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This paper introduces a unified crystal plasticity-fracture framework that explicitly models polycrystalline microstructures to investigate the transition between inter- and trans-granular creep cracking. The framework reveals how stress-dependent competition between grain-boundary cavitation and slip-induced intragranular cracking dictates the shift from trans-granular to mixed to inter-granular dominated cracking. This mechanistic understanding quantifies the linkage between microscopic fracture modes and macroscopic creep rupture behavior, including changes in ductility and creep life.
A single computational framework unifies crystal plasticity and fracture to reveal the stress-driven shift from ductile trans-granular to quasi-brittle inter-granular creep rupture.
High-temperature creep in metals remains challenging due to the complex interplay of deformation and failure mechanisms across multiple length scales. The trade-off between inter- and trans-granular cracking governs the transition of creep rupture behaviour in metallic materials. However, the micromechanical basis of the transition and its linkage to the macroscopic brittle to ductile transition in creep rupture behaviour remain unresolved. Here, the stress-dependent competition between grain-boundary cavitation and slip-induced intragranular cracking is revealed via a unified crystal plasticity fracture framework. The framework incorporates crystal plasticity, grain-boundary cavitation, and crystallographic crack propagation within an explicit polycrystalline microstructure. The microscale computation reveals the transition from trans-granular-dominated cracking at high stress levels to mixed inter- and trans-granular cracking at intermediate stresses and inter-granular-dominated cracking at lower stresses, accompanied by distinct damage localization modes and the evolution of crack paths from grain boundary to grain-interior propagation. The results further quantify the linkage between microscopic fracture mechanisms and macroscopic creep rupture behaviour, including changes in rupture ductility and creep life. Under high-stress conditions, deformation-driven trans-granular damage localization promotes ductile rupture through extensive strain accumulation, whereas under lower-stress conditions, time-dependent grain-boundary damage accumulation leads to quasi-brittle rupture through localized inter-granular fracture.