The fabrication and mechanical properties of Ti2AlC composites reinforced with the alumina oxide fibers, such as NextelTM 720 and ALBF1, were described in this thesis. Alumina fibers and Ti2AlC powders were dispersed in the water and slip cast in the molds to form green bodies. Sedimentation test were carried out to optimize pH of the slurry. It was found that suspensions prepared with PAA as a dispersant and has an excellent stability in the pH range of 4 ~ 5. Composite green bodies were densified by pressureless sintering or hot isotatic pressing (HIP) at different temperatures. The microstructure of fabricated samples was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and porosimetry. It was found out that HIPing at 1300 oC for 4 hrs at 100 MPa results in almost fully dense composites with majority phases being alumina fibers and Ti2AlC. However, fully dense Ti2AlC composites could not be obtained by the pressurless sintering, even at temperature as high as 1400 oC at which reaction between Ti2AlC and NextelTM 720 was observed. The double torsion (DT) tests were carried out at room temperature to measure the fracture toughness of the HIPed pure and 5vol% alumina fiber reinforced Ti2AlC. DT results showed increase in the fracture toughness of Ti2AlC reinforcing with NextelTM 720 alumina fibers. However, fracture toughness of the samples reinforced with ALBF1 was lower than that of pure Ti2AlC because of the low relative densities of those composites. SEM study of the fracture surfaces after DT tests showed that toughening mechanisms by crack bridging and fiber pull outs at the crack tip are operative in all reinforced samples. In addition, elastic moduli of HIPed Ti2AlC measured by Resonant Ultrasound Spectroscopy (RUS) do not show significant change due to reinforcement with alumina fibers, while the Vickers hardness of composites was found to be larger for Ti2AlC reinforced with NextelTM 720 and lower for the samples reinforced with ALBF1.

Cette étude porte sur la production et à la caractérisation de matériaux composites à base de matrices d’époxy modifiées par incorporation de particules de caoutchouc recyclées et dévulcanisées. Ces matrices sont renforcées par des fibres d'alumine (Al2O3- FA) et/ou par des nanoplaquettes de graphène (GnPs). Principalement, la fabrication, la caractérisation générale des composites ainsi que l’identification des mécanismes de renforcement à l’échelle micro et nano ont été réalisées. En outre, la fabrication de composites multifonctionnels à base de caoutchouc dévulcanisé et d'époxy a été réalisée pour des applications diverses potentielles dans les industries aéronautique et automobile. Dans un premier temps, les propriétés mécaniques et thermomécaniques des composites ont été étudiées de manière approfondie. L’étude mécanique a consisté à mesurer le module d’élasticité, la ténacité et la température de transition vitreuse. / Recycling of rubber is gaining importance across the world in many industries due to shrinking resources, increasing cost of raw materials, growing conscious about sustainable development as well as environmental issues. In the frame of the common research program between Michigan Tech University/USA and Supmeca/Paris-FRANCE, this PhD work is devoted to the design, development and characterization of recycled rubber modified epoxy-based composites . Additionally, alumina (Al2O3) fibers (AFs) and/or graphene nano platelets (GnPs) have been used as the basic reinforcements. A detailed experimental approach was adapted to these multifunctional composites for explaining of toughening mechanisms by means of fracture toughness test methods and scanning electron microscopy (SEM) on the fracture surfaces. Also, different case studies were included at the end of this work for various potential applications in aeronautic and automotive industries.

The aim of this study was to produce partially reinforced aluminum metal matrix composite components by insertion casting technique and to determine the effects of silicon content, fiber vol% and infiltration temperature on the mechanical properties of inserts, which were the local reinforcement parts of the components. Silicon content of alloys was selected as 7 wt% and 10 wt%. The reinforcement material, i.e. Saffil fiber preforms, had three different fiber vol% of 20, 25 and 30 vol% respectively. The infiltration temperatures of composite specimens were fixed as 750 &deg / C and 800 &deg / C. In the first part of the thesis, physical and mechanical properties of composite specimens were determined according to the parameters of silicon content of the matrix alloy, infiltration temperature and vol% of the reinforcement phase. X-ray diffraction examination of fibers resulted as the fibers mainly composed of deltaalumina fibers and scanning electron microscopy analyses showed that fibers had planar isotropic condition for infiltration. Microstructural examination of composite specimens showed that appropriate fiber/matrix interface was created together with small amount of micro-porosities. Bending tests of the composites showed that as fiber vol% increases flexural strength of the composite increases. The highest strength obtained was 880.52 MPa from AlSi10Mg0.8 matrix alloy reinforced with 30 vol% Saffil fibers and infiltrated at 750 &deg / C. Hardness values were also increased by addition of Saffil fibers and the highest value was obtained as 191 HB from vertical to the fiber orientation of AlSi10Mg0.8 matrix alloy reinforced with 30 vol% Saffil fibers. Density measurement revealed that microporosities existed in the microstructure and the highest difference between the theoretical values and experimental values were observed in the composites of 30 vol% Saffil fiber reinforced ones for both AlSi7Mg0.8 and AlSi10Mg0.8 matrix alloys. In the second part of the experiments, insertion casting operation was performed. At casting temperature of 750 &deg / C, a good interface/component interface was obtained. Image analyses were also showed that there had been no significant fiber damage between the insert and the component.

The aim of the present study was to investigate the effects of different levels of Saffil alumina fiber addition, magnesium content in aluminum alloy matrix and casting temperature on the mechanical behavior, microstructure and physical properties of short fiber reinforced aluminum matrix composites. The main alloying element silicon was kept constant at 10 wt%. Magnesium contents were selected as 0.3 wt% and 1 wt%. Saffil alumina fiber preforms varied from 10 to 30 vol%. The casting temperatures were fixed at 750 &deg / C and 800 &deg / C. Micro porosity was present at the fiber-fiber interactions. Closed porosity of the composites increased when fiber vol% increased, however, variation in casting temperature and magnesium content in matrix did not have influence on porosity. Hardness of the composites was enhanced with increasing fiber vol%, magnesium content in matrix and decreasing casting temperature. Alignment of fibers within the composite had an influence on hardness / when fibers were aligned perpendicular to the surface, composites exhibited higher hardness. The highest hardness values obtained from surfaces parallel and vertical to fiber orientation were 155.6 Brinell hardness and 180.2 Brinell hardness for AlSi10Mg1 matrix 30 vol% alumina fiber reinforced composite cast at 800 &deg / C and at 750 &deg / C, respectively. 30 vol% Saffil alumina fiber reinforced AlSi10Mg0.3 matrix composite cast at 750 &deg / C showed the highest flexural strength which is 548 MPa. Critical fiber content was found as 20 vol% for all composites.