Acoustic emission for in situ monitoring in metal-matrix composite processing

The attractive elevated-temperature properties of metal-matrix composities (MMCs) have not been exploited in commercial applications partly because of the high processing cost and lack of reliability in fabrication. In this exploratory study, the feasibility of using acoustic emission (AE) as an in-process, non-destructive quality control technique is examined. A variation of the squeeze casting technique is selected for investigation. Acoustic emission is employed with the intent of non-intrusively establishing whether complete infiltration has occurred during composite fabrication. The problems due to the background noise during AE monitoring are overcome by using transducers with different frequency responses. The acoustic signatures of machine noise, preform crushing and metal solidification are obtained by employing suitable transducers in a series of tests that systematically evaluate the individual processes that comprise infiltration casting. The results form a strong basis for the development of an in situ AE sensor for the infiltration process.