The tensile properties of a forged UDIMET 720Li alloy have been investigated at room temperature. The aim of this study was to increase both yield and ultimate tensile stresses using adequate thermal treatments. Classical three steps heat treatments after hot forging were applied: a solution treatment followed by a quench and a two steps aging treatment. Several combinations were investigated: four hours solution treatments, either sub-solvus (1080 C -1120 C) or super-solvus (1160 C); two different cooling rates (10 C/min or 3600 C/min); four different two-steps aging treatments: 650 C/24h/Air Quench (AQ) + 760 C

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A well known issue encountered by forgers transforming Alloy 718 consists in the appearance of coarse grain zones during the thermo-mechanical process. Although some industrial solutions have been implemented in order to get rid of this type of microstructural defect, the consequences of the presence of such coarse grained areas on the material's mechanical properties are of great interest.In this work, some zones that have undergone abnormal grain growth (AGG) have primarily been characterized from a microstructural point of view by means of both optical and EBSD observations. Special attention has been paid to grain orientation, grain boundaries and grain size distributions. In addition the effects of these microstructures on 350°C deformation controlled fatigue crack initiation mechanisms and the subsequent lifetime have been assessed as well as on 350°C tensile properties have also been evaluated.The results will be discussed with regard to microstructure/mechanical behavior relationships.

The ageing process of the powder metallurgy superalloy N18 has been investigated. This alloy exhibits a two-phase microstructure with a long range L12 ordered multimodal ' precipitation. N18 has been designed for high temperature turboengine disks applications. Superalloys however, are prone to microstructure evolution when sustained at high temperature since ' precipitates are coarsening. A method based on scanning electron microscope (SEM) image analysis is developed to qualify and quantify the material ageing. Two kinds of ageing have been considered: material temperature exposure with and without mechanical loading application. A short term quantitative law considering precipitates size, ageing time and temperature is established. In addition a long term behavior in agreement with our measurements is suggested.