Use of Laser Generated Shocks to Improve the Properties of Metals and Alloys

Originally published in Industrial Applications of High Power Laser Technology, Vol 86, 1977. This electronic reprint is made available with permission from SPIE.

Authored by Barry P. Fairand and Allan H. Clauer.

INTRODUCTION
Laboratory studies have established that the mechanical properties of different aluminum and iron base alloys can be improved by laser shock treatment. When the energy from a powerful pulsed laser is trained on the surface of a metal, a high amplitude stress wave is generated. This wave propagates into the material and alters its microstructure, which is the source of the observed improvement in the metal’s mechanical properties. The ability to generate stress waves in materials with short duration bursts of laser energy has been known for some time, (1-6) but it has only been in recent years that these stress waves have been shown to provide an effective method of altering the in-depth mechanical properties of metals. (7) Various methods have been used to increase the amplitude and duration of these stress waves in order to increase the depth
and degree of change introduced into the metal. (8-15) These techniques have generally taken the form of adding to the surface of the material various coatings and layers of material which may be opaque or transparent to the incident laser energy. The most effective method found up till now for increasing the efficiency of converting laser energy into mechanical stress wave energy has involved the use of transparent overlays. This technique has produced pressure with peak values several times greater than the Hugoniot elastic limit of most metals and alloys. When a pressure of this amplitude propagates through a material, the metal is plastically deformed in a manner similar to that observed in explosively shocked materials.

This paper discusses methods of generating high amplitude stress waves in materials with pulsed lasers and demonstrates by selected examples how these stress waves can be used to improve the properties of metals and alloys.

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