Irradiation damage behavior of Ni based alloy studied using positron annihilation spectroscopy

The present study is mainly focused on understanding the effect of Helium ion irradiation on the microstructure of a Ni-41.5%Cr-1.5%Mo alloy. For this purpose, a set of three samples were prepared by standard metallographic techniques and irradiated at fluence values of 3×10¹⁶, 2×10¹⁷, and 7×10¹⁷ ions/cm² respectively using He ion beam having energy of 65 keV. All the irradiation experiments were carried out at room temperature and in vacuum of approximate 10^-6 mbar. The irradiation damage depth profile was simulated using SRIM software. After irradiation the samples were subjected to depth dependent Doppler broadening measurements using slow positron beam. The variable energy positron fit analysis of depth dependent momentum distribution suggested formation of two different layers within the damaged region having different characteristic S-parameter values. Irradiation induced hardness was ascertained using nano indentation technique. A linear correlation between hardness and the characteristic S-parameter of the damaged region is established and rationalized. (author)