Qualification of Ni-Based Alloys for Advanced Ultra Supercritical Plants

For the realization of advanced ultra-supercritical plant operating at service temperatures of up to 720 °C plants Ni-based alloys are indispensable. This paper describes the on-going investigations on the qualification of several Ni-based alloys such as Alloy 617, Alloy 263 and Alloy 740 within the framework of the German state funded R&D initiative COORETEC. For safe design and reliable operation of components the requirements of the European Pressure Equipment Directive (PED) have to be fulfilled. Experimental work was done in order to determine the relevant material characteristics, such as long-term creep strength values for the design of critical components. Also new design methods based on numerical calculation of the creep behaviour by using a constitutive creep equation including a damage parameter are required to make full use of the strength potential but also taking into account their specific stress-strain relaxation behaviour. Investigation of the microstructure by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the as delivered and crept state show the changes in precipitation depending on time and temperature.