The present disclosure relates to nanostructured ferritic alloy (NFA) components, and more particularly, weldable components comprising an NFA and welded articles thereof.
Turbomachines such as heavy-duty gas turbines and jet engines operate in extreme environments, exposing the turbine components, especially those in the turbine hot section, to high operating temperatures. Turbine components are necessarily manufactured from materials capable of withstanding these severe conditions.
Superalloys have been used in these demanding applications because they maintain their strength up to 90% of their melting temperature and have excellent environmental resistance. Nickel-based superalloys used in heavy-duty turbine components require specific processing steps to achieve the desired mechanical properties. In some lower temperature and stress applications, steels may be used for turbine components. However, designs for improved gas turbine performance require alloys with even higher temperature capability. Nanostructured ferritic alloys (NFAs) are an emerging class of iron-based alloys that exhibit exceptional high temperature properties. These properties are typically derived at least in part from nanometer-sized oxide particulates or clusters that precipitate within the alloy matrix during hot consolidation following a mechanical alloying step. These oxide particulates or clusters remain present at high temperatures, providing a strong and stable microstructure during service.
Turbine components, such as rotors and shafts, made of conventional steel or superalloys, are typically joined to one another to form an assembly. Joining is generally performed by either bolting or welding. Removing bolt holes allows for material reduction and elimination of a key concentrated stress area in the rotor. This can lead to design flexibility and simplification. In comparison to other joining processes, conventional welding is a relatively simple and inexpensive process. Moreover, welding can generally be used to form a strong joint, while reducing the required flange height and the mass of the rotor as compared to that of in case of bolting. However, NFA components cannot be welded by conventional methods while preserving their microstructure and mechanical properties, as will be explained in more detail below.
Therefore, it is desirable to have NFA components, for example components for turbomachinery that can be welded to other components without sacrificing the mechanical properties of NFAs at operating temperatures.