Development and Application of Binary Suspensions in the Ternary System Cr2O3-TiO2-Al2O3 for S-HVOF Spraying

Abstract

Abstract Next to ZrO2, compositions in the system Cr2O3-TiO2-Al2O3 are the most used ceramic materials for thermally sprayed coating solutions. Cr2O3 coatings present good sliding wear resistance, Al2O3 coatings show excellent insulation behaviour and TiO2 striking corrosion properties. In order to combine these properties, coatings containing more than one oxide are highly interesting. The conventional spraying process is limited to the availability of binary feedstock powders with defined compositions. The use of suspensions offers the opportunity for tailor-made compositions: within the triangle of Cr2O3-TiO2-Al2O3 each mixture of oxides can be created. The formulation of binary or ternary suspensions is based on the preparation of stable single-oxide suspensions, which will later be mixed to achieve the desired composition. This procedure requires the development of water-based suspensions with suitable behavior, otherwise the ceramic particles and dissolved organic additives may interact and form agglomerates, which are prejudicial to the thermal spray process. This work presents criteria for the selection of raw materials as well as relevant aspects for the development of binary suspensions to be used in thermal spray. For procedure validation, coatings sprayed using Cr2O3-TiO2 suspensions and S-HVOF will be shortly presented and analysed in terms of their microstructure and microhardness.