Hall–Petch and grain growth kinetics of the low stacking fault energy TRIP Cr40Co40Ni20 multi-principal element alloy

Abstract

The Cr40Co40Ni20 multi-principal element alloy (MPEA) displays a single-phase face centered cubic initial structure, which partially transforms to hexagonal close packed (HCP) phase by transformation-induced plasticity (TRIP) during straining, as evidenced by nanometric HCP lamellae that provide enhanced mechanical properties. This MPEA also exhibits significant yield strength—grain size dependence, given by the high Hall–Petch coefficients (k = 667 MPa/μm−0.5 and σ0 = 299 MPa). The high activation energy for grain growth (QG = 533 kJ/mol) leads to refined grain structures after conventional heat treatments. These features, combined with the large solid solution strengthening of Cr-rich Cr-Co-Ni MPEAs, grant the Cr40Co40Ni20 alloy a great combination of strength and ductility under tension. Finally, an empirical equation is proposed to describe the stacking fault energy (SFE) of Cr-Co-Ni alloys, contributing to the prediction of the acting deformation mechanisms. Such findings highlight the potential of compositional tuning to enhance multiple strength and deformation mechanisms in the Cr-Co-Ni system.

A Hall–Petch study of the high toughness Cr40Co30Ni30 multi-principal element alloy

“…As shown in Fig. 8, the estimated toughness of the Cr 40 Co 30 Ni 30 , estimated as the area under the stress-strain curve, could be even higher than that of CrCoNi and Cr 45 Co 27.5 Ni 27.5 , two of the toughest alloys ever reported [6,19].…”

“…where r is the radius of the pinning particles and f represents its volume fraction. The particles found in the material studied in this work represented 2.4% of its volume, and were characterized (5) R c = 4r 3f , [19].…”

“…It is observed, in Fig. 7(a), several very thin lamellae crossing the FCC matrix, [19], CrCoNi [31], CrMnFeCoNi [32], and S304H stainless steel [33]. Invited Feature Paper which are either twins or HCP phases.…”

“…Grain refinement plays an important role, once it is a mechanism that is capable to conclude in increase of strength and ductility simultaneously [17]. For the equiatomic CrCoNi, grain refinement shows great strengthening of the alloy, which can be associated with the fact that its Hall-Petch coefficient stands out against other similar alloys and pure metals [18,19].…”

“…Hence, factoring the considerations regarding thermodynamic stability and solid solution strengthening calculations, the Cr-rich Cr 40 Co 30 Ni 30 MPEA was chosen as an alloy with great potential to display increased solid solution strengthening [20] and great strain-hardening rates associated with the occurrence of induced plasticity mechanisms (TWIP and TRIP) [19]. In the present work, this alloy was produced and characterized, the mechanical properties were evaluated by tensile tests at different annealing conditions to evaluate the role of grain refinement in its mechanical properties through Hall-Petch and grain growth kinetics analysis.…”