Outstanding cryogenic strength-ductility properties of a cold-rolled medium-entropy TRIP Fe65(CoNi)25Cr9·5C0.5 alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2022-03, Vol.836, p.142720, Article 142720
• Main Authors: Povolyaeva, E., Mironov, S., Shaysultanov, D., Stepanov, N., Zherebtsov, S.
• Format: Article
• Language: English
• Subjects: Alloys; Casting alloys; Cold; Cold rolling; Cryogenic temperature; Ductility; Entropy; Ferrous alloys; Fracture toughness; High strength; Liquid nitrogen; Low temperature; Martensite; Martensitic transformation; Martensitic transformations; Mechanical properties; Medium-entropy alloys; Microstructure; Phase transitions; Solid solutions; Solution strengthening; Strain hardening; Thermal stability; Transformation-induced plasticity
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2022.142720

A new medium-entropy Fe65(CoNi)25Cr9·5C0.5 (at.%) alloy was investigated both at room and liquid nitrogen temperatures in both the as-cast and deformed conditions. The deformed sample was obtained by cold rolling the alloy until a thickness reduction of 80% had been reached. During testing at −196 °C, the cold-rolled program alloy exhibited a combination of very high strength (σ0.2 = 1360 MPa, σUTS = 2070 MPa), good ductility (δ = 26%) and excellent fracture toughness (approximately 700 kJ/m2). Examination of the microstructure suggested a deformation-induced phase transition from the initial face-centered cubic (fcc) phase to the martensite body-centered cubic (bcc) phase. The enhanced mechanical properties of the cold-rolled alloy at cryogenic temperatures, in comparison with the as-cast alloy, could be associated with an increased thermal stability of the fcc phase caused by deformation-induced microstructure refinement and shifting of the main martensite transformation to later stages of strain. Substructure strengthening, interphase strengthening, and solid solution strengthening could also contribute to the high strength and good ductility of the alloy. The obtained results can expand the possibilities for the development of medium-entropy ferrous alloys for use at extremely low temperatures.