Laser melted ZrO 2–Y 2O 3 thermal barrier obtained by plasma spraying method

Abstract

The aim of the paper is to determine the influence of laser melting upon the selected physical properties of ZrO 2–Y 2O 3 ceramic coatings deposited by APS method on super-alloys which function as TBC. Laser melting which helps to eliminate pores and other structural defects of coatings deposited by plasma spraying method should contribute to the improvement of their density and durability as thermal barriers. In order to prove the assumptions made in the paper, coatings featuring varied porosity and deposited upon the nickel base super-alloys surface with the initially sprayed NiCrAlY bond coat have been subjected to laser melting and then their structure, thermal conductivity and thermal life prediction in the conditions of cyclic temperature changes from 20 to 1200 °C have been examined. It has been revealed that the coatings featuring low porosity where laser melted on part of their thickness and heated up to about 700 °C, demonstrated the highest thermal life prediction under the above conditions mentioned and at slightly lower thermal conductivity. It has been found that homogenization of chemical composition of coatings occurs during laser melting leading to the reduction of ZrO 2–Y 2O 3 phase with monoclinic lattice participation as well as to the reduction of structural stresses which accompany this phase transformation during heating and cooling process. The worked out conditions of laser melting might be used in the process of creation of ZrO 2–Y 2O 3 coats which feature high working durability upon super-alloy elements.