The correlation between the shape memory effect(SME)and the ordering degree in martensite formed through various heat-treatment processes,e.g.ice water quenching, step-quenching and aging etc.,has been studied in a Cu-26Zn-4Al alloy.The martensite or- dering degree is estimated by △d,the spacing difference of some pairs of diffracting planes with indices satisfying a relation of(h_1~2-h_2~2)/3=(k_2~2-k_1~2)/n(n=1 for 9R martensite,n=4 for 18R martensite).M 18R martensite is obtained from step-quenching,in which the value of △d increases with the holding duration of step-quenching,and the shape recovery rate η increases synchronouslly.9R martensite is obtained from direct water-quenching,the value of △d is quite large and SME is also good at just quenching state.But both △d and η decrease continuously with aging time at room temperature.This stabilization phe- nomenon of martensite is explained by the observation of TEM lattice fringe image,and it may be attributed to the clustering of quenched-in supersaturated vacancies at (001)_M close-packed plane in martensite and decreasing the ordering degree.A reduction in △d and η occuring in the specimens on step-quenching or aging at higher temperature, which may be related to the precipitation of the α-phase and the enrichment of solute atoms, decreases the ordering degree.
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