Alteration of fracture toughness (KIC) following laser shock peening of silicon nitride ceramics

Abstract

This work focuses on the development in laser shock peening (LSP) Si3N4 ceramics with a view to first observe the general effects namely; the topography, hardness, flaw size, plane strain fracture toughness (KIc). Firstly, an LSP surface treatment was conducted to establish a crack-free surface treatment. This also established a parametric window and elucidated the feasibility of treating a brittle material such as Si3N4 with a high intensity/pressure surface treatment such as LSP. Upon comparing the as-received surface with the LSPned surface elucidated a natural increase in surface roughness from an average of 1.73µm to 4.79µm. This indicated some level of material removal. In addition, a decrease in hardness was found by 4.5% and an increase in the KIc by over 21.5% through a possible induction of plasticity within the Si3N4. The microstructure of the Si3N4 also showed considerable changes after LSP surface treatment and a possible α-beta transformation were introduced which indicated surface strengthening. The work undertaken herein have shown that with further refinement of the LSP parameters, this type of laser treatment could be beneficial for strengthening advanced ceramics, particularly, as the process offers a mechanism for enhancement in fracture toughness. An alteration of such an important property of a Si3N4 would open new avenues for its applications particularly where metals and alloys fail.This work focuses on the development in laser shock peening (LSP) Si3N4 ceramics with a view to first observe the general effects namely; the topography, hardness, flaw size, plane strain fracture toughness (KIc). Firstly, an LSP surface treatment was conducted to establish a crack-free surface treatment. This also established a parametric window and elucidated the feasibility of treating a brittle material such as Si3N4 with a high intensity/pressure surface treatment such as LSP. Upon comparing the as-received surface with the LSPned surface elucidated a natural increase in surface roughness from an average of 1.73µm to 4.79µm. This indicated some level of material removal. In addition, a decrease in hardness was found by 4.5% and an increase in the KIc by over 21.5% through a possible induction of plasticity within the Si3N4. The microstructure of the Si3N4 also showed considerable changes after LSP surface treatment and a possible α-beta transformation were introduced which indicated surface strengthe...