Fabrication of intermetallic compound coatings by DC plasma spraying of Ni-Al mechanically alloyed powders

Abstract

Experimental conditions for the fabrication of intermetallic compound coatings by DC plasma spraying of Ni/Al mechanically alloyed powders have been investigated.
The results obtained are summarized as follows ;
(1) In atmospheric plasma spraying, APS, the obtained coating was composed of two or more phases : Ni-rich phase, and Alrich phase. Ni/Al MA powder seemed to be subjected to phase separation during plasma spraying. On the other hand, homogeneous intermetallic coatings were obtained by low pressure plasma spraying, LPPS, due to the diffusion of two element in the sprayed powders.
(2) The dominating factor for phase separation for MA powders during plasma spraying seemed to be the heat flow from surrounding plasma ; the contributions of other factors, such as, mixing of the powder, composition of working gas, oxidation of the powder and acceleration force in plasma flame, were negligible.
(3) By low pressure plasma spraying or HVOF spraying of MA powder, the intermetallic coating can be fabricated easily. Even in the APS process, intermetallic coating can be obtained by the spraying of sizeable MA powder.