Photoacoustic microscopic imaging of a simulated pitting corrosions for brass and aluminum plates

Imaging of simulated pitting corrosions for brass and aluminum plates with photoacoustic microscope (PAM) has been demonstrated. Two types of simulated pitting corrosions are prepared. The first one is prepared by pressing with a steel ball used to the Rockwell hardness test (Rockwell indenter). Simulated pittings with a shape of columnar shape hole are fabricated on brass and pure aluminum plates by drilling. These pittings are etched chemically with concentrated nitric acid (for brass) or hydrochloric acid (for aluminum). Nondestructive measurement of simulated pitting corrosion with PAM including the chemical phase change of the specimens was demonstrated for a first time. The obtained PAM images of brass of a columnar shaped hole made by drilling agreed well with the theory based on a heat source model. Furthermore, the phase signal ratio and the actual depth change of etched hole for aluminum showed an excellent agreement up to the accuracy of 0.1% error