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Martensite

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Martensite --- Martensitic transformations

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Alloys --- Martensite --- Shape memory alloys --- Shape memory effect --- Thermomechanical properties

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Martensite forms under rapid cooling of austenitic grains accompanied by a change of the crystal lattice. Large deformations are induced which lead to plastic dislocations. In this work a transformation model based on the sharp interface theory, set in a finite strain context is developed. Crystal plasticity effects, the kinetic of the singular surface as well as a simple model of the inheritance from austenite dislocations into martensite are accounted for.

Mechanical engineering & materials --- Martensit --- Phasentransformation --- sharp interface --- Kinetik --- martensite --- phase transformation --- kinetic

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In this master thesis, a gradient composition material was developed and characterized using direct energy deposition additive manufacturing. The goal was to enhance the mechanical properties of a pinion located in the deployment mechanism of slats produced by Sonaca. 
The materials selection resulted in choosing martensitic and ferritic steels.

Powders from Pometon and Sandvik were characterized by means of an optical microscope, differential thermal analysis, scanning electron microscope, gas pycnometer and granulometry. Pometon powders were found to contain chromium oxides while Sandvik powders showed good features.

Deposits were printed with different laser parameters. The ferritic zones of the sample exhibited in-situ oxides that were avoided by increasing the incident energy. The martensitic zones presented no porosities nor cracks. The gradient structure showed up to have no added value due to a lack of corrosion resistance as well as a hardness similar to the martensitic zone. Due to the COVID-19 outbreak, characterization of deposits was not completed.

The reference part was characterized and its properties were compared to those of the deposits. The reference part had a better surface hardness but a significantly lower corrosion resistance. Additional characterization means are required to draw conclusions on the interest of deposits compared to the currently used material and surface treatments.

Additive manufacturing, metallic materials, cladding, martensite, ferrite, hardness --- Ingénierie, informatique & technologie > Science des matériaux & ingénierie