Optimized microwave absorption properties by tailoring the morphology of carbon coated TiC nanoparticles by N2 pressure

Increasing the dielectric loss capacity plays an important role in enhancing the electromagnetic absorption performance of materials. It remains a challenge to simultaneously introduce multiple types of dielectric losses in the material. In this work, we show that the atomic and interfacial dipole polarizations can be simultaneously enhanced by substituting N species into both carbon coating layers and bulk TiC lattices of a core-shell TiC@C material. Additionally, substitution of N species results more exposed TiC(111) facets and refines the TiC grain sizes in the bulk material, which is beneficial for enhancing the scattering of the external electromagnetic waves. The maximum reflection loss of the N substituted TiC@C material is measured as ?47.1 dB with an effective absorbing bandwidth of 4.83 GHz at 1.9 mm, which illustrates a valuable way to further tuning the electromagnetic absorption performance of this type of materials.     

Microstructures and properties of nickel-titanium carbide composites fabricated by laser cladding

In this work, Ni/TiC composites were synthesized by the laser cladding technique (LCT). A scanning electron microscope (SEM), X-ray diffractometer (XRD), microhardness meter, electrochemical workstation, and friction and wear tester examined the microstructure, surface morphology, phase structure, microhardness, wear, and corrosion resistances of the Ni/TiC composites. These results indicated the Ni/40TiC composite contained finer equiaxed crystals than the Ni and Ni/20TiC composites. In addition, numerous TiC particles in the Ni/40TiC composite impeded growth of the nickel crystals, which resulted in the fine microstructure of the Ni/40TiC composite. The Ni, Ni/20TiC, and Ni/40TiC composites exhibited face-centered cubic (f c c) lattices. The average microhardness values of the Ni/20TiC and Ni/40TiC composites were approximately 748 HV and 851 HV, respectively. The Ni/40TiC composite had the lowest friction coefficient (0.43) among all three coatings, and only some shallow scratches appeared on the surface of the Ni/40TiC composite. The corrosion potential (E) of Ni/40TiC exceeded the Ni/20TiC composite, and both were larger than the Ni composite, which indicated the Ni/40TiC composite had outstanding corrosion resistance and the Ni composite had poor corrosion resistance. The corrosion current densities (i) of Ni, Ni/20TiC, and Ni/40TiC composites were 5.912, 4.405, and 3.248 μA/cm², respectively.     

Beneficial role of carbon black on the properties of TiC ceramics

This investigation aimed to study the influence of carbon black on the qualifications of TiC-based materials. For this objective, two samples, namely monolithic TiC and TiC-5 wt% carbon black were sintered by spark plasma sintering (SPS) method at 1900 °C. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were used to characterize the as-sintered samples. Introducing carbon black enhanced the relative density of TiC significantly, reaching a near fully dense substance. Phase analysis and microstructural studies manifested the formation of non-stoichiometric TiC_x in both ceramics. Although the introduction of carbonaceous additive considerably increased the thermal conductivity and flexural strength of TiC, standing at 25.1 W/mK and 658 MPa, respectively, its influence on the Vickers hardness was trivial (both ~ 3200 HV_0.1 kg). Finally, the composite specimen presented a lower coefficient of friction (~ 0.31) on average compared to the undoped TiC (~ 0.34).     

Effect of iron content on the wear behavior and adhesion strength of TiC–Fe nanocomposite coatings on low carbon steel produced by air plasma spray

In this study, the effect of Fe content on the abrasion behavior of TiC–Fe nanocomposite coatings applied on the CK45 steel substrate by air plasma spray method was investigated. For this purpose, milled TiC powder was prepared at 1, 2, 3 and 4 h milled TiC powder for 4 h was selected as the suitable sample. In the next step, a suitable sample mixture with different iron powder concentrations of 5, 10, 15, 20 and 25% was prepared by mechanical milling. The granulated mixture was applied to the substrate using air plasma spray technique. Microstructural and phase analyzes were performed using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). According to the results of Williamson-Hall calculations, the TiC crystallites' size decreased by 49 nm–29 nm, and network strain reached 0.16% by increasing milling time from 1 h to 4 h. Studies have shown that the coatings contain titanium carbide, iron oxide, and titanium oxide, with the number of phases formed depending on the amount of iron in the chemical composition. Investigation of the tribological properties of the coating layer showed that with increased iron content in the coating, the wear resistance of the samples is reduced. Hardness tests on coatings indicate that adding iron to nanocomposite from 5 to 25% reduces hardness from 1025 to 699 Hv. It can be argued that a slight increase in the adhesion strength of the coating to the substrate is due to increased wettability because of the formation of molten iron in the coating.     

Electrical performance of fine-grained Y-TZP/TiC composites obtained through a hydrothermal-assisted sol-gel process

Y₂O₃-stabilized tetragonal ZrO₂ polycrystal (Y-TZP) composites with various TiC contents were successfully synthesized via a modified hydrothermal-assisted sol-gel method. Fine precursor powders can be obtained with high crystallinity, nanoscale grain size and uniform morphology. SEM images of the ceramic products show that TiC particles are distributed homogeneously in the final Y-TZP matrix, and their average grain sizes are approximately 390–670 nm and 150–230 nm for the Y-TZP and TiC phases, respectively. A higher TiC volume fraction has a negative effect on the relative density and hardness but a significant positive influence on electrical conductivity. The electrical conductivity values are increased from 115 S/m to 1.23 × 10⁵ S/m with TiC contents varying, demonstrating that the percolation threshold is approximately as low as 11.6 vol% for the samples, which is much lower than those of previous Y-TZP/TiC ceramics. The high electrical performance is probably due to the high D (the diameters of the insulating particles)/d (the diameters of conductive particles) ratio and submicron-sized grains.     

Developing high-performance laminated Cu/TiC composites through melt infiltration of Ni-doped freeze-cast preforms

Nacre-inspired laminated composites have been proven to possess a unique combination of strength and toughness. In this study, we fabricated nacre-mimetic Cu/TiC composites via unidirectional freezing of aqueous TiC slurries containing different amounts of NiO additives, followed by ice sublimation, carbothermal reduction of NiO to Ni during sintering and then gas-pressure infiltration of the Cu melt. The introduction of Ni greatly facilitated the densification of ceramic lamellae and enhanced the interfacial bonding between Cu and TiC. The resultant composites displayed outstanding damage tolerance and anisotropic electrical conductivities. Specifically, for an ～31?vol% TiC–Cu composite containing 24?wt% Ni in the ceramic lamellae (based on the TiC content), a fracture toughness (K_Jc) of 72.5?±?1.0?MPa·m^1/2, work of fracture of 53.4?±?3.5?kJ/m², bending strength of 725?±?11?MPa and longitudinal electrical conductivity of 22.7?MS/m (～60% of the Cu matrix) were achieved, which were approx. 81%, 536%, 122% and 97% higher than those of the Ni-free composite, respectively. Noticeable toughening was demonstrated to be a consequence of multiple cracking, plastic deformation and uncracked-ligament bridging of the metal layers, as well as crack deflection and blunting. On the other hand, significant strengthening resulted from tailoring the microstructures in the ceramic layers and at the Cu/TiC interface as a result of Ni doping. We believe that the facile strategy adopted herein provides an effective way to solve the problems of wetting and bonding related to metal infiltration and can be readily extended to the preparation of other nacre-inspired metal?ceramic composites.     

Solid-state joining of SiC using a thin Ti3AlC2, TiC,or Ti filler

SiC monoliths containing 5 wt.% Al₂O₃-Y₂O₃ additive were joined using a thin Ti₃AlC_2, TiC, or Ti filler. After joining at 1900 °C for 5 h under 3.5 MPa, the joint properties were compared in terms of the microstructure, phase evolution, joining strength, and possible elimination of the joining layer. Although all samples showed a sound joint, the microstructure differed according to the filler. SiC joined with Ti₃AlC₂ filler showed an indistinguishable joining interface due to the filler decomposition followed by solid-state diffusion into the SiC base, whereas TiC filler remained at the interface without showing decomposition or diffusion. In contrast, the Ti filler showed a possible elimination of the joining layer because of the diffusion of Ti and the formation of TiC. The mean joining strengths for the Ti₃AlC₂, TiC, and Ti fillers were 300, 234, and 248 MPa, respectively, which were comparable to that of the base SiC material (250 MPa).     

Optimization of C/TiCx duplex diffusion barrier coatings for SiCf/Ti composites based on interfacial structure evolution exploration

Introducing a carbon single coating is a popular method used to protect SiC_f/Ti composites from severe interface reactions. However, carbon coatings lose their protective effect on SiC fibres at high temperature, even after a short period time. As such, given the strong demand for high temperature applications in aeronautics and astronautics a more coating which is more effective at high temperatures is desirable. In order to improve the high temperature interfacial stability of SiC_f/Ti composites, a C/TiC_x duplex coating system with different C contents in TiC_x was introduced to explore the protection of fibres at 1200?°C for 1?h. The results show that the C/quasi-stoichiometric TiC coating system protects the SiC fibres most effectively. Based on insights from the evolution of the interface structure, TiC_x has been identified as an interfacial reaction product from the C single coating, exhibiting a gradient in C content and grain size, which is different from a deposited TiC layer with a well-distributed composition and structure. The different coating structure gives rise to different ability to resist C diffusion at high temperatures, in which poor resistance ability appears in TiC_x interfacial reaction layer coming from C single coating due to short-circuit diffusion in C-rich fine-grained TiC layer and fast intracrystalline diffusion trigged by amounts of vacancies in sub-stoichiometric coarse-grained TiC layer. Therefore, C/quasi-stoichiometric TiC duplex coatings with a thick, coarse-grained quasi-stoichiometric TiC layer could effectively inhibit C diffusion by comparison to C single coatings, and is more effective than C/rich-carbon TiC duplex coatings due to the existence of short-circuit diffusion in the latter. As such, C/quasi-stoichiometric TiC duplex coatings appear to be an optimal diffusion barrier for SiC_f/Ti composites at high temperature.     

Nano TiC-Graphene-Cu composites fabrication by a modified ball-milling method followed by reactive sintering: Effects of reinforcements content on microstructure,consolidation, and mechanical properties

A two-step mechanical milling followed by a reactive sintering process was used to synthesize Nano TiC-Graphene-Cu composites from a mixture of Cu, Ti, and Graphene (GN) powders in four different compositions, and effects of reinforcements content on the microstructure and mechanical properties were studied. The results showed that a part of GN reacted with Ti atoms in the matrix, leading to the successful formation of hybrid nanocomposites. Uniform distribution of in-situ TiC with nanometer size and unreacted GN in the nanostructured Cu (Ti) solid solution were obtained. Addition of high percentage of the reinforcements led to an increase in the porosity and microhardness, coarsening of TiC nanoparticles, and decreasing the grain size of the matrix after sintering. The simultaneous presence of GN and TiC nanoparticles in the Cu matrix improved the hardness and wear resistance and reduced the friction coefficient by self-lubricating behavior. The nanocomposite with the nominal composition of Ti-40 vol % TiC showed the highest wear resistance and the lowest friction coefficient.     

TA2钛板掺杂钒离子渗碳层的耐腐蚀性能

为提高钛基双极板的耐腐蚀性能和导电性,在TA2纯钛的表面进行双辉离子渗碳,另外为降低渗碳温度,在渗碳过程中掺杂钒。使用扫描电镜和能谱分析、X射线衍射对改性层的组织结构、化学成分、物相组成进行研究,并测得改性层的界面接触电阻率、耐腐蚀性能。结果表明,在优化的制备工艺参数下,在TA2表面生成结构致密的TiC改性层、钒掺杂渗碳改性层。当压实力为140 N/cm²时,730℃下制备的钒掺杂渗碳改性层、850℃下制备的TiC改性层、TA2基体的界面接触电阻率分别是1.17、3.66、14.71 mΩ/cm²。在模拟双极板的工作环境中,测得730℃下制备的钒掺杂渗碳改性层、850℃下制备的TiC改性层的自腐蚀电流密度分别是5.238、7.563μA/cm²,均比TA2基体的腐蚀电流密度低1个数量级。在离子渗碳的过程中掺杂钒可以有效降低渗碳的工艺温度,并且提高TA2基体的导电性和耐腐蚀性能。