Acoustic emission and dilatometry for non-destructive characterization of microstructural changes in Mg based metal matrix composites submitted to thermal cycling
- Charles Univ., Praha (Czech Republic). Dept. of Metal Physics
- Technical Univ. of Clausthal, Clausthal-Zellerfeld (Germany). Dept. of Materials Engineering and Technology
Many Mg-based metal matrix composites (MMCs) have been developed and manufactured during the last decade as prospective light high-performance constructional materials. When a MMC is submitted to temperature changes (cooling down from the temperature of fabrication, cyclic temperature changes during operation of structural parts) thermal stresses arise at the interfaces owing to a considerable mismatch of the thermal expansion coefficient of the matrix and that of the reinforcement. Even slight temperature changes may produce thermal stresses which exceed the matrix yield stress, consequently, generating new dislocations at the interfaces causing microstructural changes and plastic deformation of the matrix. Long-term exposure may also result in fatigue damage. It is noteworthy that the effect of temperature variations is similar to creep under non-stationary loading conditions. Acoustic emission (AE) has been observed during thermal cycling of Mg based MMCs. Since dislocation motion and microstructural damage are generally accepted to produce AE, it is possible by AE measurements to identify and to characterize the microstructural changes and to correlate them with temperature or other parameters. The dilatometry technique enables the degree of matrix plastic deformation which superposing the thermal expansion to be determined by measuring the shape changes during testing. The combination of both methods yields non-destructively, at any instant of the test, information on the structure and operating processes over the entire volume of the specimen. This can also provide valuable information for subsequent investigations by microscopy or internal friction. The object of this paper is to report on the recently developed, combined AE and dilatometry technique and its application in a structural evolution in Mg-based MMCs subjected to thermal cycling.
- OSTI ID:
- 585979
- Journal Information:
- Scripta Materialia, Vol. 38, Issue 1; Other Information: PBD: 18 Dec 1997
- Country of Publication:
- United States
- Language:
- English
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