Impact of microstructural properties on hardness of tungsten heavy alloy evaluated by stand-off LIBS after PSI plasma irradiation

Abstract

The key issue in tokamak is change of physical properties of plasma facing materials, such as tungsten due to extreme conditions and long pulse operation. Practically, it is difficult to analyze hardness changes online through conventional methods. Hence, an online monitoring technique is much desired which measures hardness changes in fusion devices. In this study, laser induced breakdown spectroscopy (LIBS) is used as in-situ monitoring tool to measure hardness of tungsten heavy alloy (97W–2Ni–1Fe) samples after exposure to different irradiation of plasma ranging from 0.108 to 1.00 MW/m2. The exposure of PSI plasma beam is a key factor which give rise to pronounced change in crystallographic estimation, microstructural properties and surface hardness. The X–ray diffraction study revealed modification in the structure caused, by variation in the peak intensity, crystal size, dislocation line density and micro-strains upon plasma irradiation. The change in crystallographic measurements and surface hardness are well correlated with irradiated PSI power densities. Moreover, the hardness influence on LIBS intensity of tungsten heavy alloy (WHA) was carried out. The LIBS calibration curves were formed by utilizing the ratio of ionic to atomic line intensities of tungsten versus the Vickers hardness. The ratio of ionic to atomic spectral emission line intensity and plasma electron temperature (Te), significantly increases with hardness. The obtained Pearson correlation coefficient (R2) values (in case of calibration curve and plasma temperature) in measuring hardness of all investigated samples have good approximation which indicate the preciseness of LIBS approach. The achieved results in the present study by in-situ LIBS system confirmed its potential ability to estimate the hardness of WHA more efficient than other conventional method.