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 K1c of ZrO2. It was found that the best applicable equation was: K1c¼0.016 (E/H)1/2 (P/c3/2), which was confirmed to be 42 per cent accurate in producing K1c values within the range of 8 to 12MPam1/2 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 K1c value when K1c ¼0.016 (E/H)1/2 (P/c3/2) was used. This is because, the longer the crack lengths, the lower the ceramic’s resistance to indentation. This, in turn, increased the end K1c value. Also, the hardness influences the K1c, and a softer surface was produced by the fibre laser treatment; this resulted in higher resistance to crack propagation and enhanced the ceramic’s K1c. Increasing the indentation load also varied the end K1c value, as higher indentation loads resulted in a bigger diamond footprint, and the ceramic exhibited longer crack lengths.