Damage mechanism of Al₂O₃ ceramic coatings irradiated by CO₂ CW laser

Rules and mechanism of damage in Al₂O₃ coatings irradiated by CO₂ CW laser are studied in order to improve the ability of parts of equipment standing against the high power laser. Al₂O₃ coatings were sprayed by air plasma spray (APS) on the 45^# steel substrate, and then were irradiated by CO₂ CW laser from 795 W/cm² to 31830 W/cm². As the output power of the laser is increasing, its porosity is increasing and cracks are appearing and spreading quickly. And also the phase will transform from γ-Al₂O₃ to α-Al₂O₃ in the damaged areas. When the energy density is 17507 W/cm², the coatings are destroyed completely. The thermal infection field on substrate is rather small. The laser energy is depleted by the phase transformation and cracks in Al₂O₃ coatings during the laser thermal shock.