查看更多>>摘要：? 2021 Elsevier LtdThe liquid phase formation temperatures of the quinary system W-C-Co-Fe-Ni with a ratio of Fe:Co:Ni = 40:20:40 were determined by means of DSC analysis. Besides, the experimental C-window of this system with a binder content of 14.3 ± 2 wt% is accurately defined. Based on the experimental results, a thermodynamic modelling is carried out using the CALPHAD approach. Temperature-composition sections of the W-C-Co-Fe-Ni system with different binder contents are calculated to verify the rationality of the present modelling. There is a good correlation between the experimental and calculated results showing that the experimental data can be well reproduced by the present modelling.
查看更多>>摘要：? 2021 Elsevier LtdIn this paper, the wear and corrosion resistance of FeNiCoCrMox (x: atomic ratio, x = 0, 0.15, 0.20, 0.25) high entropy alloy coatings (HEACs) which prepared by laser cladding (LC) technology on 316 stainless steel (SS) was investigated. According to XRD, SEM, MicroXAM-3D, microhardness tester and electrochemical workstation tests results, the HEACs presented typical DR-ID structure with single FCC solid solution phase. The average microhardness of Mo0, Mo0.15, Mo0.20 and Mo0.25 HEACs increased by 70.1%, 77.0%, 84.9% and 90.5% relative to the substrate. Dry sliding friction and wear tests results showed that the average friction coefficient of the HEACs were significantly lower than that of 316 SS substrate. Meanwhile, it can be found that Mo0.25 HEACs had the lowest average friction coefficient which displayed the best wear resistance. Compared with Mo0 HEAC, the specific wear rates of Mo0.15, Mo0.20 and Mo0.25 HEACs decreased by 11.1%, 27.8% and 38.9% respectively. The electrochemical tests results showed that the corrosion type of HEACs was intergranular corrosion and all HEACs had a higher corrosion resistance than that of 304 SS or 316 SS. Moreover, Mo0.20 HEACs showed the best corrosion resistance due to the enhancing effect of MoO3 on Cr2O3 passivation film.
查看更多>>摘要：? 2021We synthesized a series of Cu–Ti based crystalline and amorphous brazing filler metals (BFMs) and further investigated the microstructure characteristics and melting features for comparison. The presence of precursor film together with latent heat of crystallization showed a significant effect on the enhanced wettability of amorphous BFMs/tungsten heavy alloy (WHA) system. The wetting and spreading mechanism were addressed in a view of atomic adsorption and diffusion. The brazed joints showed effective interface bonding and high shear strength, especially at elevated temperature (up to 364 MPa at 400 °C). This study demonstrates the great superiority and feasibility of amorphous brazing filler metals in the joining of WHAs.
查看更多>>摘要：? 2021 Elsevier LtdIn this paper, Hf-Mo-Nb-Ti-Zr alloy system with single BCC solid solution phase was selected as the matrix alloy. In order to design a new high temperature structural material with excellent comprehensive properties, the multiphase reinforced refractory high entropy alloys was prepared by adding metallic elements of Al or Cr and nonmetallic elements of B, C or Si into Hf-Mo-Nb-Ti-Zr alloys at the same time. The results show that the type and content of newly formed phases are closely related to the mixing enthalpy between alloying elements and the constituent elements of the matrix alloy. This provides a valuable reference for the prediction of phase formation when adding alloying elements to improve the properties of high entropy alloys.
查看更多>>摘要：? 2021 Elsevier LtdNano-scaled WC powder is an important material for preparation of ultrafine or nano-grained WC-based cemented carbides via powder sintering method. In this paper, nano-scaled WC powder was prepared based on traditional carbothermic reduction method. First, the mixture of WO3 and carbon were reacted at 1000 °C to remove all the oxygen atom. Then, according to residual carbon content in the deoxidation products, the gas-phase (by 90%H2 + 10%CH4, at 900 °C) or solid-phase carburizing process (at 1100 °C) was selected to prepare WC powder, respectively. The results indicated that the use of nano carbon black in first stage could provide a large number of dispersed nuclei, and meanwhile, a low reaction temperature was beneficial to inhibit the growth of product particles. The thermodynamic calculation, reaction behavior and nuclei growth behavior in deoxidation and carbonization stages were studied in detail. As the C/WO3 ratio was 2.5 and 3.8, the WC powder with total carbon content of 6.23% and 6.19%, particle size of 80.29 nm and 95.24 nm, and BET value of 3.88 m2/g and 4.25 m2/g was obtained by this method, respectively.
查看更多>>摘要：? 2021 Elsevier LtdThe paper presents a method of fabrication and a comparison of the characteristics of obtained cemented carbide samples based on tungsten carbide with 10% metal binder. They were synthesized by spark plasma sintering (SPS) at different sintering temperatures: Co (1200 °C), Fe and Ni (1150 °C), Cr (1500 °C), and Ti (1400 °C). During the SPS-consolidation process, investigations of the dilatometric characteristics of samples of starting powders of identical granulometric composition obtained by mixing/grinding resulting in the fractional composition in the particle size range up to 10 μm are presented. The mechanism of phase formation and microstructure of the obtained materials is investigated by XRD, SEM, and EDS. The possibility of synthesizing hard alloys WC – 10%Ti and WC – 10% Cr by the mechanism of reaction SPS synthesis with a reduction in the synthesis time in comparison with traditional sintering methods has been demonstrated. Analyses have shown that during sintering of alloys containing Ti and Cr the volume content of WC decreases to 47% because of dissolution and interaction, while in alloys containing Co, Ni, and Fe, the volume content of WC remains unchanged (85–86%). This led to a dramatic change in hardness, fracture toughness, and strength when replacing Co, Ni, or Fe with Ti or Cr.
查看更多>>摘要：? 2021The paper analyzed temperature ranges of aggregate/polymorphic state changes, phase and structural transformations in Al, Ti, WC-Co, and Ti1-xAlxN, leading to the gradient of thermo-physical and physico-mechanical properties of cathodes, substrate, and coating. The critical temperatures for Al and Ti are the points of the exo- or endothermic effect occurrence at 933 K (TmAl) and 1155.5 K (Tα-Ti→β-Ti), respectively. The hardness of the WC-Co / Ti1-xAlxN composition varies with the heating temperature of the WC-Co before coating deposition. The optimal heating interval for WC-Co is 873…963 K. The structuring process of the Ti1-xAlxN coating was investigated in the temperature range 673…1073 K before the spinodal decomposition of c-TiAlN into metallic c-TiN and dielectric-semiconductor c-AlN. Physico-mechanical properties of the Ti1-xAlxN coatings were determined using a FISCHERSCOPEH100C measurement system per the standard DINENISO14577-1. Wear tests were carried out according to the “finger-disk” scheme in a coolant-cutting fluid on a laboratory friction machine. The optimal temperature conditions for the deposition of a nanostructured Ti1-xAlxN coating with a minimum phase and elemental composition gradient and microdroplets number, a complex of high physico-mechanical properties, wear, and cracking resistance have been established. The Ti1-xAlxN coatings efficiency has been increased by controlling the thermo-physical and physico-mechanical properties of Ti and Al cathodes, the substrate (hard alloy WC-Co), and the Ti1-xAlxN coating in-process of their heating and cathodic arc evaporation. Multifunctional dependency graphs of the physico-mechanical properties and the friction coefficient of the Ti1-xAlxN coatings on the Al = x content have been developed. The relationship between the resistance of the coating to plastic deformation and the coefficient of friction has been established.
查看更多>>摘要：? 2021 Elsevier LtdThe cemented carbides have been gradually applied for marine equipment due to their high wear resistance, while the corrosive impact of seawater has a considerable effect on its wear performance. In this paper, the effect of Ni concentration on the resistance to corrosion, tribological properties, and microstructure of the cemented carbides based on tungsten carbide (WC) with metal binders sliding against silicon carbide (SiC) in seawater was investigated. The results showed that Ni element has a positive effect on the resistance to corrosion of cermet WC, and the resistance to corrosion is the best when the concentration of Ni element is 9% (WC-9Ni). In addition, the coefficient of friction (COF) of the WC-hNi/SiC tribopair first decreased and then increased with the increase of Ni concentration, and the quite low steady COF of WC-9Ni is observed. The wear mechanism of the WC-hNi balls is mainly abrasive wear, and the corrosion wear is mild. Furthermore, the wear rate of WC-9Ni is the lowest at different rotational speeds, which has great application potential in seawater hydraulic components.
查看更多>>摘要：? 2021 Elsevier LtdDue to the importance of wear behavior in tungsten base alloys, this issue has rarely been considered. The present study deal with the effect of Y2O3, its amount and sintering on the microstructural and wear behavior of W-Ni-Cu-Y2O3 alloys. After 25 h of mechanical milling, alloys containing 0–0.6 wt% of yttrium oxide nanoparticles were prepared by conventional (1400 °C, 30 min) and spark plasma sintering (1100 °C, 4 min). The composition, structure and morphology of the milled powders were investigated by SEM and XRD. Then, the microstructure, density, micro-hardness and wear behavior of the composite alloys were evaluated. The result of milling in the presence of yttria nanoparticles is a homogeneous distributed fine-grained powder whose crystallite size has been reduced from 34 to 24 nm. The addition of yttrium oxide nanoparticles caused microstructural modification including grain refinement, (Ni,Cu) binder phase distribution and reduced contiguity of the tungsten grains. Spark plasma specimens, although sintered at lower temperature, exhibited enhanced properties due to the finer grains (less than 4 μm) compared to conventional sintering. The spark plasma sintered alloys with 0.6 wt% of Y2O3 and an average grain size of 2.56 μm were found to have maximum relative density (96.9 g.cm?3), highest microhardness (504 HV) and minimum wear volume (9.5 × 10?5 cm3) and rate (0.064 × 10?7 cm3.N?1.m?1). Also, the coefficient of friction was lower and decreased with increasing of yttria for these specimens. Delamination, cracking, and brittle wear behavior in conventional sintered have turned into plastic deformation in spark plasma specimens.
查看更多>>摘要：? 2021 Elsevier LtdTungsten carbide cobalt hardmetals are commonly used as cutting tools subject to high operation temperature and pressures, where the mechanical performance of the tungsten carbide phase affects the wear and lifetime of the material. In this study, the mechanical behaviour of the isolated tungsten carbide (WC) phase was investigated using single crystal micropillar compression. Micropillars in two crystal orientations, 1-5 μm in diameter, were fabricated using focused ion beam (FIB) machining and subsequently compressed between room temperature and 600 °C. The activated plastic deformation mechanisms were strongly anisotropic and weakly temperature dependent. The flow stresses of basal-oriented pillars were about three times higher than the prismatic pillars, and pillars of both orientations soften slightly with increasing temperature. The basal pillars tended to deform by either unstable cracking or unstable yield, whereas the prismatic pillars deformed by slip-mediated cracking. However, the active deformation mechanisms were also sensitive to pillar size and shape. Slip trace analysis of the deformed pillars showed that 101ˉ0 prismatic planes were the dominant slip plane in WC. Basal slip was also activated as a secondary slip system at high temperatures.
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