Phénomènes Diffusionnels et Recristallisation Accompagnant l'Assemblage de Superalliages Base Nickel par Compression à Chaud

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Microstructural and analytical characterization of Al2O3/Al-Mg composite interfaces

Mechanical properties of composite materials are deeply dependent on the chemical and structural reactions taking place at the ceramic-metal interface. This study was devoted to the identification of these mechanisms, in a Al 2 O 3 /Al-Mg composite during squeeze-casting and heat treatment. TEM characterization and microanalysis clearly show migration of magnesium to the interface during processing of the composite. Appropriate treatments allowed to identify MgO and MgAl2 O4 clusters along the interface. Additionaly, mechanical hardening of the matrix by Mg2Si precipitation was made clear

A transference principle for systems of linear equations, and applications to almost twin primes

The transference principle of Green and Tao enabled various authors to transfer Szemer\'edi's theorem on long arithmetic progressions in dense sets to various sparse sets of integers, mostly sparse sets of primes. In this paper, we provide a transference principle which applies to general affine-linear configurations of finite complexity. We illustrate the broad applicability of our transference principle with the case of almost twin primes, by which we mean either Chen primes or ''bounded gap primes'', as well as with the case of primes of the form $x^2+y^2+1$. Thus, we show that in these sets of primes the existence of solutions to finite complexity systems of linear equations is determined by natural local conditions. These applications rely on a recent work of the last two authors on Bombieri-Vinogradov type estimates for nilsequences.Comment: 36 page

Etude des phénomènes thermiques associés à la fabrication directe de pièces en TA6V par projection laser

International audienceDirect metal deposition is an additive manufacturing process that enables to build up a component layer-by-layer by the laser melting of a metal powder on a solid substrate, using a coaxial nozzle and a powder delivery head. The heating and cooling that occur in direct laser metal deposition can generate particular thermal conditions which are responsible of the specific microstructure and grain growth and lead to specific build features in term of mechanical properties. In the present work, an experimental study concerning laser-powder interaction, process instrumentation and metallurgical properties of the built parts is exposed. Then, a thermal balance has been established from thermal data of Ti-6Al-4V

A higher-dimensional Siegel-Walfisz theorem

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Assemblage par soudage diffusion de deux superalliages. Aspects diffusionnels et microstructuraux au niveau du joint

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