Creep deformation and rupture mechanism of an advanced wrought NiFe-based superalloy for 700 °C class A-USC steam turbine rotor application

The 700 °C class Advanced Ultra-Super-Critical (A-USC) technology with higher thermal efficiency is being developed for next-generation coal-fired power plant in recent years to reduce environmental impacts of energy consumption. A new wrought NiFe-based superalloy with excellent high creep strength and low cost has been developed recently and evaluated as a candidate material for the 700 °C class A-USC steam turbine rotor application. Creep tests were conducted on the new NiFe-based alloy at 700 °C/200 MPa, 700 °C/250 MPa and 725 °C/150 MPa using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The creep-rupture testing results show the new NiFe-based alloy has better creep-rupture strength than the existing commercially available NiFe-based and even some Ni-based alloys. The focus of this study is on understanding the relative important causes of better creep resistance and reduced rupture life in grain interiors and grain boundaries. Detailed creep deformation behaviors and related creep-rupture mechanisms were analyzed and discussed to explore the potential approaches for performance improvements. The results presented are helpful in providing a new approach to design and develop novel high performance alloys for A-USC steam turbine rotor application.