WRIGHT PATTERSON AIR FORCE BASE -- Titanium is a metal that is strong, lightweight, and corrosion resistant. Commercial and military aircraft engines have relied heavily on titanium alloy components for many years.

But the material isn't perfect. In fact, one particular challenge has plagued titanium alloys since the early 1970's.

Dr. Adam Pilchak, a Materials Research Engineer at the Air Force Research Laboratory's Materials and Manufacturing Directorate, explained the problem and how AFRL and the international scientific community are working to solve it.

According to Dr. Pilchak, certain titanium alloys used in gas turbine engines can experience a phenomenon called cold dwell fatigue (CDF). Normal engine operation after a cold start imposes a high peak stress that is sustained for several minutes which can cause titanium alloy materials to 'creep' or deform at the microscopic level.

"The 'cold' aspect, which is unique to titanium alloys, occurs because titanium can creep at room temperature under sufficiently high stress levels," Dr. Pilchak said. "

This can cause a variety of issues for the Air Force. "In the absolute best case, cold dwell fatigue of titanium alloys requires more frequent inspection intervals which add costs to the life-cycle of titanium alloy engine components," he said. "At worst, CDF can lead to uncontained component failures which can be catastrophic for single-engine aircraft."

"It should be noted that CDF failures are, thankfully, quite rare in both military and civilian sectors at present due to conservative design practices. However, the problem warrants effort now more than ever as the Air Force begins to push its fleet beyond the intended design life due to fiscal constraints," Dr. Pilchak said.

AFRL is working the problem from multiple angles, including materials processing to minimize and control microstructural features that contribute to CDF, nondestructive inspection techniques for locating such features, and computer models to predict the mechanical behavior and lifetime of titanium alloy components.

Dr. Pilchak, an internationally recognized CDF expert, was invited to a workshop on the subject in Switzerland on April 14. The event, sponsored by European science association CECAM (Centre Européen de Calcul Atomique et Moléculaire), brought together leading computational and experimental scientists to develop research proposals for exploring fundamental mechanisms of CDF in titanium alloys. Dr. Pilchak gave the lead talk to the group.

"CDF is a complex, multi-faceted problem that requires workshops such as this to bring together experts from many engineering disciplines, each of whom has in-depth knowledge of a small piece of the total solution," Dr. Pilchak said. "

"This group placed a stake in the ground to define the present understanding of CDF and define the most appropriate experiments and theoretical calculations for making headway into solving this complicated problem."