Transducer Design for High Sensitivity Ultrasonic Inspection of Titanium

Abstract

INTRODUCTIONThe high-strength alloys used in the aerospace industry today are inspected ultrasonically for material anomalies which may have resulted from the manufacturing process. These materials, such as titanium alloys, often have a !arge macro-grain structure which Iimits the sensitivity of the ultrasonic inspection to material anomalies. As a result, there has been much work directed towards developing inspection techniques which minimize the Ievel of the reflections from the macro-grains and enhance the reflections from the material anomalies. In particular, the affect of transducers parameters such as transducer bandwidth, focus, and frequency on the signal-to-noise ratio of synthetic anomalies in titanium alloys has been investigated [1][2][3]. This investigation showed that the Ievel ofthe grain noise relative to a known calibration target decreases in Ti-AI6-V4 (Ti6-4) and Ti-Al5-Sn2-Zr2-Mo4-Cr4 (Ti17) and the signal-to-noise ratio of synthetic anomalies with planar geometries in Ti6-4 increases as the volume of the ultrasonic pulse in the material decreases. This paper will extend these results to planar synthetic anomalies in Ti17 and non-planar synthetic anomalies in Ti6-4. In addition, a transducer design methodology for high sensitivity inspection based on managing the size ofthe uhrasonie pulse volume is presented and the implications ofusing this method for production inspections are described. BACKGROUND