Diffusion processes during creep at intermediate temperatures in a Ni-based superalloy

Abstract

The local compositional changes associated with stacking fault and microtwin formation during creep at intermediate temperatures in a commercial Ni-base disk superalloy are explored. In order to investigate microtwin formation, an [001] single crystal of ME3 was tested in compression at 760 °C under a stress of 414 MPa – a stress-temperature regime found to promote microtwinning. Atomic resolution scanning transmission electron microscopy combined with state-of-the-art energy dispersive X-ray (EDX) spectroscopy analysis reveals the presence of Co and Cr rich Cottrell atmospheres around leading dislocations responsible for the creation of SISFs, SESFs, and microtwins. This analysis also highlights the role that tertiary γ particles inside γ′ precipitates have on γ′ shearing deformation mechanisms. Through the use of CALPHAD calculations, combined with new experimental observations, new insights into the rate-controlling processes during creep deformation are discussed.