Fracture toughness of zirconia with a nanometer size notch fabricated using focused ion beam milling

OBJECTIVES: Zirconia with 3 mol% yttria (3Y‐TZP) has been used for dental crowns and bridges due to its excellent mechanical behavior. Performing fracture toughness testing on this nanograin material, however, can be a challenge. For reliable results, fracture toughness testing requires an extremely sharp notch in the test specimen that closely approximates a very sharp crack. This study was to investigate an alternative method to produce nanometer‐sized notches, which are less than the average grain size of 3Y‐TZP, during the preparation of single‐edge V‐notched beam specimens and report the resulting fracture toughness value. METHODS: We present a method using focused ion beam (FIB) milling to fabricate nanometer‐sized notches in 3Y‐TZP. The notch tip is <100 nm wide, which is smaller than the grain size, and is consistent throughout the thickness of the specimen. RESULTS: The FIB‐notched specimens show a much reduced average fracture toughness of 5.64 ± 1.14 MPa√m compared to 8.90 ± 0.23 MPa√m for the specimens without FIB‐notches. The FIB‐milling did not appear to create any monoclinic phase prior to fracture toughness testing. Fractures originated at the FIB‐notches, and the notch size can be readily identified post‐mortem using a microscope. A considerable amount of tetragonal‐to‐monoclinic phase transformation was observed throughout the fracture surfaces. SIGNIFICANCE: FIB milling provides an alternative method to fabricate nanometer‐sized notches that are smaller than the grain size of tetragonal zirconia polycrystal. The fracture toughness determined using FIB‐notches was ~5.64 MPa√m, smaller than the specimens with V‐notches fabricated using saw blades.