This paper describes an analytical method for determining the spatial distribution of alumina inclusion particles in several ferritic stainless steels by laser-induced breakdown optical emission spectrometry with a single-shot laser scanned on the sample surface. For this purpose, an irradiation system, which comprised a Q-switched Nd:YAG laser with an average energy of 50 mJ/pulse and a precisely driven X-Y-Z sample stage, was prepared. A Czerny-Turner-mounting spectrograph equipped with an ICCD detector was employed for a time-resolved measurement of the laser-induced breakdown optical emission spectrometry signal. The intensity ratio of Al I 396.152 nm to Cr I 396.368 nm was measured each for the single shot, while the irradiation positions were step-wise moved in the X-Y direction and then the same sampling area was repeatedly irradiated by subsequent laser shots in the Z direction. The number of alumina particles was mapped from the intensity ratio of Al/Cr each for the irradiation points in both the lateral and in-depth directions, enabling the distribution of alumina particles to be presented. The resolution of our measuring system was 40 μm in the lateral position and 6-7 μm in the depth direction, which were mainly determined by the crater size of a laser shot. A typical size of the alumina particles (several μm) was smaller than their resolutions; nevertheless, the suggested method would be still more effective to give the distribution of alumina particles, especially the coarse ones, because of its rapid response for the analytical result.

Laser-beam scanning-laser-induced breakdown plasma optical emission spectrometry was applied to obtain the elemental distribution in three-dimensional direction for different surface states corresponding to chemically-pretreatments of an Al-alloy sample. The distribution of magnesium oxide inclusion particles could be estimated from the intensity ratio of Mg/Al each for the irradiation points, indicating that chemical-etching and desmutting treatments made the magnesia particles to be reduced both in the lateral and in-depth directions. The resolution of our measurement was within 200 μm in the lateral position and ca. 15 μm in the depth direction, which were mainly determined by the crater size of the laser shot. The objective of this paper is to suggest an analytical technique suitable for evaluating the spatial distribution of inclusion or contaminant particles on the surface rapidly during the chemical surface pretreatment of Al-alloy materials.