STUDY OF INCLUSIONS IN A FAILED AEROENGINE COMPONENT

The cause of the fatigue failure in the retaining ring of the compress or region of an aero-engine turbine was found to be the presence of a high concentration of nonmetallic inclusions. The results of chemical analysis were used to estimate the phases present. The most frequently observed inclusions were spinel solid solutions of the type MO . N2O3 , where M = Fe, Mn, or Mg and N = Cr or Al. The detrimental inclusions were corundum, calcium aluminates, cristobalite, and silicates. The m ost detrimental phases were traced on the surfaces of the specimens fr actured using impact loading; the comparison is being made with the po lished surfaces and the tensile specimen fracture surfaces. The inclus ions in the failed retaining ring were compared with the ones in a sim ilar component obtained from a used engine. In the case of the latter, a large number of fine and elongated (Mn, Cr, Fe)S inclusions were pr esent along with spinels. The nondeformable, rigid oxide particles are considered more undesirable than the sulfides as far as fatigue life of the component is concerned. It has been reported that the presence of sulfides may eliminate the stresses due to oxides.