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 DISEL ENGINE PISTON

LJUBICA RADOVIĆ

Military Technical Institute, Belgrade, ljubica.radovic@vti.vs.rs

DUŠAN VRAČARIĆ

Military Technical Institute, Belgrade

Abstract: A commercial aluminium cast piston for diesel engine failed during operation after a short period (about 150 km) after overhaul. In order to identify the cause of the failure, a metallurgical analysis was performed by means of visual inspection, optical microscopy (OM) and scanning electron microscopy (SEM), as well as analysis of chemical composition and hardness measurement. Seizure marks along and around the piston and changed color of connecting rod are identified. Also, the piston crown have been competely destroyed by local melting and erosion. These features are attributed to incipient melting of copper-base intermetallics, coarsening and spheroidization of the microstructural constituents. Furthermore, presence of secondary porosity observed in the microstructures in the crown vicinity, indicates that the piston was exposed to excessive temperature. All results lead to conclusion that overheating was the main cause of this failure.

Keywords: cast Al-Si alloy, piston, failure, overheating.