Mechanical Properties Of Tio2 Coatings Deposited By Low Pressure Cold Spraying

Titanium dioxide is a very popular ceramic material due to its outstanding properties, e.g. photocatalytic conversion. Titania coatings are able to activate chemical reactions on its surface. However, photocatalytic activity strongly depends on crystal structure, the size and shape of crystallites and also the surface area. This article is devoted to the mechanical tests of TiO2 coatings obtained by the Cold Spray method considered as a promising alternative to conventional techniques, such as Flame or Plasma Spray. However, the degree of the method development with regards to ceramic coatings is still low. It should be noted that the latest scientific trends show progress in the deposition of ceramic particles via cold spray. The crucial problem in obtaining thick coating seems to be the lack of ceramic deformation combined with high differences in the coefficient of thermal expansion between a ceramic coating and a metal substrate. To solve this problem, an amorphous phase known as soft-ceramic can be used. The high value of kinetic energy ensures phase transition into anatase during cold spraying. In the presented study, the mechanical properties of titanium dioxide coatings deposited by low pressure cold spraying onto aluminium and steel substrates were investigated and compared. The powders of the amorphous phase, anatase and rutile provide different coatings and thus various types of research were performed to analyse the mechanical properties of the coatings, e.g. scratch test, nanoindentation, coatings microhardness, together with SEM analysis. An amorphous coating, free from delamination and microcracks, showed the highest adhesion with a critical load of 15.8 +/- 1.3 N. All the coatings deposited onto the steel substrate showed higher hardness. Rutile formed sintered agglomerates with local hardness up to 1292 +/- 357 HV0.01 and the coating mean elastic modulus of 29.8 GPa.