Hochtemperaturbeständigkeit und Schweißeignung einer intermetallischen TiAl-Legierung für die Anwendung als Turbinenrad im Abgasturbolader

Translated title of the contribution: High temperature resistance and weldability of an intermetallic TiAl alloy for the use as a turbine wheel in the exhaust gas turbocharger

Lukas Samer

Research output: ThesisDiploma Thesis

191 Downloads (Pure)

Abstract

Charged internal combustion engines are used for vehicles on land, rails, water and in the air as well as for industrial applications. The charging by exhaust gas turbochargers have played a major role in improving internal combustion engines for several years and their importance will increase in future as long as fuels are burned as energy carrier for drive systems. By utilisation of the exhaust gas energy, an exhaust turbocharger enables an increase of the charge-air density and further on a more efficient combustion of the fuel. Due to this fact, the emission of pollutants decreases, contributing to the fulfilment of the legal limit values (Euro 6 standard). Furthermore, the technology of charging allows the concept of downsizing, in which at constant power, the size of the motor is reduced (lower cylinder capacity). Due to the corresponding weight savings a reduction in fuel consumption is achieved. In the present diploma thesis the turbine wheel of the exhaust gas turbocharger, which is exposed to an exhaust gas temperature of up to 850°C in diesel engines and 1.050°C in Otto engines and revs less than 300.000 is investigated. The analysed turbine wheel is an intermetallic TiAl alloy, an innovative lightweight material for high-temperature applications, especially the variants TNM and TNM+, which represent an attractive alternative to Ni-base superalloys. Due to the low density of the TiAl alloys the acceleration performance of the vehicle can be significantly improved. As part of this work, the high temperature resistance and weldability are considered in detail. This means, that the stability of the microstructure, the oxidation behaviour and the damage behaviour of TNM+ turbine wheels were studied after individual tests at a hot gas test rig. To gain additional knowledge about the temperature/time dependency of the microstructural stability, i.e. the limits of the materials application, isothermal heat treatments were conducted on TNM+ samples. The results were compared with the tests at the hot gas test rig. Furthermore, on a turbine wheel a protective coating against oxidation was characterized. For connecting the shaft to the TNM turbine wheel different joining technologies were considered and the joined parts were analysed in detail. The characterization of microstructures, joints and surfaces were carried out by scanning electron microscopy and energy dispersive X-ray spectroscopy. Quantitative metallography and Vickers hardness tests were applied to study the microstructural evolution of the heat treated samples.
Translated title of the contributionHigh temperature resistance and weldability of an intermetallic TiAl alloy for the use as a turbine wheel in the exhaust gas turbocharger
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Clemens, Helmut, Supervisor (internal)
  • Mayer, Svea, Co-Supervisor (internal)
Award date27 Jun 2014
Publication statusPublished - 2014

Bibliographical note

embargoed until 25-06-2019

Keywords

  • exhaust gas turbocharger
  • titanium aluminides
  • TNM
  • TNM+
  • microstructural stability
  • oxidation
  • welding

Cite this