查看更多>>摘要：Changes in the elastic constants c(ij) of disordered cubic TaCy tantalum carbide with an increasing the defectiveness of the carbon sublattice are estimated for the first time. The deviation of tantalum carbide from the stoichiometric composition TaC1.0 leads to a decrease in the elastic stiffness constants c(ij) of disordered TaCy carbide with a simultaneous increase in elastic anisotropy. The distributions of the Young's modulus E and the Poisson's ratio mu in the (100) plane and the distributions of the shear modulus G in the (100), (110), and (111) planes have been calculated as functions on the crystallographic direction [hkl] and on the relative carbon content y in TaCy carbide. The Vickers hardness H-V of disordered tantalum carbide was calculated using the inverse Pugh's ratio G/B and the experimental data on the dependences of the bulk modulus B and the shear modulus G on the composition of disordered TaCy . Influence of nonstoichiometry of nanocrystalline powders of cubic tantalum carbide TaCy on anisotropy of strain distortions is established. The value of microstrains epsilon(hkl) is estimated with allowance for their anisotropy.
查看更多>>摘要：In this study, the effect of GNP concentration on the mechanical properties of spark plasma sintered TiB2 and NbB2 ceramics was investigated. GNP reinforced TiB2 and NbB2 specimens were aimed to produce with nearly full densification. Herein, SEM investigations, Raman analysis, and oxidation behavior of the samples were reported. GNP addition into the TiB2 and NbB2 matrices showed a different effect on various properties of the composites. GNP loading tends to enhance densification by removing native oxides of both TiB2 and NbB2 matrices. GNPs were more effective in the oxygen removal mechanism for TiB2 composites than NbB2. The highest relative density was obtained for TiB2-GNP and NbB2-GNP composites as 98.6% with 7 vol% and 5 vol% GNP additions, respectively. The Vickers microhardness decreased with increasing GNPs loading for both matrices. NbB2-GNP composites possessed higher fracture toughness and better oxidation resistance than TiB2-GNP composites.
查看更多>>摘要：Refractory high-entropy alloys (RHEAs) have attracted extensive attention due to their outstanding hightemperature performance. However, high density and poor ductility are the two bottleneck problems in industrial application. This study aims to exploit novel RHEAs with high specific strength and good ductility by adding light Group IVB elements. The effect of Zr on the as-cast microstructure, density, and mechanical properties of Ti2VNbMoZrx (x = 1, 1.5, 2, and 3) RHEAs was investigated in detail. All Ti2VNbMoZrx RHEAs exhibited a disordered body-centered-cubic solid-solution phase. The as-cast microstructures changed from dendritic morphology (x =1 and 1.5) to equiaxed dendritic morphology grain (x = 2 and 3) with the increasing Zr content. The Ti2VNbMoZr2 RHEA displayed optimal mechanical properties with a compressive yield strength of 1421 MPa, a plastic strain of 31.6%, and a specific yield strength of 211 kPa center dot m3 center dot kg-1, superior to the most-reported RHEAs. The microbands along {110} and {112} slip planes, which was a typical poly slip configuration, were observed in the Ti2VNbMoZr2 alloy after compression test using ex-situ transmission electron microscopy. Furthermore, the Ti2VNbMoZr2 RHEA exhibited good high-temperature mechanical properties, showing a yield strength of 977 MPa at 600 degrees C and 386 MPa at 800 degrees C without fracture at a plastic strain of 50%. The solution strengthening model revealed that the high yield strength of Ti2VNbMoZrx RHEAs was mainly derived from the atomic radius misfit and shear modulus misfit of the Zr atoms.
查看更多>>摘要：In this work more than 2500 published experimental data on hardness and indentation fracture toughness of cemented carbides during the last 40 years have been collected. The significant number of samples displays the influence of microstructure, chemical composition, and processing on the hardness - toughness relationship of cemented carbides. Selected two-dimensional plots are presented and discussed as an example of visualization of the available experimental information. This collected record can serve as an initial reference set for the cemented carbide community using all available shared knowledge organized in one well-structured database.
查看更多>>摘要：Powder particles with spherical geometries have been found to result in better powder performance in different industries, especially Additive Manufacturing (AM), by fabricating more dense powder layers that consequently result in more desirable part properties with less defects. Plasma spheroidization process has shown an excellent capability in enhancing particle geometries of powders from a variety of materials, particle size distributions, and arbitrary initial particle geometries. The current review paper summarizes the previous conducted work on plasma spheroidization process to determine the effect of its process parameters on powder characteristics. The spheroidization process parameters, including powder feed rate, central, carrier, and sheath gas flow rates, gas mixtures, power, and chamber pressure are individually discussed. Also, the impact of these process parameters on powder characteristics, such as particle size distribution, particle trajectories, chemical impurity, microstructure, porosity, flowability, and densities are reviewed. A tradeoff among process parameters, spheroidization ratio, and evaporation rate was observed. Depending on particle size and material melting point, increasing particle residence time in exposure to plasma first increased and then decreased the spheroidization ratio overall.
查看更多>>摘要：A cBN-Al2O3-Al cutting tool material was prepared by a dual power spark plasma sintering method, and the effects of sintering temperature, holding time and Al2O3 content on the microstructure and mechanical properties of cBN-Al2O3-Al cutting tool material were studied. The results showed that the dual power sintering method strengthened the spark plasma generated between the particles, increased the uniform discharge effect of the metal Al in the sintered body, generated a local high temperature and reacted with the activated cBN to produce AlN, and inhibited the phase change of cBN. When the sintering temperature was 1500 degrees C, the holding time was 5 min, and the pressure was 50 MPa, the overall mechanical properties of cBN-Al2O3-Al cutting tool material with 50 wt% Al2O3 content were the most optimal, with a hardness of 24.45 GPa, a fracture toughness of 5.92 MPa.m(1/2), and a flexural strength of 423 MPa.
查看更多>>摘要：In this study, FeCoNiCr0.8Al0.2 high-entropy alloy was fabricated by vacuum arc melting, followed by aging treatment for different durations. And the phase structure, microstructure, mechanical properties, and tribological behavior of the alloys were systematically studied. The results show that all the HEAs in this work have good structural stability and they consist of the FCC matrix phase and gamma' precipitated phase with L12 structure, in which the FCC matrix is rich in Fe, Co, and Cr, while the gamma' precipitates rich in Ni and Al. The changes of the precipitates of the alloys with the aging time are divided into two stages. In the first stage (the aging time is 6 h, 12 h, and 24 h), the volume fraction of the precipitates of HEAs increases initially, but when the durations beyond 12 h, the size of it gradually increases but the volume fraction of the precipitates decrease. After the durations beyond 48 h, the alloy will undergo secondary precipitation effect again but the volume fraction of the reprecipitated phases is lower, and the precipitates gradually coarsen with the increase of durations. All the HEAs occurred abrasive wear and oxidative wear during the wear process. In addition, delamination wear and spalling wear occurred on the 6hHEA and the 168hHEA, respectively. The 12hHEA has the best wear properties due to the highest volume fraction and the uniform distribution of the precipitates. Our study indicates that the alloys can have good wear properties inducing a certain volume fraction of L12 precipitated phase by proper heat treatment, and it can provide theoretical reference for the development and design of the alloys with good wear resistance.
查看更多>>摘要：Organic carbon has been used as a reducing agent to reduce the oxygen content in the TZM (Titanium-Zirconium Molybdenum) alloys for the first time. The TZM alloys were prepared by the powder metallurgy sintered by hydrogen and vacuum, respectively. With increasing the organic carbon content from 0.04 wt% to 0.8 wt%, the influence of organic carbon content and sintering methods on the oxygen content of TZM alloys and their action mechanism were studied. The results show that the oxygen content of TZM alloy sintered by hydrogen decreases significantly with the increase of organic carbon. The oxygen content is as low as 300 ppm when the organic carbon is 0.8 wt%. The oxygen content of the TZM alloy varies between 50 ppm and 110 ppm under vacuum sintering. When the oxygen content decreases, the secondary phase particles precipitated in the alloy decrease the alloy's hardness due to the weakening effect of solution strengthening and secondary phase strengthening. The density of TZM alloy decreases with increasing organic carbon, whether in vacuum or hydrogen sintering. Verification experiments confirm the accuracy of the conclusion. As the oxygen content decreases from more than 3000 ppm to less than 1000 ppm, the secondary phase particles in the TZM alloy changed from mostly TiO2 and ZrO2 to Ti/Zr composite oxide particles containing zirconium-rich stripes. In the state of the lowest oxygen content, only zirconia was found in the matrix
查看更多>>摘要：Because of its high ductile-brittle transition temperature, tungsten (W) is normally alloyed with other metal elements in order to obtain high fracture strength, excellent thermal and electrical properties for industrial applications. For tungsten samples sintered using the conventional powder metallurgy methods, bonding among tungsten particles is normally through sintered necking process, thus without providing a good metallurgical bonding strength. In this paper, we proposed to apply additive manufacture methodology to synthesize two types of porous tungsten skeleton structures, honeycomb (65% porosity) and square skeleton (80% porosity), using a selective laser melting (SLM) method. Results showed that for both these skeleton structures, grains in the XY plane showed an equiaxed crystal appearance, whereas those in the YZ/XZ plane showed columnar patterns parallel to the Z axis. The measured porosities for these two types of skeletons were 52 vol% and 68 vol%, and their compressive strength values were 256 MPa and 149 MPa, respectively. Both their compressive strengths and hardness showed anisotropic behaviors, with their highest values along the direction of Z axis. Results also showed that fracture morphology and mechanisms of these skeletons under compression were quite different when they were compressed along different directions, mainly due to the formed columnar crystals of the skeletons along the Z axis. Fracture morphology along the Z axis showed transgranular fracture and tearing features, whereas those along X axis showed only intergranular fracture features.
查看更多>>摘要：In this study, pure Mo and Mo-6Ta alloy targets were produced by a manufacturing method, which is called die pressing with a combination of cold isostatic pressing and hot-pressing sintering technology, and molybdenum thin films were deposited on corning glass substrates using a DC magnetron sputtering system. The effect of alloying with tantalum on the phase structure, grain size, orientation, thin film surface morphologies and electrochemical properties has been investigated by a variety of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) with electron back-scattered diffraction (EBSD), atomic force microscopy (AFM), four-probe resistivity tester, and electrochemical analyzer. The observation of the Mo targets reveals that this manufacturing technology with alloying of tantalum can reduce the target's grain size to lower than 50 mu m with random grain orientation. The microstructure of the deposited Mo thin films indicates that the alloyed films have the higher deposition velocity with a dense fine grain structure and smoother surface. The sheet resistivity of the alloyed Mo film increases continuously with the increasing of the sputtering time, and eventually becomes higher than that of the pure Mo film. In electrochemical tests, both of the Mo films show capacitive reactance, and the capacitive arc radius of the alloyed Mo films are obviously larger than that of pure Mo films. The result of alloying with tantalum shows an increase in the corrosion potential of the Mo film from -0.5 V to -0.2 V, indicating improvement of the corrosion resistance of Mo films.
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Elsevier