难熔金属碳化物Cr_3C_2、VC、WC、TaC、NbC及Ti(C、N)粉中硫的测定

研究了燃烧──—电导法测定金属陶瓷添加剂Cr3C2；VC；WC；TaC；NbC及Ti（C、N）粉中硫的测定条件，建立了分析方法．方法相对标准偏差5％左右，仪器的灵敏度为3X10－6，最低检测限为1ppm．     

燃烧合成-铸造法制备氧化铝基金属陶瓷的研究

用燃烧合成一铸造法成功制备了致密度较高的Al2O3-Cr和Al2O3(-Cr2O3)-Cr金属陶瓷，研究了稀释剂Al2O3和Cr2O3及凝固冷却速度对金属陶瓷显微组织的影响。结果表明，添加Al2O3或Cr2O3稀释剂，可有效控制燃烧反应的剧烈程度，并形成Cr相和陶瓷基体的共晶组织。在石墨铸型冷却条件下，Cr相在陶瓷基体上分布均匀、尺寸细小，达到了亚微米级尺度。     

Electrochemical behaviour of Ni-cermet anodes containing a proton-conducting ceramic phase on YSZ substrate

Solid oxide fuel cell cermet anodes with proton-conducting ceramic phases, Ni-SrZr_0.95Y_0.05O_2.975 (Ni-SZY), Ni-CaZr_0.95Y_0.05O_2.975 (Ni-CZY) and Ni-SrCe_0.475Zr_0.475Y_0.05O_2.975 (Ni-SCZY), have been analysed by electrochemical impedance spectroscopy. The anodes were sintered on opposing faces of yttria-stabilised zirconia (YSZ) electrolyte and the polarisation behaviour studied in the temperature range 600-900 °C in various regimes of H₂ and H₂O partial pressures. The ceramic component of the Ni-CZY and Ni-SCZY cermets form an insulating phase at the interface with YSZ. Impedance spectra are composed of two dominant rate-limiting contributions attributable to electrode processes with relaxation frequencies ca. 10³ and 1 Hz at 800 °C. Both high- and low-frequency responses are sensitive to H₂O partial pressure and temperature, with activation energies in the range 1.02-1.25 and 1.19-1.35 eV, respectively. Factors influencing the origin of the rate-limiting processes are discussed, including transport limitations (oxide-ion and electronic) in the solid phases and microstructure. Proton conductivity may assist in accelerating the kinetics of the anodic reaction by widening the effective reaction area in electrodes optimised in terms of Ni content, oxide-ion conductivity and microstructure.     

Spark plasma sintered ZrC-Mo cermets: Influence of temperature and compaction pressure

The microstructure analysis and mechanical characterisation were performed on a ZrC-20 wt%Mo cermet that was spark plasma sintered at various temperatures ranging between 1600 and 2100 °C under either 50 or 100 MPa of compaction pressure. The composite reached ~98% relative density for all experiments with an average grain size between 1 and 3.5 µm after densification. The nature of SPS technology caused a faster densification rate when higher compaction pressures were applied. The difference in compaction pressures produced different behaviors in densification and grain structure: 1900 °C, 100 MPa produced excessive grain growth in ZrC; 1600 °C, 50 MPa revealed a very clear ZrC grain structure and Mo diffusion between carbide grains; and 2100 °C, 50 MPa exhibited the highest overall mechanical properties due to small clusters of Mo phases across the microstructure. In fact, this particular sintering regime gave the most optimal mechanical values: 2231 HV10 and 5.4 MPa*m^1/2, and 396 GPa Young's modulus. The compaction pressure of SPS played a pivotal role in the composites’ properties. A moderate 50 MPa pressure caused all three mechanical properties to increase with increasing sintering temperature. Conversely, a higher 100 MPa pressure caused fracture toughness and Young modulus to decrease with increasing sintering temperature.     

HVOF sprayed WC–Co coatings: Microstructure,mechanical properties and friction moment prediction

This study aims at gaining a better understanding of the microstructural features that control the mechanical and the tribological performances of WC–12 wt.% Co coatings under High Velocity Oxygen Fuel (HVOF) spraying conditions. This paper looks at the influences of the HVOF process parameters for WC–12Co material on the microstructural and the tribological behaviours of the coatings. The correlation between the coating microstructure and the wear behaviour is investigated by observing and analysing the microstructure and by studying the friction moment using enhanced statistical tool based on neural computations. According to the experimental and the numerical results, it has been shown that the spray parameters affect the phase composition, hardness and porosity of HVOF sprayed WC–12Co coatings and the correlations with HVOF process parameters are fully predictable in the steady-state regime.     

Oxidation-abrasion of TiC-based cermets in SiC medium

The aim of the current study was to investigate the effect of oxidation on abrasive wear behaviour of TiC based cermets at temperatures ranging from 20 to 900 °C. Three types of material performance maps were constructed: oxidation rate maps, wear rate maps and maps showing the effect of oxidation on abrasion. Discussion on the performance of different cermet grades is supported by the SEM images combined with EDS and XRD analysis. The results should facilitate the selection of TiC-based cermets providing optimum composition of cermets for high temperature applications.     

Joining of cemented carbides to steel by laser beam welding

Welding of dissimilar materials such as steel and cemented carbides (hardmetals, cermets) is particularly challenging e.g. because mismatches in their thermal expansion coefficients and thermal conductivities result in residual stress formation and because of the formation of brittle intermetallic phases. Laser beam welding of cemented carbides to steel appears as an attractive complementary technique to conventional brazing processes due to its high precision, high process speed, low heat input and the option of welding without filler. Here a laser welding process including pre‐heat treatment and post‐heat treatment was applied successfully to joining as‐sintered and nitrided hardmetals and cermets to low alloyed steel. The microstructure and mechanical properties of the welds are investigated by microscopy, X‐ray diffraction, microhardness measurements, and bending tests. The results reveal that the three‐step laser beam welding process produced crack‐free and non‐porous joints. Nitridation of the cemented carbides results in a significant reduction of the amount of brittle intermetallic phases. The mechanical properties of the joints are competitive to those of the conventional brazed steel‐cemented carbide joints.     

Analysis of local composition gradients in the hard-phase grains of cermets using a combination of X-ray diffraction and electron microscopy

Combination of X-ray diffraction (XRD) and scanning electron microscopy (SEM) was used for investigation of local composition gradients in the hard-phases of cermets. XRD revealed distribution of lattice parameters in hard-phase grains, from which the composition gradients in the hard-phases were estimated using an appropriate microstructure model. This microstructure model was build with the aid of SEM micrographs, which were taken with back-scattered electrons (BSE) and completed by the registration of the electron back-scatter diffraction (EBSD) patterns and characteristic X-ray spectra. SEM/BSE yielded the first information about the spatial distribution of elements in individual hard-phase grains, SEM/EBSD about the morphology, the size and the size distribution of these grains. The final interpretation of the distribution of lattice parameters, which was obtained from the X-ray line profile analysis, was done with the aid of the local elemental analysis that was performed using SEM with the energy dispersive analysis of the characteristic X-ray spectra (EDX) and the known dependence of the lattice parameters on concentration.     

缺口对金属陶瓷热冲击疲劳的影响

缺口对４０％ＮｉＴｉ（Ｃ，Ｎ）金属陶瓷热冲击疲劳有很大影响，缺口试样裂纹形核孕育期均短于无缺口试样；随缺口角度的增加，裂纹扩展速率增加，对于２０℃水、２０号机油和１０％聚乙稀醇（ＰＶＡ）水溶液３种冷却介质，后者的裂纹孕育期最长，裂纹扩展速率最慢     

Textured cermets of CeO2 (or GDC) with Co for solid oxide fuel cells anodes

Cermets composed of submicron size alternating lamellae of CeO₂, or 10% Gadolinia doped Ceria (GDC), and porous-metallic Cobalt have been prepared from eutectic oxide mixtures. A fine eutectic structure was obtained by fast directional solidification of the cobalt oxide–ceria oxide eutectic composite using the Laser Floating Zone (LFZ) technique. The resulting microstructure, with an interphase spacing down to 0.5 μm, was obtained for solidification rates of 750 mm/h. Textured cermets were obtained by subsequent reduction under H₂ containing atmosphere of the eutectic oxide composite. The reduction kinetics was studied in the 550–750 °C temperature range and effective diffusion coefficients were obtained. The reduction process does not correspond to a typical thermally activated process. The cermets are composed of ceria lamellae of about 200 nm thickness alternated with porous-metallic cobalt lamellae of ≤400 nm. The lamellar microstructure of the cermets favours oxygen ion mobility through ceria and its size can be controlled by solidification rate of the eutectic precursor. These materials are proposed as SOFC anodes.