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Mechanical damage and behaviour

Embrittlement by liquid metals

Fragilisation intro 200pxP. Paillard

During welding operations damage may occur in the materials which can render the parts unusable. We have expertise in the damage to metallic materials during shaping, particularly in the case of shaping by welding. Our studies aim to understand the phenomena inherent in the appearance of these defects and to propose solutions to our industrial partners. These solutions can be either metallurgical or actions on the welding process.

Stresses Deformation

Contrainte 200pxP. Paillard, L. Couturier

During welding and metal additive manufacturing operations, deformation of assemblies and parts can occur. In the case of welding, the parts are generally clamped, which reduces deformations but generates stresses withinin the materials. These two phenomena are due to the thermal cycles that the assemblies and parts undergo. In order to reduce the strains and stresses as much as possible, it is advisable to quantify them and, to know the predominant parameters affecting them in order toso strategies  set up strategies for reducing these phenomena may be set up. To this aimFor this we adopt bothhave experimental and numerical approaches.

Keywords: Welding, Metallic Additive Manufacturing, Residual stresses, Strains

Modelling martensitic transformation in titanium alloys

Martensite 200pixF. Tancret, E. Bertrand

Controlling, via composition, martensitic transformation in titanium alloys would allow to design materials with a superelastic, “TRIP” or shape memory behaviour. The occurrence of this transformation, upon quenching or upon deformation, was not completely understood or would invoke controversial hypotheses. The design of alloys, on its side, was largely using empirical rules with no real physical basis. Within the frame of Madeleine Bignon’s PhD thesis (2020), two new theories have been proposed to predict, as a function of composition, the occurrence of martensitic transformation upon quenching or upon deformation in titanium alloys. The developed models notably allow to design TRIP alloys with optimised properties.

Deformation mechanisms of metastable β titanium alloys

deformation TiE. Bertrand

Metastable β titanium alloys are subject to many deformation mechanisms: stress-induced martensitic transformation, mechanical twinning, dislocation glide. These deformation mechanisms give rise to unique mechanical properties such as superelasticity, shape memory effect or TRIP/TWIP effects.
The activation of these deformation mechanisms is investigated using in situ or post mortem synchrotron X-rays diffraction, EBSD and TEM and associated with crystallographic models based on Schmid factor analysis.

Keywords: Titanium alloys, EBSD, Scmid factor analysis


visuel test01P. Paillard, E. Bertrand, L. Couturier

As part of a CIFRE thesis (Quentin BOYADJIAN thesis) with a foundry on the influence of the composition of an alloy, here Lead - Antimony alloys, we studied the evolutions of microstructures in connection with the composition of the alloy (Figure 1a). In addition, we have followed the evolution of the mechanical properties of alloys over time. Indeed, lead alloys have the unfortunate tendency to change over time, even at room temperature due to microstructural modification leading to more or less marked modifications of mechanical properties depending on the alloys (Figure 1b).

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