Synthesis, processing and mechanical characterization of Ti(C,N)-based cermets through the combination of colloidal and powder metallurgy techniques

Mención Internacional en el título de doctorEsta tesis contiene artículos de investigación en anexo.The main objective of this thesis is the processing by combining colloidal and powder metallurgy techniques in aqueous medium of Ti(C,N) based cermets and their mechanical characterization.Esta Tesis Doctoral ha sido realizada entre la Universidad Carlos III de Madrid y el Instituto de Cerámica y Vidrio, siendo financiada por el proyecto MAT-2012-38650-C02-01 “Diseño de la microestructura y la microarquitectura de materiales metal-cerámicos utilizando tecnologías coloidales y pulvimetalurgicas” (MITICO) y por una Beca FPI-2013 (BES-2013-065760) del Ministerio de Economía y Competitividad.Programa Oficial de Doctorado en Ciencia e Ingeniería de MaterialesPresidente: Antonio Javier Sánchez Herencia.- Secretario: Sophia Alexandra Tsipas.- Vocal: Raquel de Oro Calderó

Estudio de la sinterización de nuevos aceros de baja aleación que contienen elementos de aleación de elevada afinidad por el oxígeno

Los aceros pulvimetalúrgicos son una alternativa a otras técnicas de fabricación como el moldeo o la extrusión, debido a que la pulvimetalurgia permite la fabricación de grandes lotes de piezas de una geometría compleja con alta calidad y a un bajo coste. Los principales elementos de aleación que se han utilizado en la pulvimetalurgia de aceros de baja aleación han sido el carbono, níquel, molibdeno, fósforo y cobre. Sin embargo, debido al incremento de su coste, ha surgido una nueva generación de elementos de aleación como el manganeso, el silicio y el cromo. Estos elementos ofrecen la posibilidad de mejorar las propiedades mecánicas de los aceros sinterizados a un coste menor que los otros elementos de aleación. En este proyecto se estudia la posibilidad de incorporar manganeso y silicio mediante una aleación maestra. El interés por emplear aleaciones maestras en la industria pulvimetalúrgica se debe tanto a la posibilidad de generar una fase líquida durante el proceso de sinterización, como a la de incorporar elementos de alta afinidad por el oxígeno, como el manganeso y el silicio, que confieren al material unas buenas propiedades mecánicas, debido al efecto de endurecimiento que producen en el material, además de ofrecer una perspectiva económicamente rentable debido al bajo coste que suponen. Mediante esta investigación, se busca analizar los efectos que producen las condiciones de sinterización sobre las propiedades de aceros modificados con adiciones de una aleación maestra Fe-Mn-Si. Los resultados obtenidos permiten encontrar las condiciones óptimas para sinterizar aceros, y obtener el material adecuado para cada aplicación concreta. _________________________________________________________________________________________________________________________Sintered steels are an alternative to other fabrication techniques such as cast or extrusion, since powder metallurgy enables the manufacture of large batches of parts with complex geometry, high quality and low cost. The main alloying elements that have been used in powder metallurgy are carbon, nickel, molybdenum, phosphorus and copper. However, due to increasing cost of these elements, a new generation of alloying elements such as manganese, silicon and chromium has emerged which offer an improvement of mechanical properties of sintered steels at lower cost than the traditionally alloying elements. This project is mainly focused in studying the addition of manganese and silicon through the use of master alloys. The aim of using master alloys in the powder metallurgy industry is usually to generate a liquid phase during sintering, and to be able to add high oxygen affinity alloying elements such as manganese and silicon which provide great mechanical properties, due to hardening effect and a low cost. This research is mainly focused in analyzing the effects of sintering conditions in the mechanical properties of steels modified with Fe-Mn-Si master alloy additions. The results obtained help to find the optimal conditions for sintered steels, and get the adequate material for each application.Ingeniería Industria

Ruled Real Hypersurfaces in the Indefinite Complex Projective Space

The main two families of real hypersurfaces in complex space forms are Hopf and ruled. However, very little is known about real hypersurfaces in the indefinite complex projective space $\mathbb{C}P^n_p$. In a previous work, Kimura and the second author introduced Hopf real hypersurfaces in $\mathbb{C}P^n_p$. In this paper, ruled real hypersurfaces in the indefinite complex projective space are introduced, as those whose maximal holomorphic distribution is integrable, and such that the leaves are totally geodesic holomorphic hyperplanes. A detailed description of the shape operator is computed, obtaining two main different families. A method of construction is exhibited, by gluing in a suitable way totally geodesic holomorphic hyperplanes along a non-null curve. Next, the classification of all minimal ruled real hypersurfaces is obtained, in terms of three main families of curves, namely geodesics, totally real circles and a third case which is not a Frenet curve, but can be explicitly computed. Four examples are described

Semiconductor-metal core-shell nanostructures by colloidal heterocoagulation in aqueous medium

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).The authors acknowledge the support of the projects S2013/MIT-2862 and MAT2012–38650-02–01, MAT2012–38650-C02–02. M. de Dios acknowledges MINECO through the grant FPI-2013 and Dr. Z González acknowledges to MINECO through the grant PTQ-13–05985

Chemical precipitation of nickel nanoparticles on Ti(C,N) suspensions focused on cermet processing

Ti(C,N)-based cermets are currently used in high speed cutting tools industry due to its high thermal stability. In previous works, Fe was proposed as metal matrix, however the use of iron as continuous matrix strongly affects the processing due to the low wetting capability of molten Fe with the reinforcement phase, Ti(C,N). To solve this problem, the use of alloys such as FeNi has been proposed, where Ni improves the wettability between the ceramic and the metal phases. This work proposes a bottom-up approach to build the cermet microstructure through the synthesis of metal nanoparticles (NPs) on the surface of Ti(C,N) micrometric particles, creating Ti(C,N)-Ni core-shell structures. For that purpose, the in-situ synthesis of Ni NPs through the chemical reduction of a Ni precursor onto the surface of micrometric Ti(C,N) particles, previously stabilized in an aqueous suspension, was proposed. Core-shell structures were characterized by X-Ray Diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), scanning transmission electron microscopy (STEM), high resolution scanning electron microscopy (HRTEM), energy-dispersive X-Ray spectroscopy (EDX) and Raman Spectroscopy.The authors acknowledge the support of the projects S2013/MIT 2862 MAT2015 70780 C4 1 P and MAT2015 70780 C4 2 P. M. De Dios acknowledges MINECO through the grant BES 2013 065760 and Dr. Z González acknowledges to MINECO through the grant PTQ 13 05985

Ti(C,N)-Fe/Ni/FeNi core-shell structures for cermets processing

Proceedings of : The World PM2016 Congress & Exhibition, Hamburg, Germany, 9-13 October 2016This work proposes an alternative bottom-up approach to build cermet microstructures through the synthesis of metal hydroxide nanoparticles (NPs) on the surface of Ti(C,N) micrometric particles, creating core-shell Ti(C,N)-Ni(OH)2 and Ti(C,N)-FeO(OH) and their subsequent calcination cycle. This calcination cycle will help us to obtain Ti(C,N)- based cermets with fine microstructure and low amount of metal binder avoiding mechanical milling, the risks of handling nanoparticles, as well as overcoming the lack of availability and the high prices of those metal nanoparticles. The obtained structures were characterized by differential thermal analysis (DTA), thermogravimetry (TG), X-Ray Diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-Ray spectroscopy (EDX).The authors acknowledge the support of the projects S2013/MIT-2862, MAT2012-38650-C02-01, MAT2012-38650-C02-02 and MAT2015-70780-C4-1-P. M. Dios acknowledges MINECO through the grant BES-2013-065760 and Dr. Z Gonzalez acknowledges to MINECO through the grant PTQ-13-0598

Interface study for the design of alternative matrixes in cermets

Proceedings of: European Congress and Exhibition on Powder Metallurgy (Euro PM2015 Congress & Exhibition), Reims (France), 4-7 September 2015.Liquid Phase Sintering (LPS) is used in the fabrication of hard materials and cermets which are difficult to densify by other approaches. During this process the melting point of the metal matrix is reached and the solid reinforcement is soluble in it. Thereby, via rearrangement and solucion-reprecipitation mechanism, these composite materials are sintered obtaining hihg density, hardness and wear resistance.For this sintering mechanism it is very important to know the solubility and wetting behaviour at high temperature of the metallic matrix and the reinforcement. In recent years one of the research topics in the field of hard materials is the search for new metallic matrixes so it becomes mandatory to study its interaction with the reinforcement from the viewpoint of solibility and wettability. This work shows a study combination of simulation tools and experimental testing of contacta angle mesurement at high temperature of the system Ni/TiCN because Ni is the conventional metallic matrix used in cermets and it is compared with the systems Fe/TiCN and Fe-15Ni/TiCN because the Fe is the main candidate for an alternative metallic matrix.The authors would like to acknowledge the financial support from the Spanish Government through the project MAT2012-38650-C02-01, the Regional Government of Madrid through the program MULTIMAT-CHALLENGE, ref. S2013/MIT-2862

Micromechanical properties of a Ti(C,N)-FeNiC composite: statistical method

XXXIV Encuentro del Grupo Español de Fractura: Santander, 29, 30 y 31 de marzo de 2017Durante los últimos años, se han invertido muchos esfuerzos para diseñar nuevos materiales alternativos a los metales duros (WC-Co), que exhiban respuestas mecánica y tribológica similar a la de estos. El excelente comportamiento de los compuestos WC-Co se atribuye principalmente a su ensamblaje microestructural, debido a la combinación de dos fases con propiedades muy diferentes a nivel local. En el presente trabajo se pretende evaluar la relación microestructura/propiedades micromecánicas de nuevos materiales compuestos cerámico-metal del sistema T i(C,N)- Fe,Ni. Para ello se ha utilizado un procedimiento sistemático que consta de varias etapas.In recent years, many efforts have been invested to design new alternative materials to substitute hardmetals (WC-Co) that exhibit similar mechanical and tribological response. The outstanding behaviour of WC-Co composites is mainly attributed to its microstructural assemblage, due to the combination of two phases with very different properties at the local level. The present work is aimed to evaluate the microstructurelrnicromechanical properties of new ceramic-metal Ti(C,N)-Fe,Ni composite systems. A systematic procedure consis ting of several stages has been used for this purpose.The currently study was suppored by the Spanish Ministerio de Economía y Competitividad through Grant MAT2015-70780-C4-3-P (MINECO/FEDER)

Novel colloidal approach for the microstructural improvement in Ti(C,N)/FeNi cermets

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 µm) in suspension 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 + Cold Isostatic Pressing (SC-CIP) and Spray-Dry + 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 optimization 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.The authors acknowledge the financial support from the Spanish Government through the projects MAT2015-70780-C4-1-P and MAT2015-70780-C4-2-P, and the Regional Government of Madrid through the program MULTIMAT CHALLENGE, ref. S2013/MIT-2862. M. Dios acknowledges MINECO through the grant BES-2013-06576