Laser Peening Process and Apparatus Using a Liquid Erosion-Resistant Opaque Overlay Coating

Abstract

The invention relates to a method and apparatus for improving properties of a solid material by providing shockwaves there through. Laser shock processing is used to provide the shockwaves. The method includes applying a liquid energy-absorbing overlay, which is resistant to erosion and dissolution by the transparent water overlay and which is resistant to drying to a portion of the surface of the solid material and then applying a transparent overlay to the coated portion of the solid material. A pulse of coherent laser energy is directed to the coated portion of the solid material to create a shockwave. Advantageously, at least a portion of the unspent energy-absorbing overlay can be reused in situ at a further laser treatment location and/or recovered for later use.

1 . A method of treating a workpiece by applying shockwaves thereto, comprising the steps of:
 applying an energy-absorbing overlay to a portion of a surface of the workpiece, said energy-absorbing overlay being composed of a liquid material resistant to dissolution by the transparent water overlay and resistant to drying;   applying a transparent overlay upon said energy-absorbing overlay; and   directing a pulse of coherent energy to said energy-absorbing overlay, said pulse of coherent energy causing a portion of said energy-absorbing overlay to vaporize and thereby generate at least one shockwave for transmission to the workpiece.   
     
     
         2 . The method of  claim 1 , wherein said liquid erosion-resistant and drying-resistant material has a combined viscosity and level of adherence such that said energy-absorbing overlay made thereof tends to conform and adhere to the workpiece under substantially static conditions yet is capable of fluid displacement when subjected to at least one shockwave. 
     
     
         3 . The method of  claim 1 , wherein said liquid erosion-resistant and drying-resistant material is a colloidal substance having at least one energy-absorbing particulate dispersed therein. 
     
     
         4 . The method of  claim 3 , wherein said colloidal substance is a mixture of an oil and graphite.