Microstructural characterization of Ti-6Al-4V X-links from the Space Shuttle Columbia

Recovered artifacts from the Space Shuttle Columbia provide a unique opportunity to examine a broad spectrum of materials exposed to the extreme environment of earth re-entry. The degradation states of these components offer a unique perspective into material behavior in this highly reactive environment. The crew module X-links, which are composed of Ti-6Al-4V and provided structural support to the crew module within the fuselage, exhibit evidence of both oxidation and combustion phenomena. The conditions supporting ignition and combustion of bulk metals are not fully understood, due to the many compounding factors affecting variable oxidation behavior of metals. Materials characterization of the Columbia X-links will yield further insight into the discrimination between the oxidation, ignition, and combustion response of titanium alloys. Widespread use of titanium alloys in space vehicles warrants a thorough characterization of their potential failure modes to help ensure the safe and reliable operation of future spaceflight vehicles. Initial microstructural state of the X-links is assessed, and affected material exhibits microstructural gradients dependent on vehicle orientation. Three distinct microstructural states were observed across the length of the X-links, according to proximity of aggravated flow.