Crack-free processing of hot-pressed silicon nitride ceramics using a pulsed YAG laser: fracture strength and residual stress

This paper describes the effect of crack-free laser processing of hot-pressed silicon nitride ceramics on fracture strength and residual stress. The fracture strength of the processed test pieces was determined by three-point bending tests. The residual stress in the processed surface was characterized by X-ray diffraction measurement. The strength of the laser-processed workpieces was reduced to 90-80% compared with that of the ground workpieces because of subsurface layer damage, which included the heat-affected layer and the residual stress layer. In particular, the latter greatly affected the fracture strength because the higher compressive residual stress layer generated during grinding was released by laser processing. It is concluded that the newly developed crack-free processing technique has great industrial possibilities.