Fretting Resistant Coatings for Titanium Alloys

摘要

The report describes a program undertaken to establish the effect of airframe design parameters upon the severity of fretting in titanium structures and to determine the ability of selected coatings to prevent fretting induced fatigue failures. A test specimen was designed to simulate a structural joint and a series of fatigue tests was performed to determine the conditions most conducive to fretting initiated failure. It was found that at low stress levels and using tapered interference fit fasteners, the number of fatigue cycles accumulated to the point that fractures originated from fretting damage. A survey was made of titanium coatings technology and testing and three coatings were selected. On the basis of their properties and minimal degradation of Ti-6Al-6V-2Sn fatigue resistance, a chemical conversion coating and a commercial anodize coating were chosen along with a dry film lubricant. Fatigue tests were made of Ti-6Al-6V-2Sn specimens protected by the coatings from Task II. The coatings essentially eliminated the fretting induced fatigue failures of Task I. Final coating performance verification tests on Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo specimens demonstrated the same improvement using dry film lubricant applied to a shot peened surface. (Author)