Upper temperature limit of atmospheric plasma spraying yttria stabilized zirconia coatings deposited with different purity feedstocks

Abstract The failure of the ceramic layer at thermal barrier coating is primarily caused by the phase transformation and excessive sintering. The phase stability, isothermal sintering status, and grain growth behavior of yttria‐stabilized zirconia (YSZ) ceramic coatings are interrelated and sensitive to the impurity elements. Two types of 8YSZ powders with different content of impurity elements were utilized as raw materials, and the single ceramic layers prepared by atmospheric plasma spraying were subjected to a long‐duration heat treatment at 1400°C for investigating the limiting thermal durability of the coatings. After 1400°C/∼300 h, 21.2% and 8.4% of nontransformable tetragonal phase (t′) were observed in the high‐purity (HP) and low‐purity (LP) coatings, respectively. It was noted that the LP coating exhibited more significant grain growth, and the reduction of impurity elements can enhance the phase stability of the coating and slow down sintering shrinkage. Under quantitative analysis, it has been determined that the HP YSZ coatings exhibit higher activation energies (223.05 ± 14.96 kJ/mol) for grain growth compared to the LP coatings (198.41 ± 3.30 kJ/mol). The mechanisms of Ti, Si, and Fe were classified and analyzed, and three different mechanisms affecting the high‐temperature stabilization of the coatings were summarized.