Additive Manufacturing of Zirconia Ceramics

Additive Manufacturing, AM, refers to a series of processes by which digital 3D design (CAD) data is used to drive the creation of a component by the layer-by-layer deposition of material. In contrast to conventional moulding techniques there are in theory virtually no restrictions regarding the geometry of the structure; highly complex parts can be printed out directly as drawn without the necessity of any simplifications. Unlike erosive techniques such as grinding or milling, where the final part is carved out of a larger body of material, AM technologies only require the exact amount of material needed for the volume of the part. This approach reduces material costs significantly, especially when the raw materials are expensive, and, in addition, there are no tooling costs.

Objects can be produced by a wide range of AM techniques, each of which has its own advantages and disadvantages in terms of object shape, size and reliability. Whilst the additive manufacturing of metals and polymers is well advanced and being adopted by industry, use of the approach for the manufacture of ceramic materials lags somewhat behind, mainly due to the somewhat intractable nature of ceramic materials. Ceramic processing is based on a series of stages typically involving the synthesis of powders, their formation into an unfired (or ‘green’) body and then their subsequent densification into a hard, usually dense part. Each of these stages is fraught with difficulties, for example, in general the finer the powder used the better the performance of the final part; however finer powders are much more difficult to handle during processing than coarser powders. Similarly, during both drying and firing the shrinkage of the part can cause cracking; because they are brittle materials the reliability of ceramics is sensitive to flaws, which may be produced during AM.

The Project

The PhD will focus primarily on the use of AM for the middle stage of the process, i.e. the ‘green forming’ stage where powders are turned into unfired bodies. Three different approaches will be compared by the student; one at the UoM (direct-write paste extrusion) and two at the UoB (ceramic lithography and centrifugal gel casting). Each of these approaches needs significant development to tailor them to processing a particular ceramic material with a particular particle size and is not a straight forward endeavour. This will allow the strengths and weaknesses of each approach to be compared and the best of the routes will be optimised with a view to being able to design the manufacturing process to the point where the subsequent microstructures and properties can be predicted. The student will be enrolled at UoB and spend approximately 1 year of their candidature at UoM.