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.

What is claimed is:  
     
       1. A method of  for treating a workpiece by applying shockwaves thereto , comprising the steps of :
 applying an  a liquid 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  the liquid energy- absorbing overlay comprising a liquid material resistant to drying, and applying a transparent overlay upon the liquid energy - absorbing overlay, wherein the liquid energy - absorbing overlay is comprised of a liquid material resistant to dissolution by the transparent overlay;    
 applying a transparent overlay upon said energy-absorbing overlay; and 
 directing a pulse of coherent energy to said  the liquid energy-absorbing overlay, said  the pulse of coherent energy being absorbed at least in part by said liquid material and causing a portion of said  the liquid energy-absorbing overlay to vaporize and thereby generate ; and  
 generating at least one shockwave for transmission to the workpiece.  
 
     
     
       2. The method of  claim 1 , wherein said  the liquid erosion-resistant and drying-resistant  material has a combined viscosity and level of adherence such that said  the liquid energy-absorbing overlay made thereof tends to conform and adhere  conforms and adheres to the workpiece under substantially static conditions, yet is capable of fluid displacement when subjected to the at least one shockwave. 
     
     
       3. The method of  claim 1 , wherein said  the liquid erosion-resistant and drying-resistant  material is  comprises a colloidal substance having  comprising at least one energy-absorbing particulate dispersed therein . 
     
     
       4. The method of  claim 3 , wherein said  the colloidal substance is a mixture  comprised of an oil and graphite. 
     
     
       5. The method of  claim 3  wherein said  the colloidal substance is a mixture  comprised of an oil and black iron oxide (Fe 2 O 3 ) . 
     
     
       6. The method of  claim 3 , wherein said  the colloidal substance is a mixture  comprised of an oil, colloidal  and at least one of graphite, carbon black, and black iron oxide (Fe 2 O 3 ) . 
     
     
       7. The method of  claim 1 , wherein said energy-absorbing overlay has a viscosity of a magnitude that permits said energy-absorbing overlay to conform with a surface of the workpiece under substantially static conditions and yet to be fluidly displaced when subjected to sufficiently dynamic conditions. 
     
     
       8. The method of  claim 7 , wherein the sufficiently dynamic conditions occur during at least one of said applying an energy-absorbing overlay step and said directing a pulse step. 
     
     
       9. The method of  claim 1 , wherein said  the liquid energy-absorbing overlay includes  comprises at least a first overlay portion and a second overlay portion, said first overlay portion being sacrificed upon impact of the pulse of coherent energy, said  the second overlay portion being reusable for a subsequent shockwave creation  generation. 
     
     
       10. The method of  claim 9 , wherein the second overlay portion is fluidly displaced laterally along the workpiece surface, away from an impingement point of the pulse of coherent energy, an amount of the second overlay portion being displaced into an other proximate treatment location upon the workpiece. 
     
     
       11. The method of  claim 10 , further comprising the further steps of :
 applying a  an additional transparent overlay on  upon the amount of the second overlay portion displaced into the other proximate treatment location; and  
 directing a second pulse of coherent energy through the transparent overlay  to the amount of the second overlay portion displaced into the other proximate location to effect a shockwave formation thereat , generating at least one shockwave for transmission to the workpiece.  
 
     
     
       12. The method of claim  11    10 , further comprising the steps of :
 monitoring the amount of the second overlay portion displaced into the other proximate treatment location, said monitoring thereof being performed prior to the step of applying the transparent overlay thereto ; and  
 adjusting a total thickness of the energy-absorbing overlay existing at the other proximate treatment location to thereby conform with a desired thickness therefor .  
 
     
     
       13. The method of  claim 1 , further comprising the step of  reclaiming any remaining amount of said  the energy-absorbing overlay. 
     
     
       14. The method of  claim 1 , wherein the coherent energy is in a form of laser energy. 
     
     
       15. A method of  for treating a workpiece by applying shockwaves thereto , comprising the steps of :
 applying an  a liquid energy-absorbing overlay to a portion of a surface of the workpiece, said  the liquid energy-absorbing overlay being composed  comprised of an adherent, uniformly spreading liquid material, said adherent, uniformly spreading liquid material being  that is resistant to drying;  
 applying a transparent overlay upon said  the liquid energy-absorbing overlay; and  
 directing a pulse of coherent energy to said  the liquid energy-absorbing overlay, said  the pulse of coherent energy being absorbed at least in part by said  the liquid material and causing a portion of said  energy-absorbing overlay to vaporize and thereby generate , generating at least one shockwave for transmission to the workpiece.  
 
     
     
       16. The method of  claim 15 , wherein said  the adherent, uniformly spreading liquid material displaces easily enough laterally when sprayed  so as to thereby  reach a coating thickness having a self-limiting maximum. 
     
     
       17. The method of  claim 15 , further comprising the step of :
 one of pre-coating and pre-spraying the workpiece with another  a second adherent, uniformly spreading liquid material prior to said step of  applying said  the liquid energy-absorbing overlay, said another  the second adherent, uniformly spreading liquid material being resistant to drying.  
 
     
     
       18. The method of  claim 17 , wherein said step of applying said energy-absorbing overlay includes supplying said adherent, uniformly spreading liquid material at locations where it is needed and one of lacking and supplied at an insufficient thickness. 
     
     
       19. The method of  claim 15 , further comprising the step of:
 cleaning the workpiece after the treating of the workpiece by applying shockwaves thereto, said step of  the cleaning the workpiece being by a spray cleaning technique.  
 
     
     
       20. The method of  claim 15 , wherein a plurality of spots are treated during the treating of the workpiece , said  the liquid energy-absorbing overlay being applied to each of  said spots  spot individually, said  the method further comprising the step of :
 removing said  the liquid energy-absorbing overlay from each said spot after performing the step of  directing the pulse of said  coherent energy upon  to each said spot.  
 
     
     
       21. The method of  claim 15 , further comprising the step of :
 using an automated means for ensuringdetecting at least one of that a correctsufficient amount of saidthe liquid energy-absorbing overlay has been applied at a given treatment spot and that the laser beampulse of coherent energy has been applieddirected at the given treatment spot prior to a next treatment step being performed .  
 
     
     
       22. The method of  claim 21 , wherein said automated means is configured for  the detecting includes measuring an applied amount of said  the liquid energy-absorbing overlay, said automated means being one of a mass/flow meter, a video monitor, a plasma monitor, and an acoustic monitor . 
     
     
       23. The method of  claim 15 , wherein at least one first spray nozzle is used for  the applying said  the liquid energy-absorbing overlay comprises applying with at least one first spray nozzle, at least one second spray nozzle being used for  the applying said  the transparent overlay comprises applying with at least one second spray nozzle, each said first spray nozzle and each said second spray nozzle having a protector fitted  associated therewith, each said  the protector being configured for shielding a segment of the workpiece from potential damage from a coating material being ejected through a given said spray nozzle . 
     
     
       24. The method of  claim 15 , wherein said drying-resistant  the adherent, uniformly spreading liquid material is  comprises a colloidal substance having  comprising at least one energy-absorbing particulate dispersed therein . 
     
     
       25. The method of  claim 24  wherein said colloidal substance is a mixture of oil and black iron oxide (Fe 2 O 3 ). 
     
     
       26. The method of  claim 24  wherein said colloidal substance is a mixture of oil, colloidal graphite and black iron oxide (Fe 2 O 3 ). 
     
     
       27. The method of  claim 15 , further comprising the step of reclaiming any remaining amount of said energy-absorbing overlay. 
     
     
       28. The method of  claim 21 , wherein the detecting comprises detecting with at least one of a mass/flow meter, a video monitor, a plasma monitor, and an acoustic monitor, an ultrasonic flow detector, an ultrasonic motion detector, and interrupted optical signals.  
     
     
       29. A method for treating a workpiece by applying shockwaves thereto, comprising:
   applying an energy - absorbing overlay to the workpiece, the energy - absorbing overlay being in liquid form, being resistant to drying, and being comprised of at least one of carbon black, graphite, and black iron oxide; and        directing a pulse of coherent energy to the energy - absorbing overlay while the energy - absorbing overlay is in the liquid form, wherein the pulse of coherent energy is absorbed at least in part by the energy - absorbing overlay.      
     
     
       30. A method for treating a workpiece by applying shockwaves thereto, comprising:
   applying an energy - absorbing overlay to the workpiece, the energy - absorbing overlay being in liquid form; and        directing a pulse of coherent energy to the energy - absorbing overlay while the energy - absorbing overlay is in the liquid form, wherein the pulse of coherent energy is absorbed at least in part by the energy - absorbing overlay, and wherein the energy - absorbing overlay is resistant to drying.      
     
     
       31. A method for treating a workpiece by applying shockwaves thereto, comprising:
   applying an energy - absorbing overlay to the workpiece, the energy - absorbing overlay being in liquid form and resistant to drying;        directing a pulse of coherent energy to the energy - absorbing overlay while the energy - absorbing overlay is in the liquid form, wherein the pulse of coherent energy is absorbed at least in part by the energy - absorbing overlay; and        applying a transparent overlay upon the energy - absorbing overlay while the energy - absorbing overlay is in the liquid form, wherein the energy - absorbing overlay is resistant to erosion by the transparent overlay.