Fretting Damage in Incoloy® 800 Tubes Against Different Support Materials

In this work the fretting wear in steam generator tubes of Incoloy® 800 in contact with AISI 304, AISI 1060 and Cu (99,9%) pads acting in a cross-tube geometry was studied. Wear surface was characterized by scanning electron microscopy (SEM) and the resulting debris were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). It was verified that in all cases, the fretting conditions corresponded to gross slip. A predominance of adhesive wear was found for Cu and AISI 1060 while abrasive wear was predominant in the case of AISI 304. It was determined that the higher the hardness of the pad material the lower the surface damage (case of the AISI 1060). Analysis of debris allowed the identification non-stoichiometric oxide phases with either a spinel structure of the type FeCr2O4.Fe3O4 and a hematite (Fe,Cr)2O3 in the case of AISI 304, while for Cu and AISI 1060 pads, the presence of CuFe2O4 spinel and (Fe,Cr)2O3 hematite were observed, respectively. The formation of spinel structures originates in an effect of mechanical alloying between the surfaces. Debris particle size distribution was found to extend in the range from tens of nanometers to few micrometers with the larger particles consisting in agglomerates of crystallites with sizes between 5 and 20 nm.