Size-dependent quasi Brittle–Ductile transition of single crystalline alpha-alumina particles during microcompression tests

Dense ceramic coatings can be fabricated through the kinetic impaction of fine solid particles at room temperature without any heat assistance or binder, and such a coating process is known as aerosol deposition (AD). In this process, solid ceramic particles that are generally fragile exhibit plastic deformation when they are refined; this is the key to the deposition and densification of ceramic coatings in AD. However, previous work has failed to address the transition criteria related to the size of ceramic particles during plastic deformation; the size is significantly associated with their fracture strength and strain. To eliminate the grain boundary effect, single crystalline alpha-alumina particles were selected and their strength and strain before fracture were systematically measured in a quasi-static compression test. The fracture strength of the alumina particles increased when the particle size decreased, and the particles exhibited quasi-plastic deformation when the fracture strength reached the compressive strength of alumina. This size-dependent brittle–ductile transition of ceramic materials in compression implies that the intragrain plastic deformation of ceramic particles can be attributed to the solid particle deposition. Thus, appropriately designing the intra grain architecture in ceramic particles may allow highly efficient deposition and further densification in AD.