Advanced Joining And Coating Technology In A Clean Environment

Abstract:

High temperature brazing is widely applied in industry as a fast and cost-effective method for joining large components used in the aerospace and the chemical industry as well as for power generation, e.g. compressor impellers or turbine parts. In steam turbines the valve seats and first stage turbine blades are subjected to steam oxidation and heavy particle erosion, especially when the turbine is running at higher steam temperatures in the range of 650 to 720C. However, at higher inlet temperatures the efficiency is increased and CO2 emission is substantially decreased. By CALPHAD modelling the formation of brittle phases at the interface can be predicted, especially after long-time thermal exposure. On this basis we are able to select a tailored coating with improved thermal stability at higher service temperatures. Brazing of diamond for grinding tools is improved by thermodynamic simulations. The interface between diamond and the braze alloy is prepared by Focused Ion Beam Method and analyzed by High Resolution TEM. It is demonstrated that by CALPHAD modelling the activity of Ti can be explained in different braze alloys. Thus the composition of the braze alloy as well as the processing parameters can be optimized in order to increase the life-time of the diamond brazed tools. Brazing at lower temperatures needs less energy. A new approach was applied to decrease the melting point of filler metals. Nano-multilayers of filler metal and a diffusion barrier layer were produced by DC magnetron sputtering. A significant melting point depression of 230C was achieved for a AlSi filler metal.

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