Revealing mechanical properties of a suspension plasma sprayed coating with nanoindentation

Solution and suspension thermal spraying is providing a more economic approach to the production of thin coatings. Advances in this new promising technology require accompanying tools to assess micro and nanosized areas within these deposits. Hydroxyapatite was deposited in an r.f. plasma using a powder and a suspension. The powder feedstock produced a dense, oriented coating, whereas the suspension led to a porous randomly oriented coating. The porosity leads to a decrease in the hardness and elastic modulus of the bulk coating, but site specific indentations on dense areas in the SPS coating revealed greater values (5 ± 0.2 vs 4 ± 0.2 GPa), possibly due to the finer grain size and crystal orientation. Nanoindentation presents a valuable tool for the assessment of the mechanical properties in solid areas of porous materials, and when used with microscopy will be valuable for the further development of SPS coatings.