Densification of Plasma-Sprayed Ceramic Coatings by HIP Treatment and Their Cracking Behavior

Abstract

The hot isostatic pressing (HIP) treatment of plasma-sprayed ceramic coatings was studied in order to improve the coating characteristics, such as microstructure and bonding strength. Stabilized ZrO2, Al2O3 and Y2O3 were coated by plasma-spraying on two kinds of metal substrates (Nb and Type 304 stainless steel). HIP treatment was performed at from 1100° to 1300°C under fixed pressure (98.1MPa) for 1h. The porosity and bonding strength of ceramic coatings were measured. The residual stress analysis was carried out and compared with the cracking of ceramic coatings. The experimental results indicated that, for Nb substrate specimens, the porosity remarkably decreased and the bonding strength increased with increasing HIP temperature. But the cracks were observed at high HIP temperature. Such cracking behavior of HIP treated ceramic coatings was explained by the residual stress calculated by FEM analysis. On the other hand, no crack was observed in coatings on Type 304 substrate, because of the compressive residual stress in coatings induced by HIP treatment. But the bonding strength decreased with increasing HIP temperature.