Thermal cycling and isothermal oxidation behavior of quadruple EB‐PVD thermal barrier coatings

Increase of energy efficiency by increasing the turbine inlet temperature is the main driving force for further investigations regarding new thermal barrier coating materials. Today, thermal barrier coatings consisting of yttria stabilized zirconia are state of the art. In this study, thermal barrier coatings consisting of 7 weight percent yttria stabilized zirconia (7YSZ) and pyrochlore lanthanum zirconate (La₂Zr₂O₇) were deposited by electron beam physical vapor deposition. Regarding thermal cycling and isothermal oxidation behavior different layer architectures such as mono‐, double‐ and quadruple ceramic layers were investigated. The thermal shock behavior was examined by thermocycle tests at temperatures in the range between T = 50 °C ‐1,150 °C. Additionally, the isothermal oxidation behavior at a temperature of T = 1,150 °C with dwell times of t= 50 h and t = 100 h was studied in the present work. The conducted research concerning the behavior of various thermal barrier coating systems under thermal cycle and isothermal load highlights the potential of multilayer thermal barrier coatings for operating in high temperature areas.     

Einsatz von Hartstoffbeschichtungen bei Spindellagern

Application of hard surface coatings for spindle bearings The demands on modern Machine Tools ascends continuously with the requirements of the production for high quality and short‐time processings. Particularly the increase of the processing‐ and removal times of the last years dues to higher loads of the main spindle bearing. The bearing as a central machine component characterises the performance of the Machine Tool for the cutting process and defines the reliability of the main spindle. The majority of the applicated spindle bearings are ball bearings. A large amount of the spindle fall‐outs is caused by a non adequate or defecitive lubrication and is effected by the tribological properties of the bearing elements. For the reduction of friction and wear nowadays several materials, coatings and lubrication additives are applied. Actual researches focus on the development of hard surface coatings (a‐C:H:W) with a nano structure for the rolling contact of ball bearings to increase their reliability. In this article the test of nano structured hard surface coating systems for the reduction of friction, warming and wear are presented. Thus the coating systems are verificated for the application in spindle bearings by pretesting. According to the evaluation the inner and outer raceway of standard‐hybrid bearings are coated and the adhesion in reference to rotational speed, resistance and wear performance at high acceleration is analysed. Concluding the emergency running properties at dry‐running condition is evaluated to identify the field of application for the coatings.