Mechanical Testing of Single Splats using Nanoindentation

Mechanical integrity is a key requirement of all thermal spray coatings for their successful application. It has been customary to obtain this information from bond strength tests, indirect assessment from the microstructure or a range of other mechanical tests that also include the resistance to crack propagation. Since the building block of thermal spray coatings consists of single splats, an assessment of solidified flattened droplets provides a key insight into the mechanical integrity of the deposits. Nanoindentation was applied to single solidified droplets deposited onto substrates preheated to a range of temperatures. A sprayed coating of the same composition was produced and annealed in a furnace to provide a reference material. Indentation on the series of solidified flattened droplets allowed the determination of hardness, elastic modulus and fracture toughness. Furthermore, an approach was developed that provides an insight into the assessment of the residual stress in a solidified droplet. This insight into the mechanical properties of single solidified droplets together with the topography, shape and structural phase provides an array of tools that are critical elements for improvement of thermal spray coatings.