Sintering behavior and mechanical properties of machinable zirconia/mica composites

ABSTRACT In order to fabricate machinable zirconia ceramics for dental restorations, zirconia/mica composites were prepared by mixing zirconia and fine mica powders, compacting the powder mixtures and then conducting pressure-less sintering of green powder compacts. The composites containing 30–49 vol% mica reached approximately full density at 1150oC. The sintering temperature was 150oC lower than that of monolithic zirconia. The mica melted during firing at above 1000oC and recrystallized during cooling. The melting of mica at above 1000oC induced rearrangement of the zirconia particles and accelerated mass-transport of zirconia through the solution-precipitation, resulting in low-temperature sintering of zirconia. Dense composites containing 30–36 vol% mica were machinable using a drill made of hard metal, while those containing 49 vol% mica were sufficiently machinable with a conventional high-speed steel tool. The machinable composite containing 30 vol% mica had a bending strength of 552 MPa and a fracture toughness of 3.9 MPa·m°5