Papers by Keyword: Dynamic Embrittlement

Abstract: Understanding damage mechanisms across scales is crucial to ensure the structural integrity of nickel-based superalloy components under demanding conditions. This study highlights key aspects of a multi-scale experimental approach for analyzing oxygen-induced cracking in Alloy 718. Microcantilever bending tests on specific grain boundaries were combined with corrosion tests and detailed analyses using high-resolution scanning electron microscopy, electron backscatter diffraction, and energy-dispersive X-ray spectroscopy. The results suggest that susceptibility to oxidative attack is significantly impacted by the type of grain boundary, emphasising the importance of local crystallography in oxygen diffusion and elemental redistribution. By bridging local microstructural features with global mechanical response, the presented multi-scale approach allows the parameterization of physically based material models and identifies grain boundary engineering as a promising strategy for improving damage tolerance.

Abstract: Cu-Cr-Zr-Ti alloys are widely used for fabrication of thrust chamber in liquid rocket engines, because of their high thermal conductivity and adequate strength. The alloy should be used in peak-aged condition to achieve the best combination of strength and conductivity. However, realization of final component involves forming and brazing operations which limit the usage of the alloy in peak aged condition. Therefore, an attempt has been made to study the effect of the simulated brazing treatment on the microstructure and mechanical properties using optical microscopy, electron microscopy, mechanical testing and hardness measurement. The high temperature brazing treatments resulted in tremendous grain growth. The measured hardness is observed to be in line with the grain size of the specimens. The hardness and tensile strength decreased in samples subjected to simulated brazing cycle, implying requirement for a post braze treatment. After the post brazing treatment the optimum mechanical properties have been achieved at room temperature. Low ductility was observed at 600°C in the samples subjected to simulated brazing cycle.

Abstract: The present paper is about dynamic embrittlement as a generic damage mechanism. It involves grain-boundary diffusion of an embrittling species at elevated temperatures under the influence of mechanical stress. The embrittling species, either coming from the material itself or from the environment, reduces the grain-boundary cohesion and, hence, causes time-dependent intergranular fracture. Evidence of the technical significance of dynamic embrittlement is given by two examples, stress-relief cracking in steels and hold-time cracking during low-cycle-fatigue loading of nickel-base superalloys. There is an obvious relationship between the grain-boundary structure and the local susceptibility to dynamic embrittlement. This was proven by mechanical experiments on bicrystals and grain-boundary-engineering-type-processed specimens.