查看更多>>摘要：In this research, NbCN-Cu films with different Cu contents were prepared by multi-target confocal RF magnetron sputtering. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray Photoelectron Spectroscopy (XPS), Raman spectrometry, Energy Disperse Spectroscopy (EDS), nano-indentation, and electrochemical workstation were used to characterize and analyze the microstructure, mechanical properties and corrosion resistance of the films. The results show that the NbCN-Cu composite films consist of crystalline face-centered cubic(fcc) Cu, face-centered cubic(fcc) NbCN, hexagonal close-packed(hcp) NbCN, and amorphous graphite and CNx phases. When Cu content was 2.6 at.%, a coherent interface was detected between fcc-Cu and fcc-NbCN, hcp-NbCN, and dislocations were detected at the coherent interface when Cu content increased to 9.5 at.%. With the increase of Cu content, the microhardness of the film first increased and then decreased. NbCN-Cu composite film with Cu content of 2.6 at.% had the highest hardness of 32.8 GPa and remarkable corrosion resistance. The self-corrosion potential of the film was 0.18 V and self-corrosion current density was 2.29 x 10-6 A/cm2.
查看更多>>摘要：Two-phase fully dense high entropy carbide (HEC) cermets were successfully prepared following the conventional cemented carbide/cermet processing route. Cold isostatically pressed equimolar TiC, VC, NbC, TaC and WC powder mixtures with 12 vol% Ni binder were pressureless sintered in the solid state and liquid phase sintering regimes respectively. A homogeneous rock-salt (space group Fm3m) HEC phase embedded in a nickel alloy binder was attained by liquid phase sintering at 1420 degrees C. Thermodynamic simulations were conducted to predict the equilibrium phases and carbide/binder phase contents. The phase evolution was investigated at seven different sintering temperatures in the 900-1420 degrees C window. Thermogravimetry and differential scanning calorimetry analysis were performed to follow up the sintering process. Electron probe microanalysis was used to map the elemental distribution as well as to quantify the constituent phase contents. Nanoindentation were performed to correlate the difference in mechanical properties of the core-rim structured HEC grains with the chemical composition. The liquid phase sintered (Ti,V,Nb,Ta,W)C - 12 vol% Ni had a Vickers hardness of 14.3 GPa and Palmqvist indentation fracture toughness of 9.2 MPa. m1/2.
查看更多>>摘要：In cemented carbides cobalt serves as a binding agent between tungsten carbide grains. The zinc process exhibits an important technique to recycle these materials. The decomposition takes place at temperatures of 900-1000 degrees C and the role of gaseous zinc in this process is poorly investigated. A specific experimental set-up was used to ensure that only gaseous zinc reacts with solid cobalt. By varying the temperatures, times and Zn: Co ratios, it was possible to ensure the formation of intermetallic phases. According to the binary Co-Zn phase diagram, phases of different composition are formed, depending on temperature and pressure. It was found that not all of the indicated phases occur simultaneously, but several do. With the support of the findings from the layer evolution between two solid as well as solid and liquid substances, it is explained which layers may form in the Co-Zn system. The multiple phase formation depends on diffusitivity and other factors such as the different melting points, the atomic radii and the occurrence of cracks. Of these, the occurrence of cracks across or between two layers represents the most likely reason.
查看更多>>摘要：The microstructure and texture evolution of Zr-xNb-0.4Mo (x = 0, 0.2, 0.4, 0.6 and 1.0 wt%) alloys are characterized using scanning electron microscopy (SEM), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) technique. The aim is to elucidate the role of primary alpha grains in the degree of transformation texture obeying the Burgers orientation relationship (OR) in Zr alloys. The primary alpha grain is produced by adjusting Nb content in Zr alloys. The crystallographic orientations of Zr-xNb-0.4Mo alloys show that the degree of transformation texture obeying the Burgers OR increases with the proportion of primary alpha grains decreasing. Until no primary alpha grains exist, the transformation texture obeys the Burgers OR strictly. The primary alpha grains can exert great influence on variant selection by restricting the growth of high-temperature beta grains and acting as nucleation sites. The fact that primary alpha grains are the origins of variant selection is observed. Meanwhile, variant selection occurs in both the duplex microstructure and full martensite plates during the water-quenching process. The texture weakening of the duplex microstructure is attributed to the new texture components given by martensite plates. In terms of microstructure, a series of precipitates, Zr3(Nb, Mo, Fe), are found in a primary alpha grain.
查看更多>>摘要：Niobium nitride (NbN) nanoparticles have successfully been synthesized at elevated temperatures (700 and 800 ?) in a single step from niobium penta-oxide (Nb2O5), magnesium (Mg) and thiourea ((NH2)2CS) in a sealed autoclave. The synthesis temperature and holding time have been optimized to obtain single phase NbN. The phase determination and morphological features of synthesized samples have been analyzed by X-ray diffraction (XRD), electron microscopic (TEM) technique. Williamson-Hall analysis has also been done to observe the effects of synthesis parameters (temperature and holding time) on lattice distortion. Moreover, TEM results revealed the presence of oxygen centers in the form of NbCpNq or NbOxNy or NbOz inside NbN nanoparticles which was also supported by TEM-EDS and X-ray photoelectron spectroscopy (XPS) results.
查看更多>>摘要：Improving the irradiation resistance of W alloys is vital to their application of plasma facing materials in future fusion reactors. In this work, quasi-spherical tungsten nanoparticles synthesized by thermal plasma were mixed with nanosized TiC to sinter nanostructured TiC dispersion-strengthened tungsten alloy. As-obtained W-TiC composite exhibited high relative density of 99.14% with suppressed grain size of about 1.12 mu m, together with well-dispersed TiC with size 50-100 nm into W grains. More importantly, semi-coherent W/TiC interface with diffusion layer of about 25 nm was formed, which highlights the tight connection between W and TiC. Furthermore, He ions irradiation results indicated that W-TiC composite exhibited excellent irradiation resistance with a damage depth of about 9.53 mu m, which is much lower than 18.26 mu m of pure W. Mechanism investigation indicated that the remarkably improved He ion irradiation resistance was attributed to the efficient capture and annihilation of irradiation-induced defects by grain boundaries and phase interfaces.
查看更多>>摘要：To improve the performance of pure tantalum manufactured by selective laser melting (SLM) and meet its application requirements in medicine and industry, this paper studied the influence of SLM process parameters on the as-built surface morphology and mechanical performance, and successfully obtained a sample with a relative density of over 99%, ultimate tensile strength of 706Mpa and fracture elongation over 32%. It's found that the scanning speed has a significant influence on the microstructure. Moreover, the fractured morphology shows that it is easy to cause cracks at the lower energy density. However, at a higher energy density, it is easy to induce defects such as keyhole induced pores. The appropriate process parameters of additive manufacturing matching the pure tantalum with higher relative density and better mechanical properties have precious value for its application in medicine and industry.
查看更多>>摘要：Direct melt infiltration does not produce sintered closed holes and considerably reduces the time required for preparation compared with pre-sintered WC skeleton followed by melt infiltration of Co. However, it may lead to alloy collapsing and deformation. In this study, WC and Co green parts were prepared via binder jet 3D printing. The two parts were stacked layer by layer then subjected to melt infiltration to prepare a WC-Co series of cemented carbides. The aim was to investigate the shape retention, infiltration conditions, and properties of the alloy after the equal distribution of Co and the direct infiltration of the Co melt into the WC green parts without pre-sintering. The effect of different Co amounts on the product was also studied. Results showed that the carbide prepared through direct melt infiltration of WC green parts without pre-sintered skeletons displayed excellent shrinkage and properties. The shrinkage of the prepared cemented carbide with a Co content of about 25 wt% was within 3% in all directions. The relative density, hardness, and fracture toughness of the alloy reached 96.65%, 11.5 GPa, and 23.5 Mpa m1/2, respectively. This work provides a simplified, and high-shape-retention method for other alloys that can be prepared through melt infiltration.
查看更多>>摘要：In the four temperature ranges of 1300-1600 C, the diffusion bonding of oxide dispersion enhanced tungsten (ODS-W) and molybdenum hafnium carbon (MHC) alloy prepared by mechanical alloying method was successfully prepared by spark plasma sintering (SPS). In this work, the interface microstructure, mechanical properties and thermal shock resistance of ODS-W/MHC are studied. At above 1500 C, the W and Mo elements at the ODS-W/MHC interface begin to diffuse, and the diffusion distance can reach 2 mu m at 1600 C. Similarly, the tensile strength of ODS-W/MHC joints is best performed at 1600 C, with tensile strengths of 425 MPa and 801 MPa at room temperature and 500 C, respectively. However, as the sintering temperature increased, the hardness of the MHC gradually increased, and ODS-W would recrystallize, resulting in a hardness at the interface between the hardness values of the two substrates. At 1600 C, the maximum hardness at the sample junction can reach 487 HV. The transient thermal load of the connector during operation is simulated by laser beam and thermal shock experiments are performed on the surface and interface of the ODS-W/MHC connector prepared at different temperatures. Compared with ODS-W, the surface of ODS-W/MHC has no obvious cracks after laser thermal shock, and the cracks generated by the sample interface above 1500 C have also been greatly improved. It can be seen from CLSM analysis that the height undulation of the surface and interface of ODS-W/MHC is significantly smaller than that of ODS-W, so the ODS-W/MHC prepared at 1600 C has good thermal shock resistance.
NSTL
Elsevier