TY - THES

T1 - Tribological performance of different material pairings of exhaust valve and valve seat under impact-sliding conditions

AU - Erlacher, Georg

N1 - embargoed until 21-12-2025

PY - 2021

Y1 - 2021

N2 - The increasing global demand for energy thrives for a sustainable dealing with respect to energy consumption and an improved efficiency with respect to energy conversion. Therefore, research is done in a broad variety of different sectors. In the automotive industry, onsite gas engines represent one way to compensate for grid disturbances and thus, guarantee a stable energy supply. Several factors influence the energy efficiency of gas engines. In particular, when considering the valve train system, a relevant factor is to keep wear as low as possible. Therefore, one crucial factor is the application of highly wear-resistant materials. But at the same time, it is also essential for these materials to exhibit enhanced thermo-mechanical properties in corrosive environments due to combustion processes. By the present thesis, selected valve/valve seat pairings were investigated with respect to their tribological properties at impact-sliding conditions. One pairing consisted of a nitrided valve with the iron-based P28 as seat face material and a homogenously composed seat ring consisting of the iron-based W77T6 alloy. The components of the second pairing were a valve and seat ring, consisting both of the cobalt-based Tribaloy T400 alloy as the seat face material. The mechanical properties and the initial microstructure of the individual component materials were examined by system analysis and materials characterization. Subsequent tribological testing at 20 and 300°C was performed on the HT-CIAT, developed at AC2T research GmbH. Metallographic methods, such as confocal white-light microscopy and scanning electron microscopy in combination with energy dispersive X-ray analysis, were applied for wear track analysis. In the case of the P28N/W77T6 pairing, adhesive and abrasive wear were the dominating mechanisms. A material transfer from the seat ring to the valve was evident. With increasing cycle numbers, the contribution of surface fatigue increased and led to the failure of the nitride layer at some spots. The dominating wear mechanisms observed for the T400/T400 pairing were mainly of abrasive nature in the beginning. With an increased number of cycles, cracks nucleated under the surface which subsequently led to the delamination of wear debris.

AB - The increasing global demand for energy thrives for a sustainable dealing with respect to energy consumption and an improved efficiency with respect to energy conversion. Therefore, research is done in a broad variety of different sectors. In the automotive industry, onsite gas engines represent one way to compensate for grid disturbances and thus, guarantee a stable energy supply. Several factors influence the energy efficiency of gas engines. In particular, when considering the valve train system, a relevant factor is to keep wear as low as possible. Therefore, one crucial factor is the application of highly wear-resistant materials. But at the same time, it is also essential for these materials to exhibit enhanced thermo-mechanical properties in corrosive environments due to combustion processes. By the present thesis, selected valve/valve seat pairings were investigated with respect to their tribological properties at impact-sliding conditions. One pairing consisted of a nitrided valve with the iron-based P28 as seat face material and a homogenously composed seat ring consisting of the iron-based W77T6 alloy. The components of the second pairing were a valve and seat ring, consisting both of the cobalt-based Tribaloy T400 alloy as the seat face material. The mechanical properties and the initial microstructure of the individual component materials were examined by system analysis and materials characterization. Subsequent tribological testing at 20 and 300°C was performed on the HT-CIAT, developed at AC2T research GmbH. Metallographic methods, such as confocal white-light microscopy and scanning electron microscopy in combination with energy dispersive X-ray analysis, were applied for wear track analysis. In the case of the P28N/W77T6 pairing, adhesive and abrasive wear were the dominating mechanisms. A material transfer from the seat ring to the valve was evident. With increasing cycle numbers, the contribution of surface fatigue increased and led to the failure of the nitride layer at some spots. The dominating wear mechanisms observed for the T400/T400 pairing were mainly of abrasive nature in the beginning. With an increased number of cycles, cracks nucleated under the surface which subsequently led to the delamination of wear debris.

KW - Gas engine

KW - Valve

KW - Seat ring

KW - Sliding wear

KW - Impact wear

KW - Gasmotor

KW - Ventil

KW - Ventilsitz

KW - Gleitverschleiß

KW - Stoßverschleiß

M3 - Master's Thesis

ER -