Scratch Induced Subsurface Deformation Behaviour of Thin Ceramic Coatings

Transmission electron microscopy has been used to study the subsurface deformation structures induced in ceramic coatings subjected to scratch testing. CVD TiN, CVD TiC (both ∼ 5 μm thick), and ∼ 2 μm thick PVD TiN coatings, all deposited on steels, were investigated. For behavioural comparison, a relatively soft, thicker ‘coating’ - an aluminised KEA28 steel of reacted layer (Al₂O₃) thickness ∼ 30 μm - was also studied. For the TiN and TiC samples, both grain boundary decohesion and in grain plasticity were found to feature prominently both in response to subsurface stresses and in contributing to friction by dissipating energy. For the coating on the aluminised steel, plasticity alone appeared as the dominant deformation mechanism. The results are discussed in relation to coating microstructure and wear performance.