Influence of Al on Reactive Flame Sprayed TiC-TiB_2 Multiphased Ceramic Coatings

By static combustion synthesis tests, Ti-B4C-C+5wt%Al was chosen as the reactive system to prepare the Ti(C0.7, N0.3)-TiB2-Al2O3 multiphased ceramic coatings on the metal substrate with a reactive flame spray technology. It is found that the coatings have the multiphased heterogeneous metastable structure, which consists of TiC0.7N0.3, TiB2, Al2O3, titanium oxide and some pores. The structure of the coatings can be divided into three kinds: the Ti(C0.7, N0.3)+TiB2 eutectic structure with the cluster-shaped TiB2 in micron-nanometer size, the structure with mass-shaped 1-2μm Ti(C0.7, N0.3) particle surrounded by the needle-shaped or strip-shaped TiB2 and the black phase of anomalous pores. The forming causes of the three kinds of structure are the same as those of the coatings with no additive Al. However the additive Al raises the reaction velocity, so the amount of ceramic phase increases, the structure becomes fine, the pores reduce and the micro-hardness of the coatings is increased.