The Research On Preparation And Properties Of Thermal Barrier Coatings On Titanium Alloy

Titanium alloys are very important light weight construction materials. They have broadapplications in aviation, and aerospace; and always have been a research focus in the field ofmaterials. However, the high temperature performance of titanium alloy is relatively poor;therefore, researches are carried out on high temperature protection technique on titaniumalloy actively.Thermal barrier coatings (TBCs) are one of the advanced high temperature protectivecoatings, and the state-of-art thermal barrier coating material 8YSZ has been successfullyapplied to the protection of aircraft engine combustion chamber and other high temperatureparts. However, little research has focused on the oxidation resistance, mechanical propertiesand thermal property of 8YSZ coatings on titanium alloy. The main purpose of this study is tofabricate 8YSZ TBCs on titanium alloy surface, study the oxidation resistance, thermalinsulation and thermal shock resistance performance of TBCs on titanium alloy.CoNiCrAlY bond coat and 8YSZ ceramic top coat are deposited on titanium alloysurface by atmospheric plasma spraying (APS). In order to research the influence of bondcoat on the performance of coating, TBCs without bond coat on titanium alloy surface werealso deposited. The performance of oxidation resistance, thermal insulation and thermal shockresistance of TBCs at different temperatures and their failure behavior were studied andanalyzed. Mechanical properties of coatings such as surface roughness, microhardness andadhesion strength were also tested in this paper.The performance of microhardness has improved greatly after spraying TBCs ontitanium alloy, and the adhesion strength between titanium alloy and coatings is well. Thethermal insulation effect of sample with bond coat or without bond coat is almost thesame.The surface temperature is higher, the greater the temperature difference betweencoating and substrate. Without doubt, the 8YSZ ceramic top coat has advantage of providingthermal protection for titanium alloy.8YSZ ceramic top coat and CoNiCrAlY bond coat have a layered structure on titaniumalloy surface. It is obvious that the microhardness of 8YSZ ceramic layer is much higher thanthat of substrate. The adhesion strength between titanium alloy and coatings is well. Theresults of thermal insulation test show that thermal insulation effect of sample with bond coator without bond coat is almost the same. It is worth noting that thermal insulation of coating has different values at different testing temperatures; and it increases with the increasingsurface temperature. The higher the surface temperature of the coating, the better the thermalinsulation effect is. Without doubt, the 8YSZ ceramic top coat has advantage of providingthermal protection for titanium alloy.Oxidation resistance and thermal shock life of samples with bond coat is better than thatwithout bond coat. The failure reason of samples with or without bond coat is mainly causedby the mismatch of thermal expansion, while for samples with bond coat on titanium alloybesides the mismatch of thermal expansion stress; bond coat oxidation and elementaldiffusion also affect coatings performance significantly. But on the other hand, because of thebond coat could provide oxidation protection for substrate at high temperatures, the TBCswith bond coat has better composite performance. Therefore, TBCs with bond coat has betterapplication prospects on titanium alloy surface, which could improve the oxidation resistanceof titanium alloys, and has good thermal shock resistance and longer thermal cycling life.