Mechanical properties and microstructure of IN713LC nickel superalloy castings

Abstract

IN713LC is a nickel-base casting alloy developed for applications requiring high strength at elevated temperatures. Its balanced composition provides a good combination of tensile and creep-rupture properties as a result of gamma-prime strengthening enhanced by solid solution and grain-boundary strengthening. IN713LC alloy performs a good castability. Castings are used in as-cast state, without heat treatment. Currently, this alloy is used widely, for example, for manufacturing of turbine wheels in turbochargers. Recently, customers demand the production of increasingly larger parts of impellers than before. This requirement has resulted in a greater weight of castings and thus different conditions during solidifying and cooling of the castings. Therefore modified castings microstructure arises. When approving the castings, mechanical values are measured by tensile test on test samples made from the centres of the castings. These test samples often exhibit lower values than required, in particular the rupture strength and elongation at room temperature. The presence of brittle niobium carbides in the structure of the alloy was identified as the main cause of this situation, which originated as a result of the slow cooling rate. Test samples made from fast cooled castings show significantly higher mechanical properties at room temperature.