Development of Ultrasonic Models for Hard-Alpha Inclusions in Titanium Alloys

This paper describes research directed towards modeling ultrasonic signals from hard-alpha inclusions in titanium alloys. The modeling effort has been made difficult by the complicated morphology of such inclusions which can include voids, cracks, core and diffusion zones. Fortunately, a large portion of hard-alpha inclusions are acoustically weak scatterers in nature, and advantage can be taken of simplifications as afforded by Born approximation and some ad-hoc interface conditions. Models along these lines have been previously developed and their validations on synthetic hard-alpha inclusions of cylindrical shape at normal incidence have been reported [1]. Extensive use of these ultrasonic models were also presented in the development of a statistical methodology for estimating the probability of detection [2,3]. In current work, we extend the model capability to include arbitrary flaw orientation and oblique incidence. Model predictions are compared with experimental data collected from titanium specimens for different beam angles, focal depths, inclusion sizes and orientations. The range of the model applicabilities and their possible extensions will be presented. Morphological modeling of the three-dimensional, naturally-occurring inclusions based on stacks of two-dimensional metallographic measurements are also described