Transformation Induced Plasticity Effects of a Non-Equal Molar Co-Cr-Fe-Ni High Entropy Alloy System

Abstract

Metastability-engineering strategy is an important topic for high entropy alloys (HEAs), owing to the transformation-induced plasticity effect (TRIP). In this work, TRIP effects of Co-Cr-Fe-Ni HEAs are investigated. Results indicate the tensile deformation-induced martensitic transformation occurs in Co 35 Cr 25 Fe 40−x Ni x (x = 0-15 at %) HEAs. The excellent combination of tensile strength (760 MPa-1000 MPa) and elongation (65-35%) owe to solid solution strengthening of Co and Cr, and the TRIP effect. In non-equal molar Co-Cr-Fe-Ni systems, with the decrease of Ni content, the values of stacking fault energy (SFE) decrease; thus, TRIP phenomena occurs. Based on the experimental investigation in three different regions of the Co-Cr-Fe-Ni multicomponent phase diagram, the face-centered cubic structured Co-Cr-Fe-Ni HEAs with VEC of~8.0 is more metastable, and TRIP phenomena are more likely to occur.

Role of magnetic ordering for the design of quinary TWIP-TRIP high entropy alloys

“…These trends are, however, not observed for Mn-containing HEAs, as pointed out in Refs. [31,33] and also in the present work. The present three Mn-containing HEAs confirm that the correlation between VEC and TRIP probability is weak.…”

“…Chen et al [32] confirmed similar trends for CrFeCoNi-based HEAs with Al, Cu, and Mo but again without Mn. Fang et al [33] have found that CrFeCoNi-based HEAs without Mn are prone to show TRIP when VEC≈8 due to the metastability of the fcc phase. These trends are, however, not observed for Mn-containing HEAs, as pointed out in Refs.…”

“…Thus, it is of high interest and significance to explore the effect of magnetism upon quinary Mn-containing HEAs. Valence electron concentration (VEC) values are also known to relate to the phase stability of HEAs [31][32][33]. For instance, recently Fang et al [33] observed that when the VEC value fall into a certain rage, a change of the deformation mechanism is expected for Cr 25 Fe 40−x Co 35 Ni x (x = 0-15 at.…”

Correlation analysis of strongly fluctuating atomic volumes, charges, and stresses in body-centered cubic refractory high-entropy alloys

“…Valence-electron concentrations (VECs) of HEAs have been previously discussed in relation to phase stabilities [56][57][58][59]. In the present study, the VEC of each alloy was computed as the average of the VECs of the constituent elements weighted by their concentrations in atomic percent, where the VECs of the elements in groups 4, 5, and 6 were taken as 4, 5, and 6, respectively.…”

Mechanical Performance and Microstructural Evolution of (NiCo)75Cr17Fe8Cx (x = 0~0.83) Medium Entropy Alloys at Room and Cryogenic Temperatures

“…It should be noted that the hardening rates of carbon-free (NiCo) 75 Cr 17 Fe 8 and low carbon (NiCo) 75 Cr 17 Fe 8 C 0.34 alloy even increased with strain in the strain range of 0.1-0.6 at 77 K. The plateau or hump of strain hardening rate in Figure 6 suggests the activation of a new deformation defect which can act as both deformation obstacles and deformation carriers. The increase of strain hardening rate with strain has been observed in various twin-induced plasticity (TWIP) [32][33][34][35] and transformation-induced plasticity (TRIP) alloys [34]. The excellent strength and ductility of (NiCo) 75 Cr 17 Fe 8 and low carbon (NiCo) 75 Cr 17 Fe 8 C 0.34 alloy in Figure 5 is attributed to the increase of strain hardening rate with strain in the strain range of 0.1-0.6 at 77 K. The tensile strength increased significantly up to~1400 MPa in carbon-containing (NiCo) 75 Cr 17 Fe 8 C 0.83 with a decent ductility of 106.…”