Effect of reverse transferred arc treating on bonding strength in low pressure plasma spraying

Bonding strength of coating to substrate in low pressure plasma spraying was investigated and the effect of reverse transferred arc treating before spraying was studied. The results are summarized as follows, (1) For the bonding strength test in low pressure plasma spraying, instead of the conventional adhesive, vacuum brazing process using Ag-Cu-In-Ti active filler metal at 1023 K was proposed and the propriety has been confirmed. (2) By the above test method, it was proved that the bonding strength of low pressure plasma sprayed coating is over 100 MPa. However, the bonding strength of coating pretreated by blasting before spraying fell down and fluctuated when the average roughness, Ra of the substrate surface was less 2μm. (3) Reverse transferred arc treating after blasting has enhanced the bonding strength of low pressure plasma sprayed coating, especially when the roughness, Ra of substrate before spraying is less than 2 μm. It is considered that the projections formed on the substrate surface by reverse transferred arc treating were buried into coating and performed the pile effect.