Deformation and fracture initiation of Ni3Al intermetallic single crystal turbine blade

Abstract

The present study deals with the determination of fracture properties of a cracked Ni3Al-based intermetallic single crystal turbine blade subjected to tensile load. The analysis has been carried out by accounting the effect of microstructure, strain hardening and damage development under monotonic loading. A continuum damage criterion combined with crystal plasticity model incorporating non-Schmid effects was employed to evaluate material damage owing to highly localised deformation. The damage evolution was defined as the function of a microstructure variable. The present coupled model was used to replicate the stress-strain behaviour of Ni3Al single crystals until material softening due to damage after necking. The model parameters were ascertained by a close match of the computed data with the available experimental data. Using the model, damage evolution near crack tip of a cracked Ni3Al turbine blade was assessed for randomly varying secondary orientations, while maintaining primary orientations same as that of along the solidification direction. The analysis helped to calculate the fracture initiation toughness (Ji) of turbine blade for various crystallographic orientations. Combined by damage formulation, analysis was continued to estimate the Ji values for different crack lengths in all the cases of orientation. Finally, triaxiality quotient (q) was computed to characterise the estimated Ji values as a function of crack tip constraints. The approach provides a useful way to analyse orientation dependent fracture behaviour of single crystal components with crack under mechanical loading.