查看更多>>摘要：This work aims to study the influence of the carbon content in a (NbC-3vol%Mo2C)-12vol%Ni-0.5vol%WC alloy on the sintering process, and its resulting effect on the microstructure and mechanical properties. NbC cemented carbides with additions of Mo or C were sintered at 1450 degrees C for 1 h in the vacuum furnace of a dilatometer and of a TGA (Thermogravimetric Analysis) device. Liquid phase sintering temperature is decreased with addition of Mo or C, leading to an early densification which limits nickel evaporation. Swelling occurs during heating in the 3 phase (NbC + Ni + liquid) domain for the high carbon content alloys. A graphite phase is observed for largest carbon contents. The C/Mo ratio also affects the phase composition and lattice parameters. The lattice parameter variation of the carbide and Ni rich-binder is explained by the variation of the metallic solute contents as a function of the overall composition. Grain growth is globally enhanced by increasing the carbon content. A significant effect of C/Mo ratio on the mechanical properties of the alloy is also observed. The Vickers hardness (HV30) decreases while the toughness (KIc) exhibits a maximum value as the carbon content increases.
Govande, Akshay R.Chandak, AayushSunil, B. RatnaDumpala, Ravikumar...
25页
查看更多>>摘要：Components working under harsh environments in power generation, marine, and aerospace sectors are subjected to severe surface degradation because of wear, corrosion, and erosion by solid particles, slurry, silt, and cavitation. Carbide-based materials exhibit high resistance to degradation under such conditions because of their high hardness and chemical stability. These carbides can be effectively deposited as coatings on the components using advanced thermal spray techniques such as plasma spraying, HVOF, and HVAF. The carbide-based thermal spray coatings are majorly based on either WC or Cr3C2 or a combination of these materials. However, the composition of the carbides, the type and percentage of binders, and process parameters significantly affect the performance of these coated components. In this article, the degradation behavior and performance of the different carbide-based coatings as a function of carbide grain size and type of metallic binders, spray process parameters, and working conditions have been critically reviewed. On the other hand, the post-processing of carbide coatings is also emerging as a promising strategy to enhance the performance by modifying and refining the structure of coatings. Hence, a comprehensive summary of the post-processing techniques such as heat treatment, laser treatment, and cryogenic treatment of the carbide coatings is also provided.
查看更多>>摘要：Laser melting deposition (LMD) additive manufacturing process has been attractive to the fabrications of pure tantalum due to the advantage of fast near net shaping of complex shaped components. In the present study, the LMD process has been applied to the fabrication of tantalum using two kinds of powders with different interstitial contents. The microstructure, chemistry, and mechanical properties of the LMD samples have been investigated to understand the strengthening mechanisms. The results show that the tantalum samples have near full dense, and large columnar grains with the growth direction slightly deviated from the deposition direction. The LMD tantalum can have high hardness of up to 300 HV, mainly due to the solid solution strengthening of nitrogen and oxygen interstitials. With relative low interstitial contents of about 400 ppm, the LMD tantalum can have ductile properties, showing ultimate tensile strength above 400 MPa, and elongations of about 14-16%, which are comparable to the properties of cold-worked tantalum. The present work suggests the LMD tantalum could have potential usages in the industry fields.
Zamharir, Mehran JaberiZakeri, MohammadRazavi, MansourAsl, Mehdi Shahedi...
9页
查看更多>>摘要：In this paper, ZrB2-SiC-Si-based ceramic composites with WC and MoSi2 additives were fabricated using SPS method and their densification behavior was investigated by phase and microstructural studies. During the SPS process and according to the prevailing conditions, WC and MoSi2 additives reacted with the surface oxide impurities of the main raw materials. As a result of these reactions and the decomposition of some raw materials, a series of oxide liquid phases formed, which were often Si-based, and due to their good fluidity, undissolved and free elements such as Zr, Mo and W moved to open porosities and grain boundaries. According to the established thermodynamic conditions, binary solid solutions and new phases such as MoB, ZrC and WB formed. The synthesis of such phases boosted the densification of the composites due to the fact that they formed in porosities or voids between the main grains. The results showed that the sample doped with 2.5 vol% WC and 2.5 vol% MoSi2 had the highest relative density (about 99%). Meanwhile, microstructural studies showed that homogeneous and dense parts can be achieved by SPS technology.
查看更多>>摘要：TiC-CoCrFeMoNi composites were fabricated via different powder metallurgy processes and their microstructures and mechanical properties were evaluated from room temperature to high temperatures up to 1273 K. One of the composites was prepared via the arc melting of raw metal powders and another was prepared via the mechanical alloying of the raw powders for the formation of a high-entropy alloy (HEA) of CoCrFeMoNi. The third composite was prepared via a reaction sintering process to form an HEA from raw metal powders. The obtained TiC-CoCrFeMoNi samples were composed of TiC phases, Mo-containing TiC phases, and HEA phases, and the microstructure varied among the three samples. The HEA phase was composed of a single fcc phase and the concentration of Mo in the HEA phases was low for all the three samples because most of the Mo atoms diffused from the HEA into the TiC hard phases. The Vickers hardness at 1273 K ranged from 62% to 64% of that at room temperature for the three samples. The bending stress started to decrease at 1173 K with increasing temperature, irrespective of the fabrication process. Thus, a low concentration of Mo in the HEA phase or a high solid solution of Mo in the TiC phase can improve the hardness and bending stress at high temperatures.
查看更多>>摘要：The work demonstrates the artificial neural network (ANN) potential applicability to predict the oxidation kinetic of high entropy alloy (HEA). For the establishment of the ANN model, an extensive experiment has been performed. Initially, spark plasma sintered (SPS) AlCrFeMnNiWx (x = 0, 0.05, 0.1, 0.5) HEAs oxidized at 700 degrees C, 800 degrees C, and 850 degrees C isothermally in thermal gravimetric Analyser (TGA) for 50 h and investigated by XRD and SEM. The HEAs exhibited multifarious behavior while adding tungsten and showed various oxides. Admittedly, alloying constituent significantly affects oxidation behavior. Thus alloying composition, exposer time, and oxidation temperature were chosen as input parameters for the modeling. At the same time, the resulting mass gain of the oxidized sample was an output of the ANN model. The ANN model attained outstanding performance during training, testing, and validation (R > 0.999). Several physical models have been compared with the proposed predictive ANN model during the kinetic law interpretation and found accuracy significantly. In comparison, the ANN predictive model provides an excellent result with the experimental data at each studied temperature for the HEAs. Unquestionably, the ANN model is a consistent and precise approach to predicting HEAs' high-temperature oxidation behavior.
查看更多>>摘要：This paper studies the underlying mechanisms to binder phase lamella formation (in WC/WC grain boundaries) in hardmetal inserts used in face turning. A distribution of lamellae orientations has been quantified for used turning inserts as well as pristine inserts and coupled to the direction of the applied stress, calculated by FEM. Furthermore, more detailed FEM calculations on the micro scale have been used to examine a suggested theory of lamella formation based on shear stresses.
查看更多>>摘要：Refractory high entropy alloys (RHEAs) emerge as promising candidate materials for ultrahigh-temperature applications. Accurate phase stability is the prerequisite for design of high-performance RHEAs, but still missing in the literature due to the big challenge in experiments. In this paper, the reliable 3rd-generation Gibbs energy expressions for pure Mo, Nb, Ta and W were firstly evaluated by integrating the physical based Segmented Regression model with thermal vacancy description from 0 K to high temperatures. The thermodynamic database of the Mo-Nb-Ta-W quaternary system was then developed by combining the established 3rdgeneration Gibbs energies with the phase equilibrium and thermodynamic data by using the CALPHAD (CALculation of PHAse Diagram) approach. The calculated phase equilibria, thermodynamic properties as well as the A2/B2 ordering transition behaviors show good agreement with those from experimental determination and theoretical calculation. The phase constitutes and elemental distributions in an equiatomic MoNbTaW as-cast alloy were experimentally investigated and compared with the non-equilibrium solidification simulations to further verify the database reliability. The high-throughput mapping of phase stability within the compositiontemperature space in various Mo-Nb-Ta-W alloys was then constructed by applying thermodynamic calculations. The alloying effects on the formation of B2 phase were systematically analyzed. The Mo-Nb-Ta-W alloys have a wide temperature region with a single A2 phase, while the A2 + B2 phase regions exist at very low temperatures. It is highly anticipated that the present accurate 3rd-generation thermodynamic database provides an important basis for efficient design and development of novel Mo-Nb-Ta-W RHEAs.
查看更多>>摘要：The first-principles calculations are employed herein to predict the electronic, elastic, and thermal properties, fracture toughness, and damage tolerance of TM5Si3B (TM = V and Nb) MAB phases. According to formation enthalpy, phonon dispersion and single-crystal elastic constants, V5Si3B and Nb5Si3B are thermodynamically, dynamically, and mechanically stable. Pugh's ratio, Cauchy pressure, hardness, fracture toughness, and elastic anisotropic indexes are calculated, and V5Si3B and Nb5Si3B are brittle, tolerant to damage, and elastic anisotropic. The possible cleavage plane and slip systems are the (0001) plane and < 1<(1)over bar>00 > vertical bar{11 (2) over bar0} and < 11<(2)over bar>0 > vertical bar {0001}, respectively, which is determined by the strong TMII-Si, TM-B, and TMI-Si bonds parallel to the (0001) plane. Finally, lattice thermal conductivity, minimum lattice thermal conductivity, and dependence of heat capacity on temperature are predicted.
查看更多>>摘要：Cemented carbides (WC-Co-Ni) with the addition of Nb and NbC respectively were prepared by the conventional powder metallurgy method. The microstructure and mechanical properties of the sintered samples were analyzed. The results indicated that the addition of Nb or NbC reduced the grain size of WC and Nb had a greater inhibition effect on WC grain growth than NbC. The transverse fracture strength of the samples first increased and then decreased with the increase of the amount of Nb and NbC, and reached 3120 MPa and 2850 MPa respectively when adding 1.0 wt% Nb and NbC. The hardness of cemented carbides showed an upward trend as the content of additives increased. The fracture toughness decreased with the increases of NbC and Nb contents respectively and the fracture toughness of NbC-added samples was lower than that of Nb-added samples. The impact toughness decreased in a mass with the increase of additives.
NSTL
Elsevier