Hot pressing of graded ultrafine-grained alumina bioceramics

The work presented investigates the processing of high-density functionally gradient alumina bioceramic with continuously decreasing grain size along its thickness. This would serve as a transitional multilayer for implants changing from a lower grade alumina with coarser bulk grain size to a higher quality alumina with finer surface grain size and superior properties. Such an approach could provide economic and performance benefits for ceramic implants in general. A model of disc geometry was used to examine the feasibility of producing this brand of materials. Sequential slip casting was successfully used to deposit green layers of varying particle sizes from 50 to 250 nm. Hot pressing at a range of temperatures (1200–1400 °C) and times (15–120 min) was carried out. Hot pressing temperature was found to have a greatest effect on grain growth and porosity within each layer. Grain growth exponents of 6–8 were obtained, signifying a pinning effect. A near fully dense compact with final grain size increasing from one side of the compact to the other was successfully produced. Surface grain sizes as low as ∼300 nm were obtained.