Positron annihilation study of vacancies in Cu-28at.%Al-4at%Ni before and after martensitic transformation

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Abstract
Temperature dependence of the lineshape parameter (H-parameter) of Doppler-broadened 511 keV two-photon annihilation line has been measured for a Cu-28at.%Al-4at.%Ni single crystal quenched from 1000 degrees C into ice water, and the behaviour of quenched vacancies before and after martensitic transformation has been investigated. The present experiment has revealed for the first time the fact that vacancies are distorted just above the transition temperature of the martensitic transformation. According to this result, the authors propose that vacancies are generally distorted just above the transition temperature of the displacive structural phase transformation. The electrical resistance measurement has been also made, and the results are compared with the temperature dependence of the H-parameter.