Fracture toughness of a zirconia engineering ceramic and the effects thereon of surface processing with fibre laser radiation

Vickers hardness indentation tests were employed to investigate the near-surface changes in the hardness of a fibre laser-treated and an as-received ZrO2 engineering ceramic. Indents were created using 5, 20, and 30 kg loads to obtain the hardness. Optical microscopy, white-light interferometry, and a coordinate measuring machine were then used to observe the crack lengths and crack geometry. Palmqvist and half-penny median crack profiles were found, which dictated the selection of the group of equations used herein. Computational and analytical approaches were then adapted to determine the K-1c of ZrO2. It was found that the best applicable equation was: K-1c = 0.016 (E/H)(1/2) (P/c(3/2)), which was confirmed to be 42 per cent accurate in producing K-1c values within the range of 8 to 12MPam(1/2) for ZrO2. Fibre laser surface treatment reduced the surface hardness and produced smaller crack lengths in comparison with the as-received surface. The surface crack lengths, hardness, and indentation loads were found to be important, particularly the crack length, which significantly influenced the end K-1c value when K-1c 0.016 (E/H)(1/2) (P/c(3/2)) was used. This is because, the longer the crack lengths, the lower the ceramic's resistance to indentation. This, in turn, increased the end K-1c value. Also, the hardness influences the K-1c, and a softer surface was produced by the fibre laser treatment; this resulted in higher resistance to crack propagation and enhanced the ceramic's K-1c. Increasing the indentation load also varied the end K-1c value, as higher indentation loads resulted in a bigger diamond footprint, and the ceramic exhibited longer crack lengths.