The thermodynamic properties of the Co-Cr-Mo ternary system have been described. Available experimental data on the system have been assessed and applied to optimize the parameters used in the thermodynamic models within the Calphad method. Meanwhile, samples were made by the powder metallurgical process and heat treated (sintered) at 1573 K to investigate the phase diagram data related to the intermetallic phases, such as σ, μ and R phases present in the system. With the optimized thermodynamic description, we are able to fit most of the experimental data in the literature and from this work. However, the one phase field of R is too narrow in the present description. Furthermore, at 1573 K the extension of the phase boundary of σ toward the Co corner needs to be improved. In addition, the calculated phase diagram at 1573 K shows a fcc-bcc-σ three-phase equilibrium near the Co-Cr binary side. This is not shown in the experimentally determined ternary phase diagram but is necessary in order to match the recent data on the Co-Cr binary system.

CALPHAD (CALculation of PHAse Diagrams) denotes the methodology used to assess thermodynamic data based on experiments as well as on first principles calculations. Essential for this method is the coupling of phase diagram and thermodynamic properties. It has been widely and successfully applied for decades in the field of materials science and engineering. Nevertheless, some shortcomings of the existing thermodynamic databases call for updated descriptions with improved thermodynamic modeling from unary, binary to ternary and higher-order systems. This thesis attempts to pioneer the development of a new generation of CALPHAD databases taking C-Co-Cr alloys with subsystems, unaries and binaries, as example. The present modeling and assessment work not only validate the new models applied in the development of the next, the 3rd, generation database, but also result in improved descriptions in a wider temperature range.In this 3rd generation database, thermodynamic descriptions are valid from 0 K up to high temperatures above liquidus. The Einstein model, rather than the polynomial basis functions used in the previous 2nd generation database, is applied to model the harmonic lattice vibration contribution to the heat capacity of condensed phases at low temperatures. In addition, terms describing the electronic excitations and anharmonic lattice vibrations, as well as the magnetic contribution, are added. A generalized two-state model is employed for the liquid phase to describe the gradual transition from the liquid to amorphous state. A revised magnetic model is adopted accounting for both the ferromagnetic and anti-ferromagnetic states explicitly. A newly suggested method to avoid violating the 3rd law of thermodynamics is adopted for e.g. stoichiometric phases. However, there is still some concern as Nernst’s heat theorem which states that 𝑑𝐶𝑃/𝑑𝑇 is zero at 0 K is not obeyed. All solution phases are modelled within the framework of the compound energy formalism (CEF).The task of the thesis is to construct an updated self-consistent thermodynamic description of the C-Co-Cr system for the third generation CALPHAD databases. The improvement is significant from a modeling point of view when compared to the second generation database. A good agreement between the calculated thermodynamic properties and the experimental data is achieved. The reliability of the extrapolations of unary and binary systems into higher order systems is demonstrated. / <p>QC 20170529</p>

Lead (Pb) is frequently used as an alloying element in brass to enhance machinability and castability. However, this element poses a significant risk to human health and the environment. The 2021 revision of the Drinking Water Directive imposed stricter limits on Pb content in brass, encouraging the development of lead-free brass. Several studies have identified tin (Sn) as a potential substitute for Pb in brass. This master’s thesis examines the thermodynamic description of the Cu-Zn-Sn ternary system, using the Swerim Cu database. The investigation involved casting five alloys in the Cu-rich corner, followed by heat treatment at 550 oC until homogenized, and quenching, after which the samples were analyzed to determine the bcc and fcc phase composition. The results were used to confirm the thermodynamic description, and the ternary parameters of the fcc and bcc phases were optimized to match the experimental results. After the optimization, a significant enhancement is achieved in the description of the Cu-Zn-Sn ternary system, which better fits the experimental data. / Bly  (Pb)  används  ofta  som  ett  legeringselement  i  mässing  för  att  förbättra bearbetbarheten och  gjutbarheten.    Detta  element  utgör  dock  en  betydande  risk för människors  hälsa  och miljön.   2021 års översyn  av  dricksvattendirektivet införde strängare  gränser  för  Pb-halten  i mässing,  vilket  uppmuntrade utvecklingen av blyfri mässing.    Flera  studier  har  identifierat tenn  (Sn)  som  ett potentiellt substitut  för  Pb i mässing.   Denna  masteruppsats  undersöker den termodynamiska beskrivningen  av det ternära  Cu-Zn-Sn-systemet  med  hjälp  av Swerim Cu-databasen.   Undersökningen innefattade  gjutning  av  fem  legeringar  i det  Cu-rika hörnet, följt av värmebehandling vid 550 oC tills de homogeniserades, och härdning, varefter proverna analyserades  för  att bestämma  bcc-  och  fcc-fassammansättningen.   Resultaten  användes  för att  bekräfta den  termodynamiska  beskrivningen,  och  de  ternära  parametrarna  för  faserna  fcc och bcc  optimerades  för  att  matcha  experiment resultaten.  Efter  optimeringen  uppnås  en betydande  förbättring  av  beskrivningen  av  det  ternära  Cu-Zn-Sn-systemet,  vilket bättre  passar experimentdata.

Cette thèse s’inscrit dans le cadre d’un programme de recherche en collaboration avec l’industrie dont l’enjeu est d’utiliser des composites à matrice céramique (CMC) pour la réalisation d’arrière-corps de moteurs pour l’aviation civile.La première partie de ce travail est consacrée à l’étude des fibres de carbure de silicium (Si-C-O) de première génération. Diverses caractérisations physico-chimiques (analyse chimique élémentaire, MEB, MET, spectroscopie Raman, RMN du solide du 29Si et du 13C, DRX…) ont permis d’établir des relations entre la composition chimique, la structure et les propriétés mécaniques des différentes fibres (Nicalon NL série 100 et 200, et Tyranno LoxM, S, ZMI et AM). Une simulation thermodynamique de la phase amorphe intergranulaire SiCxOy a été proposée en s’appuyant sur des données calorimétriques de la littérature obtenues à partir de verres d’oxycarbure de silicium.La seconde partie de ce mémoire est consacrée à l’élaboration par dépôt chimique à partir d’une phase vapeur (CVD) et à la caractérisation de revêtements d’interphase B-C-N. L’influence des conditions d’élaboration (température, pression, composition initiale des gaz) sur la composition chimique des dépôts, leur structure et leur résistance à l’oxydation sous air sec et ambiant a été étudiée. Enfin, les propriétés mécaniques de ces interphases ont été évaluées et des essais de durée de vie ont été réalisés à l’échelle du microcomposite. / This thesis is a part of a research project in partnership with the industry. The aim of the overall project is to design, develop and manufacture exhaust components made of Ceramic Matrix Composites (CMC’s) for civil aircraft engines.The first part of the work deals with the study of first generation silicon carbide fibres (Si-C-O). Various physical and chemical characterizations (quantitative elemental analysis, SEM, TEM, Raman spectroscopy, solid NMR of 29Si and 13C, X-ray diffraction …) were carried out in order to understand the relation between the chemical composition, the structure and the mechanical properties of silicon oxycarbide fibres (Nicalon NL series 100 and 200, and Tyranno LoxM, S, ZMI and AM). Besides, a thermodynamic description of the amorphous SiCxOy phase based on high temperature calorimetry data from the literature is proposed.The second part is devoted to elaboration, by Low Pressure Chemical Vapour Deposition (LP-CVD), and characterization of hexagonal boron carbonitride (B-C-N) coatings. The chemical composition, structure and oxidation resistance (in dry or ambient air) of the coatings were investigated as a function of the deposition conditions (temperature, pressure, initial gas phase composition). Finally, the use of B-C-N coatings as interphases in CMC’s (i.e. their ability to deflect matrix cracks) was investigated by tensile tests on SiC/SiC microcomposites. Their lifetime in static fatigue was also evaluated at 550°C in room atmosphere.