TY - THES

T1 - Characterization of a TNM alloy for high performance automotive applications

AU - Weißensteiner, Irmgard

N1 - embargoed until 04-03-2019

PY - 2014

Y1 - 2014

N2 - In this work the applicability of the TNM alloy for racing car valves was investigated. The most challenging areas of such valves are the head of the valve because of the hot combustion gases, the seat, which has to withstand high periodically varying contact pressures and the stem that is loaded with alternating stresses. Initially, a basic characterization of the raw material by scanning electron microscopy, hardness testing and X-ray diffraction measurements was conducted. Valve blanks were produced with a variation of the forging temperature and the subsequent cooling rate. The influence of different forging parameters on the microstructure, the hardness and the phase fractions of the prevailing phases at the above-mentioned relevant positions as a function of the local strains was analyzed. With increasing deformation, a finer microstructure and an increase in hardness was observed. Different heat treatments were conducted to study the development of the microstructure. The mechanical properties, which were tested at ambient and elevated temperatures, corresponding to the different valve positions, were analyzed by tensile tests and high cycle fatigue tests. It was found out that the highest strength and fatigue strength values are assigned to the higher deformed valve stems, which are optimal conditions for the mechanical loaded areas. The coarser microstructure of the lower deformed material shows also sufficient strength in combination with a good creep resistance, which meets the requirements in the head and seat of the valve.

AB - In this work the applicability of the TNM alloy for racing car valves was investigated. The most challenging areas of such valves are the head of the valve because of the hot combustion gases, the seat, which has to withstand high periodically varying contact pressures and the stem that is loaded with alternating stresses. Initially, a basic characterization of the raw material by scanning electron microscopy, hardness testing and X-ray diffraction measurements was conducted. Valve blanks were produced with a variation of the forging temperature and the subsequent cooling rate. The influence of different forging parameters on the microstructure, the hardness and the phase fractions of the prevailing phases at the above-mentioned relevant positions as a function of the local strains was analyzed. With increasing deformation, a finer microstructure and an increase in hardness was observed. Different heat treatments were conducted to study the development of the microstructure. The mechanical properties, which were tested at ambient and elevated temperatures, corresponding to the different valve positions, were analyzed by tensile tests and high cycle fatigue tests. It was found out that the highest strength and fatigue strength values are assigned to the higher deformed valve stems, which are optimal conditions for the mechanical loaded areas. The coarser microstructure of the lower deformed material shows also sufficient strength in combination with a good creep resistance, which meets the requirements in the head and seat of the valve.

KW - intermetallics

KW - TiAl

KW - TNM

KW - valve

KW - Intermetallische Verbindungen

KW - TiAl

KW - TNM

KW - Ventil

M3 - Diploma Thesis

ER -