Crack-Free Processing of Hot-Pressed Silicon Nitride Ceramics using Pulsed YAG Laser

Abstract

It is difficult to eliminate recast layers and cracks in laser-machining caramics. These defects significantly detract from the excellent properties of ceramics. This paper describes the feasibility of a crack-free processing method for hot-pressed silicon nitride (Si₃N₄) ceramics using a yttrium aluminum garnet (YAG) laser. The Q-switched YAG laser pulses controlled at below 500 ns in duration and 10 kHz in repetition rate are effective for the purpose of crack-free machining of Si₃N₄ ceramics because the thermal stress is most likely localized only in the laser-heated shallow area. The integrity of the crack-free surface is evaluated by the fracture strength and residual stress. The strength of laser-processed test pieces is reduced by 10 to 20% compared with diamond-ground ones because the high residual compression layer generated during grinding is removed.