Oxidation and interdiffusion in MCrAlY-type bondcoats and their correlation with TBC life

A pre-requisite for extended and reproducible lifetimes of thermal barrier coating (TBC) systems is the use of oxidation-resistant metallic bondcoats with optimized performance. Whereas in aircraft engines electron-beam physically vapour deposited (EB-PVD) TBCs with Ni-aluminide type bondcoats are used, in land based gas-turbines MCrAlY-type (M=Ni,Co) bondcoats are applied, typically in combination with a ceramic topcoat produced by atmospheric plasma spraying (APS). Failure mechanisms and parameters, which influence lifetime of the TBC-systems with MCrAlY-bondcoats will be discussed. The performance of MCrAlY-bondcoats will be shown to depend on the contents of the major alloying elements Co, Ni, Cr and Al as well as minor additions of Y and Hf. In addition, the role of manufacturing related properties such as coating thickness, porosity, surface roughness profile and oxygen content in determining TBC-system lifetime will be emphasized. The requirements of high bondcoat oxidation (corrosion) resistance and good chemical compatibility with the base material are frequently contradictory with respect to the bondcoat chemistry. One of the possible solutions to the latter problem is using multilayered bondcoats with an outer layer optimized for formation of a slowly thickening thermally grown oxide (TGO) and the bottom layer optimized for suitable mechanical properties and reduced interdiffusion with the base material. It will be shown that successful development and application of such complex, multilayer coating systems can be substantially facilitated using thermodynamic/kinetic modeling, the vast potential of which has become apparent in recent years

О взаимодействии карбазолилтиирана с карбоновыми кислотами

Изучено взаимодействие карбазолилтиирана с карбоновыми (уксусной, акриловой, метакриловой) и дикарбоновыми (адипиновой, себациновой, фталевой) кислотами. Показано, что основными продуктами взаимодействия являются олигомеры. С избытком уксусной кислоты, наряду с олигомером, выделен также продукт присоединения уксусной кислоты к карбазолилтиирану, идентифицированный как 2-меркапто-3-(9`-карбазолил)-1-ацетокси-пропан. Найдены условия получения всех олигомерных продуктов, изучены их свойства, показаны возможности применения

Methods to Elicit Forecasts from Groups: Delphi and Prediction Markets Compared

Traditional groups meetings are an inefficient and ineffective method for making forecasts and decisions. We compare two structured alternatives to traditional meetings: the Delphi technique and prediction markets. Delphi is relatively simple and cheap to implement and has been adopted for diverse applications in business and government since its origins in the 1950s. It can be used for nearly any forecasting, estimation, or decision making problem not barred by complexity or ignorance. While prediction markets were used more than a century ago, their popularity waned until more recent times. Prediction markets can be run continuously, and they motivate participation and participants to reveal their true beliefs. On the other hand, they need many participants and clear outcomes in order to determine pay-offs. Moreover, translating knowledge into a price is not intuitive to everyone and constructing contracts that will provide a useful forecast may not be possible for some problems. It is difficult to maintain confidentiality with markets and they are vulnerable to manipulation. Delphi is designed to reveal panelists’ knowledge and opinions via their forecasts and the reasoning they provide. This format allows testing of knowledge and learning by panelists as they refine their forecasts but may also lead to conformity due to group pressure. The reasoning provided as an output of the Delphi process is likely to be reassuring to forecast users who are uncomfortable with the “black box” nature of prediction markets. We consider that, half a century after its original development, Delphi is under-utilized