Coupling computational thermodynamics with density-function-theory based calculations to design L12 precipitates in FeNi based alloys. (June 2020)

• Record Type: Journal Article
• Authors: Yang, Ying; Samolyuk, German D.; Chen, Tianyi; Poplawsky, Jonathan D.; Lupini, Andrew R.; Tan, Lizhen; Ken, Littrell
• Is Part Of: Materials & design. Volume 191(2020)
• Publication Date: 2020-06
• Subjects: CALPHAD -- Density function theory -- Precipitates -- Morphology -- FeNi based alloys; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2020.108592
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: Achieving a high-volume fraction of thermodynamically stable L12 -type precipitates that are resistant to coarsening is of great importance for the development of low-cost FeNi based austenitic steels. With the aid of computational thermodynamics, this work designed two model alloys: Fe-37.4Ni-6.1Al-2.9Ti (FNAT) and Fe-45.2Ni-5.9Al-8.5Si (FNAS). Both alloys were designed to contain a similar amount of L12 precipitate in Fe-Ni matrix without forming other precipitates. Density-Function-Theory (DFT) calculation was coupled with computational thermodynamics to predict the critical radius at which the precipitates change shape from spherical to cuboidal. The calculation results suggest that critical radius for the FNAT alloy is about two orders of magnitude larger than that for the FeNiAlSi alloy. Phase stability and morphology of the L12 precipitates in these two alloys were experimentally investigated through X-ray diffraction, atom probe tomography, and scanning and transmission electron microscopy. The L12 precipitates in the FeNiAlSi system were found to be cuboidal and rod shaped, with much larger size than the spherical ones in the FeNiAlTi system, agreeing with the calculation results. This work suggested that coupling computational thermodynamics with DFT calculations can be reliably used to design L12 precipitates in FeNi based alloys. Graphical abstract: Unlabelled Image Highlights: The novelty of this work is to provide a design basis for developing low-cost Fe-Ni based superalloys. The FNAT alloy is exclusively strengthened ordered L12 precipitates without forming other detrimental intermetallic phases. The L12 precipitates in the FNAT alloy are thermodynamically stable and coarsening-resistant with desirable morphology.