Relationships between Microstructural Parameters and Time-Dependent Mechanical Properties of a New Nickel-Based Superalloy AD730™
High temperature creep and dwell-fatigue properties of the new nickel-based superalloy AD730™ have been investigated. Three microstructures have been studied in creep (850 °C and 700 °C) and dwell-fatigue (700 °C stress control with trapezoidal signals, and dwell times ranging from 1 s to 3600 s): a coarse grains microstructure, a fine grains one, and single crystalline samples. The aim of this study is to assess the influence of the grain size on creep and creep-fatigue properties. It is demonstrated that fine and coarse grains microstructures perform similarly in creep at 700 °C, showing that the creep properties at this temperature are controlled by the intragranular precipitation. Moreover, both the coarse grains and the fine grains microstructures show changes in creep deformation mechanisms depending on the applied stress in creep at 700 °C. At higher creep temperatures, the coarse grains microstructure performs better and almost no effect is observed by suppressing grain boundaries. During dwell-fatigue tests at 700 °C, a clear effect of the mechanical cycling has been evidenced on the time to failure on both the coarse and the fine grains microstructures. At high applied stresses, a beneficial effect of the cyclic unloading to the lifetime has been observed whereas at lower applied stresses, mechanical cycling is detrimental compared to the pure creep lifetime due to the development of a fatigue damage. Complex creep-fatigue interactions are hence clearly evidenced and they depend on the pure creep behavior reference.
Impact du sur-vieillissement métallurgique sur le comportement et la durabilité du nouveau superalliage pour disque de turbine René 65
Cette etude traite de l'impact du vieillissement thermomecanique sur la microstructure et sur les proprietes mecaniques du nouveau superalliage base Nickel pour disque de turbine Rene 65.Le vieillissement thermique conduit a trois evolutions microstructurales majeures, a savoir la croissance des precipites y' intragranulaires et a la nucleation de particules TCP aux joints de grains accompagnes d'une segregation de molybdene. Une methode innovante basee sur des traitements thermiques adaptes a permis de dissocier les effets de ces deux evolutions microstructurales sur les proprietes en fluage et fatigue-temps de maintien a 700° Cdu Rene 65. La croissance des precipites y' intragranulaires est majoritairement responsable de l'abattement des proprietes mecaniques. Il s'avere neanmoins que la presence des particules TCP aux joints de grains ainsi que la segregation de molybdene affectent egalement le comportement viscoplastique et la durabilite de l'alliage, contribuant a un abattement supplementaire des proprietes mecaniques. Ce phenomene est attribue a l'adoucissement localise de la matrice au voisinage des particules TCP et des joints de grains par la perte d'elements durcissants de la solution solide y.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.