Correlation between Fe-V-C alloys surface hardness and plasma temperature via LIBS technique

Surface hardness is a very important characteristic of metals. Its monitoring plays a key role in industry. In the present paper, using laser induced breakdown spectroscopy (LIBS), Fe-V18%-C1% alloys with different heat treatments have been used for making the correlation between surface hardness and laser-induced plasma temperatures. All investigated samples were characterized by the same ferrite phase with different Vickers surface hardnesses. The differences in hardness values were attributed to the crystallite size changes. A linear relationship has been obtained between the Vickers surface hardness and the laser induced plasma temperature. For comparison the relation between surface hardness and the ratio of the vanadium ionic to atomic spectral lines intensities (VII/VI) provided good linear results too. However, adopting the proposed approach of using the plasma temperature, instead, is more reliable in view of the difficulties that could be encountered in choosing the proper ionic and atomic spectral lines. To validate this approach we have investigated the shock wave speed induced by laser interaction with the used samples. It was found that harder is the material faster is the shock wave. The determination of the surface hardness via measuring Te shows the feasibility of using LIBS as an easy and reliable method for in situ industrial application for production control.