Abstract
The paper describes the failure analysis of a fractured pneumatic actuator cover plate of a turbine outlet valve of a shutdown cooling pump in a research reactor. The material of construction for the cover plate was a hypereutectic Al–Si alloy in as-cast condition. Microstructural examination of the failed plate was done using both optical and scanning electron microscopy. The microstructure consisted of needle-shaped primary silicon and Fe-rich intermetallic phases in an aluminum matrix. The microstructure also consisted of numerous shrinkage pores along the interdendritic regions. Based on microstructural and fractographic examinations, it was concluded that the cover plate had fractured due to impact loading. Acicular morphology of silicon and intermetallic phases together with high porosity greatly reduce the fracture toughness of Al–Si alloy.
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