Limit of detection and hardness evaluation of some steel alloys utilizing optical emission spectroscopic techniques

Steel alloys are of the most useful materials utilized in the manufacture of various industrial components. In this work, Laser-induced breakdown spectroscopy (LIBS) and spark-induced breakdown spectroscopy (SIBS) techniques have been used as diagnostic tools for the elemental composition of steel alloys and determination of the limit of detection (LOD). Also, the surface hardness of these alloys was measured using the ratio between the Calcium ionic and neutral lines (Ca II/Ca I) as well as the well-known method of mechanical Vickers one. The self-absorption of silicon, copper and calcium lines under investigation was corrected via comparison of the electron densities. The densities have been measured from these lines to that calculated from the hydrogen Hα-line at 656.27 nm which are in the same spectra under the same condition. Calibration curves were achieved for Si and Cu with linear regression coefficients about 0.99 and limits of detection values were 147 and 89 ppm respectively. Also, high accuracy linear relations have been obtained between Vickers mechanical hardness, the ratio between the Calcium ionic and neutral lines (Ca II/Ca I) and the plasma temperature. These results proved the importance of correcting the spectral intensity line for the self-absorption effect before the LOD measurement. Also, they confirmed the correction importance before evaluation of the hardness in LIBS experiments.