Wear and Fretting Fatigue Resistant Coatings for Titanium Alloys

摘要

Studies were performed to identify treatments to alleviate the effects of wear on fatigue properties of Ti-6Al-4V, Ti-5Al-4Mo-4Cr-2Sn-2Zr (Ti-17) and Ti-8Al-1Mo-1V. The mechanisms of wear studied were fretting fatigue and sliding wear fatigue. Fretting fatigue tests were performed using high cycle fatigue specimens with shoes bolted across the gauge sections at 25,000 psi contact pressure. The shoes induced fretting as the result of alternating bending strain motion along the edges of the contact interface. Sliding wear fatigue tests were performed by a two-step method including first the cyclic rubbing of fatigue specimens by wear shoes for 10,000 strokes of 5 mils length under 50,000 psi contact pressure. Subsequently, the specimens were tested in low cycle or high cycle fatigue to determine the effect of wear on the endurance limit. In fretting tests of Ti-6Al-4V at room temperature, and of Ti-6Al-4V and Ti-17 at 650F, a Cu shim insert between the specimen/shoe interface inhibited fretting fatigue. In sliding wear tests of all three Ti alloys at room temperature, a plasma sprayed coating of Al-bronze containing 10% carburundum polyimide prevented loss of fatigue strength. The Al-bronze/carburundum polyimide not only protected fatigue specimens to which it was applied, but also it did not cause damage to uncoated fatigue specimens against which it was rubbed. Other coatings and surface treaments evaluated did not afford complete wear protection.