Anti-fretting wear foils, shims, coatings or their combinations have been used in the compressor and/or fan section of gas turbine engines because very small movements or vibrations at the juncture between mating components have resulted in what is commonly called fretting or fretting wear. Typical component combinations include fan or compressor blades carried by a rotor or rotating disc. Such occurrence of wear can require premature repair or replacement of one or both components or their mating surfaces if not avoided. In modem gas turbine engine compressors, it has been noted that Ti alloys have relatively poor anti-fretting wear or anti-friction characteristics. For example, such Ti alloys as commercially available and widely used Ti 6-2-4-2 alloy have relatively high room temperature yield strengths, such as greater than about 100 ksi, which can result in fretting wear with an abutting member such as blade slot during operation.
One commonly used anti-fretting coating combination is a Cu--Ni--In alloy (nominally by weight 36% Ni, 5% In, balance Cu) applied to a mating surface of a component and then covered by a molybdenum disulfide solid film lubricant. The Cu--Ni--In alloy and its application to a gas turbine engine component to avoid such wear is described in U.S. Pat. No. 3,143,383 Bamberger et al, patented Aug. 4, 1964. The disclosure of that patent is hereby incorporated herein by reference. Although such an alloy has been effective for certain lower temperature uses, its yield strength is insufficient for use at higher temperatures and stresses, for example in more advanced gas turbine engines in the range of about 650.degree.-1100.degree. F. Similarly, the use of molybdenum disulfide, which is mixed with an organic binder such as an epoxy, is inadequate in that temperature range: it oxidizes and loses effectiveness above about 650.degree. F., causing extrusion of the coating combination and wear of the underlying base material.
USPTO Backgrounds
USPTO Backgrounds