Corrosion failure analysis of Ni-P film of aircraft fire detector components

Abstract

A batch of fire detectors used in the aircraft has been corroded under containing sulfur atmosphere. The fire detector was made of guide rods, seat plate, bimetallic strips, ring gasket, moving contact part and spring part. The former three components were deposited with electroless nickel-phosphorus layer. The morphology and microstructure of surface and cross-section of the layer were characterized by optical microscopy and scanning electronic microscopy. The chemical composition and phases of corrosion products were determined by energy dispersive spectrometer and X-ray diffraction, respectively. The results show that the corrosion products were mainly composed of nickel sulfate and its hydrate, indicating the layers aggravated by sulfur substances or compounds. The surface of the layer exhibited lots of microdefects, including pitting, microcracking and micropores. The failure causes of fire detectors under corrosive environments were further addressed and discussed. The failure model of electroless nickel-phosphorus layer was also established.