In-Situ Monitoring of Microstructure during Thermomechanical Simulations using Laser-Ultrasonics

Abstract Ultrasonic velocity and attenuation measurements are powerful tools to infer information about the microstructure and properties of metals and their alloys. To begin, elastic constants can be measured with precision as high as one part in 10. At this level of precision, changes in elastic constants caused by texture, phase transformations, and various internal friction phenomena can be sensed easily. Ultrasonic attenuation can be measured also. In relatively anisotropic metals such as iron and steels, ultrasonic attenuation is dominated by scattering by the grain structure. In weakly anisotropic metals, such as aluminium and its alloys, the attenuation is mostly due to internal friction mechanisms caused by moving dislocations or other phenomena. Until now, ultrasonic measurements could be done during physical simulations only with great difficulty. However, laser-ultrasonics is a remote-sensing technology that enables to easily generate and detect wideband ultrasound pulses with lasers. It works at any sample temperature and on moving samples. We have instrumented a Gleeble 3500 thermomechanical simulator with laser-ultrasound technology. This paper reviews the principles of laser-ultrasound technology and its capabilities for in-situ monitoring of physical simulations with the Gleeble.