セラミックス遮熱コーティングを施したSUS304の高温疲労破壊強度におよぼすはく離損傷の影響

抄録

Fatigue tests were conducted at both 893K and room temperature for ZrO₂-8Y₂O₃-sprayed and Al₂O₃-sprayed type 304 stainless steel. Surface strain during the fatigue test was monitored to examine the delamination of a subsurface layer using a laser speckle strain gauge. Surface strain was found to decrease when subsurface delamination occurred. The number of cycles to delamination was decided by the surface strain behavior. It was found that delamination lives of a ZrO₂-8Y₂O₃-sprayed specimen with an Atmospheric Plasma Sprayed (APS)-bond-coating and that with a thermal aged Low Pressure Plasma Sprayed (LPPS)-bond-coating were longer than those of a ZrO₂-8Y₂O₃-sprayed specimen with a non-thermal aged LPPS-bond-coating and an Al₂O₃-sprayed specimen with an APS-bond-coating. The strength of an APS-bond-coating was so low that multiple cracks occurred, while the strength of a LPPS-bond-coating was so high that a single crack occurred near the fracture surface. In case of the specimen with an APS-bond-coating, the fatigue fracture life of an Al₂O₃-sprayed specimen was longer than that of a ZrO₂-8Y₂O₃-sprayed specimen. The reason was that the crack initiated at a bond-coating penetrated into a substrate with no delamination between a bond-coating and a substrate for a ZrO₂-8Y₂O₃-sprayed specimen. In case of the specimen with a LPPS-bond-coating, the fatigue fracture life of a specimen with a thermal aged bond-coating was longer than that with a non-thermal aged bond-coating and the fatigue lives of these specimens were longer than those with an APS-bond-coating. The improvement of the fatigue fracture life was caused by the restriction of a crack initiation into the substrate due to the LPPS-bond-coating with a relatively higher strength. It was concluded that a bond-coating with high strength and high adhesive strength was effective on the improvement of fatigue fracture lives of plasma sprayed materials.