REPUBLIC OF SERBIA

MINISTRY OF DEFENCE

www.mod.gov.rs

MINISTRY OF DEFENCE

Material Resources Sector

Defensive Technologies Department

Military Technical Institute

www.vti.mod.gov.rs

Failure Analysis of a Leaded Brass Oxygen bottle Valve

IVO BLAČIĆ

Military Technical Institute, Belgrade, Serbia

Ljubica radović

Military Technical Institute, Belgrade, Serbia, ljmradovic@gmail.com

Dušan vračarić

Military Technical Institute, Belgrade, Serbia

Abstract: An oxygen bottle valve of an aircraft failed during bottle filling was received with the request to perform a failure investigation. The valve was made of an extra-high-leaded brass (62Cu-35.5Zn -2.5Pb) in the extra hard conditions (150 HV5), coated with nickel. The valve was about 28 years in service. The fractographic and metallographic analyses were performed by means of stereo and scanning electron microscopy (SEM/EDS), as well as hardness measurement. Nickel coating had unequal thickness (3-7 mm) and their fracture and spalling in some region was observed. The microstructure of the high leaded brass consists of a mixture of alpha and beta phases and lead particles. The fractographic examination revealed that the crack was originated on the grain boundary. The crack propagation exhibited both intergranular and transgranular mechanism. Results suggest that the stress corrosion cracking of the leaded brass was the main fracture mechanism.

Key words: oxygen bottle valve, extra-high-leaded brass, stress corrosion.