Anne-Françoise Gourgues-Lorenzon

Synthesis of few-layered graphene by ion implantation of carbon in nickel thin films

The synthesis of few-layered graphene is performed by ion implantation of carbon species in thin nickel films, followed by high temperature annealing and quenching. Although ion implantation enables a precise control of the carbon content and of the uniformity of the in-plane carbon concentration in the Ni films before annealing, we observe thickness non-uniformities in the synthesized graphene layers after high temperature annealing. These non-uniformities are probably induced by the heterogeneous distribution/topography of the graphene nucleation sites on the Ni surface. Taken altogether, our results indicate that the number of graphene layers on top of Ni films is controlled by the nucleation process on the Ni surface rather than by the carbon content in the Ni film.

FE modelling of bainitic steels using crystal plasticity

Models classically used to describe the probability of brittle fracture in nuclear power plants are written on a macroscale. Physical phenomena are not naturally captured by this type of approach, so that application of these models far from their identification domain (such as temperature history, loading path) may become questionable. To improve the quality of the prediction of resistance and life time, microstructural information describing the heterogeneous character of the material and its deformation mechanisms has to be taken into consideration. The objective of this work is to propose a model able to describe local stress and strain fields in an A508 Cl3 bainitic steel. This information will then be used to introduce critical variables for multiscale failure models. The microstructure of A508 Cl3 steel is made of bainitic packets (coming from former austenitic grains), which are not randomly oriented. An accurate model must take the actual microstructure into account, in order to provide realistic local stress and strain fields. Starting from experimental observations of the bainitic microstructure (texture measurements, morphological analysis), the paper first proposes a numerical model able to produce quantitatively representative numerical aggregates, then discusses the results obtained by a finite element treatment of the aggregates involving crystal plasticity.

Effect of joint line remnant on fatigue lifetime of friction stir welded Al–Cu–Li alloy

Abstract The effect of joint line remnant (JLR) on the fatigue lifetime of friction stir welds of a 2198 Al alloy in T851 condition has been assessed experimentally. The base material, sound welds (welded in one sheet) and welds with JLR (produced via welding of two sheets with a natural oxide layer) have been investigated. A strong decrease in microhardness is found for the weak weld zone that is consistent with the reduction in tensile properties compared to the base material: 45% in yield strength and 22% in ultimate tensile strength. The fatigue strengths of sound and JLR bearing welds at 100 000 cycles (R=0·1) are reduced by 10 and 15% respectively compared to the base material. Only for one-third of the JLR bearing specimens, the fatigue crack initiated in regions close to the JLR and this without reduction in fatigue lifetime.

Fracture toughness of the molten zone of resistance spot welds

A methodology for measuring the fracture toughness at crack initiation and the crack extension resistance of the molten zone of resistance spot welds under Mode I loading has been developed. The cross tensile test of U-shaped specimens was modified by crack growth monitoring and stress intensity factor determination. The resulting values of fracture toughness at crack initiation are independent of the nugget diameter and of the base material mechanical properties. The crack extension resistance seems to depend on base material mechanical properties and nugget diameter. Mixed cleavage + ductile mode associated to medium values of fracture toughness (54–90

Mechanical Behavior at High Temperatures of Highly Oxygen- or Hydrogen-Enriched α and Prior-β Phases of Zirconium Alloys

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Study of the microstructure of the Grade 91 steel after more than 100,000 h of creep exposure at 600 °C

) suggested a ductile to brittle transition behaviour. The relatively low fracture toughness (55–59

Mechanical and microstructural stability of P92 steel under uniaxial tension at high temperature

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