• Genée, Julien Genee

Abstract

This thesis research focused on interactions between slip bands – manifestation of plastic strain localization in polycrystalline metallic materials – and grain boundaries. The material chosen for the study is a nickel based superalloy (UdimetTM 720Li). Recent investigations have shown that slip bands blocked at grain boundaries can induce significant crystalline elastic rotation in highly localized regions – referred to as micro-volumes – in neighboring grains. This phenomenon is observed from room to intermediate temperatures (T < 500°C), under monotonic or cycling loading. It is responsible for the first stages of damage initiation and is at the origin of fatigue fatal cracks.A statistical analysis was carried out over a large data set of slip bands – grain boundaries interactions through SEM observations performed on pre-deformed samples. Local crystallographic configurations were investigated in order to identify those that favor or inhibit the formation of micro-volumes. A peculiar role of the twist angle - related to the alignment of slip systems on both sides of the grain boundary – was evidenced, particularly in the case of twin boundaries.Then, two strategies of numerical modeling of the interaction between a slip band and a neighboring grain using full-field finite element simulation were developed. In this work, the elastic regime only is considered and distributions of crystalline rotations, stresses and resolved shear stresses at the tip of theim pinging slip band in the neighboring grain were analyzed in order to better understand the conditions leading to the transmission of slip through the grain boundary and those leading to the termination of slip bands with or without formation of micro-volumes.

Topics

• impedance spectroscopy
• polymer
• grain
• nickel
• grain boundary
• scanning electron microscopy
• simulation
• crack
• fatigue
• superalloy