한국주조공학회

To improve the durability of the turbocharger, it is important to suppress cracking of th the turbine housing; therefore, we investigated the initiation and growth of these cr cracks. First, we initiated a crack in the turbine housing using endurance experiments. After the endurance test, cracks mainly occurred in the valve seat, the nozzle area, and t the scroll part of the turbine housing. The results of a fracture analysis of the cracks s showed that cracks in the valve seat were initiated by fatigue fracture. This seems to be caused by the accumulation of mechanical and thermal stresses due to vibration of the turbine wheel and high-temperature exhaust gas. Also, cracks in nozzle and scroll area were initiated by intergranular corrosion due to the exhaust gas. Thus, although there are differences in the cause of initiation according to the site, a concentric waveform was observed in all fracture planes. This phenomenon indicates that cracks gradually grow due to repeated stress changes, and the main causes are the temperature difference of the exhaust gas and the vibration caused by the turbine shaft.

Turbine housing, Fracture surface, Fatigue fracture, Thermal stress, Integranular corrosion