查看更多>>摘要：? 2021 Elsevier LtdBall milling is a key step in the processing of tungsten carbide parts. It ensures a good distribution of the different powders and reduces the crystallite size in the nanometer range by “mechanical alloying”. The study of the influence of the rotation speed and the milling medium on the sinterability of the WC-Co composite is important. The optimization of milling was achieved by characterizing the porosity and the grain size distribution after sintering, and the mechanical properties. The samples have been sintered under vacuum at 1400 °C for 1 h. Optimized processing parameters were found to be 300 rpm in wet milling and 450 rpm in dry milling (average grain size of 760–800 nm, hardness of 1700–1720 HV30, and fracture toughness of 10.5–11.0 MPa√m for both cases).
查看更多>>摘要：? 2022 Elsevier LtdMolybdenum alloys are excellent candidates for extremely high temperature environments, such as in nuclear thermal propulsion spaceflight systems. Spark plasma sintering is a useful manufacturing technique that allows for rapid fabrication of refractory materials that are difficult to sinter using more traditional methods. Pre-alloyed molybdenum with 30 wt% tungsten powder was consolidated using spark plasma sintering under a variety of conditions to determine the optimum sintering conditions. Hold temperatures between 1400 and 1700 °C, at sintering pressures from 10 to 50 MPa, and for hold times at maximum temperature from 0.5 to 90 min were tested. The effects of hold temperature, sintering pressure, and hold time on the microstructure and mechanical properties were examined. Higher applied pressures are necessary to achieve higher sample density at lower temperatures. Sintered densities ranging from 88.8 to 97.9% theoretical were achieved over the testing conditions, with the highest density being achieved with sintering conditions of 1700 °C and 50 MPa for 5 min. The hardness of the sintered material followed the Hall-Petch inverse grain size relationship over the investigated grain sizes. Grain growth at 1600 °C was found to follow a second order relationship with time. When compared with pure molybdenum, solid solution strengthening was observed to increase the hardness of the alloy. From these experiments and analysis, an understanding of how sintering conditions affect the density and microstructure of the alloy was developed that will allow for future development of ceramic metallic composite materials for nuclear thermal propulsion.
查看更多>>摘要：? 2022 Elsevier LtdA novel lightweight refractory high entropy alloys AlxCrNbTiV (x = 0.2, 0.5 and 0.8, in terms of molar ratios) are prepared by vacuum arc melting. In the as cast condition, the alloys have BCC phase with significant dendrite structure, with a low density of 5.82–6.38 g /cm3 and hardness increase from 462 HV0.2 to 549 HV0.2 with the solid solution strengthening effect by adding Al. Due to simultaneous dislocation motion and development of kink bands, Al0.2CrNbTiV exhibits good combination of strength and ductility at room temperature, enabling deformation in compression to ε > 50%, with yield strength of 1570 MPa, and attractive specific yield strength of 246 MPa·cm3/g. And Al0.5CrNbTiV and Al0.8CrNbTiV shows typical brittle feature. Cr2Nb-type C14 Laves phase precipitated with the compression temperature increase to 1000 °C. EBSD analysis shows discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) are activated together in the hot-compression process, and result in softening and a substantial increase in ductility of all the alloys. Furthermore, the theoretical yield stress of AlxCrNbTiV is calculated through estimating the solid solution strength effect attributed to atomic misfit and modulus misfit, and the results indicated the degree of solid solution could affect the estimation accuracy.
查看更多>>摘要：? 2022 Elsevier LtdIn the metalworking industry, hard-coated WC-Co hardmetal tools are often used in machining applications. Generally, tool life is limited by pre-existing defects in the hardmetal substrate and defects that form during tool application. The complex, multi-axial loading situations and the high temperatures present in the cutting-edge area of machining tools are among the main reasons for the formation and growth of defects in operation. At present, there is a lack in experimental setups that can replicate these conditions. In the current work a novel material testing method is presented, which uses a spherical indenter and inclined specimen surfaces to apply multi-axial loads at 700 °C. The local stress state in the specimen was calculated using finite element simulation implementing an experimentally parameterized material model considering ratchetting and creep of the substrate material. Stresses ranging from mainly compressive to tensile-compressive were predicted. Initiation and accumulation kinetics of defects in the nm- to μm size regime were studied quantitatively. The comparison of stress calculations and damage development shows that positions with tensile-compressive stresses exhibited significantly higher defect formation rates than those with mainly compressive stresses.
查看更多>>摘要：? 2022 Elsevier LtdPlastic deformation and static recrystallization of pure tantalum are studied using Electron BackScatter Diffraction (EBSD) technique. Recrystallization kinetics are discussed in light of stored energy estimation from EBSD data acquired on deformed microstructures. Characterization of deformed state reveals the influence of crystallographic orientation on the plastic deformation. Dislocation substructures are formed in the γ-fiber grains and almost no substructures are observed in the θ-fiber grains. Subsequent recrystallization directly inherits this orientation dependence of deformed state. Nucleation is promoted in the γ-fiber grains because of substructure development whereas nucleation is more sluggish to occur in the θ-fiber grains. Thus, a microstructure composed mostly of γ-fiber grains recrystallizes faster than a microstructure with a less strong texture, despite a strain nearly three times lower. At the polycrystalline scale (step size of 1.20 μm in the present case), recrystallization kinetics are better described with stored energy estimated through substructures than through dislocation density. At the substructure scale (step size of 90 nm), Geometrically Necessary Dislocation (GND) density seems to be correctly estimated; still recrystallization kinetics cannot be accounted for by this density because it does not account for the substructure formation.
查看更多>>摘要：? 2022Laser melting deposition (LMD) technology is characterized by a fast-forming speed, additive manufacturing, and a multi-axis operating system, which is suitable for preparing hard alloy parts with complex structures. This study mainly focused on analyzing the microstructure and mechanical properties of cemented carbides fabricated via LMD on different substrates. The results showed that the cemented carbide formed on the WC-20Co cemented carbide substrate had a higher density and fewer cracks and pores compared with fabricating on the 45# steel substrate because the composition of the substrate and powder had similar thermal expansion coefficients, and so the deposition effect was better. The smaller grain size in the microstructure of the cemented carbide formed on a 45# steel substrate was possibly influenced by the difference of liquid phase point and the solid solubility between 45# steel and WC-20Co cemented carbide. Firstly, 45# steel has the higher liquid phase point (1495℃) compared with WC-20Co (1320℃), which made less liquid phase produced during SLM processing. Meanwhile, the solid solubility of WC in 45# steel (7 wt%) is lower than in Co (22 wt%), the dissolution process of WC grains was limited, thus, the growth of WC grains was hindered. Compared with the samples prepared on the 45# steel, the hardness was higher for the alloys fabricated on cemented carbide substrate, which was mainly due to the higher density of the samples and the higher η-phase.
查看更多>>摘要：? 2022 Elsevier LtdIn order to encourage environment friendly manufacturing, dry machining is extensively explored and acknowledged. Consequently Functionally Graded Cemented Tungsten Carbide (FGCC) with solid lubricant was prepared by Spark Plasma Sintering at different heating rate and sintering temperature. The wear behavior of developed materials was explored by pin-on-disc tribological tests and dry machining. The attempts were made to analyze effect of key test parameters (such as load, ambient temperature, and sliding velocity) and solid lubricant over tribological behavior. The presence of solid lubricant resulted in reduced coefficient of friction (COF) and wear. The ambient temperature and load were displayed most significant influence over wear and COF respectively. Also samples prepared at high sintering temperature as well as heating rate demonstrated lower wear and COF. Additionally, the primary failure mechanism was identified as binder removal. These tribological examinations confirmed the suitability of self-lubricating FGCC as a cutting tool material for dry machining.
查看更多>>摘要：? 2022In this research, we performed studies on the in-situ formation of carbon in the ZrB2–25 vol% SiC composite prepared by the spark plasma sintering (SPS) process at 1850 °C. The sintering behavior, microstructure, and mechanical properties of the resulted composite were also evaluated. The sample showed excellent sintering behavior, and a relative density of 99.77% could be obtained. X-ray diffractometry and microstructural results confirmed the in-situ formation of carbon during the SPS process. The source of carbon was found to be a reaction between SiC and its surface oxide. Moreover, the SiO2 and B2O3 compounds could form a low melting point eutectic phase and trigger the liquid phase sintering mechanism. The resulted composite achieved the fracture toughness of 5.63 MPa.m1/2, the Vickers hardness of 18.93 GPa, the flexural strength of 741 MPa, and the elastic modulus of 481 GPa.
查看更多>>摘要：? 2022 Elsevier LtdAlthough of scientific and practical importance, very limited efforts have been made to accurately predict the properties of cemented carbide by machine learning (ML). Herein, we propose a multiple loops ML framework to predict various properties (density, coercive force, hardness, transverse rupture strength, and fracture toughness) of WC–Co based cemented carbides. High fidelity ML models for density and coercive force were firstly built using highly ranked features identified by correlation analyses to augment the training dataset with predicted data. Next, ML models were successfully trained to provide a satisfactory prediction for hardness, transverse rupture strength, and fracture toughness. The current study demonstrated the potential of the ML approach to predict the properties of cemented carbide with various additives and to further guide the design of new materials.
查看更多>>摘要：? 2022 Elsevier LtdIn this work, industrially relevant WC composites with alternative binders (Ni, CoNi, NiCr, CoCr, CoNiCr and NiCrMo) were produced and their corrosion resistance in 0.5 M NaCl was compared to conventional WC-Co system. The main objective is to develop hardmetals with higher corrosion resistance to extend the lifetime of tools and equipment, reducing the demand for new parts and maintenance, thus decreasing the total cost of the operation. The study includes different electrochemical techniques, namely corrosion potential monitoring, Electrochemical Impedance Spectroscopy (EIS) and polarization curves. The purpose is to evaluate the influence of each element on the corrosion resistance of the composites produced.
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