Microstructurally flexible high entropy alloys: Linkages between alloy design and deformation behavior. (September 2020)

• Record Type: Journal Article
• Authors: Nene, S.S.; Frank, M.; Agrawal, P.; Sinha, S.; Liu, K.; Shukla, S.; Mishra, R.S.; McWilliams, B.A.; Cho, K.C.
• Is Part Of: Materials & design. Volume 194(2020)
• Publication Date: 2020-09
• Subjects: Microstructural flexibility -- H.c.p. high entropy alloys -- Nano twins -- Nano plates -- Transformation induced plasticity; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2020.108968
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: Development of multicomponent alloys, popularly known as high entropy alloys (HEAs) provides abundant compositional space for designing a variety of HEAs, including equiatomic, dual phase and microstructurally flexible (MF-HEAs). Among them, the design of MF-HEAs further extends the HEA domain in terms of understanding adaptive phase evolution with respect to change in alloy chemistry and processing parameters. This responsive phase evolution enabled near single phase ε (h.c.p., 95%) or γ (f.c.c., 90%) dominant microstructures, depending on imposed processing strain, strain rate and temperature for a selected alloy chemistry. The γ-phase dominated HEAs showed slower yet sustained work hardening (WH) rates (~ 2000 MPa) owing to transformation induced plasticity (TRIP) effect whereas ε-phase dominated microstructure showed exceptionally high and sustained work hardening rates (2300–2700 MPa) due to formation of nano plates or twins in ε-phase upon deformation. Therefore, MF-HEA design leads to exceptional strength–ductility synergy (1100-1250 MPa, 30-43%) irrespective of the dominance of either γ- or ε-phase in the starting microstructure owing to selective operation of deformation mechanisms in the dominant phase. Graphical abstract: Unlabelled Image Highlights: Metastability based alloy design led to flexible microstructural evolution in which either thermodynamically stable γ-phase or unstable ε-phase was obtained at room temperature. The main strain accommodation mechanism in γ phase is TRIP exhibiting SN ((111) γ ∥ (0001) ε and 10 1 ¯ γ ∥ 11 2 ¯ 0 ε ) orientation relationship among γ/ε interfaces. Activation of non-basal activity assisted nano-plate formation at early stages and nano-twinning at later stages accommodated the deformation in ε phase. Flexibility-based design opened an uninvestigated compositional as well as mechanical property domain that is useful for higher flexibility in safe engineering design.