Cermet Phase Research Articles

Evolution mechanism of Ti(C,N)-based cermet microstructure under microwave sintering

Experimental studies of microwave-sintered cermets were carried out at different sintering temperatures and holding times to investigate their microstructure evolution mechanism. Results of the study show that: (1) As sintering temperature increases, main microstructure evolution mechanisms of cermets are as follows: metal-phase melting, hard-phase skeleton filling of large pores in hard-phase skeletons, secondary rearrangement of the liquid phase (the liquid phase gradually fills the space between grains), and cooling down (precipitation–crystallization–reattachment); (2) As holding time increases, main microstructure evolution mechanisms of cermets are as follows: complete filling of large pores in the hard-phase skeleton, secondary rearrangement of the liquid phase, intense dissolution precipitation enhancing the formation of core-rim phase, and secondary homogeneous arrangement of the liquid phase. The special electromagnetic effects of microwave-sintered cermets and their influence on the sintering process were analyzed. It was found that both tip-discharge effect and hot-spot effect occurring during the microwave sintering process are conducive to the sintering process. The formation process of core-rim phase of cermets was also studied. Results show that: (1) Cermets form black core–white rim–grey rim structure via dissolution–precipitation and precipitation–crystallization phenomena; (2) Cermets form white core–grey rim structure through agglomeration of small particles, dissolution–precipitation, and precipitation–crystallization phenomena.

Effect of laser power on the microstructure and corrosion resistance of laser cladding Mo2NiB2 coatings

In this study, Mo2NiB2 coatings were prepared by the laser cladding technique and the relationship between coating microstructure and corrosion resistance with cladding power was analyzed. The results showed that Mo2NiB2 was reactively generated in all coatings while Mo2FeB2 and (Fe, Ni) were also present in the coatings due to dilution of the substrate. There was a good metallurgical bond between the coating and the substrate. The white cermet phase and black Fe-rich phase alternated within the coatings. As observed from the surface, the ceramic phase spreads out in a flattened shape and the black Fe-rich phase was present in a large number of pores. Due to the overdilution of the substrate, the volume of the ceramic phase decreased at a power of 800 W and the Fe content within the coating increased. The corrosion resistance of the coatings increased as the laser power increased from 500 to 700 W. Then the corrosion resistance of the coatings decreased at 800 W due to the excess Fe content and the decrease in the relative content of Mo2NiB2 and (Fe, Ni). Mo2NiB2 coating prepared at 700 W has the best corrosion resistance.

Preparation and Evaluation of Hardness and Wear Properties of WC-Co Particulates Reinforced 7075Al Composites

Aluminium matrix composites (AMCs) have found uses in aircraft, rocket engineering, vehicle engineering, energy sector, infrastructure areas, marine and military applications, sports and recreation utilization because of its enormous mechanical strengths and sensible wear resistance features. The experimental results of 7075Al-WC-Co composites’ mechanical and tribological properties are provided in this article. The matrix is Al7075 and the reinforcement is planetary ball milled WC-Co in cermet form with particulates size range from 30-40 μm. Liquid metallurgy route was followed to develop 7075Al composites reinforced with 6, 9 and 12 wt.% of WC-Co. The tests were carried out on 7075Al and composites in accordance with ASTM specifications. According to the experimental results, the hardness of 7075Al-WC-Co composites is discovered to be raised by increasing the percentage volume of cermet phase. Wear attributes of the WC-Co containing composite were superior in terms of wear resistance. The manufactured composites were characterized using SEM and EDAX. Worn surface of the composite samples are studied before and after wear test.

The Microstructure Evolution Process and Flexural Behaviours of SiC Matrix Ceramic Infiltrated by Aluminium Base Alloy.

In this paper, an infiltration approach was proposed to generate a Ti3Si(Al)C2 transition layer in SiC matrix composites to effectually strengthen SiC ceramics. The infiltration temperature played a significant role in the evolution of the microstructure, phase composition, and flexural behaviours. Molten aluminium base alloy fully penetrated SiC ceramic after infiltration at different experimental temperatures (800–1000 °C). The phases in the reaction layer on the surface of SiC ceramic samples varied with the infiltration temperature. When infiltrated at 800 °C, only SiC and Al phases can be found in SiC composites, whereas at 900 °C, a reaction layer containing Ti3Si(Al)C2 and SiC was produced. The Ti3Si(Al)C2 phase grew in situ on SiC. At 1000 °C, the Ti3Si(Al)C2 phase was unstable and decomposed into TiC and Ti5Si3. The cermet phase Ti3Si(Al)C2 was synthesized at a relatively low temperature. Consequently, the flexural modulus and three-point bending strength of samples infiltrated at 900 °C was enhanced by 1.4 and 2.4 times for the original SiC ceramic, respectively.

Performance of membranes based on novel Ce0.8Sm0.2O2-δ /Ag cermet and molten carbonates for CO2 and O2 separation

• SDC-Ag cermets exhibit outstanding wettability against molten carbonates. • Cermet shows metallic-like electrical conductivity; therefore, σ cermet ≫σ MC. • The cermet phase shows no degradation induced by molten carbonates. • Simultaneous CO 2 and O 2 separation are achieved for the long-term test. This work proposes a cermet infiltrated with a mixture of Li 2 CO 3 /Na 2 CO 3 /K 2 CO 3 as a dense membrane to selectively separate CO 2 and O 2 at high temperatures. The cermet consisted of a mixture of the Ce 0.8 Sm 0.2 O 2-δ (SDC) ceramic and silver as the metallic phase. This type of membrane is a novel design of the ceramic/carbonates type and represents an improvement of state-of-art designs by avoiding microstructural changes in the metallic phase and improving chemical inertness and wettability with the carbonate phase. First, an SDC nanostructured powder was chemically synthesized by direct combustion of urea: lanthanide nitrates-based deep eutectic solvent; then, SDC and silver powders were mixed in a 50:50 vol% ratio by using high energy ball milling. The mixture was uniaxially pressed and sintered to form a support. This cermet exhibited excellent wettability properties against the ternary molten carbonate phase; therefore, it readily allowed infiltration of the molten salts to form a dense membrane. Hence, the cermet showed excellent electronic conductivity as well as corrosion resistance in contact with carbonates for 200 h of continuous immersion. The cermet-carbonate membrane showed permselectivity by separating CO 2 and O 2 at high temperatures. It reaches simultaneous permeation values of 0.49 and 0.26 ml·min −1 ·cm −2 , for CO 2 and O 2, respectively, at 850 °C. Finally, continuous permeation tests at 825 °C for 85 h proved the excellent chemical stability of the cermet-carbonate membrane. Any chemical reactivity was not observed between the cermet and the carbonates.

First-principles predictions of electronic, elastic, and optical properties of ScBC and YBC ternary cermet phases

In order to better understand the physical properties and provide theoretical support for the applications of ScBC and YBC ternary cermet phases, the electronic, elastic, optical and phonon properties of ScBC and YBC were calculated by the first-principles calculations. ScBC and YBC were thermodynamically and dynamically stable based on the formation enthalpies and phonon dispersions. The charge density difference and bond population showed that B-2s, 2p and C-2s, 2p states were hybridized to form stronger B–C covalent bonds in ScBC and YBC. The calculated elastic properties indicated that these ternary ceramic phases are brittle and elastic anisotropic with the elastically anisotropic order of ScBC > YBC. Finally, the optical properties, including the dielectric function, reflectivity and absorption coefficient, were investigated, and the results showed that YBC and ScBC have optical anisotropies.

Structural-phase surface composition of porous TiNi produced by SHS

The study aimed to characterize the structural-phase composition of the porous SHS TiNi surface explored by the GIXRD method. The surface layers at a depth of up to 100 nm mainly consist of amorphous nanocrystalline intermetallic oxycarbonitrides Ti4Ni2(O, N, C) with nonmetallic inclusions of different structural variants and routes of origin. Fine-porous alloys were synthesized at ignition temperatures of 450 °C–480 °C. A distinct feature of the surface of crystalline phases therein was shown to be a low degree of crystallinity (up to 40%) and presence of multifarious glass and cermet phases evident as NiSi2, NaAlSiO (SO4), SiO2, MgSi2, and CaCO3. Conversely, large-pore alloys ignited at temperatures of 280 °C–330 °C have a higher degree of crystallinity (up to 70%). An individually selected GIXRD technique and precision structural phase analysis are capable to determine a set of other superficial nonmetallic and cermet phases reported as CaTiO3, Si (P2O7), CaSiO3, MgAl2O4, TiNiAl, as well as the Ti3SiC2MAX phase.

A comparative study on microstructure and properties of Ti(C,N)-based cermets with the various Cr doping methods

In this work, the effects of chromium doping methods on the microstructures and properties of Ti(C,N)-based cermets were investigated systematically. The results showed that the existence state of Cr element in the cermet was influenced by the different doping methods. The additive pure Cr powders might cause the appearance of Cr particles and solutions in the binder phase of cermets. However, with the addition of NiCr powders, the Cr element might distribute in the binder phase of cermet. The Cr3C2 addition could make Cr element disperse in the rim and binder phase. Moreover, the Cr atoms dissolved into binder phase might have the solid solution strengthening effect on the binder phase, which increased the hardness of cermets. The Cr element in binder phase could improve the oxidation resistance of cermets owing to the existence of chromium oxide layer in the internal oxidation region. Furthermore, the diffusion process of Mo atoms to the surface during oxidation was prevented by the dissolved Cr element in the binder phase, which led to the increased bonding strength between oxidation layer and unoxidized substrate. In addition, a larger amount NiCr powder addition had the excellent reinforcing effect on the corrosion resistance of cermets due to the appearance of stable chromium oxide film on the binder phase.

Reducing the Metal Content in PCD Polycrystalline Diamond Layer by Chemical and Electrochemical Etching

This article is devoted to investigating polycrystalline diamond compacts (PDCs), which find broad application in drilling, tool-and-die, and building branches of industry. They are a complex composition of diamond and cermet phases. The diamond phase consists of diamond grains of various granulometric compositions and shapes and forms a strong hard skeleton. A cermet phase serves as a binder. The presence of catalyst metals in a diamond layer of bilayer PDC composite materials lowers their operational properties, because the difference in thermal expansion coefficients between diamond grains and catalyst can lead to material cracking in the cutting process, while a high temperature when fabricating the diamond tool and its operation in the cutting zone can lead to the reverse diamond–graphite phase transition. In order to increase wear-resistance characteristics of diamond PCD composites formed using catalyst metals (cobalt and tungsten), etching of metals from the surface of the tool working zone is performed by two methods, notably, electrochemical and chemical. Electrochemical etching is performed in sulfuric acid with various current modes and concentration, and chemical etching is performed in a mixture of hydrochloric and nitric acids and a mixture of fluoric and nitric acids. The distribution of the chemical composition over the depth of PCD samples after etching is performed using scanning electron microscopy. It is established that electrochemical etching is more active kinetically, while chemical etching is promising for industrial application. Abrasive tests of PCD samples before and after etching show the absence of a noticeable effect of both electrochemical and chemical etching of their abrasive ability.

Fabrication and wear mechanism of Ti(C,N)-based cermets tools with designed microstructures used for machining aluminum alloy

In this work, microstructure of Ti(C,N)-based cermets can be designed and controlled with extra carbon additions. The influences of microstructure on the mechanical properties and wear mechanism of cermets tools are investigated systematically by scanning electron microscope, X-ray diffraction and machining test of 7075 aluminum alloys. The increasing carbon additions in cermets can react with alloy elements dissolved in binder phase of cermets and promote the formation of rim phase, which may induce the disappearance of Co3W3(C,N) phase (η phase), reduction of core phase content and increase of rim phase content. With increasing carbon additions, the hardness of cermets decreases slightly, while transverse rupture strength of cermets can increase firstly and then decrease. Moreover, increasing carbon additions can augment the friction coefficient of Ti(C,N)-based cermets, which may induce improvement of cutting temperature and aggravation of abrasion at a relatively low cutting speed. However, with increasing cutting speeds, the existence of Co3W3(C,N) phase in cermets tools can accelerate wear process of tools.

Improvement in microstructure and properties of Ti(C,N)-based cermets with Ruthenium additions

The effects of additive Ru powders on the microstructure, mechanical properties, abrasion resistance and corrosion resistant of Ti(C,N)-based cermets manufactured by sinter-HIP treatment are investigated systematically by scanning electron microscope, transmission electron microscope, machining test and electrochemical method. The additive Ru elements in cermets can diffuse into the binder phase of cermets, which can refine Ti(C,N) grains, reinforce binder phase of cermets through solution strengthening mechanism, and improve the mechanical properties of cermet significantly. The Ti(C,N)-based cermets with 1.0 wt% Ruthenium addition can possess the excellent hardness of 92.6 HRA, fracture toughness of 9.11 MPa m1/2 and transverse rupture strength of 2806 MPa. Moreover, the existence of Ruthenium in binder phase can enhance abrasion resistance of cermets, reduce wear rate of cermets cutting tools, and increase the lifetime of tools obviously. In addition, the addition of 0.5 wt% Ruthenium in cermets may inhibit the dissolution process of binder phase in hydrochloric acid solution and improve the corrosion resistant of cermets.

Ti(C,N)-Based Cermets: Critical Review of Achievements and Recent Developments

The paper describes briefly the historical development and presents in more detail solid-state properties such as hardness, heat conductivity, thermal expansion and mechanical properties of titanium carbonitride Ti (C,N), the basis of the hard phase of cermets. The metallurgy of Ti (C,N)-based cermets with respect to microstructure formation during sintering and the impact on properties are presented in more detail. The various influences such as W and/or Mo content, Mo/W ratio, C content and C/N ratio, binder phase content and binder phase composition (Co/Ni), sintering time, dwell time, alloy state of powders and grain size were critically evaluated and are presented in form of fracture toughness vs. hardness graphs. A table gives a reference list on the study of these influences. TRS data on cermets were collected and summarised in a separate table, too. The focus is put on grades which have the potential of being fabricated soon in industrial processes for production of cermet tools. Application examples for metal cutting, sawing and chip bonding are presented. In two final sections recent modifications and achievements such as graded microstructures, multicomponent binder, and hybrid microstructures are also briefly presented together with an outlook on the future potential of cermet applications.

Distributed microcracking process of WC/Co cermet under dynamic impulse compressive loading

Cermet Materials (CM), for example, WC/Co, have very good mechanical, thermal and wear properties. They are used for manufacturing of cutting tools. However, their behavior under dynamic loads is still not properly understood.Experiments, e.g. Siegl and Fischmester (1988) and Ravichandran (1994), indicate that the fracture energy of WC/Co is expended through ductile failure of the Co: (1) close to the binder/tungsten carbide interface (Liu et al., 2017) [64] or by (2) dimple rupture across the interphase (Sigl and Exner, 1987) [22]. Stress concentrations around grain boundaries lead to initiation of microcracks which are dispersed by dynamic loading.The main goal of the paper is to investigate the previously formulated models of the two-phase composite (Sadowski et al., 2005, 2006, 2007; Dębski and Sadowski, 2014, 2017) [47–51] in the case of dynamic compressive pulses that are common in the case of cutting tools. We have taken into account complex spatial distribution of cermet phases, grain/binder interfaces modeled by interface elements, possibility of cracks appearance within binders using interface elements as well, and rotation of brittle grains.The obtained results show that microcracking process and stress distributions are different for quasi-static and dynamic loadings. Early development of microcracks distribution revealed by damage parameter was observed.

REDUCING METAL CONTENT IN PCD POLYCRYSTALLINE DIAMOND LAYER BY CHEMICAL AND ELECTROCHEMICAL ETCHING

The paper is dedicated to the study of PDC (polycrystalline diamond compact) diamond composites, which are widely used in drilling, tool and construction industries. They constitute a complex composition of diamond and cermet phases. The diamond phase consists of diamond grains of various grain-size compositions and shapes, and forms a strong, solid scaffold. The cermet phase acts as a binder. The presence of catalyst metals in the diamond layer of PDC two-layer composites deteriorates their performance properties, since the difference in the coefficient of thermal expansion between diamond grains and the catalyst can lead to material cracking during cutting, and the high temperature during the manufacture of the diamond tool and its utilization in the cutting area can lead to the reverse diamond-graphite phase transition. The paper describes the process of metal etching from the surface of the tool working area by two etching methods: electrochemical and chemical, for the purpose of improving wear characteristics of PCD diamond composites obtained using catalytic metals (cobalt and tungsten). The electrochemical etching was carried out in sulfuric acid under various current regimes and concentration; chemical etching was carried out in a mixture of hydrochloric and nitric acids and in a mixture of hydrofluoric and nitric acids. Post-etching in depth distribution of chemical composition in PCD samples was studied using the scanning electron microscopy. It was established that electrochemical etching was kinetically more active, and chemical etching was promising for industrial applications. The abrasive tests of PCD samples carried out before and after the etching showed no significant effect of both electrochemical and chemical etchings on their abrasive property.

Magnetization of TiC–10TiN–xMC–yNi (MC = Mo2C, WC) cermets

Magnetization of TiC–10TiN–xMC–yNi (MC=Mo2C, WC, x=0, 2, 4, 6, 8mol%, and y=20, 40mol%) cermets was investigated. Room-temperature (RT) saturation magnetization Ms. of Mo2C-containing cermets decreased non-linearly with increasing x, and it tended to zero at x=8 for y=20 and x≥6 for y=40. At x=8, Curie temperature Tc of Mo2C-containing cermets was about 50K for y=20 and 116K for y=40, respectively. RT Ms. of WC-containing cermets initially decreased, then increased and decreased again with increasing x, and it had the minimum at x=4, which was about 6.12emu/g for y=20 and 10.16emu/g for y=40, respectively. At the same x and y, Mo2C-containing cermets had lower RT Ms. than WC-containing cermets. The strong suppression effect of Mo2C addition on magnetization of TiC–TiN–Ni cermets, in comparison with WC addition, was mainly attributed to high solubility of Mo2C in Ni-based binder phase of cermets.

The importance of phase purity in Ni–BaZr0.85Y0.15O3−δcermet anodes – novel nitrate-free combustion route and electrochemical study

A novel, nitrate-free, combustion method has been developed to prepare Ni–BaZr0.85Y0.15O3−δ (Ni–BZY) cermet anodes for proton ceramic fuel cells. Nickel acetate and 30% H2O2 were used as starting precursors for the combustion reaction into which pre-prepared BZY powders were dispersed. The advantages of this nitrate-free combustion method have been demonstrated by comparison to a more common nitrate/glycine combustion route. The results demonstrate that use of the nitrate-free precursors is essential to avoid partial decomposition of the pre-prepared BZY phase. Employment of the more common nitrate-based precursors, due to their acidic nature, results in removal of Ba from the perovskite phase and formation of Ba(NO3)2, subsequently leading to the presence of BaY2NiO5 in the final product. The impact of Ni–BZY phase purity on resultant polarisation behaviour has been assessed as a function of water vapour and oxygen partial pressures for electrodes of comparable microstructure. Partial decomposition of the perovskite phase limits performance by increasing the higher frequency polarisation resistance and this phenomenon is suggested to be associated with impaired proton transport in the oxide cermet phase. The novel actetate–H2O2 combustion method here described may be of interest for the formation of other ceramic oxide materials, offering economical advantages over more classical nitrate-based combustion routes, as well as significant environmental benefits due to the avoidance of releasing NOx gases.

High-temperature mechanical properties of reduced NiO–8YSZ anode-supported bi-layer SOFC structures in ambient air and reducing environments

This paper describes a study of the mechanical properties of the bi-layer half-cell structures of solid oxide fuel cells (SOFCs) at elevated temperatures in both ambient air and reducing environments. Half-cells with a thin, dense electrolyte layer of 8YSZ, supported by a thick, porous NiO–8YSZ anode precursor structure, were reduced in a gas mixture of 5% H2–95% Ar at 800°C for selected time periods of up to 8h. The development of the essential porous microstructure when forming the Ni–8YSZ anode cermet phase and its resulting effects on the equibiaxial strength, hardness and elastic properties of the half-cell structure were investigated in detail. Two sets of samples with different anode thicknesses were studied simultaneously to determine the effects of anode thickness on the SOFC structure's mechanical properties. The results were analyzed in relation to the porosity and composition of the samples.

Studies on phase formation, microstructure development and elastic properties of reduced NiO–8YSZ anode supported bi-layer half-cell structures of solid oxide fuel cells

Half-cell structures of solid oxide fuel cells (SOFCs) with a thin and dense electrolyte layer of 8YSZ supported by a thick and porous NiO–8YSZ anode precursor structure were reduced in a gas mixture of 5% H2–95% Ar at 800°C for selected time periods in order to fabricate cermets with desired microstructure and composition, and to study their effects on the elastic properties at ambient and reactive atmospheres. It appears that 2h of exposure to the reducing conditions is enough to reduce ∼80% of NiO with an enhanced porosity value of 35%. The Ni–8YSZ cermet phase formation in the anode was analyzed with X-ray diffraction (XRD) in correlation with its microstructure. The elastic properties were determined after the reduction, at room and elevated temperatures using the impulse excitation technique. At room temperature the decrease in the Young's modulus was about 44% (after 8h of reduction) and can be attributed mainly to the changes in the microstructure, particularly the increase in porosity from ∼12% to 37%. Young's moduli of the as-received precursor and reduced anodes were evaluated as a function of temperature in air and reducing atmosphere. The results were explained in correlation to the initial porosity, composition and oxidation of Ni at the elevated temperatures.

Microstructure analysis and wear behavior of titanium cermet femoral head with hard TiC layer

Titanium cermet was successfully synthesized and formed a thin gradient titanium carbide coating on the surface of Ti6Al4V alloy by using a novel sequential carburization under high temperature, while the titanium cermet femoral head was produced. The titanium cermet phase and surface topography were characterized with X-ray diffraction (XRD) and backscattered electron imaging (BSE). And then the wear behavior of titanium cermet femoral head was investigated by using CUMT II artificial joint hip simulator. The surface characterization indicates that carbon effectively diffused into the titanium alloys and formed a hard TiC layer on the Ti6Al4V alloys surface with a micro-porous structure. The artificial hip joint experimental results show that titanium cermet femoral head could not only improve the wear resistance of artificial femoral head, but also decrease the wear of UHMWPE joint cup. In addition, the carburized titanium alloy femoral head could effectively control the UHMWPE debris distribution, and increase the size of UHMWPE debris. All of the results suggest that titanium cermet is a prospective femoral head material in artificial joint.

Evaluation of elastic properties of reduced NiO-8YSZ anode-supported bi-layer SOFC structures at elevated temperatures in ambient air and reducing environments

Elastic properties of Ni-8YSZ anode-supported bi-layer SOFC structures were studied at elevated temperatures up to 1,000 °C in both ambient air and H2 environments. The anode samples with desired porosity and microstructure were fabricated by reducing a NiO-8YSZ anode precursor structure in a gas mixture of 5% H2–95% Ar at 800 °C for selected time periods up to 8 h. The development of the essential porous microstructure in forming the Ni-8YSZ cermet phase was analyzed with SEM. It was observed that the room temperature elastic moduli and hardness of the anode samples decrease significantly with increasing fraction of reduced NiO. Since the elastic properties of fully dense Ni, NiO, and 8YSZ are comparable to each other, the decrease in the magnitude in elastic moduli and hardness is evidently due to the colossal increase in porosity in the reduced Ni-8YSZ cermet anodes because of the reduction of NiO to Ni. At elevated temperatures, the Ni-8YSZ anodes show a complex profile of Young’s modulus as a function of temperature, which is significantly different from the unreduced NiO-8YSZ samples. When studied in ambient air, the Young’s modulus of the Ni-8YSZ samples decrease slowly up to ~250 °C, then more rapidly from 250 to 550 °C, and finally it increases monotonically with the increase in temperature. However, in reducing environment, the Young’s moduli values decrease continuously throughout the temperature range. Two sets of samples of different thicknesses were studied simultaneously to highlight the effects of the sample thickness on the elastic properties of the anodes.