Abstract
The effect of preheating on coating process was investigated in low pressure plasma spraying. In this study, microstructure, bonding strength and blast erosion property were examined for the coating which consists of Ni based superalloy as a substrate and CoNiCrAlY spraying material. The results are summarized as follows.
(1) High bonding strength over 72 MPa of coating to the substrate by low pressure plasma spraying, is derived from the diffusion zone formed adjacent to the coating interface.
(2) 1073 K preheating coupled with the plasma spraying causes short-time diffusion adjacent to the coating interface that is equivalent to the vacuum-furnace heating at approximately 1373K.
(3) The blast erosion property of low pressure plasma sprayed CoNiCrAlY is close to the stainless steel rather than the atomospheric plasma sprayed coating.
(4) Low pressure plasma sprayed coating which is preheated over 873 K, consists of the top layer with higher blast erosion rate and excellent layers with low blast erosion rate under it. It is considered that in-situ sintering phenomenon caused by sufficient preheating and the subsequent spraying would improve combining strength between sprayed particles.
(5) Plasma flame treatment just after spraying improves the blast erosion property of the top layer in low pressure plasma coating.
