碳含量对Ti(C,N)基金属陶瓷组织和性能的影响

综述了添加碳量对金属陶瓷组织和性能的影响。在一定范围内,随碳添加量的增加,组织细化,粘结相中Mo、W、Ti等元素的溶解度降低;添加碳量过少或过多都会使材料的相组成离开两相区,生成第三相η相(TiNi3)或游离碳,而第三相的生成会显著降低金属陶瓷的机械性能。     

Electrochemical dissolution of hard metal alloys

Different components of hard metals such as TiC, TiN, pure Ti and the binder metals Fe, Co and Ni were investigated in neutral sodium nitrate solutions by cyclovoltammograms at current densities up to 35 A/cm². All combinations of TiN and TiC dissolve anodically. The surface of pure Ti is blocked by the anodic surface oxide which is not removed by cathodic current densities up to 30 A/cm². Cathodically all samples were conductive and showed a strong hydrogen evolution. The binder metals Fe, Co and Ni should be free of oxide films at cathodic potentials. Anodically, Co dissolves in an active state while Fe and Ni show a potential shift to the passive region. Our surface model developed for machining of Fe seems to be applicable to all other materials except pure Ti.     

Effect of Ta addition on the microstructures and mechanical properties of in situ bi-phase (TiB2-TiCxNy)/(Ni-Ta) cermets

In this work, in situ bi-phase (TiB₂-TiC_xN_y)/(Ni-Ta) cermets were fabricated via a combined combustion synthesis and hot-pressing (CSHP) method in a Ni-Ti-BN-B₄C-Ta system. The effects of Ta addition on the reaction process, phase constituents, microstructures and mechanical properties of the (TiB₂-TiC_xN_y)/(Ni-Ta) cermets were studied. Ta is shown to dilute the system and lead to a small number of intermediate phases (Ni₂₀Ti₃B₆ and Ni₃Ti) that are retained in the products. Furthermore, the addition of Ta can markedly refine the ceramic particles and decrease the size and quantity of voids. The evaluation of the mechanical properties revealed that an increase in the Ta content resulted in increases in the compression strength (σ_UCS) and hardness and that the fracture strain (ε_f) increased first and then decreased. The cermet with the optimal addition of 5?wt% Ta possessed the best mechanical properties without decreasing the value of ε_f (2.9%). The addition of 5?wt% Ta resulted in a compressive strength of 3.37?GPa and the highest hardness of 1909 Hv, which is an increase of ~16% and ~22%, respectively, compared to cermets without added Ta.     

Freeze casting of porous Ni-YSZ cermets

Dual-phase porous Ni-YSZ cermets were fabricated via the freeze casting of a ceramic/camphene slurry. After removing the frozen camphene via sublimation at room temperature, the green samples were sintered for 3 h in air at various temperatures, ranging from 1100 to 1350 °C, and then reduced in an Ar-5% H₂ atmosphere at 700 °C for 3 h. The fabricated Ni-YSZ cermets showed 3-D pore channels formed by the replication of the entangled camphene dendrite network and small pores in the Ni-YSZ walls produced by partial sintering of the NiO-YSZ composite. Furthermore, the fabricated samples were found to possess reasonable electrical conductivities, thus rendering them suitable for use as the basic components of planar solid oxide fuel cells (SOFCs).     

High temperature erosion of Cr3C2-NiCr thermal spray coatings — The role of phase microstructure

Cr₃C₂-NiCr thermal spray coatings are extensively applied to mitigate erosion at temperatures above 450-550 °C. The aim of this work was to extend the current comparison based knowledge towards a mechanistic interpretation of the high temperature erosion of Cr₃C₂ based thermal spray coatings. Coatings that span the range of industrial quality were assessed. They were eroded under high temperature (700 °C and 800 °C), aggressive (impact velocity 225-235 m/s) conditions designed to simulate the high velocity erodent impacts within a turbine environment. The influence on the erosion response of high temperature induced changes in the coating microstructure and composition with extended in-service exposure was assessed by heat treating selected samples to generate a steady state microstructure prior to testing. In spite of the marked variation in coating microstructure the erosion rates were comparable across the range of coatings tested. The significance of this conclusion is discussed in terms of the erosion mechanism.     

Wear-resistant ceramic and metal–ceramic ultrafine composites fabricated from combustion synthesised metastable powders

Dense Ti–Al₂O₃–TiC cermet and TiC–TiB₂ ceramic composites have been fabricated by high-pressure high-temperature (HPHT) sintering starting from metastable nanostructured powders obtained by means of a technique based on the self-propagating high-temperature synthesis (SHS) process. The microstructural observations showed that an ultrafine microstructure was retained in the sintered composites thanks to the limited grain growth allowed by the short sintering duration of the HPHT method. The sintered TiC–TiB₂ and Ti–Al₂O₃–TiC fine-grained bulk composites exhibited high values of hardness and Young modulus. The tribological characterization confirmed the good properties of both the materials in terms of wear-resistance and makes them very promising candidates for demanding applications. The influence of the ultrafine grain size on physical and tribological properties of the densified materials is discussed.     

Effect of secondary carbides addition on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-based cermets

(Ti, W, Mo, V)(C, N)-based cermets were prepared by mixing Mo₂C, WC and TaC with ultrafine (Ti, W, Mo, V)(C, N) powders, and then processed via a conventional P/M technique. The effect of Mo₂C, WC and TaC on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co systems was investigated. The Mo₂C content was varied from 0 to 10 wt.% and additive WC or TaC was added at a level of 5 wt.% with Mo₂C addition. The results show that the densification of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co cermets was improved significantly by the addition of Mo₂C. With the increase of Mo₂C content, there is a coarsening tendency in the microstructure of (Ti, 20W, 15Mo, 0.2V)(C, N)-8Ni-7Co system, but the refinement for (Ti, 15W, 5Mo, 0.2V)(C, N)-8Ni-7Co. TaC addition decreases the density of (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo₂C-8Ni-7Co cermet and thus weakens its bending strength. (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo₂C-5WC-8Ni-7Co cermet has optimal mechanical properties: bending strength of 1999 MPa, hardness (H_v) of 1677 MPa and toughness of 9.95 MPa m^1/2 respectively by adding WC, which is due to its ultrafine and weak core/rim structure.     

Corrosion protection of Sunselect, a spectrally selective solar absorber coating, by (3-mercaptopropyl)trimethoxysilane

The formation of a protective layer from (3-mercaptopropyl)trimethoxysilane (MPTMS) on commercial Sunselect, cermet-based spectrally selective coating (Alanod, DE), was studied by non-electrochemical (infrared reflection–absorption—IR RA, X-ray photoelectron spectroscopy—XPS), electrochemical (cyclic voltammetry (CV) in the presence of a redox probe (Cd⁺²), and potentiodynamic (PD)) techniques. By simple immersion and subsequent dip coating of the Sunselect substrate in the MPTMS sol, the hydrolyzed MPTMS precursor was adsorbed on the substrate, forming a protective layer imparting corrosion stability to Sunselect in a salt spray chamber for at least 20 days, outperforming any other sol–gel coating used so far for the corrosion protection of Sunselect. This was attributed to the penetration of MPTMS into the porous cermet structure through the upper antireflective Sn-oxide layer, as shown from XPS depth profile. Detailed analysis of the hydrolysis and condensation reactions of the MPTMS precursor by ²⁹Si NMR and IR spectroscopic techniques is reported.The most important finding was the observation that the applied MPTMS layer did not affect the spectral selectivity, as inferred from the solar absorptance increase of 1% and thermal emittance increase of not more than 2%.     

添加碳对Ti（C,N）基金属陶瓷组织和性能的影响

研究了添加碳量对Ｔｉ（Ｃ，Ｎ）基金属陶瓷组织和性能的影响。结果表明，添加碳量对组织和性能影响很大。不加碳时，组织中出现了η（Ｎｉ３Ｔｉ）相，材料表面形成了ＴｉＯ相，添加１％左右碳可获得正常的两相组织，具有最好的性能。添加碳量超过１．３％时，组织中出现了游离石墨，使性能降低，且随添加碳量的增加，游离石墨形状由团絮状向均匀分布的颗粒状转变。