TABLE OF CONTENTS The MA process is suitable for the production of MCrAl (Y) (M=Fe, Ni or Co) types of powder like MA-754 superalloy which can be plasma-sprayed in a low pressure chamber to provide oxidation and corrosion-resistant coatings on gas turbine blades and vanes [43]. By employing a fine mixture of mechanically alloyed Cu/Al 2O 3 composite powder for low pressure plasma spraying, a fine structure uniform coating has also been applied [44]. However, such coatings have been found consisting of two layers: matrix-rich layer and dispersoid layer. This separation presumably takes place due to the lack of wettability and to some extent by the acceleration caused in the plasma jet.
A uniform single phase intermetallic coating of Ti 3Al has been obtained by employing MA Ti-Al powder for RF plasma spraying [44]. The interdiffusion of Ti/Al takes place quite quickly during the process of spraying, which results in the formation of Ti 3Al intermetallic phase. Moreover, an intermetallic matrix coating has also been obtained using MA Ti-Al-10vol.% Si 3N 4 powder. A fine distribution of Si 3N 4 is obtained along with the other phases like Ti 5Si 3 and TiN exhibiting decomposition of the ceramic phase [44]. Using DC plasma spraying, a Cu/Ti/C MA powder coating of uniformly dispersed TiC in a copper matrix has been obtained [45]. These coatings have slightly higher hardness due to homogeneously dispersed structures.
Thus, the proper selection of the...
