Composition Of Cermets Research Articles

Synergistic effect of Nb and Mo on the microstructural formation of the Ti(C,N)-high chromium ferrous-based cermets

In this study, Ti(C,N)-Fe-based green cermets with different metallic alloying elements have been consolidated by pressureless liquid-phase sintering. The addition of different metallic binders on Ti(C,N)-based cermet such as Nb and Mo on high chromium Ferrous based binder has been investigated. Detailed analysis of the phase constitution was conducted using thermodynamic calculations and experiments, as well as a systematic study of the microstructure evolution and room temperature mechanical properties including hardness and fracture toughness was conducted. The Nb and Mo addition to the binder system affects the sintering temperatures and can significantly affect the phase formation and microstructural development. Scanning electron microscope (SEM) and Energy dispersive spectroscopy (EDS) technique were used to examine the microstructure, composition, and fracture surface of cermets. The addition of the Mo, and Nb reveals lower porosity and finer microstructure as compared to the reference material (Ti(C,N)-Fe-Cr). The refinement of microstructure improves mechanical properties such as hardness and fracture toughness of Ti(C,N)-Fe-Cr-Mo-Nb-based cermets. Further, the addition of these binder elements may reduce the formation of Fe-Cr-based intermetallic complex carbides, allowing cermets to perform better in terms of toughness and corrosion resistance. As a result of the experiments, it is evident that Nb and Mo dissolve in Ti(C,N) and form solid solutions during sintering. The increased number of coreless grains, spinodal decomposition, and crack deflection in cermet further enhance the fracture toughness.

Using infiltration and self-propagating high-temperature synthesis processes for manufacturing cermets. Review

Cermets are ceramic-metal composite materials (composites) with a relatively high content of ceramic phases from 15 to 85 % by volume. In the 20th century cermets were considered mainly as composites of high-temperature carbide, oxide, nitride, boride and silicide ceramic phases with metallic phases of the iron group, but in the 21st century the concept of cermets has significantly expanded due to the appearance of composites made of ceramic and metal phases with lower melting points including sulfides and MAX phases, as well as light and low-melting metals (Al, Mg, Cu, Ag, Pb, Sn). Therefore, cermets began to be considered not only as tool, heat-resistant and wear-resistant heavy structural materials, but also as light, strong structural materials for the production of vehicles, and as functional materials for various purposes. However, quite often cermets are characterized by such disadvantages as a tendency to brittle destruction, the difficulty in achieving structural uniformity and reproducibility, as well as fault detection, and the high cost of cermet manufacturing. It determines the need in their further development, research to improve the composition, structure and properties of cermets, searching for new applications, developing new manufacturing methods and reducing the cost of their production. Various cermet manufacturing methods are discussed such as solid-phase, liquid-phase, gas-phase, and in-situ methods. The methods of infiltration with molten metals, the effect of wetting, and the conditions for spontaneous infiltration are considered in more detail. The results of using the method of self-propagating high-temperature synthesis (SHS) are also described in detail including a new cermet manufacturing method proposed by the authors of this review based on the use of the SHS of a porous ceramic skeleton followed by spontaneous infiltration with molten metal.

Effect of synthetic Mo2FeB2 powder on the microstructure and mechanical properties of Mo2FeB2-based cermets

In this study, synthetic Mo2FeB2 powder was utilized to fabricate Mo2FeB2-based cermets. The influence of Mo2FeB2 powder on phase composition, microstructure, interfacial characteristics and mechanical properties of cermets was systematically investigated. It was found that two distinct grains were formed in the microstructure due to the addition of Mo2FeB2 powder, namely matrix grains and core/rim grains. Among them, matrix grains were in-situ generated by reaction boronizing sintering and exhibited elongated shape, and the undissolved Mo2FeB2 particles formed equiaxed core/rim grains through the dissolution-precipitation mechanism. With increasing Mo2FeB2 content from 0 to 92.5 wt%, the number of core/rim grains gradually increased while matrix grains continued to decrease, and average grain size decreased from 2.51 to 1.16 μm. In addition, a coherent relationship was formed between (220)Grain and (110)Binder at the core/rim grains-binder interface, thus enhancing interfacial bonding strength. When Mo2FeB2 content reached 92.5 wt%, the hardness, strength and toughness of cermets were found to be 88.5 ± 0.2 HRA, 2203 ± 25 MPa and 21.8 ± 0.3 MPa·m1/2, respectively.

The effect of carbon on phase composition and microstructure of cermets based on Mo2NiB2 boride

This work investigates the effect of carbon alloying on the phase composition and microstructure of cermets based on the ternary boride Mo2NiB2. The sequence of precipitation of hard phases depending on the Mo/(B + C) ratio was determined. It is shown that at Mo/(B + C) close to 1, the phase composition is represented by boride Mo2NiB2, carbide Mo2C and nickel binder. The increase of Mo/(B + C) ratio leads first to the formation of additional Mo2C carbide, characterized by increased nickel content, and then to the appearance of κ-phase Mo10Ni3C3B. The relationship between the phase formation, porosity, hardness and fracture toughness of sintered cermets is revealed.

Interface-reinforced Mo2FeB2-based cermets prepared by multi-step sintering under rapid cooling

A novel approach was proposed to synthesize Mo2FeB2-based cermets using multi-step sintering combined with rapid cooling. The results revealed that the rapid cooling resulted in the formation of several nanocrystalline regions at grain boundaries, which corresponded to the γ-Fe phase without allotropic transformation, and greatly increased the crack propagation resistance. In addition, two completely different highly coherent interfaces were observed due to the sudden decrease in diffusion driving force, improving the interfacial bonding strength. The current study presented the phase composition, interfacial characteristics and performance of Mo2FeB2-based cermets.

Research of the structure and properties of cermets based on nickel and aluminum oxide

In this work, the production of cermets in the system of nickel-aluminum alloy – aluminum oxide by the method of mechanical activation and spark plasma sintering was carried out. The analysis of the features of the microstructure of composites, phase analysis at room and elevated temperatures, as well as the dependence of the flexural strength on the temperature and composition of cermets are presented.

Influence of Mo addition on microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in-situ carbothermal reduction of TiO2

Series of Ti(C,N)-based cermets, with various amounts of Mo, are fabricated by in-situ carbothermal reduction of TiO2. SEM, TEM, XRD and EDS analysis are utilized to analyze the phase composition and microstructure of as-prepared cermets. The results reveal that the volume percentage of white-core grains in as-prepared cermets significantly larger than that in cermets fabricated by traditional methods. In addition, there are two types of white core/gray rim grains. One is the grains with bright white cores and the other is grains with offwhite cores. Mo plays an important role in the formation of rims and white cores. With increasing Mo addition, the rims of grains with white core tend to be complete and the rims of grains with black core become thinner. The volume percentage of grains with white core significantly increases due to the diffusion of Mo during solid-state sintering. Moreover, the dislocation formed in rim phase adjusts the misfit of rim/binder interface. As a result, the semi-coherent interface is observed in rim/binder interface of grains with black core. Overall, the cermet, with Mo content of 14 wt %, renders optimal mechanical properties, with fracture toughness (KIC) of 11.2 MPa m1/2, transverse rupture strength (TRS) of 2403 MPa and a hardness of 90.8 HRA.

Керметы на основе TiC для плазменного напыления

The microstructure and microhardness of eleven volumetric cermets based on TiC carbide with nickel and cobalt based matrices after liquid-phase sintering at a temperature of 1400 °C were studied. It is supposed to use the research results for the subsequent formation of a powder for plasma spraying of coatings. The compositions of the matrix, additional hardening phases, and carbon were selected taking into account the specific features of the formation of plasma coatings: a decrease in the carbon content and high solidification rates of the sprayed particles with the formation of additional nanosized carbides and an increase in the volume fraction of carbides from 70 % to 88 %. As the matrix, we used the traditional composition for cermets with TiC carbide, NiCr – Mo, and industrial powders, PGSR brands, Ni – 13.5 Cr – 2.7 Si – 4.5 Fe – 0.37 C – 1.65 B, and TAFA 1241F Co – 32 Ni – 21 Cr – 8 Al – 0.5 Y. The ring zone on TiC carbide is formed with the participation of WC, Cr3C2, TiN, matrix phases and additional carbon in the composition of cermets, 1 – 2.8 %, as a result, the initial volume fraction of TiC carbide increases 70 to 88 %. Additional carbon is consumed to reduce oxygen content at the stage of sintering (reduction of oxides). After sintering, cermets have high microhardness values at a load on an indenter of 20 G, 1940 – 3210 kgf/mm2, and lower values at a load on an indenter of 200 G, which was explained by a scale factor. The maximum calculated contribution of the hardness of the hardening phases to the hardness of the cermet was established for cermets with a Co matrix of 3681 kgf/mm2.

Strengthened Ti(C, N)-based cermets using high-energy ball-milled NiTiC binders: Microstructure and mechanical properties

High-energy ball-milled NiTiC powders were used for preparing Ti(C, N)-based cermets. Effect of NiTiC content on the morphology, composition, interface structure and mechanical properties of cermets were investigated. NiTiC binders promoted the formation of inner rims on Ti(C, N) cores and hindered their coalescence, leading to well-distributed microstructure. Binder had little effect on the composition of rims, but greatly affected the interface structure of core-rim and rim-binder. Complete inner rim could decrease the lattice mismatch between outer rim and core, forming highly coherent interface. With increasing the Ti-C in Ni, the rim-binder boundaries evolved from semi-coherent to coherent interface, due to the decreased lattice mismatch. Small difference in Vickers hardness of cermets was found, with the values ranging from 1622 to 1684 N/mm2. Bending strength of cermets increased from 1330 to 2073 MPa, with the Ti-C content from 0 to 20 wt%. Further increasing the Ti-C could lead to thick rims, resulting in decreased strength and toughness. This work showed us a way to strengthen the Ti(C, N)-based cermets via modifying the interface structure.

The Influence of Technological Regimes of Synthesizing a Solar Furnace on the Phase Composition of TiO2-CuO Cermets and the Optical Properties of Coatings on Their Basis

We present the results of studying the effect of technological synthesis regimes of a solar furnace using the method of a partial metal reduction of one of the oxides on the phase formation of cermet composite materials of the TiO2-CuO system. It has been established that the phase composition of the synthesized cermet composite materials depends on the carbon concentration, melting temperature and cooling rate. The dependence of the spectral-optical properties of selectively absorbing coatings on the production technology and properties of synthesized composite materials has been presented. It has been found that the coatings fabricated by melting in air with overheating at a melt cooling rate of about 105–106°C/s have the highest values of the integral absorption coefficient, α s = 91.0–94.5%.

Technological Peculiarities of Chromium Carbide-Based Iron Alloy Bonded Cermet

Cr3C2-Ni cermets exhibit high hardness and excellent corrosion, oxidation, abrasive and erosion resistance. However, nickel is toxic and carcinogen and because of that great efforts were made to displace or replace nickel in the composition of cermets. Therefore, in the present research chromium carbide-based cermets with FeCr-type ferritic binder was fabricated and investigated. Composites were sintered at different conditions: vacuum and spark plasma sintering. Spark plasma sintered cermets demonstrated acceptable structure and mechanical characteristics. Chemical composition of chromium carbide-based iron alloy bonded cermets was analyzed by energy-dispersive X-ray spectroscopy and structural analysis was carried out using X-ray diffraction. Sintered cermet consists of two main phases: α-Fe and (Cr,Fe)7C3 complex dicarbide. Mechanical characterizations – hardness and fracture toughness – was performed. Also oxidation rates were determined.

Comparison of Ti(C, N)-based cermets by vacuum and gas-pressure sintering: Microstructure and mechanical properties

Ti(C, N)-based cermets with different carbon content were prepared by vacuum sintering and gas pressure sintering (Ar, 20MPa). Effects of carbon content and sintering method on the microstructure, composition and mechanical properties of cermets were studied. Results showed average grain size and thickness of rim phase to increase with higher carbon or by gas pressure sintering, which was caused by the accelerated dissolution-precipitation process. More uniform morphology with broadened grain size distribution was obtained by gas pressure sintering, leading to improved density and properties. Cermets with 0.8wt%C showed the best mechanical properties, i.e. 2105MPa (TRS), 10.55MPam1/2 (KIC), and 1581 (HV10), although containing residue Ni2(W, Ti)4C. Further increasing the carbon addition leads to thick rims and high amount of white core-grey rim phases, which can deteriorate the properties. Adequate control of size and composition of the core-rim structure plays a key role in ensuring satisfactory mechanical properties.

Core-rim structure formation in TiC-Ni based cermets fabricated by a combined thermal explosion/hot-pressing process

TiC-Ni-based cermets were obtained by thermal explosion from different elemental mixtures (Ti, C, Ni and X, where X=Cr, Mo or W) and subsequently densified by hot-pressing under a cyclic load. The whole process was performed in a single stage in the same experimental device according to the following thermal and pressure procedure: a heating rate ramp up to 1573K without applying any load followed by an isothermal dwelling under a compressive cyclic load of 32MPa. The thermal explosion synthesis occurred during the heating ramp at a temperature close to 1273K that was practically independent of the starting nominal composition. The influence of different refractory elements on the chemical composition and microstructure of cermets was studied. SEM characterization showed that only with Mo and W, the cermets developed the characteristic core-rim structure. A high densification was achieved, but decreased when the refractory elements were added. Nevertheless, in these cases higher hardness values were obtained.

Preparation of self-lubricating Ti(C,N)-based cermets by solid carburization and wear behavior

In this work, self-lubricating Ti(C,N)-based cermets were prepared by solid carburization. The sintered cermets were wrapped by carburizing agent and sintered again at 1440°C with different time. The microstructure and composition of cermets were studied. The wear behavior of cermets containing graphite phase was also evaluated using a block-on-ring tribometer. The results showed that the carbon content increased gradually in binder phase with carburizing time. When the carburizing time was 3h, the carbon got saturated in binder phase. When the carbon content exceeded the solubility in the binder, excessive carbon precipitated and formed graphite phase. Uniformly distributed graphite clusters formed in cermets after carburization for 4h. The graphite clusters consisted of flocked graphite particles. With the carburizing time extended to 5h, the graphite clusters became large and some of them interlaced together. Besides, the wear results indicated that the volume loss of cermets containing graphite phase was half of that without graphite due to the formation of smooth tribofilm on the worn surface of cermets.

Morphology evolution of TiC-based cermets via different sintering schedules

Solid state sintering, liquid phase and cooling stages play different roles in determining the final morphology and composition of cermets, especially the well-known core-rim structure. In this work, TiC-(5–25wt%)WC-11Mo2C-18(Ni-Co) cermets were prepared and sintered by different sintering schedules. Morphology evolution and rim phase composition during sintering from 1250°C to 1600°C were investigated. Effects of sintering stages on the final morphology of cermets were also studied. It was shown that submicron (Ti, W, Mo)C grains tend to precipitate in binder during the cooling for cermets with high WC content. After the formation of outer rims during liquid sintering stage, interface reaction began to take effect between the rims and core. Coreless (Ti0.76, W0.13, Mo0.11)C ceramic grains would be formed under high temperature (1600°C) for TiC cermets with 25% WC. Long time sintering at solid state favored the formation of black core-thick inner rim and bright core-grey rim phases, while cooling near the melting point could result in submicron bright particles. This study provided not only a better view of the formation of rim-core structure but also an easier way to control the final morphology of cermets via reasonable changing the sintering cycle.

Electromagnetic attenuation property of multiphase Fe–Fe3O4–Al2O3 cermets near percolation threshold

Cermets are widely applied as attenuating materials due to high electromagnetic loss and better mechanical properties. In this paper, multiphase cermets composed of iron, iron oxide and alumina were successfully prepared by a two-step in situ synthesis process, which includes pressureless sintering and a selective reduction in hydrogen atmosphere. The phase composition and microstructure of cermets were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. It is shown that nanosized cuboid Fe particles and octahedral Fe3O4 particles are distributed in alumina matrix. The permittivity and permeability of composites were tested with radio frequency impedance analyzer (0.01–1.00 GHz). The results show that permittivity presents obvious frequency dispersion. Furthermore, dielectric constants of multiphase cermets get enlarged due to the enhancement of interfacial polarization. On the other hand, there is a magnetic loss peak in permeability spectra, which indicates typical relaxation behavior. It is possible to achieve better electromagnetic attenuation property by adjusting process parameters.

Characterization of TiC-FeCrMn Cermets Produced by Powder Metallurgy Method

TiC-NiMo cermets combine relatively low density with high hardness. Because nickel is known as a toxin and allergen and allergy to nickel is a phenomenon which has assumed growing importance in recent years there has been a flurry of activity to find alternatives to the nickel binder in cermets. It is also the global research and technical development trend in the powder metallurgy cermets industry. In present research TiC-based cermets with FeCrMn binder system were fabricated. Three different sintering conditions were used (vacuum sintering, sinter/HIP and sintering under low Ar pressure). Because of high vapor pressure of manganese different sintering conditions and technologies were investigated to depress the Mn-loss during sintering. Chemical composition of TiC-FeCrMn cermets after different sintering conditions were analyzed by energy-dispersive X-ray spectroscopy (EDS) and mechanical properties – hardness and fracture toughness were evaluated on the samples. Results of research showed that Ni-free TiC-based CrMn-steels bonded cermets compare unfavorably with cermets bonded with CrNi austenitic steels in terms of fracture toughness and corrosion resistance. Noticeable Mn-loss during vacuum sintering can be avoided when sintering under low Ar gas pressure.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7364

Phase evolution, microstructure and properties of Y2O3-doped TiCN-based cermets

Y2O3-doped TiCN-based cermets were prepared by pressureless sintering with powders TiC, TiN, Ni, etc. as main starting materials. The influence of sintering processes and Y2O3 on properties of TiCN-based cermets were investigated. The phase composition of TiCN-based cermets almost had no change with Y2O3 addition. The fullly densified TiCN-based cermets were achieved by P-2 sitering process. The fracture surface showed lots of small dimples caused by hard phase particles pulling-off, and the left hard phase particles were attached to the arborous dendritic matrix. The Vickers hardness, fracture toughness and bending strength of TiCN-based cermets increased firstly and then decreased with the increment of Y2O3 content. When Y2O3 contents were both 0.8 wt.%, compared with the P-1 sintered samples, the Vickers hardness, fracture toughness and bending strength of the P-2 sintered samples reached 14.84 GPa, 8.66 MPa·m1/2 and 660.4 MPa, which were increased by 7.9%, 6.1% and 45.8%, respectively.

Comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering

A suitable sintering method is important to obtain the Ti(C,N)-based cermets with superior properties. In this paper, Ti(C,N)-based cermets were fabricated by hot-pressing sintering (HP) and conventional pressureless sintering (PLS) technology, respectively, to investigate the influence of different sintering methods on the microstructure and mechanical properties of cermets materials. The microstructure, fracture morphology, indention cracks and phase composition were observed and detected using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The transverse rupture strength (TRS), Vickers hardness (HV) and fracture toughness (KIC) were also measured. The results reveal that all of the Ti(C,N)-based cermets exhibit core–rim microstructures with black cores, white cores and grey rims embedded into metal binder phases. The grain size of the samples fabricated by HP is much finer and the structure is more compact than those fabricated by PLS, while there exist pores in the HP sintered samples. The sintering process has no influence on the phase composition of cermets, but affects the phase content and crystallinity. The samples fabricated by PLS present higher transverse rupture strength, fracture toughness and density than samples fabricated by HP. However, the HP sintered samples possess a higher hardness.

Oxidation-abrasion of TiC-based cermets in SiC medium

► Methodology for studying of oxidation-abrasion is proposed. ► No positive effect of further molybdenum concentration increase in the precursor powder on wear performance of TiC-(Ti, Mo)C-Ni cermet was observed. ► Abrasion can have positive effect on formation of oxide layer at high temperature. The aim of the current study was to investigate the effect of oxidation on abrasive wear behaviour of TiC based cermets at temperatures ranging from 20 to 900 °C. Three types of material performance maps were constructed: oxidation rate maps, wear rate maps and maps showing the effect of oxidation on abrasion. Discussion on the performance of different cermet grades is supported by the SEM images combined with EDS and XRD analysis. The results should facilitate the selection of TiC-based cermets providing optimum composition of cermets for high temperature applications.