Influence of eutectic phase precipitation on cracking susceptibility during forging of a martensitic stainless steel for turbine shaft applications

The presence of the eutectic phase (delta ferrite + M23C6) in martensitic stainless steels brings significant deterioration of the in-service mechanical properties of the critical components such as turbine shaft made of these alloys. In the present study, thermodynamic and kinetics of eutectic phase formation during solidification and the reheating stages before forging of a large size X38CrMo16 martensitic stainless steel ingot are investigated. Material characterization and microstructural evolution were characterized in three different zones of a large size ingot. It was observed that the forging temperature and the solidification rate were the two most effective parameters influencing the volume fraction of the eutectic phase and its morphology. Optical and electron microscopy observations along with Energy Dispersion Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD) measurements were used in the investigation. The results showed that the eutectic phase precipitated primarily at the grain boundaries. Furthermore, a clear evolution on the morphology and volume fraction of the eutectic phase including thin film-like and skeleton-like carbides was found from the outer surface to the center of the ingot along the radial direction. EDS analysis revealed the substantial presence of chromium, molybdenum, and carbon within the M23C6 along the grain boundaries. Phase transformation and the precipitation phase sequences were analyzed as a function of temperature and composition of eutectic transformation using the Thermo-Calc software and the predictions were validated with experimental findings

Superalloy Cooling System for the Composite Rim of an Inside-Out Ceramic Turbine

International audienc

Nanomechanics insights into the performance of healthy and osteoporotic bones

10.1021/nl402719qNano Letters13115247-5254NALE

Post-yield and failure properties of cortical bone

Ageing and associated skeletal diseases pose a significant challenge for health care systems worldwide. Age-related fractures have a serious impact on personal, social and economic wellbeing. A significant proportion of physiological loading is carried by the cortical shell. Its role in the fracture resistance and strength of whole bones in the ageing skeleton is of utmost importance. Even though a large body of knowledge has been accumulated on this topic on the macroscale, the underlying micromechanical material behaviour and the scale transition of bone's mechanical properties are yet to be uncovered. Therefore, this review aims at providing an overview of the state-of-the-art of the post-yield and failure properties of cortical bone at the extracellular matrix and the tissue level