Laser ultrasonic generation at the surface of a liquid metal

Conference · Sun Jan 01 04:00:00 EST 1995

OSTI ID:10116669

Walter, J B; Telschow, K L ^[1]; Conant, R J ^[2]

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1. Idaho National Engineering Lab., Idaho Falls, ID (United States)
2. Montana State Univ., Bozeman, MT (United States). Dept. of Mechanical Engineering

The noncontacting nature of laser-based ultrasonic measurement has made it attractive in many applications. While most applications thus far involve solid samples, molten metals encountered in some stages of metal processing appear well suited to this technique. Possible applications for liquid metals include locating and characterizing the liquid/solid interface; characterizing a surface layer, contaminant, or alloying constituent; and measuring the temperature of the sample surface or bulk. This work aimed to characterize laser generation of ultrasound in liquid metals to facilitate the development of techniques for these applications. This paper describes measurements of the angular distribution and energy dependence of laser-generated ultrasound in mercury at ambient temperature. Mercury was chosen as the model liquid metal because it is liquid at room temperature, and so should have negligible temperature gradients beyond those produced in the laser generation process, and because it exhibits a very shallow optical penetration depth. Brief descriptions about the theory of laser generation by thermoelastic and ablation sources at the surface of a liquid metal are included. Both thermoelastic expansion and ablation cause similar ultrasound generation in liquid metals when laser generated ultrasonic pulses are directed perpendicular to the surface of liquid metals. The ultrasonic pulse amplitude is proportional to the absorbed laser pulse energy for both mechanisms. The simple threshold model presented for ablation describes the transition from thermoelastic generation with the model`s two parameters being material dependent. For mercury, ablation produces about 100 times larger ultrasonic pulse amplitudes than thermoelastic expansion and has a threshold of about 6 MW/square cm. Molten metals offer a good medium for studying ablation, since the surface is always refreshed and ablation, at least for mercury, dominates ultrasonic generation above the threshold.

• Research Organization: Idaho National Engineering Lab., Idaho Falls, ID (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States); Department of the Interior, Washington, DC (United States)
• DOE Contract Number: AC07-76ID01570
• OSTI ID: 10116669
• Report Number(s): EGG-M--94170; CONF-9408208--1; ON: DE95004999
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104
42 ENGINEERING
420500
ABLATION
ANGULAR DISTRIBUTION
ENERGY ABSORPTION
LIQUID METALS
MATERIALS TESTING
MERCURY
NEODYMIUM LASERS
PENETRATION DEPTH
PERFORMANCE TESTING
PHYSICAL PROPERTIES
TEMPERATURE GRADIENTS
THERMOELASTICITY
ULTRASONIC TESTING
ULTRASONIC WAVES
ULTRASONOGRAPHY