On the Establishment of an Appropriate Method for Evaluating the Residual Stresses after Laser Surface Treatment of ZrO2 and Si3N4 Engineering Ceramics’

A new approach of predicting the residual stresses following a CO2 and
fibre laser surface treatment of Si3N4 and ZrO2 engineering ceramics is
proposed. The approach used a three-point bending test to predict the
localized residual stresses present within the engineering ceramics by
using condition of static equilibrium and bending moment. This allowed
one to determine the local microscopic residual stresses present and an
understanding of the stress state within the surface and through the crosssection of the as-received and the laser irradiated engineering ceramics.
The findings showed that both of the CO2 and the fibre laser irradiated
samples induced tensile residual stress into the engineering ceramics
through the high temperature gradient that was inhibited by the laser surface treatments in comparison to the as-received samples of the two
engineering ceramics. The results were more significant for the fibre laser
surface treated ZrO2 engineering ceramic in particular as opposed to the
CO2 laser radiated ZrO2 engineering ceramic. It was postulated that the
difference in the depth of energy absorbed by the fibre laser in comparison
to the CO2 laser as well as the temperature difference between the two
lasers was inducing different level of thermal energy into the sub-surfaces
of the ZrO2 and the Si3N4 engineering ceramics. This inherently had
generated variation in the residual stress induced within the bulk of the
engineering ceramics as there was more expansion and contraction
produced within the samples irradiated by the fibre laser as opposed to the
CO2 laser which produced lower processing temperature.