Mechanical properties and yield strength modeling of a medium entropy alloy containing L12 precipitates

Abstract

Medium/High Entropy Alloys (M/HEAs) exit over immense compositional fields, which represent a challenging opportunity for the development of alloys with optimized properties. To realize their potential, we need to be able to predict properties of interest from different compositions effectively. Precipitation strengthened alloys are of wide interest, but their yield strength modeling is not simple because many factors as precipitate type, size, fraction, and composition play important roles. The Cr29.7Co29.7 Ni35.4Al4.0Ti1.2 (at%) alloy was designed to have a highly concentrated Cr-Co-Ni face centered cubic matrix with L12 precipitates. In the present work, this alloy was aged at 850 °C for times up to 166 h and had its yield strength measured in the different aging conditions through tensile tests. A recently developed model to calculate the solid solution contribution in FCC multi-principal element alloys was coupled with classical grain-boundary strengthening and precipitation hardening models to predict the yield strength of the studied alloy. We show that the different strengthening contributions can be modeled independently with satisfactory accuracy. The results can be easily extrapolated to other alloys of the Cr-Co-Ni-Al-Ti system. An empirical relationship to estimate the room temperature lattice parameter of FCC alloys is also proposed. A promising route to explore the vast compositional space of M/HEA and design new precipitation hardening alloys with optimized mechanical properties is suggested.