Correlating Ultrasonic Attenuation and Microtexture in a Near-Alpha Titanium Alloy

摘要

Near-α titanium alloys are an integral part of aeroengines; however, since the 1970s, it has been recognized that laboratory and field components fail in a reduced number of cycles when a dwell at the peak stress is imposed. Research over the last few decades has shown that one of the primary reasons for the debit in fatigue life is related to the presence of microtexture in these alloys. Many aeroengine components were forged before the concept of microtexture, and its deleterious effects, had been realized. Thus, because of the increased potential for early failure of these components, a need exists for a nondestructive method to assess the degree of microtexture present in legacy hardware in order to separate those which are prone to dwell fatigue failure from those that are not. Hardware with a high degree of microtexture can be scheduled for more frequent inspections to reduce the risk of in-flight failure. The present work describes a methodology by which this can be achieved using ultrasonic attenuation measurements of the component in pulse-echo imaging mode. The results indicate nearly linear dependence of ultrasonic attenuation on microtextured region size in the d/λ = 0.1 to 1.0 range, where d and λ are the effective microtexture region size in the direction of wave propagation and the ultrasonic wavelength, respectively.