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, С_sd, ranging from 4.6 to 5.47 e/a were studied. The effect of these characteristics on the hardness and elastic 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 elastic modulus of the alloys were determined from nanoindentation curves plotted with a Micron Gamma 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 elemental composition of the samples led to a noticeable change in the lattice parameter, type II microstresses, sizes of CSDs, microhardness, and elastic modulus. The maximum high values of type II microstresses and the minimum sizes of CSDs were observed for the alloys having a rather high average mismatch between the atomic sizes of the elements constituting the alloys. An increase in the electron concentration in the alloys led to higher hardness and elastic modulus and lower lattice parameter The increase in the type II microstresses was also accompanied by higher hardness and elastic modulus of the alloys. The microhardness of alloys H significantly exceeded that calculated according to the mixture rule, H_mix, and was determined by solid-soluble hardening (ΔH = H – H_mix in the range 2.9–6.4 GPa). Type II microstresses precisely calculated from the X-ray line width can be used for measuring the distortion of the solid solution lattice and assessing the solid-solution hardening. The relationship between the level of solid-soluble hardening, elastic modulus, and size of lattice microdistortions (type II microstresses) was proposed.