Effects of laser shock peening on silicon nitride ceramic with varying sintering additive ratios

Silicon nitride ceramic (Si₃N₄) for industrial applications is conventionally manufactured with sintering additives, and the properties of Si₃N₄ change significantly based on the contents of these additives. In this study, we investigate the effects of laser shock peening (LSP) on Si₃N₄ sintered with varying ratios of sintering additives.

The Si₃N₄ samples were sintered with a mixture of Y₂O₃, MgO, and SiO₂ sintering additives at 5, 7, 9, and 11 wt%. A Nd:YAG laser (wavelength = 532 nm, maximum pulse energy = 1.4 J, repetition rate = 10 Hz, pulse duration = 8 ns, beam diameter = 11 mm, top-hat profile) was used to irradiate the Si₃N₄ samples. The samples were coated with a protective layer (100 μm thick aluminum foil) and a water layer to confine plasma. LSP of Si₃N₄ with 5 % sintering additives resulted in a slight change in surface hardness but a 77 % decrease in surface compressive residual stress. In contrast, LSP of Si₃N₄ with 11 % sintering additives led to a simultaneous increase in surface hardness (7.3 %) and surface compressive residual stress (67 %), indicating a significant difference in the effectiveness of LSP depending on the ratio of sintering additives. Additionally, the surface of Si₃N₄ with 11 % sintering additives showed evidence of grain refinement after LSP. It was demonstrated that the bending strength of Si₃N₄ with 11 % sintering additives increased by 15.2 %, and the depth of the fracture origin was significantly deepened.