Evaluation of fracture toughness of ZrO2 and Si3N4 engineering ceramics following CO2 and fibre laser surface treatment

Abstract

The fracture toughness property (K 1c ) of Si 3 N 4 and ZrO 2 engineering ceramics was investigated by means of CO 2 and a fibre laser surface treatment. Near surface modifications in the hardness was investigated by employing the Vickers indentation method. Crack lengths and geometry were then measured by using the optical. A coordinate measuring machine was used to investigate the diamond indentations and to measure the lengths of the cracks. Thereafter, computational and analytical methods were employed to determine the K 1C . An increase in the K 1C of both ceramics was found by the CO 2 and the fibre laser surface treatment in comparison to the as-received surfaces. The K 1C of the CO 2 laser radiated surface of the Si 3 N 4 was over 3 % higher in comparison to that of the fibre laser treated surface. This was by softening of the near surface layer of the Si 3 N 4 which comprised of lower in hardness, which in turn increased the crack resistance. The effects were not similar with the ZrO 2 ceramic to that of the Si 3 N 4 as the fibre laser radiation in this case had produced a rise of 34% compared to that of the CO 2 laser radiation. This occurred due to propagation of lower crack resulting from the Vickers indentation test during the fibre laser surface treatment which inherently affected the end K 1C though an induced compressive stress layer. The K 1C modification of the two ceramics treated by the CO 2 and the fibre laser was also believed to be influenced by the different laser wavelength and its absorption coefficient, the beam delivery system as well as the differences in the brightness of the two lasers used.

Development in laser peening of advanced ceramics

“…Typically, laser beam absorption also depends on the particular wavelength applied at the material surface. Particularly for ceramics, laser in the range of 1µm wavelength and under, tends to produce sufficient absorption [14][15][16][17] . …”

Laser shock processing of polycrystalline alumina ceramics

“…Their work show that tailoring LSP parameters can increase the surface hardness of alumina by up to 100% and the fracture toughness by 42%. Shukla and Lawrence applied the CO 2 and the fiber laser surface treatment to increase the fracture toughness of ZrO 2 and Si 3 N 4 ceramics . It was observed that the fracture toughness modification of these ceramics was influenced by different laser wavelengths and its absorption coefficient, the beam delivery system, and the brightness of the lasers .…”

“…Shukla and Lawrence applied the CO 2 and the fiber laser surface treatment to increase the fracture toughness of ZrO 2 and Si 3 N 4 ceramics . It was observed that the fracture toughness modification of these ceramics was influenced by different laser wavelengths and its absorption coefficient, the beam delivery system, and the brightness of the lasers . These early studies attributed the improved mechanical properties to the compressive residual stress induced by LSP, but did not elucidate the microscale mechanistic mechanisms .…”

Characterization and modification of technical ceramics through laser surface engineering

“…The beam travelled the length of 7 mm across the width of the as-received (laser unaffected) HAZ and the laserengineered surfaces areas. Mechanical effects such as change in hardness were investigated by using the Vickers indentation (Vickers (HVTM); Armstrong Engineering, Ltd.), which was followed by a calculation of the fracture toughness parameter (K 1c ) using empirical equations from the literature [48][49][50][51]. The temperature measurement was conducted using an infrared thermometer device (Cyclops 100 B; Land instruments international Ltd.) on the surface and also by using a precision fine wire (0.20 diameter  152 mm in length), R-type thermocouple (P13R, Omega Instruments Ltd.).…”