Sintering Of Cermets Research Articles

Sintering of Cermets: A Case Study of Sintering Ni–Co Ferrite with Ag-, Cu- and Ni-Dispersed Alloy Particles

Literature has shown that the development of ferrite cermets makes possible the enhancement of the mechanical properties of these ceramics for applications in electronics, magnetomechanical sensors, and inert anodes. In this work, a Ni–Co ferrite powder was mixed with metallic powders, compacted, and sintered. The metallic powders used were Ag–Ni and Cu–Ni, prepared by mechanical alloying, and commercial Ag and Ag–Cu powders. The microstructures, crystal structures, and chemical compositions of the sintered samples were analyzed. The Cu–Ni cermet did not present traces of second phases in its XRD pattern, and the experimental results indicate a high reactivity between the ferrite and the Cu–Ni alloy. In the Ag–Cu and Ag–Ni cermets, the composition of the metallic particles was nearly 100% Ag after sintering. It was observed that, for the production of ferrite particulate cermets, the composition, particle size, and melting point of the metallic phase must be carefully adjusted in order to obtain a material with proper chemical composition and microstructure (uniform distribution of the metallic phase and no cracks in the metal–ceramic interfaces).

Microstructural evolution during sintering of cermets studied using interrupted sintering experiments and novel 2D and 3D FESEM based techniques

During sintering of cermets the dissolution and precipitation of dissolved MeCs lead to the well-known formation of a core-rim structure. To investigate the microstructural evolution during sintering the sintering process was interrupted at different temperatures and the formation of the core-rim structure traced. EDS mappings and point scans as well as 3D-FIB tomography scans were carried out to study the distribution of added MeCs like Mo2C or WC on ion-beam prepared samples. The studied cermet consisted of a Ti(C,N) hard phase with a mixed Co and Ni binder and added Mo2C. The results show i.e. that within the rim area not only a high amount of MeC exists, but also that during the final stages of sintering in some grains binder inclusions within the rim area and Mo inclusion within the core appear.

Sintering technology of Ti(C, N) base cermets

The variations of chemical compositions, phases, microstructure evolution and shrinking of cermets compact debinded in H 2 or in vacuum and sintered subsequently in vacuum were studied systematically using chemical analysis, back scattering scanning electron microscopy (SEM), and X-ray diffractometry (XRD). The total carbon of cermets debinded in H 2 is lower than that debinded in vacuum by 0.4%–0.5%. The contents of carbon and oxygen are decreased sharply when being sintered at 1 100–1 300 °C. The decomposition reaction of nitrogen is conducted sharply at 1 300 °C. However, the decomposition of nitrogen is inhibited while the liquid phase appears, and then begins again above 1 500 °C. The solution reaction of TaC and Mo 2C into ring phase starts at 1 200 °C, and WC into ring phase at 1 300 °C is finished. Therefore, the heating rate during sintering of cermets between 900 °C and 1 350 °C is important.

Advanced WC–Co cermet composites with reinforcement of TiCN prepared by extended thermal plasma route

The synthesis of titanium carbonitride (TiCN) powders by thermal plasma using extended arc thermal plasma reactor and the effect of TiCN reinforcement for the development of advanced WC–Co cermets has been studied with respect to hardness and fracture toughness. These classes of materials are being investigated for future application in wear-resistant seals, cutting tools, etc. Metallurgical reactions and microstructural developments during sintering of cermets and functionally graded cemented carbonitrides are being investigated by analytical methods such as differential thermal analysis/thermo-gravimetric analysis, X-ray diffraction and analytical Scanning electron microscopy with energy dispersive X-ray spectroscopy. By an in-depth understanding of the complex phase reactions and the mechanisms that govern the sintering process and metallurgical reactions, new cermets and different types of functionally graded cemented carbonitrides with desired microstructures and properties have been attempted to develop. The significant improvement of micro-hardness was observed with optimal concentration of TiCN reinforcement addition in WC–Co system without sacrificing much fracture toughness value of the composite cermets.

Liquid-phase sintering of cermets and graded cemented carbo nitrides

Liquid-phase sintering of cermets and graded cemented carbo nitrides

Gasanalyse beim Sintern von Hartmetall durch TA-imulation

The processes taking place during outgassing and sintering of different hard metals are investigated by Simultaneous Thermal Analysis (Thermogravimetry and Differential Thermoanalysis) coupled with Mass Spectrometry. In this paper an overview on the application of these methods is given. The progress of gas reactions, their kinetics and the reaction products themselves are characterized more in detail. Main products of the outgassing during the sintering of hard metals are hydrocarbons, carbon monoxide, carbon dioxide and partly nitrogen. The outgassing during the sintering of conventional WC-Co hard metal is finished at relatively low temperatures (approximately 800‡C). The outgassing during the sintering of cermets and of hard metals containing mixed carbides takes place up to higher temperatures (partly up to the formation of the liquid phase). Critical temperature ranges of technological processes may be determinated.

Sintering of cermets based on corundum and molybdenum

The application of the VK 94-1 ceramic powder in the molybdenum-containing cermets makes it possible to decrease the temperature required for obtaining dense materials (by approximately 100°C). In order to produce dense materials, it is necessary to limit the initial porosity of the compacts and to establish its relation with the sintering conditions. Increasing the degree of dispersion of molybdenum makes it possible to obtain a material possessing more uniform structure and higher density and strength. The presence of molybdenum decreases (inhibits) recrystallization of corundum grains and permits one to obtain a stable structure that is resistant to high temperature heating cycles.

Sintering cermets based on molybdenum, nickel, and alumina in atmospheres of dry and moist hydrogen

We studied the sintering of cermets based on molybdenum, nickel, and aluminum oxide in an atmosphere of dry and moist hydrogen. It was established that the presence of water vapors facilitates a reduction in the sintering temperature of molybdenum-containing cermets, and yields dense nickel-containing ones. In the concluding stages of sintering the density of the cermets can be adequately high, which apparently is due to the reduction in the rate of growth of the corundum crystals.

Sintering of tungsten-alumina cermets in the presence of a liquid phase

A study was made of the solid- and liquid-phase sintering kinetics of tungsten-alumina cermets. The energy of activation for the sintering of the cermets was determined. The free surface energy of tungsten, the boundary free energy of tungsten, and the surface energy at the tungsten-alumina, boundary were evaluated. The structure of the cermets was studied. On the basis of experimental results, conclusions are drawn regarding the mechanism of mass transport in the sintering of tungsten-alumina cermets. In the first stage of sintering, the processes taking place are linked with the migration and annihilation of line defects. In the second stage of sintering, shrinkage is limited by processes of volume self-diffusion in tungsten. The presence of a liquid phase activates processes occurring both in the first stage of sintering, by creating an additional driving force for the process of activated sliding on boundaries, namely, the surface tension of the melt, and in the second stage of sintering, by establishing conditions enabling mass transport to occur in the tungsten by a boundary diffusion mechanism.

Diffusion of aluminum in the iron-bronze binary system

The investigation of the simultaneous diffusion of a number of elements from one source is of great scientific and practical interest [1]. This type of diffusion prevails, for example in the welding and soldering of alloys, sintering of cermets, phase transformations in complex alloy steels etc.