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A high entropy alloy (HEA, CoCrFeNiMn) synthesized by mechanical alloying was used as the binder for the densification of WC by a pressureless high temperature procedure. Three different WC were used by modifying its microstructure with a high energy ball milling treatment. The alloy content in the HEA-WC mixture was varied from 10 to 30% vol. The microstructure and properties of the sintered composites were studied by X-ray diffraction, scanning electron microscopy and microindentation. [ABSTRACT FROM AUTHOR]

A titanium-tantalum-niobium carbonitride solid solution, (Ti,Ta,Nb)(C,N), was synthesised in a planetary mill via a mechanochemical process that involves a mechanically induced self-sustaining reaction (MSR) from stoichiometric Ti/Ta/Nb/C mixtures that are milled under a nitrogen atmosphere. The influence of the spinning rate of the planetary mill, which determines the impact energy of the milling process, on the ignition time (t ig ) of the MSR process as well as the chemical homogeneity of the final product was analysed. The results indicated that the dependence of t ig on the spinning rate followed a potential function with a potential factor of 4.85, implying a remarkable reduction in the milling time required to induce the self-sustaining reaction at increasing spinning rates (i.e., from 4200 min at 200 rpm to 15 min at 800 rpm). However, the chemical and structural characterisation of the obtained products at ignition without any extra milling treatment indicated that a single solid solution phase was only obtained at the lowest spinning rates (i.e., less than 300 rpm). At increasing rates, the relative amount of the intended solid solution phase continuously decreased, and new undesirable secondary phases were formed. Despite the long milling times required for the milling experiments that were performed at the slowest spinning rates, iron contamination from the milling media was negligible due to the low intensity milling regime. [ABSTRACT FROM AUTHOR]

Abstract: Monophase nanocrystalline powders belonging to the La 1− x Sr x MnO 3± δ system (0≤x≤1) with a perovskite structure have been obtained by mechanochemistry synthesis using a planetary ball milling equipment from La2O3, SrO, and Mn2O3 mixtures. The solid state reaction was complete after one hour of milling treatment. For all the compositional range, the diffraction domain was very small and the structure appeared as a pseudo cubic perovskite. After annealing at 1100°C under static air, the symmetry evolution due to the La substitution by Sr was analyzed by X-ray and electron diffraction. Samples with x=0, 0.25, 0.5, and 0.75 were assigned to R-3c space group (167) in the rhombohedral system and perovskite structure. However, the symmetry of the last term of the system (x=1), SrMnO3±δ sample, changed to P6 3 /mmc space group (194) in the hexagonal system. The terms with x=0.8, 0.85, and 0.9 presented mainly rhombohedral symmetry. [Copyright &y& Elsevier]

Cermets based on Ti(C,N) have interesting properties, such as high wear resistance, high chemical stability and good mechanical strength at high temperature, but to become a viable alternative to cemented carbides, the fracture toughness and damage tolerance must be significantly improved. Complete solid-solution cermets (CSCs) have been proposed to further improve the mechanical properties of these materials. However, to develop this family of cermets with a high level of quality and reliability, using pre-fabricated complex carbonitrides is necessary instead of unalloyed mixtures as the raw ceramic material. A mechanochemical process called mechanically induced self-sustaining reaction (MSR) is suitable to obtain these complex carbonitrides with high stoichiometric control. On the other hand, high entropy alloys (HEAs), which can also be obtained by mechanochemical processes, are a good candidate to replace the current binder phase in cermets because they exhibit high strength and ductility at high temperature and good resistance to both wear and corrosion. In this work, a new family of CSCs based on (Ti,Ta,Nb)C x N 1 − x with HEAs belonging to the Fe-Co-Ni-Cr-Mn-V system as the binder phase is developed by mechanochemical processes. With only two constituent phases, these cermets have a simple microstructure but a high compositional complexity because both the ceramic and binder phases are complex solid solutions with at least five components. [ABSTRACT FROM AUTHOR]

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: Cermets with a nominal composition (Ti0.8Ta0.2C0.5N0.5— 20wt.% Co) were synthesised by a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental powder blends. The MSR allowed the production of a complex (Ti,Ta)(C,N) solid solution, which was the raw material used for the sintering process. The pressureless sintering process was performed at temperatures between 1400°C and 1600°C in an inert atmosphere. The microstructural characterisation showed a complex microstructure composed of a ceramic phase with an unusual inverse core–rim structure and a Ti–Ta–Co intermetallic phase that acted as the binder. [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]