Phase identification of hard precipitates in PS304 coatings

This paper presents the details of the detection of an unexpected (enigmatic) phase resulting from heat treatment of a tribocoating labelled PS304. This coating, consisting of chromium oxide powder in a Ni-Cr base powder and lubricated by silver metal and fluorides of barium and calcium, provides a plasma sprayed lubricious multitemperature wear and oxidation resistant surface layer for challenging wear applications. Primarily based on X-ray diffraction structural analysis, a chromium disilicide compound has been identified to form as a result of the heat treatment of the coating. A source of the significant strengthening of the coating by the heat treatment process is explained on the basis of the formation of the disilicide compound and its properties. The strengthening effect of fugitive silicon present in such trace levels is recognised for the first time as having a potential for use in many tribocoating systems as a cost effective and efficient strengthening approach.