Stress formation within the first layer in plasma sprayed coatings

The residual stresses within plasma sprayed coatings are an important factor which can influence the lifetime of the coatings. The investigation of the evolving stresses during deposition and post-deposition cooling of YSZ coatings by measuring in-situ the specimen’s curvature by the so-called ICP sensor is a powerful tool to identify the different stress generation factors.

Under certain spray conditions one can observe that the first torch pass leads to a significantly higher increase in specimen´s curvature than the following deposition passes, which indicates significantly higher stresses within the first coating layer.

The reason for this steep curvature increase is suggested to be a stronger bonding of those splats being connected directly to the substrate. The underlying mechanisms were investigated. The slope of this increase depends on the spray parameters as well as on the substrate conditions, which was investigated also.