Bulk metallic glasses (BMGs) exhibit promising application prospects for its excellent mechanical properties. However, during machining, severe tool wear appeared for their high strength, high hardness and low thermal conductivity, exacerbated by the coupled mechanical and thermal impact. In order to investigate the effects of mechanical and thermal impact on tool wear behavior, the tool wear behavior of interrupted cutting BMGs at varying cutting speeds and interruption frequencies were analyzed in this work, as well as the underlying mechanisms about the influence of mechanical and thermal impact on tool life. With the increase of cutting speed, the tool failure form changed from adhesive wear to peeling and chipping. The increase in interruption frequency rendered the cutting process closer to continuous cutting and improved tool life. The cutting tool failure form was characterized with coating peeling, cutting-edge chipping and adhesive wear. Moreover, the maximum normal stress and transient maximum cutting temperature at varying cutting speeds and interruption frequencies were calculated to analyze their combined influences on tool life. The results demonstrated that tool life was governed by the combined effects of mechanical and thermal impact. When the interruption frequency increased, the maximum normal stress would also be much higher, then the tool life would be mainly influenced by the mechanical impact. However, as the cutting speed increased, the transient maximum temperature significantly increased and the transient maximum normal stress was relatively small at this situation. Then the tool life was mainly determined by the thermal impact.

Refractory high-entropy alloys (RHEAs) have excellent mechanical properties and thermal stability. A unique light emission phenomenon appeared during the cutting of the WNbMoTaZr RHEA, which may cause injury to operators and ignite combustibles. In this work, the light emission characteristics under varying cutting parameters as well as the generation mechanisms were investigated. The light emission was observed when the cutting speed reached 50 m/min. It was found that the light emission is caused by the exothermic oxidation of Zr in chips, due to the rise in cutting temperature. With the change of cutting depth and feed rate, chip width and curvature also changed, affecting the Zr content and heat accumulation, which in turn influenced light emission and chip melting. Since most of the cutting heat was taken away by the chips, light emission had a limited effect on the machined surface quality. Thereafter, the formation mechanism of the recrystallized grains, existing on the chip melting surface, was analyzed, which is substantially different from the recrystallization mechanism under high-speed cutting. The results indicate the redistribution of elements on the melting surface of the chip, and the formation of recrystallized grains enriched with Nb and Ta elements. This was attributed to the combination of heat generated by light emission and cutting, which melts the chip surface and causes dynamic recrystallization.

The work-hardening behavior of refractory high-entropy alloy (RHEA) and its influence on the corrosion resistance of the machined surface have been investigated. The results showed that the work-hardening degree exhibited an increase in cutting force when the feed rate increased from 0.032 mm/r to 0.1 mm/r. As the work-hardening degree of the RHEA increased, the maximum hardness and the work-hardening thickness increased gradually, reaching 586.2 HV and 580 μm, respectively. And the surface roughness decreasing from 0.8 μm to 0.66 μm, then increasing from 0.66 μm to 1.013 μm. In order to investigate the mechanism of work hardening on the microstructural evolution of the RHEA, the microstructure of the superficial layer and the matrix was studied. The results indicated that the dendrite proportions of the superficial layer increased from 103.58

A series of (TiVFexTa)90W10 (x = 0.2, 0.35, 0.5 and 0.7, noted as Fe0.2, Fe0.35, Fe0.5 and Fe0.7) refractory high-entropy alloys (RHEAs) with high yield strength and Vickers hardness were designed and prepared. With the increase of Fe content, the strength and hardness of (TiVFexTa)90W10 RHEAs also increased, and the typical Fe0.7 alloy exhibited a high strength of 2256 MPa and a high Vickers hardness of 778 HV. Single BCC phase was observed in the Fe0.2 RHEA, while the BCC and Laves phases were found in the Fe0.35, Fe0.5 and Fe0.7 RHEAs. The results show that precipitations appeared in the inter-dendritic regions with the inclusion of more Fe content, resulted in the formation of such dual phase structure, improving the strength. The strengthening mechanisms of the (TiVFexTa)90W10 RHEAs were mainly related to the solid solution strengthening and refinement of dendrite, where the average size of dendritic regions was reduced from 121.7 μm to 30.4 μm. The presence of Laves phase also hindered the propagation of dense slip lines, enhancing the strength. RHEA cutting tools was then fabricated from the Fe0.7 alloy and compared with commercial YG8 cemented carbide tools for copper cutting. The machined surface by RHEA tool demonstrated lower surface roughness, and the cutting force was also lower than that by YG8 cemented carbide tools. The findings provide useful guidance for developing high-strength RHEAs for cutting tool applications, exploring the application prospects of RHEAs in industry.

Refractory high-entropy alloys (RHEAs) have broad application prospects due to its excellent mechanical properties, yet there is little information about its cutting process. And the excellent mechanical properties would accelerate the tool wear during the cutting process. Therefore, the tool wear behavior of machining RHEAs at different cutting speeds was investigated in this work. The results showed that adhesive wear and diffusion wear were the main wear mechanisms. With the increase of cutting speed, the high temperature led to the thermal softening of material, and the material adhered to the tool surface under the effect of high pressure, resulting in adhesive wear. Meanwhile, with the increase of cutting speed, the adhesive accumulation on the flank face became obvious, which aggravated the adhesive wear. In addition, the Zr, Mo and Nb elements were detected in the internal cross section of the tool, indicating that there was diffusion wear. And it was the most serious on the flank face. With the increase of cutting temperature, the diffusion depth also increased. Moreover, a tool flank wear rate model was established, and the prediction error was within 5 %. Based on the wear rate model, the diffusion wear rate increased significantly with the increase of cutting temperature. And the adhesive wear rate was always larger than the diffusion wear rate.

The plastic deformation of bulk metallic glasses (BMGs) is characterized by serrated plastic flows, leading to catastrophic failures, while the prediction of such catastrophic failures is still challenging. In this work, three basic deep learning neural network models, including the Long Short-Term Memory (LSTM), Transformer and Gate Recurrent Unit (GRU), as well as two improved models, the LSTM+Transformer (LSTM+T) and GRU+Convolutional Neural Networks (CNN), were used to predict the plastic flow information of BMGs with different sample aspect ratios and compression rates. The Pearson correlation coefficients among nine parameters, showing the correlations between the load drop and elastic energy accumulation rate, were calculated by heatmap. This also aids in the selection of features and prediction targets in subsequent model training, helping to reduce overfitting. Considering factors such as training set size, model applicability, and prediction accuracy, the failure of BMGs was monitored and predicted in real time from two perspectives: multiple and single data sets. The predictability of load drop and the strain of load drop initiation were observed from the results of multiple sets of data, and the LSTM model can predict their development effectively. Subsequently, the LSTM model was trained specifically using a single set of data, where the improvement on the predictions for peak stress, and the strain of the load drops initiation was achieved. This work provides a new method that predicts the catastrophic failure of BMGs and the damage characteristics for similar solids.

Anisotropic pitting mechanisms were investigated during electropolishing (EP) of Zr-based bulk metallic glass (BMG) surfaces in a chloride-containing alcohol-based electrolyte. Electrically discharge-machined (EDMed) and mechanically polished (MPed) BMG surfaces were selected as the typical preprocessing surfaces. NaCl-ethylene glycol solution was selected as the electrolyte because of its ability to avoid solvent decomposition and form high-viscosity complexes on surfaces to lower the surface roughness. The surface roughness and morphology of both specimens under varying EP parameters were examined and compared. With the optimized parameters, the recast layer of the EDMed surface was removed, and a decrease of more than 50

A theoretical model of surface roughness prediction for high-speed machining Zr-based bulk metallic glasses was established. The roughness components of the prediction model, including plastic side flow, material recovery, cutting vibration and kinematics were discussed. The cutting forces and machined surface morphology were studied to characterize the cutting vibration and plastic side flow, respectively. Specially, the cutting vibration during machining was characterized with radial force amplitude. The surface morphology of the Zr-based bulk metallic glass (BMG) was mainly characterized with plastic flow traces, molten droplets, dimples, adhensions and ploughing marks. The presence of material recovery would effectively improve the surface quality and, on the contrary, the presence of plastic side flow would deteriorate it. Finally, the surface roughness prediction model was validated with turning experiments under varying tool geometric parameters, and the calculated surface roughness showed good agreement with the measured results. The present results are beneficial to revealing the underlying mechanisms for machined surface roughness, and can provide basis for optimizing cutting parameters and surface quality for industry.

Refractory high entropy alloys (RHEAs) have great potential for applications in aerospace and nuclear energy fields, however, most developed RHEAs still exhibit limited room-temperature compressive plasticity, high activation and high density, which limits their engineering applications. To overcome such issues, the high-performance, low-activation W-Ta-Ti-V-C RHEAs with reduced density were designed, and the effects of composition on the regulation of microstructure and properties were characterized. The phase structure of the W-Ta-Ti-V-C RHEAs evolved from a single-phase BCC structure to a duplex BCC+FCC structure by doping C, and the phase interfaces also converted from coherent to semi-coherent. The yield strength and hardness of W-Ta-Ti-V-C RHEAs reached to the maximum values of 1465 MPa and 528 HV in W15Ta15Ti34V35C1 RHEA with increasing W content, while achieved 1530 MPa and 505 HV in W10Ta20Ti30V35C5 RHEA with increasing C content. All RHEAs presented excellent plasticity exceeding 20%, and some RHEAs even did not fracture. The refined dendrites and visible micro-precipitates provided additional strengthening mechanisms for promoting the improvement of compressive strength. The slip bands were found to initiate within the harder dendrites, while their propagation was hindered by the softer interdendrites. The dislocation movement was also hindered by the harder precipitates via the pinning effect. Moreover, the plastic deformation of the RHEAs was activated by the wavy dislocations within the BCC-structured matrix and coordinated by the dislocation evolutions within the FCC-structured precipitates. The heterogeneous interfaces and the dislocation evolutions induced the synergistic deformation of the matrix and precipitate, promoting the achievement of excellent mechanical properties superior to similar RHEAs. The present findings not only provide effective guidance for designing high-performance RHEAs, but also shed more light on the strengthening mechanisms and deformation behaviors of RHEAs.

Although high-entropy alloys (HEAs) have superior comprehensive performance, it is still challenging to design HEAs with good combinations of strength and plasticity because of the huge combination space and complex elemental properties. In this work, a machine learning (ML) model was proposed to better predict HEAs with good combinations of yield strength and compressive plasticity simultaneously. Phase classification, plasticity classification and strength regression models were established respectively. A ML model was then constructed by fusing these models together using particle swarm optimization algorithm. Examples of quaternary Ti35V35Zr5W25, quinary Mo13Ti28W12Nb23Zr24, and six-principal element Mo6Ti34V35W15Ta5Zr5 refractory high-entropy alloys (RHEAs) were developed and examined to validate the prediction effectiveness of the ML model. These RHEAs demonstrate yield strength and fracture strain of 1415 MPa, 1476 MPa, 1265 MPa and 23.8 %, 30.6 %, and 26.7 % respectively. Finally, the important features of the ML model were interpreted using SHAP, and the crystal structures of predicted RHEAs were determined mainly by the combination of atomic and electronic parameters, where VEC played an important role.

Although refractory high entropy alloys (RHEAs) have the potential to serve as nuclear materials, designing a high-performance alloy that can simultaneously endure extreme environments, such as elevated temperatures and radiation exposure, remains a significant challenge. In this work, elements with high melting points and low activation characteristics are selected to design Ti30V30Cr5Zr5Ta30-xWx (x = 5, 10, 15, 20 at.%) RHEAs that exhibit good high-temperature strength and irradiation resistance. The phase structure, mechanical properties, deformation mechanisms, and irradiation resistance of the RHEAs were investigated and discussed. All the lowactivation Ti30V30Cr5Zr5Ta30-xWx RHEAs exhibited excellent phase stability. Typically, the Ti30V30Cr5Zr5Ta15W15 RHEA exhibited a yield strength, specific yield strength, and plasticity of 1607 MPa, 172.42 MPa & sdot;cm3/g and 22.7 % respectively at room temperature. At 800 degrees C and 1000 degrees C, it still had a yield strength of 851 MPa and 558 MPa respectively. The high strength of the Ti30V30Cr5Zr5Ta15W15 RHEA was attributed to the solid solution strengthening mechanism, in which the W element played an important role. The deformation mechanism of Ti30V30Cr5Zr5Ta15W15 RHEA at both room temperature and elevated temperatures was primarily governed by dislocation slip. Using low-energy and high-flux He ions, the irradiation resistance of the Ti30V30Cr5Zr5Ta20W10 and Ti30V30Cr5Zr5Ta15W15 RHEAs were also investigated. They demonstrated better radiation resistance surpassed that of pure W, showing remained flat surface and stable phase structure.

Zirconium-based bulk metallic glasses (BMGs) show significant challenges in machining for their excellent mechanical properties. In order to gain a comprehensive understanding of the BMGs machining, it is important to study the chip formation process. Firstly, the von Mises equivalent stress, temperature, equivalent plastic strain, and strain rate during the chip formation process were analyzed through finite element simulations (FEM). Subsequently, this study investigated the chip morphology of the BMGs. Energy dissipation analysis revealed that the energy consumed in serration formation process increased with increasing cutting speed, feed rate, and cutting depth. Finally, the Weibull distribution model was utilized to analyze the stability of the adiabatic shear band spacing under different cutting speeds. The results indicated that a lower cutting speed led to more stable chip formation and better surface quality. The present findings provide a theoretical basis for optimizing machining quality and enhancing surface performance of Zr-based BMGs.

Bulk metallic glasses (BMGs) have shown great application potential in engineering because of their excellent mechanical properties, such as high strength and high hardness. But they also bring in great difficulties to their machining. To solve the machining problems, the low-speed cutting characteristics of a Zr57Cu20Al10Ni8Ti5 BMG (at.

Understanding the plastic deformation mechanisms is vital for exploring the ductilization strategies of refractory high-entropy alloys (RHEAs). In this work, differing from the well-known Portevin-Le Chatelier (PLC) effect, a unique serrated flow was observed in a (FeVCr)90W10 RHEA with a plastic strain larger than 50 %. The serrated flows were observed within a specific strain range from approximately 3 %-17 %, rather than occurring throughout the entire plastic strain range. A spontaneous transition of serration type was observed during deformation, without activations such as the change of temperature and strain rate. The formation and evolution mechanisms of such serrated flow, and their effects on enhancing plasticity, were revealed. Serrations in stressstrain curves and slip bands in deformed microstructure occurred simultaneously, suggesting a potentially-linked relationship. A high average Schmid factor (SF) of 0.445 for the RHEA suggested that the slip system was easily activated, which was the primary cause for the serrated flow. Cyclic compression tests indicated that due to work hardening, a higher energy was required to activate the slip event in subsequent plastic deformation. TEM characterizations indicated that the pinning effect of the high-density planar dislocation bands on dislocations and the dislocation entanglements were the primary mechanisms of the serration type transition. Additionally, by annealing, the alloy showed nearly serration-free plastic flow and also significantly-reduced plasticity, which further confirmed that the occurrence of serrated flow is beneficial for enhancing the plasticity of the RHEA.

Refractory high-entropy alloys (RHEAs), as a new kind of alloy with many excellent properties, exhibit attractive application potential in harsh environments. Achieving better processing surface integrity plays an important role in accelerating their practical engineering applications. In this work, based on the material removal mode-driven design strategy, two RHEAs, W10Ta20Ti34V35C1 and W15(TaVZr)85, were subjected to multi-pass wire electrical discharge machining (WEDM). The surface integrity was characterized and the effect of dendrite structure on WEDM removal mechanism was investigated. The results have shown that by multi-pass processing, the thickness of recast layer and volume fraction of deposited materials significantly decreased. Especially, the surface roughness of W10Ta20Ti34V35C1 and W15(TaVZr)85 RHEAs was reduced by 67.38

The poor surface quality of selectively laser melted Ti6Al4V limited its application in critical fields. When using the solution with the solvent of ethylene glycol, electropolishing (EP) is an environmentally friendly method to improve surface roughness. However, the influence of the water absorption property of ethylene glycol on the surface roughness is rarely reported. In this study, polarization curve tests indicated that the solution with a suitable drying time had a better passivation ability than the undried solution. After EP with a voltage of 18 V and drying time of 24 h, the surface roughness Ra was reduced by 61.73

Bulk metallic glasses (BMGs) show excellent physical and chemical properties. However, during the machining of BMGs, the poor thermal conductivity led to severe tool wear. Among the various factors influencing the tool wear, cutting temperature and stress field played the most significant roles. In order to study the influence of cutting temperature and rake face stress field on tool wear behavior, the tool wear mechanisms of machining BMGs at different cutting speeds and corner radii were investigated in this study. The changes in wear morphology of the tool rake face and flank face were analyzed. The main wear mechanisms were adhesive wear and abrasive wear. Moreover, the cutting temperature was calculated to characterize the influence of cutting speed on tool wear behavior, and the influence of corner radius on tool wear behavior was also analyzed with considering the stress field on the rake face. With the increase in cutting speed, the cutting temperature increased from 777 K to 1216 K, with an increase of 56.5 %, leading to the thermal softening and hardness reduction of workpiece material. This resulted in enhanced adhesion on the rake face and diminished grooving on the flank face. As the corner radius increased, the maximum normal stress decreased from 1732 MPa to 986 MPa, a decrease of 43.07 %, which reduced the ploughing effect of hard particles on the tool surface and diminished the abrasive wear on the rake face. And it also reduced the adhesion tendency on the rake face, thereby reducing the adhesive wear.

Tool wear and surface quality are significantly influenced by work hardening during machining. This work focused on the work hardening behavior during the machining of WNbMoTaZrx (x = 0.5 and 1.0) refractory high entropy alloys (RHEAs). The effect of polycrystalline cubic boron nitride tool geometric parameters on cutting forces, Vickers hardness, and the microstructure of machined side surface of RHEAs was studied. It was found that the RHEAs showed different degrees of work hardening. Compared to WNbMoTaZr0.5, the softer and tougher interdendrites of WNbMoTaZr1.0 compressed the dendrite area under the grinding and squeezing effect of negative chamfering surface, which effectively reduced the degree of work hardening and led to the appearance of abnormal cutting forces. The changes of negative chamfer angles and tool corner radius also affected the degree and behavior of work hardening. In conclusion, RHEAs showed different work hardening behaviors, including dendrite refinement, dendrite breakage, and dendrite compression, which in turn resulted in different degrees of work hardening and increase in cutting force.

The anodic electrochemical behaviors of selective laser melted Ti6Al4V were analyzed in environmentally friendly solutions, including NaCl solution, NaCl-ethylene glycol (NaCl-EG), and choline chloride-ethylene glycol (ChCl-EG). The passive and transpassive behaviors of Ti6Al4V in NaCl-EG and ChCl-EG were similar, which was significantly better than that in NaCl solution. This is because a better corrosion resistant passive film generated in the solvent EG than in the deionized water, despite with the same electrical conductivity. Typically, when the applied voltage increased to 30 VSCE, the current density was only 103.33 mA cm-2 in NaCl-EG and 92.22 mA cm-2 in ChCl-EG, which was much smaller than the 2287.78 mA cm-2 in NaCl solution. Additionally, the surface morphology also confirmed that the samples had a better corrosion resistance in NaCl-EG and ChCl-EG than the NaCl solution, regardless of the applied voltage. Finally, electrochemical surface treatment was conducted on samples in all solutions, and the best surface quality was obtained in NaCl-EG. A more uniform and thicker passive film is generated in the NaCl-EG and ChCl-EG than that in the NaCl solution.XPS results reflect the main composition of passive films is similar in all environmentally friendly solutions.The current density in NaCl-EG or ChCl-EG is always lower than that in NaCl solution whatever the applied voltage is.Electrochemical surface treatment verifies that the film generated in NaCl-EG has the best uniformity.

The influence of negative chamfer angle on the machined surface quality of WNbMoTaZrx (x = 0.5, 1.0) refractory high entropy alloys (RHEAs) was investigated. The results showed that the increase of negative chamfer angle can improve the machined surface quality of RHEAs. Such improvement was mainly attributed to the plough press effect of the negative chamfer surface and the self-healing ability of the machined surface. With the increase of the negative chamfer angle, the shear angle decreased, resulting in the elongation of the shear slip band and the increase of cutting force. During machining, the negative chamfer surface would press the materials in the metal stagnation area onto the machined surface, resulting in a smooth machined surface. Meanwhile, the high temperature caused the workpiece surface to develop a self-healing ability, which smoothed the ridge of the ploughing groove. Finally, the machined surface quality of RHEAs had been significantly improved to Ra = 0.5 µm. In addition, the morphology of the chip and machined surface was examined, where the machined surface was mainly characterized with plastic flow, side flow, and ploughing grooves. The chip-free surface was mainly characterized with tooth top, shear band, and burr. With the increase of negative chamfer angle, the serrated inclination angle slowly decreased because of the shear angle decrease. The main tool wear for the machining of RHEAs was adhesive wear. This work provides useful guidance for improving the machined surface quality of RHEAs.