed the formation of a primary hexagonal AlB2-type HEB matrix with localized compositional fluctuations, alongside Al2O3 as a grain-boundary secondary phase and Ni reacting to form minor Ni2B to enable liquid-phase densification. Al2O3 provided effective grain-growth pinning, while Ni enhanced densification but promoted coarsening at higher contents. Among composites with varying Ni/Al2O3 ratios sintered at 1625 degrees C, the HEB-3 wt% Ni-7 wt% Al2O3 composition exhibited the finest grains and best mechanical properties. Further optimization at 1400-1550 degrees C identified 1550 degrees C as optimal, achieving 96.1% relative density, fracture toughness of 6.86 MPa & sdot;m1/2, and flexural strength of 526 MPa. Improvements arose from grain refinement, crack deflection by Al2O3, and reduced defects. The synergistic use of Ni and Al2O3 offers an effective strategy to balance densification and mechanical performance in HEBs for extreme-environment applications.

Taking the evolution of material behavior during the cutting process of the FeCoNiCrCu high-entropy alloy as the research object, this paper investigates the segregation behavior of principal elements during cutting, analyses the formation mechanism of principal elemental segregation from an energy perspective, and discusses the effects of this behavior on chip formation and machined surface generation, so as to provide a theoretical reference for the engineering application of high-entropy alloys. The results demonstrate that during the cutting of FeCoNiCrCu, the cutting temperature and cutting deformation induce the diffusion of vacancies associated with the principal elements, thereby resulting in principal elemental segregation; when the cutting speed exceeds 300 m/min, Cu and Cr undergo significant diffusion, with Cu tending to form enrichment zones and exhibiting mutual exclusion with Cr. The segregation of principal elements promotes the formation of plastic slip bands in the chip, which elevates the material deformation degree, leading to the generation of serrated chips and an increase in serration frequency during cutting; meanwhile, the increased deformation degree refines the grains in the deformation zone and contributes to the formation of ultrafine grains.

Compared to traditional carbide ceramics, high entropy ceramics (HECs) exhibit higher hardness, oxidation/ corrosion resistance, wear resistance, and lower thermal conductivity. However, their low fracture toughness remains a key challenge to widespread application, necessitating further improvements to expand their applicable domains. A gradient (HfNbTaTiZr)C-based composite was synthesized via spark plasma sintering, incorporating graphene (G), SiC nanowire (SiCnw). A five-layered gradient-structured HEC/SiCnw-G composite with a layer thickness ratio of 0.2 was fabricated, featuring a G content of 0.2 wt% in the surface layers and 0.10 wt% in the central layer, while the SiCnw content was 0.5 wt% in the surface layers and 1.5 wt% in the central layer. The composite exhibited exceptional mechanical properties, with a hardness of 24.97 GPa, flexural strength of 734.78 MPa, and fracture toughness of 8.61 MPa & sdot;m1/2. The increased hardness and flexural strength result from enhanced densification and grain refinement. The toughening mechanisms included a mixed intergranular and transgranular fracture mode, crack deflection, crack bridging, and crack branching, collectively enhancing fracture resistance.

(NbTaTiWZr)C-based micro-nano composites were fabricated by spark plasma sintering employing multi-layer graphene (MLG), Ni, and Al2O3 as reinforcements. It is demonstrated that excellent mechanical properties were achieved for MLG, Ni, and Al2O3 hybrid addition with a hardness of 21.73 GPa, a flexural strength of 572.4 MPa, and a fracture toughness of 7.65 MPa m1/2. Enhanced densification together with inhibited grain growth contributed to the simultaneously improved hardness and flexural strength. The major toughening mechanisms were determined as microcracks, crack deflection, crack bridging, crack stopping, MLG wall, MLG pull-out, MLG bending, and MLG wrapping grains. Furthermore, outstanding tribological performance occurred to the (High entropy ceramic) HEC-Ni-Al2O3-MLG with a friction coefficient of 0.23 and wear rate of 4.32 x 10- 7mm3N- 1m- 1, as a function of graphene acting as a lubricating friction layer and the enhanced mechanical responses.

TiB2 based materials have attracted extensive attention due to its considerable hardness and elastic modulus, excellent wear/ corrosion resistance as well as exceptional electrical/ thermal conductivity. The potential structural and functional applications of TiB2 based materials include reentry vehicles, cutting tools, thermal insulation boards, new energy batteries, ballistic protection high temperature nuclear reactors. However, the poor densification together with inferior fracture toughness dramatically limited the practical application of TiB2. Herein, we critically survey, summarize, and discuss the recent advances on preparation and mechanical properties of TiB2-based materials, focusing on the current understanding of densification and toughening strategies and mechanisms. Borrowing the concept of cemented carbide, cemented TiB2 is proposed in this review, highlighting the different binder phase on improving the densification of TiB2, including metal, intermetallic, ceramic and high entropy alloy. Subsequently, through discussing the factors influencing the efficiency of toughening TiB2, we determine and compare various toughening approaches on TiB2. Furthermore, the challenges and prospects of high performance TiB2 for future scientific researches and practical possibilities are also briefly summarized. We believe a thorough summary of the densification and toughening mechanisms will significantly contribute to the development of dense, strong and tough TiB2 materials in a much more efficient way, advancing them for further wide applications.

The rapid development of computer simulation technology has provided theoretical and technical support for the performance prediction of ceramic materials. A two-dimensional simulation model was established to investigate the effect of the graphene (G) and gradient structure on the mechanical properties of (HfNbTaTiZr)C. Voronoi mosaics were applied in Abaqus to characterize the particle distribution of high entropy ceramics (HECs). The G/(HfNbTaTiZr)C–Al2O3 gradient ceramics were characterized through the formation of cohesive elements within grain boundaries and grains of each element using Python language. The fracture toughness, flexural strength and hardness of G/(HfNbTaTiZr)C–Al2O3 gradient ceramics were investigated through simulation model. The toughening mechanisms of G/(HfNbTaTiZr)C–Al2O3 gradient composites were investigated by establishing crack growth model. The simulation consequences are consistent with the experimental results in the literature, which verifies the accuracy of the simulation consequences. The toughening mechanism is validated through crack propagation experiments and its correctness is testified. Therefore, the simulation consequences are conducive to improving the design efficiency of HECs.

High entropy carbide ceramics(HECC)are solid solution of inorganic compounds with five or more prin-cipal metal cations.Research interests in HECC are dramatically sparked by the enormous possibilities in composition-microstructure-property tailoring.As widely acknowledged,HECCs enjoy higher hardness and oxidation/corrosion/wear resistance,as well as lower thermal conductivity than conventional engi-neering carbide ceramics,making them the most potential candidates for state-of-the-art structural and functional applications in extreme service conditions.Despite the advantages,however,the poor den-sification coupled with low fracture toughness significantly limited the practical applications of HECC.Adding to the difficulty,the literature available for toughening HECC is woefully limited.In considera-tion of this insufficiency,we apply towards offer a comprehensive,critical review of the mechanical be-havior of HECC,highlighting the densification enhancing strategies(carbon content,sintering techniques,grain size,sintering aids,etc.)as well as toughening methods including particle toughening,whisker/fiber toughening,synergistic toughening,graphene-carbon nanotube toughening,to further the service reliabil-ity of HECC in practical industrial applications.Furthermore,despite some significant successes,important directions for further development of HECC are given as multi-dimensional gradient HECC,additive man-ufacturing of HECC,processing-composition-microstructure-property relationship prediction and genomes of HECC based on machine learning,and high-throughput computing,etc.

材料塑性变形在不同的应变率加载下服从不同的规律,为正确认识应变率对动态变形的影响,以位错运动分析为基础,推导了不同应变率下材料变形的黏性行为规律,通过霍普金森压缩(SHPB)和金属切削实验,获得了从102/s～105/s及以上应变率范围的塑性变形过程,研究了7075铝合金的应变率效应,总结了3个表征应变率效应的参量并提出相应的计算方法.发现塑性变形过程应变率增大到某临界值(大于104/s且小于1.5×104/s)后,7075铝的塑性变形控制机制将从热激活机制转变为位错阻尼机制,通过分析切削过程切屑的变形程度认为,材料充分变形与软化时间不足是产生应变率效应的主要原因.

The flow stress increases with the increase in strain rate. This phenomenon is the strain rate effect of plastic deformation. Hopkinson experiment (102–104 s−1) and metal cutting experiment (> 104 s−1) of AA7075 aluminum alloy were conducted at room temperature (20 °C) to better understand the strain rate effect of materials in a wider strain rate range. Results show that when the strain rate is in the range of 1×104–1.3×104 s−1, the plastic deformation control mechanism of AA7075 aluminum alloy begins to change from thermal activation mechanism to dislocation damping mechanism. The viscous behavior of material deformation during cutting is shown as linear correlation between strain rate and stress. Analysis of the deformation degree of cutting chips reveals that insufficient times for deformation and softening are the main reasons for the strain rate effect.

Metal cutting speeds are getting faster with the development of high-speed cutting technology, and with the increase in cutting speed, the strain rate will become larger, which makes the study of the metal cutting process more inconvenient. At the same time, with the increase in strain rate, the dislocation movement controlling the plastic deformation mechanism of metal will change from thermal activation to a damping mechanism, which makes the metal deformation behave more like a fluid. Therefore, it is necessary to explore new ways of studying machining from the perspective of fluid flow. Based on this, a fluid model of the metal cutting process is established, and a method for calculating the strain rate is proposed from the point of view of flow. The results of the simulation and measurements are compared and analyzed. The results show that the strain rate on the rake face will be affected by the friction between the chip and tool; the nearer the distance between the chip layer and tool rake face, the bigger the strain rate will be. The strain rate in the central shear plane is much larger than in other areas along the shear plane direction, and in which two ends are the biggest. It can achieve rougher, quantitative research. This shows it is feasible to study machining from the viewpoint of fluid flow, though it still needs a lot of theoretical support and experimental confirmation.

Background: Machining is an important method for manufacturing parts. It is characterized by high cutting speed with a considerable influence of high-frequency vibration. Various relevant papers and patents have studied vibration transmission and isolation in the machining process. Objective: To investigate vibration transmission and isolation in the machining process, and simplify the cutting process of a machine tool. Methods: Firstly single-layer and double-layer vibration isolation models are established, the substructure matrix analysis method is adopted and the vibration power flow transmission characteristics of double-layer vibration isolation system under complex excitation are analyzed. Secondly, the optimal control strategy based on the minimum power flow inputted into the base is proposed. Then the control effect of the active actuator under different installation modes is analysed and compared. Results: It has been proved that low-frequency coupling is characterized by the rigid mode of the workpiece or the grinding wheel when cutting, whereas high-frequency coupling exhibits the dynamic characteristics of the machine tool bed. A good vibration isolation effect can be achieved for three types of installation modes in a double-layer vibration isolation system, and only the actuators installed between the vibration source and the middle mass exhibit the best control effect. Conclusion: The vibration isolation model has been established and the optimal installation mode of the actuator in the double-layer vibration isolation system has been found. And the paper provides a reference for the study of vibration transmission, control of machine tools and the elimination of grinding chatter.

High-speed metal cutting has been widely studied around the world for its high efficiency and quality.However,a quantitative study on many physical parameters of the cutting is still difficult when the cutting speed is high.By investigating the feasibility of studying the strain rate from the perspective of material flow,a method for strain rate calculation is proposed based on mesh measurement.The distribution of strain rate of the metal in the cutting process is obtained,and the data obtained from calculation are compared with those from measurement.The results show that the strain rate on the rake face will be affected by the friction between the chip and the tool.The nearer the distance between the chip layer and the tool rake face,the greater the strain rate will be.The strain rate in the central shear plane is much larger than that in other areas along the shear plane direction,with the strain rate in the two ends being the greatest.The quantitative study physical parameters of high-speed cutting can thus be obtained by using this method from the perspective of material flow.

High-speed machining has been widely studied around the world for its high efficiency and high quality. However, conducting a quantitative study on many physical parameters is difficult when cutting speed is high. A simple and effective measurement and calculation method is necessary in engineering application. From the flow point of view, a difference calculation method through mesh length measurement is proposed, which can be easily used to determine the strain rate distribution of high-speed cutting. The distribution of strain rates for aluminum alloy 7050 cutting has been obtained; the results show that the strain rates are as high as 10(5) s(-1) during high-speed cutting, and the strain rates near the tool tip are higher than those in other areas in the second deformation zone. In the direction of shear plane, the strain rates are gradually reduced from the center of the first deformation zone to the exterior. The deformation rate in the rake face direction is higher than that in the shear plane direction. (C) 2016 Elsevier Ltd. All rights reserved.

Strain rate in high-speed metal cutting is high, and properties of chip flow under high strain rate conditions are different under low cutting speed conditions. Shear stress and shear strain rate have a linear relationship; hence, the behavior of chip flow during high-speed metal cutting is more similar to fluid than to solid. Therefore, metal cutting should be analyzed by using fluid analytical method. This article investigated the fluid-like properties of chip flow during high-speed metal cutting and determined velocity, pressure, and strain rate distributions on rake face and shear plane. A speed stagnation point is located some distance from the tool tip on the rake face. The location of this point influences the life of the cutting tool and the quality of the finished surface. The pressure peaks, decreases along the rake face, and then reaches zero at some point away from the tool tip. This point represents the separation of the chip from the tool. The total stress on the shear plane is the sum of tensile stress, pressure stress, and shear stress. The strain rate is related to velocity; its value rapidly increases at the tool tip and the free surface corner and then decreases.

In high speed metal cutting,the irreversible dislocation motion and multiplication result in the plastic deformation of the metal,and its velocity are proportional to the drag force of the solid.Therefore,the effect of viscosity becomes more and more important in describing the material dynamic behavior.The damping mechanism of dislocation in high speed metal cutting is described from the fluid aspect;a model for high speed machining is established based on fluid mechanics.The velocity distribution,the pressure distribution and the strain rate distribution are calculated by solving the Navier-Stokes equation and energy equation,which provides a new method to study high speed machining.Analytical results show that approximating the behavior of metal cutting by a fluid model during high speed machining is not irrelevant.A speed stagnation point is located at some distance from the tool tip on the tool rake face on which the maximum value of the pressure occurs,with zero speed.Its location influences the life of the tool and the quality of the finished surface.The pressure decreases along the rake face and reaches zero at some point away from the tool tip,which is the point of separation of the chip from the tool.The value of the strain rate exhibits a rapid increase from the tool tip to the free surface corner,and then decreases outwards.

In high speed metal cutting momentum would be large and the strain rate can be exceedingly high, the viscosity of material must take into account in studying the chip deformation. Model the high speed machining as fluid flow is much better than as solid. A laminar flow method is applied in this paper to analyze the velocity distribution, the pressure distribution, the temperature distribution and the strain rate distribution of high speed metal cutting. Analytical results showed that a speed stagnation point is located at some distance from the tool tip on the tool rake face, on which the maximum value of the pressure occurs, with zero speed; its location influences the life of the tool and the quality of the finished surface. The value of the pressure decrease along the rake face and reaches zero at some point away from the tool tip, which is the point of separation of the chip from the tool; The value of strain rate get a rapid increase from the tool tip to the free surface corner then decreased outwards.