Nanomechanical analysis of the mechanical behaviour of selected up-quenched and step-quenched Cu–Zn–Sn shape memory alloys

The impact of quenching treatment on the mechanical characteristics of Cu–Zn–Sn-based SMAs is investigated using nanoindentation approach conducted at 100–200 mN loads. Two compositions labeled A (Cu_71·19Zn_15·6Sn_{12· 1}Fe_1.05) and B (Cu_63·73Zn_26·1Sn_9·3Fe_0.82) were subjected to step/ up-quenching procedures. The microstructure was composed of Cu₄ and γ-Cu₅Zn₈ parent phases with sparse distribution Fe₄ and Cu₃Sn precipitates in the matrix for the up/step-quenched A samples. The step-quenched B samples comprised Cu₃Sn and Fe₄Zn₉ precipitates in Cu4 and γ-Cu₅Zn₈ parent phases, whereas the up-quenched B samples is composed of Cu₃Sn and Fe₇Zn₃ second phases. The nanomechanical properties of composition B samples were generally superior to those of composition A samples. For B alloys, the superelasticity increased from 91.91 %, 86.97 %, and 85.01 % at 100 mN load to 93.41 %, 91.80 %, and 88.75 % at 200 mN load for the step-quenched, up-quenched, and direct-quenched samples, respectively. The reduced elastic modulus at 100 mN lie in the range of 122.23–131.84 GPa for the step-quenched samples; 119.86–128.81 GPa for the up-quenched samples; and 116.79–125.16 GPa for the direct-quenched samples. Step-quenching thermal procedure efficiently enhanced the nanomechanical characteristics of the alloys.