Patrice Jacques

Critical assessment of the process of growth of a YBa2Cu3O7-delta layer on Y2BaCuO5

A layer of YBa2Cu3O7-delta (123) can be grown on a Y2BaCuO5 (211) substrate by reaction with a mixture of 3BaCuO(2) + 2CuO. This reaction has been studied in the temperature range of 930 to 980 degrees C. The reaction is never complete but levels off when the CuO present in the reactant mixture is exhausted, The liquid dissolves an excess of CuO and the 211 substrate becomes covered by co-precipitation of 123 grains and CuO inclusions. The formation of 124 and related polytypoids is favoured by the Cu-rich stoichiometry of the reactant liquid. The growth of the 123 grains follows a parabolic law. The presence of a thermal gradient during reaction does not affect the orientation of the grains but has an influence on the thickness of the 123 layer.

Fatigue Crack Initiation in a Two Phase B-Metastable Titanium Alloy: Influence of Microstructural Parameters

A new generation of α/β titanium alloys with enhanced performance over density ratio is currently receiving lots of attention from the aerospace industry. One of the critical parameter is the fatigue resistance in the both low and high cycle fatigue (LCF and HCF) regimes, in particular the crack initiation. Fatigue initiation is strongly influenced by several characteristics of the microstructure such as grain size, grain orientation and misorientation (e.g Jin et al. [1]). Up to now, the initiation of fatigue cracks in the new low cost beta (LCB Ti alloys) has been characterised only in the case of a fully β microstructure (Hu et al. [2], Krupp et al. [3], Floer et al. [4]). Furthermore, hardly anything can be found in the literature on the fatigue crack initiation in multiphase Ti-based microstructures.

Microscale characterisation of deformed microstructures of TRIP-assisted and multiphase

The improvement of the mechanical behaviour of high performance steels brings about a renewed interest for the work hardening rate resulting from deformation-induced martensitic transformation or mechanical twinning. Even if these mechanisms are known for quite a long time, the deformation – transformation interactions that they induce is not yet fully characterised and understood. This study aims at characterising the microstructure evolution of a Fe-Mn steel grade during straining thanks to TEM and high resolution OIM. Particular patterns of austenite – e and a’ martensite are found.