Boron nitride nanosheets as an effective strategy against the slow crack growth and hydrothermal ageing in zirconia composites

This paper explores the effectiveness of boron nitride nanosheets in preventing the premature failure of yttria-stabilized tetragonal zirconia ceramics, particularly in humid environments. A simple, low-cost and scalable technique -shear exfoliation in a kitchen blender- was used to prepare BNNS, and pure zirconia and composites with 1, 2.5 and 5 vol. % BNNS were spark plasma sintered. Accelerated hydrothermal ageing experiments in autoclave revealed a remarkable improvement of low temperature degradation resistance in all the composites. Fracture toughness and slow crack growth of the composites with 1 and 2.5 vol. % BNNS were evaluated by bending tests performed in notched specimens. Although the composites presented fracture toughness values similar to those of the reference zirconia, an increase of ∼18 % on crack-tip toughness was achieved. Similar R-curves evaluated in air and in oil-impregnated 2.5 vol. % BNNS composites revealed a limitation of stress-assisted corrosion by water in zirconia, thanks to the BNNS incorporation.