Tensile behavior of Cu–35Zn (wt%) α-brass alloy at liquid helium temperature

Abstract

To evaluate the reliability of the mechanical properties of α-brass Cu–35Zn (wt%) alloys at extremely low temperatures, we performed tensile tests at 298, 77, and 4.2 K with an initial strain rate of 1 × 10⁻³ s⁻¹. Results showed that the yield strength, ultimate tensile strength, and tensile elongation increased as the tensile temperature decreased. Moreover, only two tensile curves obtained at 298 and 4.2 K exhibited a serrated flow. The serrations appearing at 298 K were caused by dynamic strain aging based on the interaction between diffusible Zn solute atoms and mobile dislocations, whereas those appearing at 4.2 K resulted from mechanical instability based on the edge dislocation avalanche. The increasing tensile strength with a decreasing tensile temperature originated from a combination of four different factors: 1) an increase in the yield strength because of a rise in the Peierls–Nabarro stress; 2) increases in the dislocation densities because of the suppression of dynamic recovery; 3) an increase in the number of dislocation structures due to the changes in the dislocation density and slip planarity; 4) an increase in the number of mechanical twins owing to the higher given tensile strength and lower stacking fault energy. The increase in tensile elongation with a decreasing tensile temperature was caused by the more aggressive formation of mechanical twins and dislocation structures, which caused a delay in stress localization. This aggressive formation also resulted in a finer and denser dimple morphology with a decreasing tensile temperature.