Effect of Cr addition on the γ′ strengthened CoNiCrAlMo compositionally complex alloy

Abstract

The present study illustrates the effect of varying Cr content in Co_51-xNi₃₀Al₁₀Mo₅Nb₂Ti₂Cr_x (x = 2, 5, and 8 at.-%) compositionally complex alloys (CCAs). STEM-EDS analysis suggests a change in Mo partitioning from equal in both the phases (γ and γ′) in CCA-2Cr to the γ phase in CCA-5Cr and CCA-8Cr alloys. This peculiar compositional partitioning with Cr content beyond 2% brings a change in γ′ precipitate morphology from cuboidal to spheroidal in CCAs. The shape change-induced reduction in strain energy rendered a decrease in γ′ coarsening rate by ∼ 1/2, i.e. from 11.5 to 4.6 nm³/s in the CCA-2Cr and CCA-8Cr alloys, respectively. All three alloys show an anomalous increase in 0.2% proof stress (PS) with temperature and achieve peak values at 770°C.

KEYWORDS:

• Compositionally complex alloys
• thermodynamic calculations
• partition coefficient
• mechanical properties
• coarsening kinetics

Acknowledgements

The authors would like to acknowledge the microscopy facility available at the Advanced Facility for Microscopy and Microanalysis (AFMM) centre, Indian Institute of Science, Bangalore.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

KC is grateful for the financial support from Department of Science and Technology (DST) in the form of SERB distinguished Fellowship. KC also acknowledges the Gas Turbine Materials and Processes (GTMAP) programme of Aeronautics Research and Development Board, DRDO, for the financial support.