Surface hardness comparison for materials having different matrices via laser-induced breakdown spectroscopy

Hardness testing is one of the essential tests in material science. Consequently, there is a growing demand for fast, reliable, and portable hardness techniques. Laser-Induced Breakdown Spectroscopy (LIBS) is a promising tool for relative hardness estimation. Its efficiency, lack of sample preparation, and portability make it a preferred choice over other methods. The LIBS has been mainly used to assess the relative hardness of materials with the same matrix. In this work, we present that the LIBS can compare the hardness of samples of totally different matrices. The relation between samples surface hardness and ionic to atomic spectral lines intensity ratio and the relation between the samples surface hardness and excitation temperature (Te) were studied on tungsten carbide alloys and ZrO2/YO2 ceramic. The LIBS optimum delay results showed the best delay to be 1500 ns using a gate of 2000 ns. McWhirter's criterion confirms the fulfillment of the LTE conditions. It was found that atomic spectral lines intensity ratio is linearly dependent on material's density instead of hardness, and Te. Also, it was found that there is a good agreement between the hardness measured by LIBS and the conventional mechanical hardness. Our study shows that the LIBS can be used for the relative hardness measurement of materials with different matrices.