Laser surface modification of metal-coated ceramics

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Abstract
Pulsed excimer laser radiation has been successfully employed in the improvement (> 50%) of fracture strength of metal-coated ceramics. Thin metallic layers (∼500 Å) of nickel were deposited on silicon nitride and silicon carbide substrates and further irradiated with pulsed excimer (xenon chloride, krypton fluoride) laser pulses. The laser energy density was varied from 0.4 to 2.0 J cm −2 to optimize the formation of mixed interfacial layers. The formation of interfacial layers was studied by transmission electron microscopy and Rutherford backscattering spectrometry techniques. Detailed heat flow calculations using implicit finite difference methods were performed to simulate the effects of intense laser irradiation on metal-coated ceramic structures. Three different mechanisms were found to play an important role in the improvement in the fracture strength of these ceramics. Theoretical calculations showed that the displacement of the crack tip away from the free surface by laser surface modification can lead to a 100% improvement in the fracture strength of the ceramic.