Ni Cermet Research Articles

A comparative study on the oxidation behaviour of NbC-Ni, WC-Co, and high entropy carbide-Ni based cermets

The oxidation behaviour of NbC-13.5(wt%)Ni, NbC-5.7Mo2C-13.3Ni and WC-12Co was compared to that of equimolar quinary (Ti0.2V0.2Nb0.2Ta0.2W0.2)C-10Ni and non-equimolar senary (Ti0.2V0.2Nb0.2Ta0.2Mo0.1W0.1)C-10Ni high entropy carbide (HEC)-Ni cermets. Isothermal oxidation experiments were performed at 700 °C, whereas non-isothermal calorimetric experiments were conducted to determine the onset temperature of oxidation. HEC-based cermets exhibited superior oxidation resistance and a unique oxide layer morphology, which was attributed to the formation of a chemically complex oxide scale mainly consisting of (Ti,V,Nb,Ta,Ni)Ox and Ni(Mo,W)O4. The NbC-based cermets showed the least oxidation resistance and formed a porous oxide layer of Nb2O5 and (Nb,Ni)Ox, whereas WC-Co showed an intermediate oxidation behaviour with respect to the HEC-Ni based cermets. All composites followed a linear oxidation rate law, and the senary HEC cermet demonstrated the slowest oxidation kinetics.

Microstructure and mechanical properties of (Ti, W, Mo, Nb, Ta) (C0.78, N0.22) high entropy cermets with 5–25 wt% Co–Ni binders

In this study, high entropy (Ti0.6,W0.1,Mo0.1,Nb0.1,Ta0.1)(C0.78,N0.22) ceramics (HECN) powders were synthesized by carbothermal reduction nitridation. (100-x) HECN-(x/2) Co-(x/2) Ni (x = 5–25 wt%) cermet was prepared by vacuum sintering. The relationship between microstructure and mechanical properties of HECN-based cermet sintered at 1450 °C and 1500 °C was studied. The results show that the second phase (W,Mo,Ti)3+x(Co, Ni)3−xC appears at both sintering temperatures, and its content decreases with the increase of binder Co, Ni content and sintering temperature; At the same time, the grain size of the hard phase of the cermet grows with the increase of Co and Ni content. In terms of mechanical properties, at both sintering temperatures, the cermet showed a decrease in hardness and an increase in fracture toughness with the increase of Co and Ni content, while the bending strength increased and then decreased. Among them, when the content of Co and Ni is 20 wt%, the bending strength of HECN-based cermet sintered at 1450 °C is the best, and the bending strength reaches 1640 MPa. This is attributed to the combined influence of many elements in high entropy cermet, which on the one hand leads to serious lattice distortion; On the other hand, improving the wettability and density of the cermet has a strengthening effect on the cermet. In addition, with the increase in Co and Ni content, the plastic deformation of the bond phase will inhibit crack propagation. The main paths are crack deflection and crack bridging, which increase the energy required for crack propagation and lead to a gradual increase in fracture toughness.

Macro and micro-scale material removal mechanisms during ECM/hybrid laser-ECM of a passivating multiphase NbC–Ni cermet

Electrochemical machining (ECM) is a non-contact and athermal machining process where the material removal is accomplished through controlled anodic dissolution of the workpiece governed by Faraday laws. ECM process has been hybridized with several other processes for improving material processing windows. Hybrid laser electrochemical machining (LECM) synergistically applies electrochemical and laser process energies with added benefits of escalated reaction kinetics leading to enhanced transpassive dissolution, weakening of passivation layer, process localisation and uniform dissolution. The laser energy acts as a localised and controllable heat source thereby offering multi-fold processing benefits. For alloys and cermets, a characteristic surficial fingerprint is the presence of inhomogeneous multiphase dissolution and sporadically distributed passivation layer, necessitating addition of aggressive reagents in electrolytes. LECM has the potential to addresses these challenges while processing in pH neutral electrolytes. Previous works have very limited analysis on the macro and micro removal mechanisms while processing relevant strategic materials and multitude of applications of LECM remain unexploited. Therefore, this work presents in-depth investigations into macro and micro-scale material removal mechanisms of ECM/LECM on sintered niobium carbide with nickel binder (NbC–Ni), which is a potential cobalt-free alternative to tungsten carbide. The results revealed new insights into the removal behaviour of the constituent phases which differed from the first principles and their interaction with the laser. During ECM, the Ni phase dissolved preferentially and influenced the surface pattern and particle breakout which was reduced with laser assistance. The surface evolution characteristics were also analysed based on the ridge-crevice pattern. Additionally, the weakening of passive layer was correlated with the pulse analysis that revealed quantitatively the different process regimes occurring during ECM and LECM. The grain level study revealed that orientation effects still exist during LECM and the grains with higher surface energy (FCC (001) vicinal planes) passivated more and dissolved less. Furthermore, the improvement in surface quality, overcut and reduction in particle breakout with LECM process makes it promising for machining newer recipes of metal carbides.

Facile synthesis of high entropy carbide-nickel based cermets by in-situ carbo-thermal reduction of transition metal oxides

Equimolar and non-equimolar high entropy carbide-nickel based cermets were successfully prepared by in-situ carbo-thermal reduction of constituent metal oxides in a single pressureless vacuum sintering cycle at 1420°C. The carbon content in quinary (Ti0.2V0.2Nb0.2Ta0.2W0.2)Cx-10wt.%Ni and senary (Ti0.2V0.2Nb0.2Ta0.2W0.1Mo0.1)Cx-10wt.% Ni high entropy carbide cermets was varied (x = 0.6–1.0). Two-phase HEC-Ni cermets were formed at x = 0.75–0.85, whereas M6C (η-phase) and graphite phase coexisted at lower and higher carbon contents (x = 0.6, 0.9 and 1.0) in both HEC 5 and HEC 6 systems. In HEC 5, submicrometric WC precipitates were observed, which were attributed to the limited solubility of hexagonal-WC within the in-situ formed HEC 5 phase, contrasting with HEC 6 where no such precipitations were formed across the entire carbon content range. The partial replacement of W with Mo in the (Ti0.2V0.2Nb0.2Ta0.2W0.1Mo0.1)Cx-10 wt% Ni cermets promoted solid solution formation at lower temperature, and the grain size and hardness decreased and the fracture toughness increased. Both HEC-Ni cermets showed a homogeneous distribution of elements within the carbide phase, resulting in (HV30) hardness around 16 GPa and a fracture toughness around 8 MPa.m1/2. The phase evolution was systematically investigated by interrupting the sintering cycle at 600–1400 °C, employing XRD analysis. Thermodynamic calculations were performed to predict the critical reaction temperatures for carbo-thermal reduction. To evaluate the intrinsic mechanical properties of each phase and establish the correlation with microstructural features, micromechanical mapping was performed utilizing the high-speed nano-indentation technique.

A novel wear-resistant and corrosion-resistant Mo2NiB2–Ni cermet coating prepared using fast hot pressing sintering

A new fast hot pressing (FHP) sintering method was used to prepare Mo2NiB2–Ni cermet coating to solve the problems of small scale and high energy consumption in the production. The synthetic phase and microstructure of the Mo2NiB2–Ni cermet coating were studied, and friction and wear as well as electrochemical corrosion performance were also tested. The results indicated that the Mo2NiB2–Ni cermet coating was composed of two phases, the Mo2NiB2 hard phase and the Ni metal-bonded phase. A metallurgical bond interface resembling interlocking teeth was formed between the Mo2NiB2–Ni cermet coating and the stainless steel substrate, thereby enhancing the bonding strength of the interface. Compared with the Mo2FeB2–Fe cermet coating, the Mo2NiB2–Ni cermet coating had certain wear resistance and excellent corrosion resistance. The high hardness of the Mo2NiB2 hard phase, the low mutual solubility between the Ni metal-bonded phase and the Si3N4 balls, and the generated mechanical mixing layer reduced the friction coefficient and the adhesive wear, which improved the wear resistance. The higher open circuit potential and the formation of the passivation film during the corrosion process enhanced the corrosion resistance of the Mo2NiB2–Ni cermet coating.

Study on wear protection performance of HVAF WC–Cr3C2–Ni coatings deposited on crystallizer surface

A crystallizer is the most crucial component of the continuous casting and rolling process, and it is required to operate effectively at high temperatures and loads for an extended period. In this study, WC–Cr3C2–Ni cermet coatings with high strength and wear resistance were deposited on the surface of a copper alloy crystallizer using high-velocity air-fuel spraying. The microstructure of the coating and its protective effect on the substrate at different temperatures were analyzed. The coating on the copper substrate was uniform and dense, with a porosity of 0.34 % and stable phases. Wear test results at room temperature showed that copper substrate underwent oxidative peeling failure when subjected to wear, and exhibited severe abrasive and adhesive wear, while WC–Cr3C2–Ni coating had no peeling damage on the surface when subjected to wear. In addition, the friction coefficient of the substrate was reduced from 0.624 to 0.489, thus significantly improving the wear resistance of the crystallizer surface. At high temperature (300 °C), the friction coefficient of coating increased to 0.676. Although the degree of oxidation and fatigue wear of the coating increased, the surface of the coating remained intact without any failure area. WC–Cr3C2–Ni coating protected the crystallizer continuously under high-temperature loading conditions for a prolonged time, indicating enhanced service life of the crystallizer. This study provides significant findings for developing new crystallizer coatings.

Effect of WC on the microstructure and mechanical properties of TiB2–CoNi cermets

The microstructure and mechanical properties of the vacuum sintered (80-x)TiB2-xWC −10Co-10 Ni (x = 0, 2.5, 5, 7.5, 10, 12.5) cermets were studied by XRD, SEM, EPMA and TEM analysis. The results show that the TiB2-7.5 WC based cermets exhibited excellent comprehensive properties with relative density, Rockwell hardness, transversal rupture strength and fracture toughness of 99.44 ± 0.18 %, 17.50 ± 0.71 GPa, 2108 ± 29 MPa, and 12.21 ± 0.29 MPa m1/2, respectively. The XRD diffraction peaks of TiB2, W2CoB2, WB and CoNi binder were detected in cermets with WC addition. The HCP TiB2 core-FCC (Ti, W, Co, Ni) (B, C) rim structure was formed in TiB2-WC based cermets with FCC CoNi binder. The coherent interface formed between the TiB2 core and (Ti, W, Co, Ni) (B, C) rim phase, as well as the amorphous CoNi thin layer formed at the interface between (Ti, W, Co, Ni) (B, C) rim and CoNi binder phase, both of them were suggested to improve the interfacial bonding strength of TiB2-WC based cermets.

Synthesis, microstructure, and properties of novel series of (Ti, W, Mo, Nb, Ta) (C0.78, N0.22) high entropy ceramic-based cermets

Five high-entropy carbonitride ceramic (HECN) powders consisting of pentavalent cations (Ti,W,Mo,Nb,Ta) (C0.78,N0.22) are synthesized by the carbothermal reduction-nitridation (CRN) method. Subsequently, a series of 85HECN-7.5Co-7.5Ni(wt.%) cermet is fabricated employing the powder metallurgy method. The phase constitution, microstructure, and composition distribution of the HECN powders are analyzed. The synthesis temperature of the HECN powders is reduced by 100 °C compared to the non-high-entropy (Ti,Me) (C,N) ceramic powder when ΔSmix >1.5R, which demonstrates that the high entropy effect promotes the synthesis of solid solution powder. A uniform element distribution, 600 nm single-phase (Ti0.6,W0.1,Mo0.1,Nb0.1,Ta0.1) (C0.78,N0.22) high-entropy ceramic solid solution powder, could be synthesized through the CRN at 1400 °C for 2 h under a 2 kPa N2 atmosphere. Subsequently, five types of (Ti,W,Mo,Nb,Ta) (C0.78,N0.22)-Co-Ni high-entropy cermets are prepared via vacuum sintering at 1500 °C for 1 h. Among them, the (Ti0·6W0·1Nb0·1Ta0·1Mo0.1) (C0.78,N0.22)-Co-Ni cermet exhibited the most outstanding performance with a Vickers hardness of 2053.4 HV, fracture toughness of 12.3 MPa m1/2, and TRS of 1220 MPa, which present an increase of 17.0 %, 16.2 %, and 60.0 %, respectively, compared with the non-high-entropy TiCN–Co–Ni cermet. It was attributed to the addition of high-entropy ceramic powders, which resulted in fine grain strengthening, severe lattice distortion, and long crack deflection paths. This study presents a novel approach for the preparation of high-entropy Ti(C,N)-based cermets.

Microstructure control and mechanical property improvement of Cr3C2-Ni cermets by using solid-solution powders

Microstructure control and mechanical property improvement of Cr3C2-Ni cermets by using solid-solution powders

Influence of AlN addition on the microstructure, mechanical properties and oxidation characteristics of NbC-Ni cermets

Herein, NbC–Ni cermets with various AlN contents (0–9.0 wt%) are prepared using powder metallurgy, and their microstructure, mechanical properties, and oxidation characteristics are investigated. The addition of AlN dissolves the binder and forms Ni3Al, which can inhibit the dissolution–reprecipitation process and refine the average grain size of NbC, thereby resulting in enhanced mechanical properties of the cermets. Cermets with 1.0 wt% AlN exhibit the highest hardness (HV101,470 kg/mm2) and TRS (1365 MPa). With an increase in AlN content, excess Al exists as a metallic phase in the cermets. This destroys the continuity of the cermet structure and decreases its hardness and transverse rupture strength. For oxidation test at 700 °C, NbC in the cermets is oxidized primarily to Nb2O5, and the Ni binder is transformed into binary oxides, such as (NiNb2O6)0.6667. The oxidation weight gain of the NbC cermets decreases after the addition of AlN, which can be attributed to the formation of Ni3Al, thus slowing the oxidation of the binder. Further addition of AlN up to 3.0 wt% deteriorated the oxidation resistance because cracks were generated at the boundary of the Nb2O5/Al2O3 interface, which accelerated the oxidation process.

Effect of Ni content on the corrosion behavior of Mo2NiB2–Ni cermet in H2SO4 solution

To promote the utilization of Mo2NiB2–Ni cermet under sulfuric acid drew corrosion conditions, it is essential to elucidate the resistance mechanism of these cermets to sulfuric acid corrosion. In this study, the corrosion behavior of Mo2NiB2–Ni cermets with different Ni content in 90 wt % H2SO4 solution at 110 °C was investigated, and the corrosion resistance mechanism was analyzed. The results reveal that the corrosion weight losses and corrosion rates of the cermets decreased with increasing Ni content. Mo2NiB2–Ni cermets with higher Ni contents exhibited improved corrosion resistance. This improvement can be attributed to the generation of a considerable amount of NiSO4 corrosion products from the Ni binder phase corroded by H2SO4, which led to the subsequent formation of a large-scale, flat, and dense corrosion products layer with a certain thickness. This effectively prevented further erosion of the inner matrix and improved the corrosion resistance of the cermet. Additionally, the electrochemical results indicate that the corrosion product layer hindered the passage of electric charges through the layer, which inhibited the corrosion reaction.

Effects of secondary carbide addition on the mechanical properties of (Ti1-xTMx)C-based 20Ni cermets (TM = V, Mo, and W): a study combining ab initio calculation and experimental results

ABSTRACT In recent years, significant efforts have been devoted towards the development of high-performance cermets with superior hardness and fracture toughness for engineering applications. In this study, a (Ti1-xTMx)C solid solution of a Ni cermet was prepared based on a combination of ab initio calculation and experimental results. The structural stability, mechanical properties, and microstructure of the cermet were investigated. A screening process was conducted using ab initio calculations to determine the optimal composition of (Ti1-xTMx)C (TM = V, Mo, and W) (x = 0–0.3125). The enhancement of the mechanical properties was analysed by calculating the electronic properties of the (Ti1-xTMx)C solid solutions. Additionally, we evaluated the powder morphology, microstructure, and mechanical properties of (Ti1-xTMx)C–20Ni by using experimental methods. The (Ti0.7W0.3)C–20Ni cermet exhibited enhanced hardness and fracture toughness in relation to conventional TiC–Ni cermets. Computational and experimental results indicated that the addition of secondary carbides improved the overall material properties.

Perovskite-Based Materials As Alternative Fuel Electrodes for Solid Oxide Electrolysis Cells (SOECs)

Enhancing the lifetime of SOECs is a challenge to overcome regarding their commercialization. A major impact on the lifetime of a cell during electrolysis operation, particularly under thermoneutral potential and high current densities, is the degradation of the currently used electrode materials, mainly the Ni-based fuel electrode. Among other things, nickel migration, as well as agglomeration, is leading to a significant performance loss after a certain operating time. Hence, preventing degradation mechanisms of the fuel electrode during operation is a necessity to be tackled for using it commercially. Therefore the development of alternative materials which combine sufficient performance with the lowest possible degradation rate is needed. Perovskite-based materials have been investigated in the last years as all-ceramic possible substitutes.In this work, four perovskites (i.e., strontium-iron-niobate double perovskite (SFN), a strontium-iron-titanate material (STF), a lanthanum-strontium-titanate (LST) and a lanthanum-strontium-iron-manganese (LSFM)) were examined as alternative electrode materials. The aim is to substitute the active fuel electrode, at the moment commonly consisting of Ni cermets, with a perovskite-based electrode while at the same time using state-of-the-art materials for the remaining cell components.The first task here was to look at the chemical stability between the new electrode material and the electrolyte under the standard conditions used to manufacture fuel electrode-supported SOECs.Therefore, the compatibility between these perovskites with a yttria-stabilized-zirconia (8YSZ) electrolyte and how nickel inside the fuel electrode affected the chemical stability during sintering in air at 1400 °C for 5 h was investigated. At this point, SFN double perovskite shows the lowest interaction between the electrode and electrolyte after thermal treatment.A thorough evaluation of all preliminary tests (including compatibility, stability in reducing atmospheres and redox stability tests) indicates that SFN shows so far the best results of the four materials in terms of application as fuel electrode material, followed directly by STF.Thus SFN and STF were chosen to be evaluated in single cell tests. The tests of pure SFN and STF electrodes are carried out with electrolyte-supported single cells exhibiting an LSCF air electrode and symmetrical cells, respectively. CV-characteristics and impedance spectra are measured at varied operating conditions. Impedance spectra are evaluated by the distribution of relaxation times (DRT). These examinations are carried out to give an insight into the electrochemical properties of pure perovskite-based fuel electrodes in order to obtain a base for further optimization.

Microstructure, mechanical property and cutting performance of (Ti,W)C/Mo/Co/Ni cermet tool material prepared by spark plasma sintering and high frequency induction heating

The (Ti,W)C/Mo/Co/Ni cermet tool material is produced using a combination of spark plasma sintering and high frequency induction heating (HFIH-SPS) mixed sintering technology. This study investigates the influence of various sintering parameters on the microstructure and mechanical properties of (Ti,W)C/Mo/Co/Ni cermet tool material. The findings indicate that the rapid sintering densification of (Ti,W)C/Mo/Co/Ni cermet tool material can be achieved by the mixed sintering technology at a lower sintering temperature. The rapid sintering process observed in this study can be mainly attributed to the plasma activation effect generated by pulse current and the Joule heat effect produced by the metal particles under high frequency induction. The optimized relative density of the (Ti,W)C/Mo/Co/Ni cermet tool material reaches 99.10%, with the hardness of 20.28 ± 0.58 GPa, the fracture toughness of 7.74 ± 0.14 MPa·m1/2 and the flexural strength of 796.12 ± 36.55 MPa. The indentation of (Ti,W)C cermet exhibits a regular cross shape, and the indentation edge is smooth, which indicates a good fracture toughness. The high mechanical properties of (Ti,W)C/Mo/Co/Ni cermet tool material are mainly attributed to the interaction between crystal grain boundary solute strengthening and dislocation movement. The tool has shown good cutting performance during the subsequent dry cutting of 40Cr steel, with the lowest surface roughness Ra value of 1.097 µm.

Performance and sulfur tolerance of a short stack with solid oxide cells using infiltrated strontium titanate based anodes

Solid oxide fuel cell (SOFC) technology offers reliable and efficient power generation from electrochemical oxidation of fuel gasses. State-of-the-art (SoA) anodes based on Ni cermets are prone to poisoning by fuel impurities, including sulfur. Next generation anode materials should be more robust towards sulfur poisoning e.g. in the event of failure or expiry of desulfurization units utilized in SOFC systems. Herein we present the performance and sulfur tolerance of short stacks with large area electrolyte supported cells with Ni:Ce0.8Gd0.2O1.9 (CGO) and FeNi:CGO co-infiltrated La0.4Sr0.4Fe0.03Ni0.03Ti0.94O3 (LSFNT) anodes tested under real-life conditions using reformed grid natural gas and an upstream, bypassable desulfurization unit. The initial performance at 750 °C and 850 °C was similar to a SoA cell with Ni/CGO cermet anode for both types of infiltrate. Bypassing the desulfurization unit led to a much lower performance loss compared to SoA. Additionally, the cells with LSFNT anodes showed almost complete recovery of performance after stopping the exposure to sulfur, whereas the reference SoA cell experienced some degree of irreversible degradation. Based on the promising initial performance and tolerance towards failure of desulfurization units, LSFNT anodes infiltrated with non-noble electrocatalysts are attractive candidates for next generation SOFC systems.

Effect of milling time and sintering temperature on the microstructure and binder distribution of spark plasma sintered NbC-Ni cermets

Niobium carbide (NbC) based cermets are emerging as strong contenders to replace conventional tungsten carbide (WC) based cermets for applications involving abrasion and wear resistance due to their superior mechanical, physical, and chemical properties. NbC cermets with various binders have been explored in literature and nickel has emerged as a promising candidate binder material. Mechanical mixing (MM) followed by spark plasma sintering (SPS) has been shown to be one of the effective methods to synthesize NbC-Ni cermets. However, the effect of certain crucial process parameters during the MM + SPS process on the end product have not been established. To address this, the present study reports the effect of ball milling time and the effect of sintering temperature on the microstructure, binder distribution, hardness, and indentation fracture toughness of NbC – 16 vol% Ni cermets synthesized using MM + SPS. Insufficient milling time resulted in inhomogeneous binder distribution in the consolidated cermets and sintering above a certain temperature resulted in complete loss of binder. Therefore, the combination of sufficient milling time and an appropriate sintering temperature was essential to obtain a consolidated cermet with homogeneous microstructure and uniform mechanical properties.

Effect of Cr3C2 addition on the microstructure, magnetic and mechanical properties of TiC–TiN–WC–C–Ni cermets

This study explored the effect of Cr3C2 content (0, 0.5, 1, 1.5, and 2 mol%) on the microstructure, magnetic properties and mechanical behavior of TiC–10TiN–6WC–4C–(15,30) Ni (mol%) cermets after vacuum sintering. The results show that just Ti-based carbonitride ceramic grains and Ni-based binder phase were presented in the experimental cermets, and the mean size of ceramic grains reduced with the increase of Cr3C2 content. By adding Cr3C2 into cermets, the Cr concentration in binder phase obviously raised. However, Ti concentration in binder phase decreased continuously as Cr3C2 content increased, while the W concentration remained nearly constant. Saturation magnetization and remanence of cermets decreased with increasing Cr3C2 content, which was primarily ascribed to the increased amounts of antiferromagnetic Cr element in the Ni-based binder phase. When Cr3C2 content exceeded 0.5 mol%, cermets became paramagnetic at room temperature. Cermets with 15 and 30 mol% Ni had Curie temperatures of roughly 138 K and 28 K by 2 mol% Cr3C2 addition, respectively. Therefore, Cr3C2 addition is very effective in suppressing the ferromagnetism of cermets. Moreover, transverse rupture strength and hardness of cermets first raised and then declined with the addition of Cr3C2.

The effect of Mo2C additions on the oxidation resistance of (Ti,W)CN cermets as base material for the production of cutting tools

The effect of Mo2C secondary carbide on the oxidation resistance of (Ti0.93W0.07)CN0.3-20%Ni cermet was investigated using DSC-TG, isothermal oxidation, XRD, and SEM/EDS characterisations. Adding Mo2C secondary carbides to (Ti, W)CN cermets is one of the methods used for improving their mechanical properties. However, Mo2C secondary carbides bring a detrimental effect to oxidation resistance. The isothermal oxidation results of the samples at 750 °C possessing 0% and 2% MO2C follow the parabolic law, while in the samples containing 5% and 8% Mo2C, the rate of oxidation and the spallation of the oxide scale increased significantly. The thickness of the oxide layer in the cermet containing 5% of Mo2C increased three times, whereas the mass per unit area of the detached oxides in the 8% Mo2C specimen dramatically increased up to 100 times. The investigations revealed that the increase in the amount of W and Mo on the cermet material, as well as the formation of a multi-zone oxide layer, are the main reasons for oxide phase propagation.

Study on the microstructure and mechanical properties of microwave sintered NbC–Ni cermets reinforced by multilayer graphene

In recent years, NbC–Ni cermets has been proposed as a potential substitute for WC-Co cemented carbide in machining and other fields because of its economy and good performance, which has attracted extensive attention of scholars. Research on improving its mechanical properties will help to explore its application potential. Graphene-reinforced NbC–Ni cermets were prepared using a microwave sintering technique, and the effects of multilayer graphene (MLG) on its mechanical properties and microstructure were investigated. The experimental results show that the addition of a certain content of graphene contributes to the densification of the material and inhibits the grain growth. The Vickers hardness, toughness, and bending strength increased and then decreased with an increase in the MLG content. When 0.75 wt% MLG was added, the comprehensive mechanical properties of NbC–Ni cermets were optimal, with a Vickers hardness, fracture toughness, and bending strength of 1297.5 kg/mm2, 18.23 MPa m1/2, and 1464.5 MPa, respectively, which were 12.01%, 38.95%, and 18.97% higher than those without MLG. At low MLG content, the graphene sheet layers were well dispersed in the matrix grain boundaries, whereas graphene agglomerates and pores appeared in cermets with 1 wt% MLG, which degraded their mechanical properties. The strengthening and toughening mechanisms of MLG include grain refinement, large-angle deflection of cracks, crack bridging, and pullout of graphene sheet layers.

Sintering behavior of 8YSZ‐Ni cermet: Comparison between conventional, FST/SPS, and flash sintering

AbstractCermets are ceramic metal composites. The metallic phase in the cermet typically undergoes oxidation during sintering in air. Electric field‐assisted sintering processes such as field‐assisted sintering technology/spark plasma sintering (FAST/SPS) and flash involves very high heating rates, short processing time and low processing temperature. The main aim of this work was to see if field‐assisted sintering techniques can prevent the oxidation of the metallic phase in the cermet. Sintering behavior of 8YSZ‐5 wt.% Ni cermet was studied by three different techniques namely; conventional sintering, FAST/SPS and flash sintering. Phases and microstructure were analyzed through X‐ray diffraction and scanning electron microscopy, respectively. Temperature and time required for sintering the samples via FAST/SPS and flash sintering was significantly lower than that during conventional sintering. In addition, we found limited grain growth during FAST/SPS and flash sintering. During conventional sintering in reducing atmosphere (Ar and vacuum), Ni particles retained their elemental state, however the extent of densification was poor in the cermet. FAST/SPS in argon and vacuum resulted in almost complete densification (relative density > 97%) and Ni particles were retained in their elemental state in the cermet. During flash sintering in air, the samples sintered to a high densification (relative density ∼98%), however, Ni particles were completely oxidized.