Cermet Composites Research Articles

High temperature/low speed sliding wear behavior of Ni-Cr-W matrix composites against IC10 pin

Ni-Cr-W matrix cermet composites were prepared using powder metallurgical technology, and their microstructures, phase compositions, and mechanical properties were determined. Specifically, the tribological performances of the Ni-Cr-W composites were evaluated at a speed of 0.5 mm/s from room temperature to 800 °C, and their friction-reducing mechanism was clarified. The results showed that the NiCrW/Al2O3/Ag composite had the highest mechanical strength, with a 94.5 % increase in tensile strength compared to NiCrW/Al2O3. The NiCrW/Al2O3/SrCO3 composite exhibited the best high-temperature tribological performance because the chemical reaction on the friction surface generated new lubricating phases consisting of NiO, WO2, WO3, and Sr2CrO4. These acted synergistically lubricate and anti-wear with the Al2O3, Cr2O3, and NiCr2O4, and formed a continuous glaze layer on the wear surface. Furthermore, the multiple roles of nano-alumina in the obtained composite and its service in friction were discussed.

On the effects of B4C addition on the microstructure, mechanical properties, wear and thermal stability of TiCN- Co -Cr3C2-Si3N4 cermets developed by vacuum hot pressing

This paper reports the development of TiCN - Co - Cr3C2 - Si3N4 cermets modified with the addition of B4C. Cermets of three different compositions with varying B4C in TiCN - Co - Cr3C2 - Si3N4 were fabricated. The TiCN, Co, Cr3C2, Si3N4 and B4C powders in the combinations 80%TiCN-5%Co-5%Cr3C2–5%Si3N4–5%B4C; 75%TiCN-5%Co-5%Cr3C2–5%Si3N4–10%B4C; 70%TiCN-5%Co-5%Cr3C2–5%Si3N4–15%B4C were ground in a ball milling unit for six hours at a speed of 300 rpm at a ball-to-powder ratio of 10:1. The powders were then sintered in a vacuum hot press at a temperature of 1600 °C and a pressure of 50 MPa with soaking time of 90 min. For comparison purpose, 90%TiCN-5%Co-5%Cr3C2 cermet was prepared. The microstructure of the sintered cermets revealed the core-rim structure. The Vickers hardness test was done with a load of 10 Kg and for duration of 10 s. Fracture toughness was measured using the crack length data obtained from the hardness test using scanning electron microscopy. The cermet with a composition 75% TiCN-5%Co-5% Cr3C2–5% Si3N4–10% B4C produced higher hardness of 26.53 ± 0.56 GPa and fracture toughness of 10.29 ± 0.18 MPam and 70% TiCN-5%Co-5% Cr3C2–5% Si3N4–15% B4C showed high fracture toughness value of 11.23 ± 0.09 MPam with hardness value of 21.05 ± 0.10 GPa. The cermet composition 75% TiCN-5%Co-5% Cr3C2–5% Si3N4–10% B4C retained the hardness of 16.85 GPa even after annealing at 600 °C. The sintered cermets tend to form TiO2 which determines the hardness of the annealed cermets at a range of 600 °C – 1000 °C. The presence of these oxides tends to decrease the hardness. The wear test was performed taking the cermet as the pin material. The abrasive and adhesive wear mechanisms were dominant in the cermets. The harder precipitates formed tend to increase wear resistance by reducing the wear rate. The harder precipitates (TiN and TiB2) formed mainly due to the addition of Si3N4 and B4C, this addition promotes adhesive wear by a tribolayer formation.

Effects of rare earth oxide additions on the corrosion resistance of TiC-based cermets

TiC-based cermets have inadequate corrosion resistance despite wide use in high-performance applications. Rare earth dopants like Nd2O3 and Yb2O3 aim to improve cermet properties, but their impacts on corrosion are unclear. This work prepared 0.7 wt% Nd2O3- and Yb2O3-doped TiC cermets via vacuum sintering. Experimental results revealed that Nd2O3 doping enhances corrosion resistance by promoting α-FeOOH in corrosion products, while Yb2O3 doping has little effect. First-principles calculations confirmed that Nd promotes α-FeOOH formation. By elucidating contrasting dopant impacts on corrosion, this study provides new insights to guide optimization of rare earth-containing cermet compositions for superior corrosion resistance.

Outstanding mechanical and ablation resistance of C/C–ZrC–W composites prepared via slurry impregnation and reactive melt infiltration at 1500 ℃

To improve the mechanical properties and ablation resistance of Cf-reinforced ceramic-based materials, ZrC–W cermet composites (C/C–ZrC–W) were prepared in C/C preforms using slurries and low-temperature reactive melt infiltration, and their microstructure, formation mechanism, and mechanical and ablation properties were investigated. The obtained results revealed that the formation of C/C–ZrC–W composites involved the dissolution–precipitation and C diffusion processes. Owing to the precipitation of W nanoparticles in the ZrC phase and interdiffusion of W/ZrC, the fabricated C/C–ZrC–W composites exhibited superior mechanical properties with a flexural strength of 280.65 ± 12.84 MPa and fracture toughness of 13.87 ± 0.56 Mpa.m1/2. The formation of a Zr–W–O dense oxide layer resulted in the excellent ablation performance of the C/C–ZrC–W composites in oxyacetylene flame with a temperature of 2200 °C, and their mass ablation rate and linear ablation rate were 1.14 mg/s and 2.42 µm/s, respectively. The described method can be potentially used for preparing high-strength, high-toughness, and ablation-resistant materials at low temperatures.

Development of TiCN-Co-Cr3C2-Si3N4-based cermets with improved hardness and toughness for cutting tool applications

ABSTRACT A TiCN-Co-Cr3C2-based cermet, with the addition of 5wt. % and 10wt. %Si3N4 and a reference sample without Si3N4 addition were prepared by the spark plasma sintering technique. The average hardness and fracture toughness of the 90TiCN-5Co-5Cr3C2(SN00) cermet-sintered specimens were e14.85±3.11 GPa and 6.78±0.61 MPaÖm, respectively. The cermet composition 85TiCN-5Co-5Cr3C2-5 wt. % Si3N4(SN05) enhanced the hardness and fracture toughness to 20.90±0.825 GPa and 7.23±0.45 MPaÖm, respectively. Further addition of 10 wt%Si3N4 with 80TiCN-5Co-5Cr3C2(SN10) decreased the hardness value to 16.18±0.279 GPa due to a decrease in the density of defects. However, the fracture toughness steadily increased to 9.34±3.10 MPaÖm. The cermet composition 85TiCN-5Co-5Cr3C2-5Si3N4 (SN05) showed an appreciable improvement in hardness and toughness values due to the formation of a core-rim structure, with the core consisting of TiCN and the rim with TiN, TiO2, TiSi, Co2C, CrN and Cr2Si.

Increase of specific interfacial coherence in nanocrystalline ceramic-metal composites

A new strategy to establish a large number of interfacial coherence in nanocrystalline multi-phase composites was proposed. The route consisting of amorphization, crystallization and in-situ reaction was demonstrated using WC-Co composites as a typical example. Characteristics of crystal nucleation, growth crystallography, and phase transformation were studied in detail on the atomic scale for the ceramic grains. Mechanisms for the formation of specific interfacial coherence in the prepared nanocrystalline ceramic-metal composites were disclosed. Assisted by the interfacial coherence, the continuity of local deformation is maintained from metal to ceramic phase, resulting in a uniform strain extension instead of stress concentration at the interfaces. The present nanocrystalline composite achieved outstanding mechanical properties with simultaneously high hardness and fracture toughness. The findings in this work provide new insights to tailor grain structure and interface relationship in cermet composites for superior comprehensive mechanical performance.

Technological features of the synthesis of heat- resistant ceramics in the NiO‒YSZ system with the possibility of using additive technology

Technological aspects of the synthesis of heat-resistant ceramics in the NiO‒YSZ system through an oxidizable nickel-based cermet composite, including testing the use of additive synthesis technology, which makes it possible to obtain products of complex shape, have been studied. Based on the results of the synthesis, the key functional characteristics of the materials were determined. In particular, it was found that the process of oxidation of prototypes is accompanied by an increase in the volume of ceramics by about 10 %. Ill. 10. Ref. 13.

Tribological behavior of NiCrW-based self-lubricating composites against IC10 alloy under high temperature and extremely slow sliding speed

NiCrW-Al2O3-SrCO3-Ag cermet composites were prepared, and the sintering properties, microstructure, mechanical properties and tribological behaviors of the composites were investigated. The results show that the composite with 5 wt% SrCO3 and 5 wt% Ag has the best friction and wear properties in a wide temperature range, which is attributed to the synergistic lubrication and antiwear role of the newly generated phases such as Sr2CrO4, NiO and WO2 caused by the chemical reactions and the inherent phases, e.g. Ag, NiCr2O4, Al2O3 and Cr2O3. The grain refinement, deformation and stress absorption of the wear track subsurface structure increase gradually under the coupling action of temperature and friction shear force, making high and low temperatures exhibit different wear mechanisms.

Microstructure, interfacial characteristics, and wear performances of Cu–Fe–SiC cermet composites

AbstractThe Cu–Fe metal‐based ceramic grinding wheel material with SiC as abrasive was prepared by the powder metallurgy process of ball milling and hot pressing sintering. Cu–Fe–SiC cermets with Cu:Fe mass ratios of 4:1, 1:1, and 1:4 were designed by changing the composition of metal binder. The phase composition, microstructure, mechanical properties, and grinding properties of Cu–Fe–SiC cermets were systematically studied. The effect of Cu–Fe binder ratio on the microstructure and properties of cermets was analyzed. The results show that with the increase of Fe content, the density and hardness of cermets increase gradually, indicating that the mechanical properties are improved. Because the Fe in the adhesive can react with the abrasive SiC to form the reaction bonding interface, the Cu–80Fe–SiC cermets with higher Fe content have better adherence. The grinding test results of Cu–80Fe–SiC cermet show that the friction coefficient is .341, the surface roughness is 6.64 μm, the residual stresses parallel to the grinding direction are 353.3 MPa, and the residual stresses perpendicular to the grinding direction are 140.9 MPa. With the increase of Fe content, the wear mechanism changes from ploughing and cutting to friction.

Reaction Behavior and Formation Mechanism of ZrB2 and ZrC from the Ni-Zr-B4C System during Self-Propagating High-Temperature Synthesis

Self-propagating high-temperature synthesis (SHS) is a good way to prepare ZrB2-ZrC/metal cermet composites. In this work, ZrB2-ZrC/Ni cermet composites with various Ni contents were successfully fabricated by SHS using the Ni-Zr-B4C system. The effects of Ni content and particle size of the B4C powder on the SHS reaction were investigated. The results indicated that with an increase in Ni content, the adiabatic temperature, maximum combustion temperature, ignition delay time, and ceramic particle size in the product all showed a gradually decreasing trend. The SHS products and the ignition of the SHS reactions were significantly dependent on the B4C particle size. The formation mechanism of ZrB2 and ZrC during SHS from the Ni-Zr-B4C system was proposed based on the combustion wave quenching experiment.

Vanadium (oxy)nitride as a new category of anode for direct ammonia solid oxide fuel cells cells

Ammonia (NH3) is considered a potential energy carrier to be used as a fuel in energy conversion devices, such as solid oxide fuel cells (SOFCs). Nonetheless, in the presence of NH3, traditional Ni-containing anodes may suffer from poor chemical stability, resulting in its partial conversion to nickel nitride. We, therefore, propose a new composite anode for direct ammonia solid oxide fuel cells made of a metallic conducting phase, vanadium (oxy)nitride (VON), and an oxygen-ion conducting phase, (ZrO2)0.92(Y2O3)0.08 (YSZ). X-ray diffraction (XRD) reveals that the VON material is chemically compatible with YSZ. Good thermal stability was also shown under reducing conditions by thermogravimetry (TGA). Electrochemical impedance spectroscopy (EIS) showed that peak performing composition is composed of 50:50% vol of VON:YSZ at 850 °C, yielding comparable performance to that of previous reports on traditional Ni-YSZ cermets. The electrode mechanism under NH3 fuel was found to be similar to that of traditional Ni-based cermet compositions using hydrogen fuel, due to the predicted thermal decomposition of ammonia under the studied operation temperatures, i.e., ≥650 °C, while sensitivity to flow rate considerations was also highlighted. To the best of our knowledge, this work reports a completely new category of anodes for SOFC applications.

Cermet nuclear waste forms: Phase identification and connectivity

A cermet material is by design a microscopically heterogeneous composite wherein a ceramic phase coexists with a metal phase. One of the propositions of this combination is to improve decay heat removal from the ceramic phase if this material type is used as a nuclear waste form; the ceramic phase consisting primarily of long-lived, beta-radiation-emitting oxides from nuclear fission products. Intuitively, heat removal improves if more of the metal phase is added and if it is also the continuous phase (connected) while the oxide phase is dispersed; the latter stands immobilized by a protective metal barrier. Therefore both phase identity and connectivity are necessary to evaluate the thermo-chemical-mechanical properties of a cermet; chemical composition alone is not sufficient. Assuming the cermet composite is chemically durable, the central question arises: where are the oxide and metal phases spatially located after the material has been processed in its final form? This work describes the usage of computer-aided analysis of energy-dispersive x-ray elemental maps to identify the oxide and metal phases, and compute its connectivity. We use two-dimensional slices of processed cermet pellets, therefore it is a destructive analysis. All pellets were manufactured with 75 wt% of metal former elements and 25 wt% of oxide formers typical of nuclear waste compositions. We determined that all samples consist of four micro-phases, namely, metal, oxide, metal-oxide overlap (or solution), and apparentvoid (or lost due to numerical approximations) phases. The computed area fraction for the micro-phases decreases in the order: metal, oxide, metal-oxide and void. The metal phase is shown to be the continuous phase while the others, discontinuous. However in one sample, there is an overlap of oxide formers and metal formers which could lead to a loss of immobilization barrier and thermal conduction path. A follow-up study demonstrates that these samples are likely thermally anisotropic.

Binder-jetting of TiCN-based cermets

ABSTRACT Additive Manufacturing is experiencing an upswing in many sectors of industry for a broad variety of materials. Processes are mainly developed for polymers and metals. For ceramics, hardmetals and especially cermets there are only a few additive processes suitable. The powder-based technique Binder-Jetting is one of these suitable processes with high productivity and relatively low green density. Within this study, TiCN-based cermets are printed by Binder-Jetting for the first time. The complexity of influences of the morphology and composition of cermet powders are discussed in regard to bulk density and material properties of printed and sintered parts. Studied TiCN-based cermet compositions represent different Ni and Mo2C contents. Main points of this investigation are further the adjustment of ratio of the raw materials for good sintering behaviour and their influence on the microstructures and as a function of varied sintering temperatures.

Preparation, microstructure and performance of interference microwave absorbing cermet composites with frequency–selective screens

Interference microwave absorbing cermet composites with frequency–selective screens (AC/FSS) were successfully prepared by sintering a ceramic green body embedded with stainless–steel wire mesh screens via a rapid heating method. The addition of the screens made the AC/FSS composites increase slightly in density and open porosity and remain unchanged in surface Vickers hardness and compressive strength. Both the number and structure parameters of the screens had a significant effect on the microwave absorbing performance of the AC/FSS composites. The weak microwave absorption by the small amount of zinc oxide and poor microwave interference by the single–layer screen made the AC/FSS composites possess modest microwave absorbing performance. Moreover, the AC/FSS composites showed an improved microwave absorbing performance due to the significantly enhanced microwave interference by the double–layer screens. By optimizing the structure parameters of the upper and lower screens, the AC/FSS composites with double–layer screens possessed surprisingly good microwave absorbing performance with the whole reflectivity–versus–frequency curve below −10 dB, a mean reflectivity as low as −12.9 dB and the lowest reflectivity of −15.2 dB at 12.4 GHz in the 8.0–18.0 GHz frequency range.

Features of microstructure and thermoelectric properties of the cermet composites based on grained Bi2Te3 matrix with locally-gradient Ni@NiTe2 inclusions

Starting Bi2Te3 and Ni powders were spark-plasma-sintered (SPS) to prepare thermoelectric cermet composites consisting of thermoelectric Bi2Te3 matrix with different content, x, of ferromagnetic Ni filler (x = 0.00, 0.50, 0.85, 1.25 and 1.50 at. %). Grained Bi2Te3 matrix of composites is texturing under sintering. Texturing degree is x-dependent that is attributed to ability of Ni particles act as lubricant. New trigonal NiTe2 phase is formed under SPS-process. The Ni and NiTe2 phases correspond to filler Ni@NiTe2 (“core”-“shell”) inclusions. Forming these inclusions is originated from chemical interaction between Bi2Te3 and Ni during SPS-process. A Ni→NiTe2 reaction is accelerated with increasing x that results in growing Ni@NiTe2 inclusions and increasing fraction of shell. Thermoelectric properties of composites are x-dependent that is due to non-monotonic changes in texturing degree, size of the inclusions and concentration of majority carriers with increasing x. Thermoelectric figure-of-merit of composites is remarkably enhancing as compared to that of Bi2Te3 matrix.

Electrical percolation behavior and microstructure fractal characterization of graphite reduced hot-pressing Cu/Cu2O cermet composites

Electrical percolation behavior and microstructure fractal characterization of graphite reduced hot-pressing Cu/Cu2O cermet composites

Abrasion and Erosion Resistance of Cermets: A Review.

WC-based hardmetals are employed widely as wear-resistant ceramic–metal composites for tools and wear parts. Raw materials supply, environmental concerns and some limitations of hardmetals have directed efforts toward development of alternative wear-resistant composites–cermets. We present a current state of knowledge in the field of ceramic-rich (≥50 vol%) cermets behavior in abrasion and erosion conditions, which are the dominant types of wear in many industrial applications. Distinction is made between two-body and three-body abrasion, solid-particle erosion, and slurry erosion. Cermets, in particular TiC-, Ti(C,N)- and Cr3C2-based composites and hardmetals, are compared for their abrasive and erosive wear performance and mechanism. The review enabled formulation of tribological conditions in which cermets may be comparable or have potential to outperform WC-Co hardmetals. Hardmetals, in general, outperform cermets in abrasion and solid-particle erosion at room and moderate temperatures. However, cermets demonstrate their potential mainly in severe conditions—at elevated temperatures and corrosive (oxidation, electrochemical corrosion) environments.

Ultrafast high-temperature sintering to avoid metal loss toward high-performance and scalable cermets

•Cermets were achieved by an UHS method •Our UHS method can inhibit the metal volatilization for high material quality •Our UHS method can sinter a range of cermet compositions, shapes, and sizes •This approach potentially expands the application of cermets in various fields Cermets embrace the high hardness of a ceramic and the good ductility of a metal. Therefore, they potentially meet the ever-increasing demands of new materials for harsh environments in energy generation and conversion. However, cermet sintering faces many challenges, such as metal volatilization, grain coarsening, and poor wettability of the metal with the ceramic, which affect the microstructure and thus mechanical properties. Herein, we apply an ultrafast high-temperature sintering (UHS) method to sinter cermets at a high temperature in only seconds. The high temperature leads to good wettability of the metal with the ceramic, while the short sintering time limits the loss of metal components and accurately controls the grain growth. We demonstrate the UHS method using a model cermet composed of a Ni-based superalloy and aluminum oxide, where we obtain dense microstructure, minimal nickel loss, and uniform grain size. Owing to these merits, good mechanical properties and oxidation resistance are achieved. Cermets embrace the high hardness of a ceramic and the good ductility of a metal. Therefore, they potentially meet the ever-increasing demands of new materials for harsh environments in energy generation and conversion. However, cermet sintering faces many challenges, such as metal volatilization, grain coarsening, and poor wettability of the metal with the ceramic, which affect the microstructure and thus mechanical properties. Herein, we apply an ultrafast high-temperature sintering (UHS) method to sinter cermets at a high temperature in only seconds. The high temperature leads to good wettability of the metal with the ceramic, while the short sintering time limits the loss of metal components and accurately controls the grain growth. We demonstrate the UHS method using a model cermet composed of a Ni-based superalloy and aluminum oxide, where we obtain dense microstructure, minimal nickel loss, and uniform grain size. Owing to these merits, good mechanical properties and oxidation resistance are achieved.

Effect of spark plasma sintering temperature on microstructure and thermoelectric properties of the cermet composites consisting of Bi2Te2.1Se0.9 matrix and Co@CoTe2 inclusions

Novel cermet Bi2Te2.1Se0.9+0.33 ​wt% Co composite has been prepared via spark plasma sintering (SPS) the starting Bi2Te2.1Se0.9 and Co powders at different SPS-temperatures (TS ​= ​598, 623, 648 and 673 ​K). During the sintering, initial Co inclusions transform into final filler Co@CoTe2 (“core”-“shell”) inclusions, randomly distributed inside textured grained Bi2Te2.1Se0.9 matrix. Forming these inclusions is originated from high-temperature chemical interaction between Bi2Te2.1Se0.9 and Co. Main features in microstructure and thermoelectric properties of the cermet composite found with increasing TS are: (i) a texturing degree of grained Bi2Te2.1Se0.9 matrix gradually decreases that is attributed to reducing in ability of initial nanometer Co particles to act as lubricant; (ii) a fraction of the Co core decreases, and a fraction of the CoTe2 shell increases that is related to acceleration of Co→CoTe2 reaction at higher temperatures; (iii) the specific electrical resistivity and the Seebeck coefficient reduce, whereas the total thermal conductivity increases that can be originated from growth of electron concentration due to local Co doping. Highest value of the thermoelectric figure-of-merit equal to ∼0.8 was observed for the composite, SPS-treated at 673 ​K.

Fabrication and characterization of FeCoNiCrMn,(Al) high entropy alloy based (Ti,Ta,Nb)(C,N) cermet

From nanostructured mechanically synthesized powder a set of FeCoNiCrMn,(Al) based (Ti,Ta,Nb)(C,N) cermets were fabricated and sintered by a pressureless procedure. Highly dense cermets were obtained, and the nature of chemical change, microstructure, mechanical properties and coarsening kinetic of ceramic phase were characterized by image analysis, microindentation, scanning electron microscopy and X-ray diffraction. The design of the material was performed using a set of three different chemical cermet composition and three different sintering temperatures, or comparative purposes.