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Highlights: [•] Cermets/hardmetal laminates as potential candidates for high-speed machining. [•] Strong interfaces between cermet and hardmetal adjacent layers. [•] Migration of molten binder during sintering. [•] Compressive and tensile stresses in the hardmetal and cermet layers, respectively. [•] Combined effect of toughness and compressive stresses on crack shielding. [Copyright &y& Elsevier]

Abstract: Complete solid-solution cermets based on titanium–tantalum carbonitride using a starting nominal composition with 80wt.% of (Ti0.8Ta0.2)(C0.5N0.5) and 20wt.% of Co were performed by pressure-less sintering at 1550°C for different times (from 0 to 180min) in an inert atmosphere. Chemical and phase analyses were conducted using X-ray diffraction (XRD), elemental analysis and energy dispersive X-ray spectrometry (EDX). The binder mean free path and the contiguity of the carbonitride particles were used to rationalise the microstructural effects of the mechanical behaviour. Mechanical characterisation included determining the Vickers hardness, the fracture toughness (conventional indentation microfractures, IM), the dynamic Young''s modulus (ultrasonic technique), the biaxial strength (ball on three ball) and a detailed fractographic examination. Finally, the experimental findings were combined with a theoretical fracture mechanics analysis to estimate the critical processing flaw sizes. Binder-less carbonitride clusters, pores and coarse carbonitride grains were the main defects observed and were responsible for the fractures. [Copyright &y& Elsevier]

Abstract: (Ti,Ta)(C,N) solid solution-based cermets with cobalt as the binder phase were synthesised by a two-step milling process. The titanium–tantalum carbonitride solid solution (the ceramic phase) was obtained via a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental Ti, Ta, and graphite powder blends in a nitrogen atmosphere. Elemental Co (the binder phase) was added to the ceramic phase, and the mixture was homogenised by mechanical milling (MM). The powdered cermet was then sintered in a tubular furnace at temperatures ranging from 1400°C to 1600°C in an inert atmosphere. The chemical composition and microstructure of the sintered cermets were characterised as ceramic particles grown via a coalescence process and embedded in a complex (Ti,Ta)–Co intermetallic matrix. The absence of the typical core–rim microstructure was confirmed. [Copyright &y& Elsevier]

Abstract: TiC x N y /Ti–Ni and TiC x N y /Ti–Co composites formed by ceramic and intermetallic binder phases were produced by pressureless sintering at 1400°C from powders synthesized by a mechanically induced self-sustaining reaction (MSR) process. Four different composites were characterized using high-resolution electron microscopic techniques, in both scanning (SEM, HRSEM) and transmission (TEM, HRTEM, ED, EDS and EELS) modes and using an energy filtered technique (EFTEM) associated with electron energy loss spectroscopy (EELS). The microcharacterization showed that the ceramic phase with an fcc-cubic structure displayed a short-range order in many crystals detected by diffuse scattering in the ED patterns. This was possibly due to a sequence of C, N, and vacancies of both atoms along certain directions in the structure. On the other hand, even though the binder phase was introduced as metal in the reaction process, it was formed by Ni–Ti or Co–Ti known intermetallic compounds (NiTi2, Ni3Ti, and Co3Ti). An unknown Ni–Ti intermetallic structure with a Ni:Ti ratio close to 2:1 was only found in one of the synthesized composites and displayed a cubic structure with a lattice parameter, a, of about 8.7Å. [Copyright &y& Elsevier]

Abstract: The properties of TiC x N1−x /(Ni or Co) cermets sintered by a pressureless method from powder mixtures, and obtained for the first time by a mechanically induced self-sustaining reaction process (MSR), were studied. The hardness, toughness, friction and wear coefficients, and oxidation resistance were determined. It was shown that cermets obtained from powdered materials synthesized in one single MSR step possessed improved mechanical properties, similar to those obtained in cermets with more complex bulk compositions. Higher wear resistances were observed in cermets whose hard phase was richer in carbon. The oxidation resistance of the cermets depended primarily on the binder composition. This resistance was better for those cermets with cobalt as the binder. Superior oxidation resistance was displayed when small amounts of W or Mo were incorporated into the binder. [Copyright &y& Elsevier]

Abstract: TiC x N1−x -based powdered cermets were synthesized by a one step mechanically induced self-sustaining reaction (MSR) process from mixtures of elemental powders, and subsequently sintered by a pressureless method. The composition and microstructure of the ceramic and binder phases before and after the sintering process were studied by X-ray diffraction, scanning and transmission electron microscopy, and electron diffraction. The powdered cermets showed excellent binder dispersion and a nanometer character for the ceramic and binder particles. The TiC x N1−x stoichiometry was consistently richer in carbon than expected from the raw powder composition. An important amount of titanium was present in the binder after MSR synthesis, and intermetallic Ti–Ni or Ti–Co phases were obtained in some cases. After sintering, the binder phase was always constituted by intermetallic compounds. The morphology of the ceramic phase in the final bodies was dependent on the C/N ratio of TiC x N1−x and its growth primarily occurred through a coalescence process. The presence of titanium in the binder reduced hard particle solubility in the melted binder and its grain growth. [Copyright &y& Elsevier]

High entropy alloys have been proposed as novel binder phases in cemented carbides and cermets. Many aspects related to the stability of these alloys during the liquid phase sintering process are still unclear and were addressed in this work. Consolidated Ti(C,N)-based cermets using four different (Co,Fe,Ni)-based high entropy alloys as the binder phase were obtained. The chosen alloys - CoCrCuFeNi, CoCrFeNiV, CoCrFeMnNi and CoFeMnNiV - were previously synthesized through mechanical alloying and a single alloyed solid solution phase with fcc structure and nanometric character was always obtained. The powdered alloys and the consolidated cermets were analyzed by X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectrometry and transmission electron microscopy. Differential thermal analysis was employed to determine the melting point of the four high entropy alloys that ranged between 1310 °C and 1375 °C. Although a high temperature of 1575 °C was required to obtain the highest cermet densification by pressureless sintering, porosity still remained in most of the cermets. Best densification was achieved when CoCrFeNiV was used as the binder phase. During liquid phase sintering, different compositional changes were observed in the ceramic and binder phases. A core-rim microstructure was observed in cermets containing V in the alloys (CoCrFeNiV and CoFeMnNiV), since this element was incorporated to the carbonitride structure during sintering. A slight Cr segregation was detected in cermets containing Cr, leading to CrTi-rich alloys in small binder regions. However, a great Cu segregation was produced when CoCrCuFeNi was used, and the formation of two different fcc alloys -a Cu-rich and a Cu-depleted- was observed. Finally, a loss of Mn was also evidenced in CoCrFeMnNi and CoFeMnNiV, probably due to its sublimation at the sintering temperature. • CoCrCuFeNi, CoCrFeNiV, CoCrFeMnNi and CoFeMnNiV used as binder in Ti(C,N) cermets. • The best candidate to be used as binder is CoCrFeNiV. • CoCrFeMnNi and CoFeMnNiV can be used if Mn sublimation is avoided during sintering. • The use of CoCrCuFeNi is discouraged due to Cu segregation during sintering. • CoCrFeNiV binder transforms into CoCrFeNiTi. due to Ti–V exchange during sintering. [ABSTRACT FROM AUTHOR]