This work deals with issues of preparation of intermetallics based on iron, nickel and titanium aluminides. It works with an idea of preparation of bulk material by reaction synthe-sis from kinetic spraying deposits by cold spray. Theoretical part is concerned with phases and compounds of these aluminides for structural applications, their characteristics and present fabrication. In experimental part there are studied microstructures created by annealing of deposits.

Abstract This research is designed to investigate the occurrence of interdiffusion-induced mesopores, Brownian motion, cleaving and healing and defect clusters in three binary composites, i.e. Ni1-xO/Co1-xO, Ni1-xO/ZrO2 and Co1-xO/ZrO2 of the Ni1-xO-Co1-xO-ZrO2 system. Firstly, the (NimCo1-m)1-£_O/Ni-doped Co3-dO4 composites prepared by reactive sintering Ni1-xO and Co1-xO powders (1:2 molar ratio, denoted as N1C2) at 1000oC with or without further annealing at 720oC in air were studied by X-ray diffraction and electron microscopy to clarify the formation mechanism of mesoporous spinel precipitates. Submicron-sized inter- and intragranular pores, due to incomplete sintering and grain boundary detachment, prevails in (Ni0.33Co0.67)1-£_O protoxide with rock salt structure; whereas nanosize pores due to Kirkendall effect were restricted to the spinel precipitates having Ni component progressively expelled upon annealing. A rapid net vacancy flux and a tensile misfit stress perpendicular to the protoxide/spinel interface caused the formation of elongated and aligned {100}-faceted mesopores in the spinel precipitates with a relatively low equilibrium vacancy concentration. Aligned mesopores in diffusion zone of nonstoichiometric metal oxides have potential applications on thermal barrier bond coating and mass-transport limited heterogeneous catalysis. Also, this thesis deals with the reorientation and shape change of low-crystal-symmetry (non-cubic) ZrO2 within the high-crystal-symmetry grains of Co1-xO/Ni1-xO cubic rock salt-type structure. ZrO2/Co1-xO composites 1:99 and ZrO2/Ni1-xO composites 1:9 in molar ratio were sintered and then annealed at 1650oC for 24 and 100 h in air to induce reorientation of the embedded particles. Transmission electron microscopic observations in both systems indicated that the submicron tetragonal/monoclinic (t/m) ZrO2 particles fell into three topotaxial relationships with respect to the host Co1-xO/Ni1-xO grain: (1) parallel topotaxy, (2) ¡§eutectic¡¨ topotaxy i.e. [100]Z//[111]C,N, [010]Z//[0 1]C,N and (3) ¡§occasional¡¨ topotaxy [100]Z//[111]C,N, [01 ]Z//[0 1]C,N. The parallel topotaxy has a beneficial low energy for the family of {100}Z/C,N and {111}Z/C,N interfaces. The change from the occasional topotaxy to an energetically more favorable eutectic topotaxy was likely achieved by a rotation of the ZrO2 particles over a specific (100)Z/(111)C,N interface. Brownian-type rotation is probable for the embedded t-ZrO2 particles in terms of anchorage release at the interphase interface with the Co1-xO/Ni1-xO host. Detachment or bypassing of rock salt type grain boundaries could also cause orientation as well as shape changes of intergranular ZrO2 particles. Zirconia-polymorphism-induced cleaving and spontaneous healing by precipitation was studied in Co1-xO polycrystals containing a dispersion of ZrO2 particles. Conventional, analytical, and high-resolution transmission electron microscopy indicated that the Co1-xO matrix cleaves parallel to {100} and {110} planes and heals itself by co-precipitation of parallel-topotaxial ZrO2/Co3-£_O4 particles upon cooling. Due to size effect and matrix constraint, nanometer-size ZrO2 precipitates at cleavages were able to retain tetragonality upon further cooling to room temperature. Paracrystalline array of defect cluster was shown to form in Zr-doped Ni1-xO and Co1-xO polycrystals while prepared by sintering at relative high temperature, i.e., 1650oC to increase the defect concentration. Paracrystalline array of defect clusters in Co3-£_O4 spinel structure also occurred when doped with Zr4+ at high temperature or cooled below 900oC to activate oxy-precipitation of Co3-dO4 at dislocations. transmission electron microscopic observations indicated the spinel precipitate and its paracrystal predominantly formed at the ZrO2/Co1-xO interface and the cleavages/dislocations of the Co1-xO host. Defect chemistry consideration suggests the paracrystal is due to the assembly of charge- and volume-compensating defects of the 4:1 type with four octahedral vacant sites surrounding one Co3+-filled tetrahedral interstitial site. The spacing of paracrystalline distribution is 3.3, 2.9 and 4.9 times the lattice parameter for Zr-doped Ni1-xO, Zr-doped Co1-xO and Zr-doped Co3-dO4. This spacing between defect clusters is about 0.98 times that of the previously studied undoped Co3-dO4. There is much larger (3.4 times difference) paracrystalline spacing for Zr-doped Co3-£_O4 than its parent phase of Zr-doped Co1-xO.

This thesis deals with reaction synthesis of materials Fe–Al, Fe–Cu and Fe–Ni from cold spray. In literature analysis are introduced these systems and for each system there is brief description of binary equilibrium diagram. Furthermore here are some short explanations of diffusion, Kirkendall effect and other possible processing technologies of intermetallic materials. In experimental part, samples of sprayed materials were annealed and then microstructural changes were investigated. This thesis contains photographs of microstructure, results from scanning electron microscopy, X-ray, and measurements of microhardness.

No description available.

Les systèmes barrière thermique actuels connaissent une importante dispersion de durées de vie liée principalement aux ondulations de surface du revêtement métallique β-(Ni,Pt)Al provoquant l’écaillage du dépôt céramique. Les revêtements γ-γ’ riches en platine sont étudiés en tant qu’alternative au système actuel. Ce travail de thèse s’est intéressé à l’élaboration des revêtements γ-γ’ riches en platine sur un superalliage à base de nickel, l’AM1 à partir de procédés conventionnels : dépôt électrolytique de platine et aluminisation courte. Les mécanismes de dégradation par oxydation cyclique à 1100°C ont été étudiés sur des systèmes revêtement/AM1 et sur des systèmes barrière thermique. Pour comparaison, trois types de revêtement ont été élaborés : γ-γ’ Pt seul, γ-γ’ Pt+Al et β-(Ni,Pt)Al. Ces essais ont mis en évidence une meilleure tenue à l’oxydation cyclique des systèmes revêtus γ-γ’ Pt+Al comparée aux deux autres systèmes revêtus. L’importance de l’ajout d’aluminium dès l’élaboration sur la tenue à l’oxydation cyclique a été soulignée. La modélisation p-kp a mis en avant une augmentation de la proportion d’écaillage au cours du temps du fait de la dégradation de l’interface métal/oxyde et une augmentation du kp du fait de la formation d’un oxyde à croissance plus rapide. Outre l’oxydation, les phénomènes d’interdiffusion lors des tous premiers instants à haute température ont été étudiés à partir de matériaux modèles (Ni13Al et Ni11Al10Cr) et de revêtements de Pt et/ou de Pt-Ir. Ces essais ont mis en avant la rapide formation de la phase α-NiPtAl, les transformations de phases et les chemins de diffusion à 1100°C dans les systèmes Ni-Al-Pt et Ni-Al-Cr-Pt. L’effet du chrome et de l’iridium sur les cinétiques de diffusion a été évalué. La modélisation de l’interdiffusion a mis en évidence les interactions chimiques entre les espèces et une sursaturation en lacunes dans la zone d’interdiffusion prouvant que l’effet Kirkendall est responsable de la formation des pores. / TBC systems currently used in aircraft engines with a Pt-modified aluminide coating β-(Ni,Pt)Al show an important lifetime dispersion due to the surface undulations of the bond-coating. This phenomenon called rumpling leads to the ceramic scale spallation and is the most common degradation mechanism. Pt-rich γ-γ’ bond-coatings have been extensively studied for their corrosion and oxidation resistance, and as a lower cost alternative to β-(Ni,Pt)Al bond-coatings. The aim of this work was to fabricate Pt-rich γ-γ’ bond-coatings on a first generation Ni-based superalloy, the AM1. Conventional processes were used as a platinum electroplating and a short aluminizing step. The failure mechanisms occurring by cyclic oxidation at 1100°C were studied on coating/superalloy systems and on TBC systems. Three kinds of coatings were fabricated: Pt-only γ-γ’, Pt+Al γ-γ’ and β-(Ni,Pt)Al. These tests highlighted the best oxidation resistance for the Pt+Al γ-γ’/AM1 systems when compared with the two other systems. Al addition during the coating fabrication is necessary to improve the lifetime. The p-kp modeling results pointed out that the oxide scale spalling probability p increases due to the metal/oxide interface degradation with time. If the spallation increases, a breakaway locally occurs with the formation of a fast-growing oxide explaining the kp progression. The interdiffusion phenomena were also investigated during the first times at high temperature from model alloys (Ni13Al and Ni11Al10Cr) and Pt and/or Pt-Ir coatings. These investigations emphasized the rapid formation of the α-NiPtAl phase, the phase transformations and diffusion paths at 1100°C in the ternary Ni-Al-Pt and quaternary Ni-Al-Cr-Pt systems. Chromium and iridium effect was evaluated on the diffusion kinetics. Interdiffusion modeling highlighted the chemical interactions between the species and a vacancy supersaturation in the interdiffusion zone proving that Kirkendall effect is responsible for void formation.