METALLURGICAL EVALUATION OF FAILED AIRCRAFT STAINLESS STEEL EXHAUST SYSTEM COMPONENTS
ALLEGHENY LUDLUM STEEL CORP BRACKENRIDGE PA
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A total of twelve samples from small aircraft exhaust systems were investigated metallurgically. Three of the samples, referred to as baseline, were from new, unused systems. These were examined metallographically for general microstructural characteristics and chemically analyzed. The other samples were from systems which had failed while in flight operation. These samples were examined metallographically and analyzed chemically to determine the causes of failure. The samples were representative of a number of designs and different types of failures which have been encountered. Practically all the materials were AISI Type 321, a titanium-stabilized austenitic stainless steel. Examination of the baseline samples showed microstructures of the base metal, weld and weld heat-affected zone to be normal. Four samples failed because of excessive oxidation or high temperature corrosion due apparently to uneven flow of gases, resulting in local overheating, carburization, and probably more rapid attack by the products of combustion, especially lead compounds. Four other samples from mufflers of similar design and one sample of a different design showed fatigue cracks. The failures were attributed to excessive vibrational andor thermal stresses in the presence of abrupt changes in section size and likely locations for crack initiation.
- Properties of Metals and Alloys