Identification of chemical surrounding and type of vacancy defects in the damaged region of ion irradiated Ni–Cr alloy

Abstract

Identification of defects such as vacancy, ion-vacancy complex, vacancy clusters and voids etc. in the damaged region of ion-irradiated alloys is required to establish the structure–property relationship. Positron annihilation spectroscopy, due to very high propensity of positrons towards open volume defects, is extensively used to characterize the vacancy defects in the damaged region of ion irradiated alloys. However, in the absence of model calculations, experimental observations are qualitatively attributed to different possibility of defects in the damaged region. In the present study, positron lifetime and Doppler broadening calculations in different configurations of defects such as vacancy, vacancy cluster, ion-vacancy complex and implanted ions clusters have been performed in Ni–40% Cr alloy considering irradiation induced damage using H, He and Ar ions. The variations observed in positron lifetime and line shape parameters clearly show the effect of chemical surrounding and type of defects on positron annihilation characteristics. On comparison with experimental data, defect type and their chemical environment have been unequivocally identified in the damaged region of He ion-irradiated Ni–Cr alloy. The observed trends of positron annihilation characteristics could be applicable to a number of transition metal alloys for identification of ion-irradiation induced defects.