Eddy Current Evaluation of Electrical Anisotropy in Polycrystalline Ti-6AL-4V
High strength titanium alloys find a significant number of applications throughout the aircraft industry for gas turbine engine and airframe components. Ti-6A1-4V is an alloy that has been around since the 1950’s and has been used extensively for fan blades, disks, and superplastically formed and diffusion bonded structures. This alloy has been studied and tested in virtually every conceivable way and a great deal is known about the material in terms of its capabilities, yet there are still lingering performance issues that evade researchers. A recent initiative by the Air Force to better understand conventional Ti alloys from the standpoint of High Cycle Fatigue (HCF) has brought to light some intriguing research in the nondestructive characterization of polycrystalline titanium alloys. The major goal of this research is to detect and characterize the microscopic defects or fatigue damage precursors associated with HCF and to understand some of the physical characteristics of the nucleation and growth of low-level, mechanically imparted damage. From a nondestructive inspection viewpoint the goal boils down to finding and interpreting signals from smaller and smaller “defects.” With this approach, the identification of smaller defects early in the service life of the component presumably leads to higher reliability of the aircraft through the removal of flawed components for rework, scrap, or further study.