The influence of grain boundary character distribution on the high-temperature creep behavior and damage mechanism of Inconel 718

Abstract

Thermomechanical processing as the main method of grain boundary engineering (GBE), can modulate the grain boundary character distribution (GBCD) in turn affects the mechanical properties and stability of alloys at high temperature. In this study, the microstructural evolution and creep behaviour of different GBCD alloys were investigated during the creep process at 660 °C and 690 MPa, and the effect of GBCD on high temperature creep behaviour and associated damage mechanism were analyzed from the viewpoints of grain size, recrystallisation and dislocation motion. The findings indicate that the larger grain size prolongs the steady-state creep duration, which is beneficial to the increase of creep life. During the creep process, the coherent twin boundary is susceptible to transformation into non-coherent twin boundary, resulting in the loss of its difficult-to-migrate properties and increased susceptibility to becoming recrystallisation nucleation sites. Furthermore, the formation of twins is conducive to the stimulation of dynamic recrystallisation. Discontinuous dynamic recrystallisation, characterised by the nucleation and growth of grains, occurs concurrently with continuous dynamic recrystallisation with strain gradients and orientations. The combined effect of these processes is grain boundary slip and restricted dislocation migration, which in turn alter the creep properties of the alloy.

Keywords

• Inconel 718
• Grain boundary engineering
• Recrystallisation
• Creep behaviour
• Damage mechanism