Polycrystalline Ni-base superalloys (PXs) are used for applications where operating temperatures exceed 900 °C [1]. There is a permanent driving force towards higher thermal efficiencies and longer component lives which drives the development of new alloys. In the present work, we explore new PX compositions derived from the Nimonic family, referred to as C-263. The material was produced following an ingot metallurgy processing route including vacuum induction melting and subsequent thermomechanical treatments (including hot and cold rolling). Seven alloy compositions were considered, altering the levels of Al, W and Ti, with the objectives to (i) extend the stability range of the γ’ phase and (ii) to promote solid solution strengthening. Different aging parameters were considered to identify optimum peak-age conditions for each alloy and to identify the most promising material (VDM Alloy C-264). The effects of alloy compositions and heat treatments on the creep resistance and on the evolution of microstructures during creep was analysed, combining miniature tensile creep testing with analytical scanning and transmission electron microscopy (SEM and TEM). Moreover, atom probe tomography (APT) helped to understand the effect of local alloy chemistry on the partitioning of elements between the γ- and the γʼ-phase (matrix and particles, respectively). Effects associated with internal oxidation also were considered. For the alloys C-263 (commercial reference material) and the newly developed VDM Alloy C-264, the creep activation parameters n (stress exponent) and Q (apparent activation energy for creep) were determined [2] and discussed in the light of results reported in the literature for similar PXs. Directions for further alloy development research are discussed, i.g. VDM Alloy C-265.
[1] W. Betteridge et al., Materials Science and technology 9, 1987, 682-694
[2] J. Hunfeld, Mater. Des., 2021, 110174