In this work, the combination of colloidal and powder metallurgy techniques was proposed as an alternative route to produce Ti(C,N) based cermets with a 15 20 vol% of Fe/Ni alloy (85/15 wt%) as metal matrix. The novelty of this processing route is based in the mixture of fine powders (1 3 mm) in sus pension which promotes the uniformity of the phase distribution and consequently its reactivity, leading to 99.9% dense cermets with 1300 Vickers Hardness (HV30). The preparation of colloidal and chemically stable slurries of non oxide and metal powders in aqueous media is a key step of the process. Highly concentrated aqueous slurries of Ti(C,N), Fe, Ni and C powders were prepared and mixed. Then bulk pieces were shaped by Slip casting (SC), Slip Casting þ Cold Isostatic Pressing (SC CIP) and Spray Dry þ Uniaxial Pressing of the obtained spherical granules (SDP). The composite formulation and the thermal treatment were optimized to prevent Ni sublimation during sintering as well as to improve liquid phase sintering in terms of wetting and reactivity among well packed particles. The effective dispersion of the slurry and the synergistic effect of combined techniques yielded the preparation of reliable materials by the SDP process with 15 wt% of FeNi with the addition of 0.5 wt% of C. The opti mization of the composite formulation and the processing parameters improves both density and hardness of a finer microstructure of the composite after a short sintering treatment (120 min) at 1450 C in vacuum.

Given the great interest generated in the last years by the searching of new binders in hard materials, a work methodology has been created that allows the design of new metalceramic combinations. It includes the study of the solubility between the new binder and the reinforcement during the design of the binder composition combined with the knowledge of the sintering behavior of the cermet by monitoring the contact angle of the liquid phase formed at high temperature.Iron is considered as the main alternative binder in cermets; however proper compositions are still under development as it is necessary to improve the sintering. This work propose the use of Ni as sintering aid to improve the wettability without the introduction of secondary phases. The article shows a comprehensive study of the high temperature behavior, in terms of solubility and wettability, of the system FeNi/Ti(C,N) , and the results are compared with the study of the conventional system Ni/Ti(C,N). A better understanding of the high temperature behavior between binder and reinforcement allows to design new compositions and to search strategies to improve the densification of the cermets.

It is well known the interest of the scientific community in substituting the traditional cemented carbides (WC-Co) by alternative ceramic-metal systems. In this regard, Ti(C,N)based cermets arise as excellent candidates due to their exceptional mechanical, tribological and thermal properties. In this work, microstructurally different Ti(C,N)-FeNi cermets were processed using a combination of colloidal and powder metallurgy techniques. Three distinct ceramic/metal phase ratios were used: 85/15, 80/20 and 70/30 (volume fraction) of Ti(C,N) and FeNi respectively. Microstructural parameters and micromechanical properties (hardness and stiffness) of the three composite systems and their constitutive phases were assessed. Small-scale hardness was evaluated by means of massive nanoindentation testing and statistical analysis of the gathered data, under the consideration of three mechanically different phases: Ti(C,N) particles, metallic binder and a composite-like one, corresponding to probing regions containing both constitutive phases. It is found that values of local hardness for both composite-like and metallic phases increase as the ceramic/metal phase ratio rises. In particular, local hardness values are determined to be significantly distinct for the metallic binder in the three cermets investigated. Results are discussed and rationalized on the basis of the constrained deformation imposed for the harder phase to the softer and more ductile one. Estimated effective flow stress values for the metallic binder as well as detailed inspection of crack-microstructure interaction and fractographic features point out the effectiveness of FeNi as reinforcement phase and toughening agent for Ti(C,N)-base cermets.

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In contrast to complex syntheses for the preparation of colloidal nanocomposites in a core-shell structure proposed in the literature, we present herein a facile colloidal route based on a heterocoagulation process promoted by the electrostatic interaction among ceramic NiO nanoplatelets and metallic Ni nanoparticles (NPs). Before the heterocoagulation process, NiO and Ni were synthetized separately in presence of ultrasound, by chemical precipitation and chemical reduction of the same nickel precursor, respectively. After that, NiO-Ni core-shell nanostructures were prepared forcing the electrostatic interaction among surfaces in aqueous medium. The surface charge balances of both types of particles were tuned effectively by adjusting the pH in a free-additives suspension. For the surface modification of NiO by Ni, the ceramic suspensions maintain a positive zeta potential at pH 9, while the surface of metallic particles is negatively charged. Then the uniform coating of NiO platelets, by the electrostatically induced coagulation with Ni NPs, was favors. The degree of coverage and the formation of NiO-Ni core-shell nanostructures were followed referring the evolution of zeta potential with the geometric calculation in terms of size and morphology of both nanoparticles, and then corroborated by field emission scanning electron microscopy (FESEM).