Preparation and properties of thermal barrier ceramics gradient coating by flame spraying

With optimizing the chemical compositions of the coating layer and the transition layer, a dense Al₂O₃/Fe thermal barrier gradient coating with a sound metallurgical bonding was prepared using an oxyacetylene flame spraying. The results show that the Al₂O₃ distributes uniformly in the coating. An excellent metallurgical bonding between the steel base and the coating as well as a graded distribution of the chemical compositions from the base to the coating surface is obtained. As compared with the conventional Al₂O₃ thermal barrier coating and the thermal barrier coating using the Ni as bottom layer and the Cu as transition layer, the bonding strength, flexural strength and heat shock resistance improve significantly. The efficiency of the thermal barrier is found to increase with the amounts of the coating layers and the content of the Al₂O₃.