The low fracture toughness of ceramic materials poses significant challenges for them to be used in structural applications. In many cases this is due to the low energy dissipated ahead of the crack tip in the absence of a large plastic zone. Several ways to enhance the fracture toughness have been proposed over the last years, including modifying the chemistry or microstructure of monolithic ceramics, to promote for example crack deflection or phase transformation ahead of the crack tip. However, these events happen at a micro/nanometre scale and are difficult to observe in real time.
In this work we present a new TEM in-situ nanomechanical setup which enables the propagation of stable cracks in brittle materials while observing their microstructures at the micron and nanoscale. This has been done by modifying the traditional Double Cantilever Beam (DCB) geometry used in conventional fracture experiments. We have used the setup to test a variety of structural ceramic materials, including SiC and partially and fully stabilised zirconia (PSZ and FSZ). Our measurements in zirconia show how tetragonal to monoclinic transformation happens in PSZ but not in the cubic form of FSZ. In PSZ, we are able to observe the nucleation and growth of the monoclinic phase ahead of the crack tip and its behaviour upon unloading. We can also use the crack opening displacement (COD) data to measure fracture toughness values at the nanoscale.
The aim of this research is to guide the design of new structural ceramics and study their fracture behaviour at the nanoscale. This will include for example, grain boundaries in polycrystalline ceramics or interphases in ceramic composites.