Search

Ti(C,N)-based cermets with different levels of Tantalum carbide (TaC) were fabricated through mechanical activation and subsequent in situ carbothermal reduction method, and microstructure and mechanical performance were studied. It was found the core-rim structure of the cermets became progressively pronounced as the TaC content increased, and when content of TaC reached at 6 wt %, a brighter inner rim phase could be observed in some hard phase particles. The grain size of the cermets decreased and then rose, reaching the finest grain size at 2 wt % TaC. As the TaC content increased, the overall comprehensive mechanical properties of the cermet, especially the TRS (Transverse Rupture Strength) value has been improved. Moreover, a new parallel orientation between the (1 1 1)R and (110)B planes formed at the solid solution phase/binder interface. Coherency was observed between the (200)R and ( 1 1 1 )B planes of the rim/binder interface in the hard particles with a core-rim structure. The cermet with 6 wt % TaC had the optimal comprehensive mechanical properties of 2399 ± 20 MPa for TRS, 87.9 ± 0.2 HRA for hardness and 19.1 ± 0.2 MPa m1/2 for fracture toughness. This was ascribed to the solid solution strengthening of the (Ti,Ta,Mo)(C,N) phase and improved interfaces between the binder and hard phase. The improved properties of the hard particles have also improved the thermal shock resistance of cermets, with a maximum critical thermal shock temperature of 470 °C.

Ammonia protonic ceramic fuel cells (PCFCs) have potential to be a highly efficient power source of high energy density. However, the inadequate catalytic activity of the existing anodes for utilization of ammonia greatly limits the performance of PCFCs. Here we report a Fe-modified state-of-the-art Ni cermet anode with greatly enhanced activity and durability toward utilization of ammonia. Cells with a Fe-decorated Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3 (Ni-BZCYYb) anode demonstrate an excellent performance, achieving peak power densities of 0.360, 0.723, 1.257, and 1.609 Wcm−2 at 550, 600, 650, and 700 oC, respectively, which are the highest performance of solid oxide fuel cells fueled on ammonia. In addition, the cells show an excellent durability when operated at a constant current density of 0.5 A cm−2 (or power density of ~0.435 Wcm−2) at 650 oC. The superior activity and durability of the Fe-modified Ni/BZCYYb anode is attributed to the alternation of NH3 adsorption strength and N2 desorption barrier heights, as confirmed by first-principles based mechanistic and microkinetic modeling. Our research provides a valuable guidance for the development of efficient electro-catalysts for ammonia PCFCs.

A new cermet material based on titanium carbide with a complex bond consisting of nichrome and nickel, additionally hardened with chromium carbide and a solid solution of chromium in titanium carbide, has been obtained. The influence of the technological parameters of the SHS-extrusion method (the delay time before the application of pressure, the pressing pressure, the speed of the press plunger movement) on the length of the extruded rod is studied, the optimal parameters are found. The microstructure and phase composition of the obtained material was investigated, the physical and mechanical characteristics were measured, and a comparison with analogs was given. It is shown that the microstructure, phase composition, and crystal lattice parameters of the phases do not change depending on the diameter of the extruded rod.

In this work, a novel Mo(Co,Fe)B cermet was prepared using Mo, Fe, Co and B powders and the reaction boronizing sintering route. The phase transformation, thermal behavior, densification behavior, microstructure and mechanical properties of cermets are systematically investigated. After sintering, the microstructure of cermets was composed of Mo(Co,Fe)B hard and CoFe binder phases. The formation of Mo(Co,Fe)B phase during solid-state sintering occurred by the reactions of 2Fe + B → Fe2B, 2Co + B → Co2B and 2Mo + Fe2B + Co2B → 2Mo(Co,Fe)B. During liquid-phase sintering, two liquid phases, namely L1 and L2, were sequentially generated by the reactions of CoFe + Fe2B + Co2B → L1 and CoFe + L1 + Mo(Co,Fe)B → L2, respectively. The as-obtained cermet exhibited excellent comprehensive mechanical properties with hardness of 89.5 ± 0.2 HRA, transverse rupture strength of 1927 ± 31 MPa and fracture toughness of 17.5 ± 0.4 MPa•m1/2. In summary, these findings look promising for future preparation and application of low-cost and high-performance ternary boride cermets.

A ceramic–metal composite (cermet) of uranium nitride (UN) particles embedded in a tungsten-molybdenum (W/Mo) alloy matrix is being considered as reactor fuel for nuclear thermal propulsion (NTP). One possible issue is the loss of fissile uranium atoms during reactor operation. We begin by reviewing historical data that suggest that a likely mechanism for fuel loss is transport of free uranium along metal grain boundaries and through cracks to free surfaces. We then employ simple two-dimensional (2D) mesoscale simulations to provide insights into crack formation and free uranium transport in a W/Mo–UN cermet. Phase-field fracture simulations show that cracks form during cooling at the fuel–matrix interface and then within the fuel particles. Transport simulations show that cracks at the fuel–matrix interface and within the fuel accelerate fuel loss. Mechanical and diffusion data are needed for UN and W/Mo alloys to make these preliminary predictions more accurate.

This study is devoted to the technology of producing cermet coatings using self-propagating high-temperature synthesis (SHS). The importance of the study is related to the universal usage of flat electric heaters and protective coatings intended for various purposes. A technique is proposed to obtain electrically conductive coatings by the SHS in powdered Ni + Al and Ti + Al + C mixtures. Specific features of the evolution of the autowave SHS in these mixtures are investigated. The mixture is deposited on a ceramic base as a layer of a suspension in isopropyl alcohol (0.2–2.0) × 10–3 m in thickness using a stencil. The effect of the thickness of the powdered mixture layer on the velocity of front propagation and maximum temperature is studied. These parameters are shown to naturally increase with an increase in thickness. The coating based on the Ni + Al mixture is found to consist of NiAl and Ni3Al intermetallic compounds, while that based on Ti + Al + C is found to consist of TiC and MAX phases of Ti2AlC and Ti3AlC2. The coating based on intermetallic compounds consists of rounded particles that are fused together and contains NiAl and Ni3Al phases. The coatings obtained from the Ti + Al + C mixture contain needle-shaped crystals of MAX phases and interspersed rounded particles of titanium carbide. The content of the NiAl and Ti2ALC target phases increases with the increasing layer thickness. Coatings based on NiAl, Ni3Al, and Ti2AlC, Ti3AlC2 heat-resistant phases (0.2–1.2) × 10–3 m in thickness with a specific electrical resistance of 0.1–0.6 μOhm m are obtained.

This paper discusses the relationship between the elongation and compression behavior and microstructural changes under redox cycles of porous Ni(O)–YSZ cermets for solid oxide fuel cells (SOFC). Mechanical damage in SOFC and SOEC is one of the most important degradation factors governing the electrical performance of cells. Therefore, it is necessary to know the mechanical properties of each component material, such as elastic and deformation properties, in the operating environment. Particularly, of the Ni(O)–YSZ cermets which currently makes up 90% of the volume of the cell, with present mainstream anode supported SOFC and SOEC. Therefore, understanding the properties of the Ni(O)–YSZ cermets plays an important role in ensuring the performance of the entire SOFC and SOEC. In this study, the microstructural changes of Ni(O)–YSZ cermet by reduction, re-oxidation and re-reduction were observed in detail using microstructural observations and systematically compared with the dimensional change behavior. For the dimensional change behavior, a simple model considering the initial porosity and Ni content is proposed, which successfully predicts the dimensional change due to re-oxidation. Furthermore, Ni(O)–YSZ cermets with high Ni content show large initial dimensional changes, but the dimensional reversibility improves with increase of the number of redox cycles.

Internal dry reforming (IDR) of methane for biogas-fed solid oxide fuel cell (SOFC) applications has been experimentally investigated on planar Ni-GDC (cermet anode) electrolyte-supported cells. This study focuses on the effect of CO2 concentration, current density, operating temperature, and residence time on internal methane dry reforming. A single cell is fed with different CH4/CO2 mixture ratios between 0.6 and 1.5. Extra CO2 recovered from carbon capture plants can be utilized here as a reforming agent. The I-V characterization curves are recorded at different operating conditions in order to determine the best electrochemical performance while the power production is maximized, and carbon deposition is suppressed. The outlet gas from the anode is analyzed by a micro gas chromatograph to investigate methane conversion inside the anode fuel channel and to understand its influence on the cell performance. Relatively long-term experiments have been performed for all gas mixtures at 850°C under a current density of 2000 A m−2. The results indicate that when the cell is fed with biogas with an equimolar amount of CH4 and CO2, carbon deposition is prevented, and maximum power density is obtained.

Reversible Solid Oxide Cells (r-SOCs) are an attractive electrochemical energy conversion technology that can act as both a Solid Oxide Fuel Cell (SOFC) for power generation, and a Solid Oxide Electrolysis Cell (SOEC) for steam electrolysis. Unfortunately, Ni-zirconia cermet, which is widely used in SOFCs, has the problem that the electronically conductive phases, Ni, agglomerates due to redox reactions and breaks the conductive path, resulting in performance degradation. In this study, we fabricated an alternative fuel electrode with a stable conductive structure using both an ionic conductor Ce0.9Gd0.1O2 (GDC) and an electronic conductor Sr0.9La0.1TiO3 (LST), and we co-impregnate Ni and GDC to the fuel electrode using only Ni as an electrocatalyst. The durability of the conventional fuel electrode and our alternative fuel electrode was compared and evaluated, and the potential of the alternative fuel electrode material was demonstrated.

To achieve high efficiency of 65% LHV in the solid oxide fuel cells (SOFCs), the fuel utilization should increase to the level of over 80%, which is 10-15% higher fuel utilization (Uf) than the standard condition, and severe degradation can occur at the component materials. When the current density is controlled in the stack level, there might be the distribution of fuel utilization in the cells due to the distribution of fuel gas, water vapor pressures, and temperatures. So far, many studies were examined on the clarification of degradation mechanism under fuel cell operation. In this report, recent achievements of the Japanese national projects (NEDO projects) are presented, especially on the rapid evaluation methods for degradation (2018-2019) and most recent “Development of advanced evaluation and analysis technologies for the durability of Solid Oxide Fuel Cells stacks (2020-)”. Especially, the anode durability was discussed with different kinds of cell-stack geometry at high fuel utilization. The degradation mechanism and fuel utilizations are compared at the planer and flat tubular type cell-stacks. We discussed the microstructure change and stability of the Ni-YSZ cermet anode at high Uf and current density conditions.

Herein, Mo2FeB2-based cermets, with nominal composition of Mo2FeB2-2.06Fe-2.9Ni-2.5Cr-xWC-0.04C (x = 0, 2.5, 5, 10 wt %), are fabricated by multi-step sintering to investigate influence of tungsten carbide (WC) content on microstructure and mechanical properties. Results reveal that the microstructure of WC-free cermets resembles that of traditional cermets. However, microstructure of WC-containing cermets (x = 2.5 wt %) is composed of fine black core/grey rim Mo2FeB2 grains and coarse white-colored coreless Fe3(W,Mo)3C grains. Furthermore, at x ≥ 5 wt %, most of white coreless Fe3(W,Mo)3C grains are transformed into a white core/black rim structure. From these observations, it can be concluded that growth of nearly round-shaped Mo2FeB2 grains is through diffusion-control, leading to normal grain growth (NGG), whereas the growth of polyhedral Fe3(W,Mo)3C grains is dictated by the interfacial reactions, resulting in 2D nucleation and partially abnormal grain growth (AGG). In addition, grain size distribution of WC-containing cermets exhibits distinct bimodal characteristics, where average grain size is smaller than that of WC-free cermets. More importantly, presence of WC significantly improves the mechanical properties, resulting in superior fracture toughness of 25.1 ± 0.5 MPa m1/2 and hardness of 90.3 ± 0.1 HRA, at x = 5 wt %, without compromising much of transverse rupture strength.

A single-step wet-chemical synthesis of NiO-SDC (Sm3+ doped ceria) colloidal ink for the inkjet printing (IJP) of nanostructured anodic layers with enhanced catalytic activity for solid oxide fuel cells (SOFCs) is developed and characterized. Dynamic light scattering, scanning electron microscope, and Raman spectroscopy revealed stable nanoparticles with the main size of 11.85 nm within the ink solution. Rheology parameters were analyzed, and the anode was printed. Porous post-sintered Ni-cermet layer, with a thickness of 15−25 μm contained near-spherical nanoparticles of 40−80 nm, was obtained. X-ray diffraction confirmed the phase composition of the cermet layer. Electrical impedance spectroscopy demonstrated a significant reduction, by more than 80 %, in the area-specific resistance of the IJP half-cell in comparison with the Screen-printed half-cell. The microstructure engineering using IJP provides fabrication of the cermet NiO-SDC layer with a conjugated structure, which ultimately enhances the catalytic activity of the SOFC.

Tungsten carbide (WC) is the most important tungsten compound, and the main component of WC-Co cermet composites. WC-Co are widely used engineering materials due to the combination of high hardness and strength of tungsten carbide with the toughness and plasticity of the metallic binder. The direct synthesis of WC from tungsten concentrate containing ∼70% WO3 has been achieved by carbothermic reduction. Mineral/carbon black mixtures were prepared by planetary ball milling and subjected to annealing at 1150 °C in flowing Ar. Specific leaching treatments have been developed to remove foreign phases and obtain pure WC powders. This new process allows about 50% energy saving, -34% CO2 emissions, and significantly lower amounts of industrial waste, with respect to the classical hydrometallurgical tungsten extraction and subsequent pyrometallurgical WC synthesis, widely used in tungsten industry. WC powders obtained by carbothermic reduction of the mineral were employed to prepare sintered WC-8 wt %Co samples that showed high density (>99%), hardness (1490 HV), and toughness (14.6 MPa·m1/2). These findings demonstrate, for the first time, that the carbothermic reduction of tungsten concentrates does represent a viable process for energy efficient and sustainable synthesis of WC powders to be used in the production of cemented carbides.

The present work investigated the microstructure and mechanical properties of TiCx-Cu cermets before and after thermal shock tests. Thermal shock temperature was from 800 °C to 1200 °C and number of cycles was from 1 to 20. The results indicated that TiCx-Cu cermets with co-continuous structure exhibited a stable and excellent thermal shock resistance. When quenched at 1000 °C for 1 cycle, the residual flexural strength of the cermet increased to 882 MPa, which was 10.1% higher than that without thermal shock. After 20 cycles of thermal shock, the residual flexural strength still maintain 760 MPa. When quenched at 800 °C and 1200 °C, the strengths of cermet decreased correspondingly, which were caused by the thermal mismatch between metal and ceramics and effusion of Cu or collapses of oxide layer, respectively. Herein, the recrystallization and refinement of metal phase grains caused during the thermal shock process, resulting in the superior thermal shock performance of cermet.

Herein, Ti(C,N)-based cermets prepared via mechanical activation and subsequent in situ carbothermal reduction was studied. The correlation between microstructural and mechanical performance of these cermets was investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Results indicated that with the increase in tungsten carbide (WC) content, hard particles of ceramic gradually evolved from complete solid solution to partial solid solution with a little quantity of core–rim structure. Mean particle size of the cermet first increased, and then, slightly decreased. In addition, grain shape gradually changed from relatively faceted to nearly round. Initially, with the increase in WC content, the increase in transverse rupture strength (TRS) and slight increase in hardness were related to the strengthening of both solid solution and fine grains. However, with further addition of WC, the decrease in hardness was primarily because of lower hardness of (Ti,W,Mo) (C,N) phase with higher W content. Extremely high toughness of cermets with WC content of 0 and 3 wt% was mainly due to the decrease in interface area compared to traditional cermets, which resulted in significant reduction in interfacial strain between the rim and core. Moreover, toughness improvement of cermets containing 6 to 12 wt% of WC was due to comprehensive effect of superb coherent relationship of black core/grey rim particles, semi-coherent relationship with high-density dislocations of solid-solution particles, and solid-solution strengthening of white core-grey rim particles.

The present study was intended to investigate the performance dependence of the solid oxide fuel cells on the pore structure of the supporting cathode. The Sr-doped lanthanum manganite/yttria-stabilized zirconia electrodes with different pore structures were prepared, and their inner surfaces were modified with nano-scale Sm0.2Ce0.8O1.95-δ (SDC). The cell supported on the electrode with a straight pore structure demonstrated much higher maximum power densities than the one supported on the electrode with a tortuous pore structure, e.g., 652 vs 308 mW cm−2 at 800 °C. Impedance analysis revealed that the straight pore structure together with SDC-modified pore surface not only promoted the surface oxygen exchange, but also enhanced the transport of oxygen species to the reaction sites and conduction of oxide ions and electrons in the electrode. The ceramic cathode-supported cell survived 20 redox cycles, showing much better stability than the cermet anode-supported cell. Further research on the supporting cathode is needed to increase the power output density required for practical applications.

The process of formation of a multilevel multilayer B4C – Ti-6Al-4V cermet coating by the method of SLM is studied. The coating is characterized by presence of heterogeneous zones differing in the mechanical properties. It is shown that the use of the B4C – Ti-6Al-4V powder mixture with ceramics concentration 20 wt.% is not expedient, because it causes deficit of the metallic matrix and formation of cracks. At 10 wt.% ceramics in the powder mixture with alloy Ti-6Al-4V the wear resistance of the coating increases by a factor of 4.2.

In this study, bulk Cr3C2-20 wt % Ni cermets were successfully fabricated by high-energy milling and pressureless sintering in a vacuum furnace. Microstructures, elements distribution, and high temperature oxidation mechanism were researched by SEM, EPMA, and differential thermal analyzer (DTA), respectively. Oxidation kinetics regularity of bulk Cr3C2-20 wt % Ni cermets was investigated at 600–800 °C for the first time. Isothermal cyclic oxidation experiments were studied using the heat-treatment furnace for 100 h. The results indicated that the porosity decreased, while the hardness, bending strength, and fracture toughness increased with an improvement in the vacuum degree. Cr3C2-20 wt % Ni cermets displayed outstanding oxidation resistance and the dynamic oxidation curves followed the parabolic rate law. Besides, the oxidation rate constants increased three orders of magnitudes with an increase in the oxidation temperatures from 600 °C to 800 °C. The mechanism of the oxidation resistance was the generation of the protective and dense oxide layers on the sub-surface of the oxidation specimens, which hindered the diffusion of Cr3+, Ni2+, O2 and effectively protected the substrate from further oxidation.

In this paper, the base of the charge used for the production of porous materials is made up of industrial waste generated by machine-building factories, which consists of metal oxides (oxide scale of alloy steel) and metal powders. Therefore, it is important to study the creation of new porous permeable cermet materials (PPCMs) with partial or complete addition of the metal and metal oxide powders. The effect of chromium oxide, as well as chromium and nickel metals on the physical, mechanical, and functional properties of the materials, obtained by the self-propagating high-temperature synthesis method, was studied. The physical and mechanical characteristics of the obtained materials with different component content of the charge have been determined. The introduction of chromium oxide into the Fe2O3-Al2O3–Al reaction mixture creates a more homogeneous alloy structure with the formation of continuous iron oxides, while the introduction of chromium leads to a more uniform distribution of cermet component in the matrix, which enables a more uniform distribution of the structural components. The introduction of nickel into the initial charge leads to the formation of Ni-Al intermetallic compounds in the Fe-Ni-Al reaction system. An exothermic nature of this process causes higher solubility of Ni in Al and decreased phase separation. This also results in a decreased pore size along with increased strength and corrosion resistance of the PPCMs.

In this study, Cr3C2-25NiCr cermet coatings were fabricated by atmospheric plasma spraying on 304 stainless steel substrate. Then, the coatings were sealed with a Polytetrafluoroethylene (PTFE) emulsion by using two methods: conventional impregnation and ultrasonic vibration. The phase composition, surface morphology, porosity, permeability of PTFE emulsion into the coating, wear and corrosion resistance of the coatings were investigated. The results showed that in the PTFE sealed coatings, besides carbide phases, a PTFE phase with an hexagonal crystal structure was formed. The PTFE covered the surface of the coating. The ultrasonic vibration method increased the permeability of the PTFE emulsion into the coating by more than 2 times that of the conventional impregnation method. The PTFE sealed coating by ultrasonic vibration method had a lower porosity, higher wear and corrosion resistances in 3.5 wt.% NaCl solution than the PTFE coating sealed by conventional impregnation method and PTFE unsealed coating.

The permanent importance of molds and dies in the industry motivates new studies to obtain optimized parameters and processes, which contribute to the reduction of their wear and increase of their life cycle. Regarding this, coated forming tools are often applied and this paper aims to investigate the influence of the surface preparation of hardened AISI D2 steel substrate on the adhesion characteristics of an AlCrN coating deposited by physical vapor deposition (PVD). For this, an end milling process with different cutting conditions was applied and the coating was tested by indentation and scratch tests. From the obtained results, it could be observed that cermet cutting inserts used in milling process led to higher compressive residual stresses and lower roughness values in the substrate in comparison to cemented tungsten carbide inserts, increasing the critical load required for coating failure. Although scratch tests demonstrated enough sensitivity to differentiate substrate surface properties, indentation tests had no success.

This study aims to investigate the correlation between flow velocity and cavitation erosion (CE) characteristics of high-velocity oxygen-fuel (HVOF) sprayed Cr3C2-NiCr (CN) and WC-Cr3C2-Ni (WCN) coatings in 3.5 wt% NaCl medium, except for the microstructures, mechanical properties and electrochemical behaviors. In comparison with the CN coating, the WCN coating shows higher values of elastic modulus (E), hardness (H), H/E and H3/E2 as well as lower porosity, resulting in lower volume loss rate (VLR) and enhanced CE resistance in NaCl medium at each value of flow velocity. The VLR values of both coatings increase as the flow velocity increases. The change of the CE progresses in NaCl medium of the CN coating is the formation of cavitation pinholes, pits, craters and oxidation films coupled with the exfoliation of chromium carbide particles when the flow velocity is 23.4 and 33.5 m s−1 as well as the brittle fracture structure with layers delamination accompanied by the oxidation films when the flow velocity is 41.9 m s−1. In a wide flow velocity range, the formation of cavitation pinholes, pits and micro-cracks along with the oxidation films are addressed as the dominant CE mechanism in NaCl medium of the WCN coating.

Surface degradations such as oxidation occur in gas turbines at locations such as turbine blades, where the temperature is high. Instead of these defects the turbines are less powerful and noisy. The present research is on High Velocity Oxy-Fuel coating of SuperCo-605 using a 25 percent Cr3C2-NiCr with 75 percent NiCrAlY fused blend cermets powder. Oxidation experiment was conducted on both coated and uncoated SuperCo605 in an air condition at 750 °C. Thermo-gravimetric research performed cycles of 1-hour heating and 20 min of cooling. Weight calculation was performed after each cycle. Weight calculation was performed after each cycle. The samples were characterized using XRD and SEM / EDS after conduction of 50 cycles. The coated sample has been found to be more resistant to oxidation than the uncoated sample. SEM / EDS surface morphology showed the surface is of oxide formation in rich. Gravimetric analysis showed that the sample's weight gain follows a parabolic relation with time. Compared with the uncoated sample the rate constant for the coated sample was much lower.

Preservation of surface integrity of engineering assets has been achieved by laser cladding of nickel matrix composites in recent years. Ceramic-metal (cermet) coatings offer outstanding surface performances, improved mechanical, thermal and tribological capabilities. In this study, nickel matrix composites with two different compositions of an ultra-high temperature boride reinforcement namely, ZrB2, was considered. Laser cladding of Ni-ZrB2 binary coatings was successful. The microstructural orientation of the coatings was studied as scanning electron microscopy revealed the general transition of mixed cellular grains and dendrites to fine crystals with increasing depth from the free surface towards the substrate. It was observed that the interfacial region of Ni-10% wt. ZrB2 coatings were characterized by smaller cellular grains. Microhardness, oxidation behaviour and tribological tests were conducted on coatings containing 5 and 10% wt. ZrB2. Phase analysis displayed the secondary phases formed within the cermet coatings, which were responsible for the improved microhardness of Ti-6Al-4V alloy. Furthermore, the effect of scanning speed during laser cladding was investigated. Results revealed that Ni-10% wt. ZrB2 fabricated at a deposition speed of 1.2 m/min showed the most suitable surface performance amongst the cermet coatings.

Purpose. Substantiation of the possibility of obtaining composite cermet electric arc coatings using TiC powder as a strengthening phase, determination of their physical and mechanical properties. Methodology. The microstructure of the composite cermet electric arc coatings was studied by computer metallography using a ZEISS Gemini SEM 500 scanning electron microscope. The chemical composition was determined by X-ray spectral analysis; phases were identified by measuring their microhardness on a PMT-3 device. The bond strength of the obtained coatings was determined by the method of pulling out the pintle on a tensile testing machine UMM-5. Findings. Composite cermet coatings of the steel 65G-TiC system were obtained by the electric arc spraying using TiC powder in a free state. The influence of the technological parameters of spraying on the amount of the carbide phase in the coating was established, and their microstructure was investigated. The porosity, microhardness of the phases in the coating and its bond strength were determined. Originality. For the first time, composite cermet electric arc coatings of the steel 65G-TiC system were obtained by using a powder of strengthening phase in a free state. Their microstructure, microhardness and bond strength were investigated. The technological spraying modes of electric arc coatings have been established, which provide the optimal content of the strengthening phase to achieve their maximum bond strength with substrate. Practical value. The application of the research results obtained in the work, namely, the determination of the optimal technological parameters of spraying for the formation of cermet electric arc coatings with the maximum level of physical, mechanical and operational properties, makes it possible to meet the requirements for the restoration and hardening of worn surfaces. This leads to an increase in the service life of parts not only in mining, but also in other industries.

WC based cermet coatings deposited by thermal spray techniques are extensively used in applications where superior sliding wear resistance is a primary need. The present study aims to investigate relative effect of different counter faces on WC-Cr3C2-Ni composite coatings developed by high-velocity oxy-fuel (HVOF) technique for the coefficient of friction, wear factor and damage to the coatings during the dry sliding tests. The experiments were following ASTM G99 on the ball-on-disc tribometer at room temperature with counter bodies alumina (Al2O3), silicon nitride (Si3N4) and bearing steel (ASTM 52100). The detailed information about wear mechanisms of coatings has been accumulated by scanning electron microscope (SEM). The outcomes from the testing of the coating were relatively studied with wear volume loss against each of the counter body. The tribo-pair formed by WC-Cr3C2-Ni coating with Si3N4 recommended as the least coefficient of friction has been recorded during dry sliding process. The wear of WC-Cr3C2-Ni coatings against Al2O3 ceramic counter balls is maximum and has been dominated by abrasive grooving, brittle cracking and spalling.

The first results of the initial stage of studying the possibility of using the pellet oxide fuel with the addition of metallic uranium nanopowder in VVER reactors are reported. Comparison with other types of ATF fuel is performed. The considered cermet fuel has obvious advantages over the oxide and mononitride fuels. Some parameters of cermet fuel also make it preferable over silicide fuel.

Improvement of the sluggish oxygen reduction reaction (ORR) is the key to lower the operating temperature of conventional solid oxide fuel cells (SOFCs). Developing a novel nanostructure in the cathodic catalyst layer is one of the efficient ways to reduce the operating temperature while improving fuel cell performance. In this paper, all components of low-temperature SOFCs were prepared on a nanoporous substrate by the sputtering method. For the performance enhancement at low temperature, an ultrathin Pt-Gadolinium Doped Ceria (GDC) cermet interlayer was deposited on the cathode side of electrolyte and demonstrated. A significant improvement in electrochemical performance was observed in the Pt-GDC interlayer fuel cell compared to a reference cell. The peak power density of Pt-GDC cathodic cermet interlayer cell was 334 mW/cm2 at 500 °C, which was 42.7% higher than that of the reference cell. Through additional analysis, we confirmed that the observed performance enhancement was attributed to the ultrathin cathodic cermet interlayer, which increases the triple phase boundary and enhances the reaction kinetics for ORR.

Ni–La2O3 cermet hydrogen electrode having almost no ionic conductivity still exhibits excellent electrochemical performance owing to the hydrogen spillover process from high hydrogen adsorption capability on the La2O3 surface. In this work, we develop Ni–La2O3 cermet hydrogen electrode originating from the in-situ decomposition of the La2NiO4+δ(LNO) oxide, and then perform the electrochemical properties for quasi-symmetrical solid oxide fuel cells (Q-SSOFCs), which own YSZ electrolyte support wrapped GDC barrier layer. The area specific resistance (ASR) of LNO air electrode increases from 2.09 to 7.41 Ω cm2, with the temperature of decreasing from 800 to 600 °C. The electrochemical performances of Q-SSOFCs with Ni–La2O3 cermet hydrogen electrode and LNO air electrode are characterized, and the values of the peak power density and the electrode polarization resistance (Rp) of the symmetrical electrodes measured at 800 °C are 245.18 mW cm−2 and 0.61 Ω cm2. These results indicate that the hydrogen spillover process of Ni–La2O3 cermet hydrogen electrode can greatly promote the hydrogen oxidation reaction.

The analysis of modern approaches in choosing compositions of cermets based on TiC carbide and Ni matrix doped with additional Mo, W, Cr, Nb, and Ta carbides is carried out. The hardness and transverse strength of the cermets based on TiC carbide and Ni matrix increases with the use of additional Mo, W, Cr carbides owing to the formation of an annular zone around TiC. The calculated microhardness of carbides in the cermet increases with an increase in their volume fraction and with the use of Mo, W, and Cr carbides. On the basis of an analysis of the literature, TiC–Cr3C2–WC–TiB2–SiC–Mo–B–Si–Ni cermets with additional carbon content for plasma coatings are proposed and studied. Mechanical alloying and liquid phase sintering at temperatures of 950, 1250, and 1450°C are used to evenly distribute the carbides in the base phase and to establish strong bonds between them with high values of microhardness, up to 2438 kgf/mm2 at a load on the indenter of 20 G and 2030 kgf/mm2 at a load on the indenter of 200 G. The maximum values of microhardness are obtained at higher sintering temperatures at which the minimum content of oxygen is fixed. The positive effect of carbides based on W, Mo, and Cr on the organization of a strong titanium carbide compound with a base phase is confirmed experimentally, which is proved by the calculated value of the contribution of microhardness of TiC carbide to the cermet microhardness. At a volume fraction of the carbides of 77% and a load on the indenter of 20 G, the contribution of microhardness of the carbide is equal to 2906 kgf/mm2, which is close to the TiC hardness of 3200 kgf/mm2. This contribution of microhardness is equal to 2145.5 kgf/mm2 at a load on the indenter of 200 G.

Thin and porous anodes need three important properties, high porosity, moderate catalytic ability, and no carbon deposition, when using hydrocarbon fuels for the operation of solid oxide fuel cells (SOFCs). Nickel-based (Ni/YSZ) cermets might perform serious carbon deposition using hydrocarbon fuels. Instead, many researches select Cu-based cermets to extend the application period. This study chose half replaced cermet (50%Cu–Ni in Y-doped ZrO2), and verified the effects of H2 formation and carbon deposition comparing to other two series, i.e. Ni-YSZ and Cu-YSZ. Three ingredients were homogeneously mixed and reduced, then sintered to the porosity of 54 ± 3%. The re-dox properties under various atmospheres and the permeability of made cermets have been investigated. The results showed that 50%Cu–Ni with 8YSZ performed moderate catalytic ability, low cracking rate for CH4, and good electric conductivity of 1503 S cm−1 at 650 °C. The sample is suitable for using CH4 fuel for SOFCs.

Solid oxide fuel cells (SOFCs) based on Ni-based cermet anodes suffer from severe sulfur poisoning when operated on H2S-containing fuels (

SrFe0.2Co0.4Mo0.4O3-δ (SFCM) is a ceramic oxide that has the potential to replace conventional Ni-based cermet anodes and is appropriate for use in solid oxide fuel cells operating at low temperatures (below 650 °C). SFCM was shown to be phase stable with n-type conductivity above 43 S/cm under reducing conditions and reversibly creates secondary phases under oxidizing conditions with p-type conductivity around 4 S/cm at 600 °C. SFCM begins desorbing oxygen and creating vacancies under nitrogen at 350 °C and continues to do so above 800°C. Under oxidizing conditions, SFCM remains near stoichiometric, with oxygen non-stoichiometry changes below δ = 0.003. Once exposed to reducing conditions, SFCM can obtain a non-stoichiometry up to δ = 0.176 due to the reduction of the three multivalent B-site cations resulting in a low enthalpy of formation for oxygen vacancies at 109 kJ mol − 1. This data is used to propose a low pO2 defect equilibrium model and diagram to explain the oxygen vacancy generation behavior under reducing conditions across temperatures.

Reasons are considered for unsatisfactory operation of the energy-absorbing device of railway wagon drawbar, whose main element is a friction plate with special energy-absorbing cermet coating. The main specifications for the friction plate are resistance to shock loads, resistance to thermal cycles in the temperature range from ambient temperature to 850–870°C, good resistance to shear stresses, friction coefficient stability in this temperature range, lack of seizure to friction wedge material made of steel, and long operating life up to 10,000 loading cycles. According to results of metallographic studies using optical and scanning electron microscopy with energy dispersion microanalysis it is established that the poor quality of the friction plate metal composite coating is caused by the following factors: localization of eutectic containing sulfur, iron, and manganese along the “ceramic-substrate” boundary, and presence of oxide films on the surface of precursor powder particles. As a result of this excess interfaces arise in cermet material that are areas of microcrack formation during cermet operation. Thermal stresses arising during metal composite briquette manufacture lead to crack development at the interface of metal composite and a steel base. Application of unevenness to the steel base of metal composite material in a hydrogen or endogas atmosphere makes it possible to avoid both thermal cracks and subsequent metal composite separation during operation. An improvement in operating characteristics is confirmed during laboratory tests under conditions approximating operational.

Alumina-coated cubic boron nitride (c-BN) particles (c-BN@Al2O3) were prepared using a heterogeneous nucleation method. Then, they were added to a (Ti,W)C-based cermet tool material after synthesis via vacuum hot-press sintering. The microstructure and mechanical properties of the (Ti,W)C-based cermet tool material with varying c-BN@Al2O3 contents were recorded and analyzed. The results show that with increasing c-BN@Al2O3 concentration, the relative density, flexural strength, fracture toughness, and Vickers hardness all increase first and then decrease, and the average grain size first decreases and then increases. The introduction of Al2O3 into the c-BN particles used for surface modification can improve the wettability and interfacial bonding strength between the c-BN and matrix particles, restrain the grain growth of the matrix particles, and improve the flexural strength of cermet tool materials. The addition of c-BN@Al2O3 also alters the crack propagation mechanism of the cermet tool material and introduces multiple toughening mechanisms to improve the fracture toughness of the cermet tool material. The high hardness of c-BN and Al2O3 is the main reason for the increase in hardness; however, excessive addition of such material reduces the relative density, resulting in a decrease in hardness.

The use of a powder mixed dielectric is one of the promising measures to overcome defects such as non-uniform thickness, voids and micro-cracks of hard coatings obtained via the electrical discharge coating (EDC) process. The quest for finding appropriate powders suspended in EDC dielectric still continues. In this paper, reduced graphene oxide nanosheets (RGONS) are explored as the additives of EDC dielectric to fabricate TiC containing composite coatings with superior tribological performance. The influences of RGONS on the surface integrity, microstructure and tribological performance of the as-prepared coatings are investigated. RGONS with lipophilic modification effectively reduce spark energy and disperse the discharges throughout the machined surface due to their uniform dispersion in the discharge gap. This allows the formation of compact coatings with banded microstructure composing of a mixture of equiaxed and columnar TiC grains within the martensite matrix. Such unique microstructure improves the as-prepared coatings’ resistance to adhesion and abrasion wear, as well as fatigue and fracture. As a result, they show obviously lower coefficient of friction and wear rate compared to the coatings obtained using a bare dielectric.

The influence of Cr and W addition on microstructure and mechanical properties of Mo2FeB2-based cermets, prepared by multi-step sintering, is systematically evaluated by XRD, SEM, EDS, and TEM. After liquid-phase sintering, the final microstructure of Cr-doped Mo2FeB2-based cermets is similar to that of traditional Mo2FeB2-based cermets. The cermet, with 2.5% Cr content, exhibits superior comprehensive mechanical properties, i.e., Rockwell hardness, transverse rupture strength (TRS) and fracture toughness of 87.6 HRA, 2179 MPa and 21.7 MPa m1/2, respectively. In contrast, for W-doped Mo2FeB2-based cermets, a large amount of W-enriched (Mo,Fe,W)3B2 solid solutions precipitated around undissolved Mo2FeB2 particles, resulting in the formation of black core/gray rim structure. Particularly, a transition layer, with several atomic layer thickness, is observed between (Mo,Fe,W)3B2 rim phase and Fe-based binder phase, which corresponds to B-deficient (Mo,Fe,W)3B2−x orthorhombic boride phase. Moreover, the lattice mismatch between (Mo,Fe,W)3B2 and (Mo,Fe,W)3B2−x is found to be 1.9%. When doped with 5 wt% W, Mo2FeB2-based cermet exhibit superior comprehensive mechanical properties with Rockwell hardness of 84.6 HRA, TRS of 2088 MPa and fracture toughness of 24.4 MPa m1/2. The increase of fracture toughness (KIC) can be ascribed to the presence of W-rich transition layer.

This paper presents the results of obtaining and studying the structure and properties of cermets based on powders of aluminum oxide and nickel–aluminum alloy doped with 0.1 wt % of aluminum–magnesium spinel nanoparticles sintered by the electrospark method on a FCT-HP D 25 unit in argon at t = 1470°C for 30 min. The results of the NiAl–65Al2O3 charge TG and DSC analysis at up to 1300°C are presented. It is found that the MgAl2O4 spinel in the form of individual nanoparticles (60 nm) or aggregates (less than 700 nm) are present along the grain boundaries of the composite. Internal friction studies at t = 20–900°C and high-temperature X-ray phase analysis at t = 700, 800, and 900°C were carried out to describe the degradation mechanisms of the strength properties of the materials. The effect of nanoparticles on the internal friction of the composite within Δt = 20–900°C in the NiAl–65Al2O3–0.1MgAl2O4 system is shown. Potential mechanisms for cermet strength-property degradation with increasing temperature are discussed. It is suggested that the appearance of extrema on internal friction curves at high temperatures can be caused by shifted phase boundaries of intermetallic compounds and the oxide component due to different coefficients of thermal expansion (CTE). A positive effect of doping with spinel nanoparticles on the short-term heat resistance of cermets at t = 750°C is found. The study of short-term heat resistance at t = 750°C shows that the sample with nanoparticles is more stable than the unmodified sample, which can be associated with the influence of interfacial hardening zones formed around nanoparticles according to the Obraztsov–Lurie–Belov theory and a number of studies carried out on metal matrices.

A comparative analysis of the features of the formation, morphology, and electrochemical activity of composite anodes of solid oxide fuel cells was performed using nanosized particles of NiO and Ce0.8Gd0.2O2 – δ. The direct introduction of NiO nanoparticles into cermet composition leads to technological problems during screen printing of electrode layers associated with the oxidation of organic components of electrode pastes with oxygen, which is desorbed from the NiO surface. Such problems can be solved by pre-heating treatment of NiO. However, this treatment and subsequent firing of the anodes leads to an increase in the particle size to submicron. An increase in electrochemical activity can be achieved by impregnating the anodes with the formation of nanosized catalytically active particles on their surface.

Cu-based cermets suitable for electrodes in Symmetric and Reversible Solid Oxide Fuel Cells (SR-SOFCs) based on the Cerium Gadolinum Oxide (CGO) electrolyte were developed and successfully tested in the intermediate temperature range (600–800 °C). The Cu/CGO cermets were prepared by means of a self-combustion based citrate procedure and the effects of synthesis conditions were studied. Characterization of the Cu/CGO nanocomposites by XPS, XRD, SEM, TPR suggested that this procedure allows obtaining highly dispersed CuO on the cerium gadolinium oxide. Conversion higher than 80% was observed above 600 °C in methane total oxidation. Synthesis parameters affected both properties and catalytic performance. The behaviour under redox conditions was studied by operando high-energy XRD under oscillating H2/O2 feed. Reducing conditions converted CuO into Cu(0) passing through an intermediate Cu2O phase while increasing the conductivity and the reactivity. This structural modification was completely reversible. The high stability, reversibility, catalytic activity and electrochemical performance make these electrodes promising for SR-SOFCs.

Silicon nitride (Si3N4) based cermets are very popular due to their versatile applications like high temperature engine parts, cutting tools, refractory and structural applications. Here, in this work, Si3N4–Mo (Si3N4 as matrix and molybdenum as reinforcement) and Si3N4–Mo–Si (Si3N4 as matrix, Mo and Si as reinforcement) cermets are fabricated through powder metallurgy route and phase evolution, micro-structure and mechanical properties are analyzed. Three initial powder compositions of 90Si3N4–10Mo (S90M10), 75Si3N4–25Mo (S75M25) and 75Si3N4–15Mo–10Si (SMS) (all in wt%) are prepared through planetary milling and total additive amount of 5, 10 and 15 wt% of Y2O3 and Al2O3 are mixed (equal wt ratio of each) with milled base powder, cold compacted and followed by conventional pressure-less sintering at 1500 °C for 1 h. The effects of additives and reinforcements on phase evolution, microstructure and mechanical properties are discussed. From XRD and SEM analysis of sintered pellets, the presence of molybdenum silicide (i.e. Mo3Si, Mo5Si3 and MoSi2) in all the cermets is confirmed. It has been observed that the relative density and hardness values are increased with the increase in additive wt%. Comparing all the cermets, 75Si3N4–15Mo–10Si with 10 wt% additives has shown the maximum compression strength and fracture toughness of 134.2 MPa and 8.89 ± 0.34 MPa.m1/2 respectively. The maximum relative density of 75.24% is observed in S90M10 and hardness of 8.81 ± 0.13 GPa is found in S75M25 both cermets containing 15 wt% of additives. The transformation from α- to β- Si3N4 is observed in all the cermets after sintering.

Comparative studies of cermet coatings with titanium carbide and matrices from high-speed steel grade 10Р6М5 and self-fluxing alloy based on nickel H77X15C3P2 were carried out. The powders were obtained by self-propagating high temperature synthesis (SHS). The coatings were formed by plasma spraying with local protection. The introduction of additional carbon into cermet TiC–10Р6М5 + 2.38 C made it possible to compensate for carbon losses during plasma spraying and to form a coating with an additional carbon content of 1.35%. The content of the titanium carbide phase in the coating is retained; however, the period of the carbide lattice is reduced, the more so for the coating with a nickel-based matrix. The content of oxygen and nitrogen in the coatings with respect to the initial powders increases mainly in the cermet containing the steel matrix. The presence of silicon and boron in the cermet grade obtained with the matrix from the alloy H77X15C3P2 did not reduce the loss of carbon in the coating. The microhardness of the obtained coatings, measured with a load on the indenter of 20 g, is 19–65% higher than the microhardness of the particles of the sprayed powders. The highest values of microhardness, 16.34 GPa, were obtained in a cermet coating sprayed from a powder with an additional carbon content of 45.23 TiC–52.39 10Р6М5–2.39 C.

Self-propagating high temperature synthesis (SHS) was used to obtain porous cermet membranes based on a mixture of aluminum oxide, silicon carbide, and magnesium oxide powders. The obtained membranes are catalytically active. The surfaces of the open pores in them were modified by rhenium-tungsten active components using the alkoxy method. The highest selectivity in terms of propane (about 60%) is achieved at temperature 600°C. In addition, the optimal conditions for implementing the propane dehydrogenation process is temperature 650°C at which the quite high selectivity for the most important monomers remains with a relatively small contribution of accessory processes.

The effects of tungsten carbide addition on the microstructure, mechanical properties and corrosion resistance of Ti(C,N)-based cermets prepared by the sinter-HIP method are investigated through scanning electron microscope, X-ray diffraction, electron back scattered diffraction, mechanical test and electrochemical method. The results show that the appropriate WC addition has an important influence on promoting the formation of core-rim microstructure of cermet, increasing the wettability of ceramic phase and binder phase, and improving the mechanical properties. Ti(C,N)-based cermet with 5 wt% WC addition has the highest hardness of 92.4 HRA and excellent wear resistance. However, excessive WC addition causes the appearance of slight white core phase containing plenty of W and Ti element in microstructure, which increases the fracture toughness, and reduces the hardness and wear resistance of cermet. Additionally, the electrochemical result shows that the addition of 5 wt% WC in cermet has the optimal corrosion resistance in 1 mol/L hydrochloric acid solution.

A composite cermet consisting in a Ni–Fe alloy and Ce0.9Gd0.1O2-x (CGO) was prepared and used as an electrocatalytic pre-layer in a conventional solid oxide electrolyser (SOEC) for the co-electrolysis of H2O and CO2. The electrocatalyst showed two main phases ascribed to trevorite (NiFe2O4, 78 wt %) and metallic Ni (22 wt %) and an average crystallite size of 27 nm. The role of the Ni–Fe electrocatalyst in promoting CH4 formation was analysed by comparing gas-chromatographic and electrochemical results obtained for coated and bare cells. A slight increase of series resistance was observed for the coated cell (0.85 vs 0.53 Ω cm2) at 525 °C. However, the coated cell demonstrated an enhanced CH4 production in the entire temperature range investigated (525–800 °C). Contrarily to what observed for the bare cell which mainly produced syngas, the coated cell allowed to achieve a high yield of methane (between 67% at 525 °C and 35% at 800 °C) with selectivity to CH4 between 94% at 525 °C and 51% at 800 °C. The selectivity to CO for the coated cell was relatively low (between 6% at 525 °C and 48% at 800 °C). Whereas, the bare cell showed 98–100% selectivity to CO along the entire temperature range). Durability studies showed the possible occurrence of delamination issues as consequence of carbon formation at the interface between the supporting cathode and the electrolyte as observed from the morphological analysis of SOEC cells after operation.

In order to improve the performance of the anode of solid oxide fuel cells, the cermet anodes were synthesized by employing a carbonate co-precipitation method and calcined at different temperatures (500 °C-800 °C). The fabrication of pellet from calcined powder was done by uniaxial pressing. These pellets were then characterized to investigate the effect of calcination temperature on their microstructure, thermal behavior, porosity, and carbonate bonding along with conductivity. The carbonates formed within the synthesis process has shown a strong effect over the properties of the Ni-SDC. It is observed that Ni-SDC maintained its chemical compatibility during each process. The thermal gravimetric analysis showed that more weight loss occurred for the specimen calcined at low temperature. Due to the porosity increases with calcination electronic conductivity and performance will also be enhanced.

The ironing limit of aluminium alloy cups with lubricants containing nanoparticles and a tool steel die was investigated, and was compared with the limits with tungsten carbide and TiCN based cermet dies. The use of the conventional tool steel die is desirable in the industry due to low tool cost. Although the limit of lubricant without particles in the tool steel die was low, the limit with lubricants containing nanoparticles was same or higher than those of the tungsten carbide and TiCN based cermet dies with the commercial oil containing sulphur-based additives. The lubricants containing particles in ironing for aluminium alloy cups with the conventional tool steel die were effective to increase the ironing limit.