Microdistortions, Hardness, and Young’s Modulus of Multicomponent Bcc Solid Solutions

Abstract

The phase composition, type II microstresses, and coherent scattering domains (CSDs) of multicomponent (medium- and high-entropy) bcc solid solutions with an average electron concentration, Csd, ranging from 4.6 to 5.47 e/a were studied. The effect of these characteristics on the hardness and Young’s modulus was analyzed. The alloys were melted in a MIFI-9 vacuum arc furnace using components with a purity of at least 99.5 wt.%; the ingots were remelted six times. The hardness and Young’s modulus of the alloys were determined from nanoindentation curves plotted with a Micron Gamma unit under a load from 0.98 to 2.94 N using a Berkovich diamond pyramid under automated loading and unloading. A relatively small change in the quantitative chemical composition of the samples led to a noticeable change in the lattice parameter, type II microstresses, CSDs, microhardness, and Young’s modulus. The greatest possible type II microstresses and minimum CSD sizes were observed for the alloys characterized by high average mismatch between the atomic sizes of their constituent elements. Increase in the electron concentration in the alloys led to higher hardness and Young’s modulus and lower lattice parameter. Increase in the type II microstresses was also accompanied by higher hardness and Young’s modulus. The microhardness H of alloys significantly exceeded that calculated with the mixture rule, Hmix, and was determined by solid-solution hardening (∆H = H – Hmix ranging between 2.9 and 6.4 GPa). Type II microstresses precisely calculated from the X-ray line width can be used for measuring the distortion of the solidsolution lattice and assessing solid-solution hardening. The relationship between the magnitude of solid-solution hardening, Young’s modulus, and lattice microdistortions (type II microstresses) was proposed.