Exploring the fundamentals of Ni-based superalloy single crystal (SX) alloy design: Chemical composition vs. microstructure

The present work contributes to a better understanding of the basic assumptions and principles behind the design of Ni-based single crystal superalloys (SXs). For this purpose, we cast and heat-treat four SXs and compare their creep performances: ERBO/1 (with Re) and three ERBO/15 variants (no Re but increased levels of Ti, Mo and W). We show that Re can be replaced by other elements without losing creep strength. To come to this conclusion one has to consider both, alloy composition and microstructure. We analyze the mechanical, microstructural and chemical results (creep rates, gamma'-volume fractions, average gamma'-particle sizes, average gamma-channel widths and the chemistry of gamma- and gamma'-phases) obtained for ERBO/15 and its two leaner variants (less Mo: ERBO/15-Mo and less W: ERBO/15-W). ERBO/15-Mo and ERBO/15-W show higher creep rates than ERBO/15, because they exhibit lower Mo and W concentrations in the gamma-channels. This results in higher diffusion rates, accelerated rafting and faster dislocation climb at gamma/gamma'-interfaces. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).