Bare metal laser shock peening

Abstract

A method of making a laser shock peened article includes bare laser shock peening a bare metallic surface of a substrate of the article without using an ablative coating and forming a pre-stressed region having deep compressive residual stresses extending into the article and a recast layer above the pre-stressed region. Removing just the recast layer with an abrasive vibratory process with an abrasive media. The vibratory process may include one or more of the following: abrasive tumbling including packing the article within a bed of abrasive particles and shaking the article within the bed during a tumbling cycle, mechanical peening including peening the article with small particles which either abrade and/or shatter a brittle surface of the recast layer, and abrasive polishing including loading the article into a bed of paste including abrasive particles and oscillating the bed across and around the article.

1 . A method of making a laser shock peened article comprising the following steps: 
 (a) bare laser shock peening a bare metallic laser shock peening surface of a substrate of the article without using an ablative coating on the metallic surface and forming a pre-stressed region having deep compressive residual stresses imparted by laser shock peening extending into the article from a laser shock peened surface and a recast layer above the laser shock peened surface and the pre-stressed region, and    (b) removing just the recast layer with an abrasive vibratory process with an abrasive media.    
   
   
       2 . A method as claimed in  claim 1  further comprising the vibratory process including an abrasive tumbling process including packing the article within a bed of abrasive particles and shaking the article within the bed during a tumbling cycle for a period of time.  
   
   
       3 . A method as claimed in  claim 2  further comprising the period of time of the tumbling cycle being in a range of several minutes to several hours.  
   
   
       4 . A method as claimed in  claim 3  further comprising the tumbling cycle being run at vibratory frequencies in a range from a few Hz to several hundred Hz.  
   
   
       5 . A method as claimed in  claim 2  wherein the abrasive media includes stones characterized as having a size range from about  0 . 2  inches to  1 . 0  inches.  
   
   
       6 . A method as claimed in  claim 1  further comprising the vibratory process including mechanical peening of the article with small particles which either abrade and/or shatter a brittle surface of the recast layer.  
   
   
       7 . A method as claimed in  claim 6  further wherein the small particles are glass beads.  
   
   
       8 . A method as claimed in  claim 1  further comprising the vibratory process being an abrasive polishing process including loading the article into a bed of paste including abrasive particles and oscillating the bed across and around the article.  
   
   
       9 . A method as claimed in  claim 1  further comprising the vibratory process including a combination of two or more of the following processes: 
 an abrasive tumbling process including packing the article within a bed of abrasive particles and shaking the article within the bed during a tumbling cycle for a period of time,    a mechanical peening process including peening the article with small particles which either abrade and/or shatter a brittle surface of the recast layer, and    an abrasive polishing process including loading the article into a bed of paste including abrasive particles and oscillating the bed across and around the article.    
   
   
       10 . A method as claimed in  claim 1  further comprising the bare laser shock peening including providing a confining medium over the bare metallic surface and firing a laser beam through the confining medium onto the bare surface with sufficient power to vaporize material of the substrate to form the pre-stressed region having deep compressive residual stresses imparted by laser shock peening extending into the article and the recast layer above the pre-stressed region.  
   
   
       11 . A method as claimed in  claim 1  wherein the article is a gas turbine engine airfoil having a leading edge and pressure and suction sides and the bare laser shock peening is performed at least on a portion of the bare metallic surface along the leading edge on both the pressure and suction sides of the airfoil simultaneously.  
   
   
       12 . A method as claimed in  claim 11  further comprising the vibratory process being an abrasive tumbling process including packing the article within a bed of abrasive particles and shaking the article within the bed during a tumbling cycle for a period of time.  
   
   
       13 . A method as claimed in  claim 12  further comprising the period of time of the tumbling cycle being in a range of several minutes to several hours.  
   
   
       14 . A method as claimed in  claim 13  further comprising the tumbling cycle being run at vibratory frequencies in a range from a few Hz to several hundred Hz.  
   
   
       15 . A method as claimed in  claim 12  wherein the abrasive media includes stones characterized as having a size range from about  0 . 2  inches to  1 . 0  inches.  
   
   
       16 . A method as claimed in  claim 11  further comprising the vibratory process being a mechanical peening including peening the article with small particles which either abrade and/or shatter a brittle surface of the recast layer.  
   
   
       17 . A method as claimed in  claim 16  further wherein the small particles are glass beads.  
   
   
       18 . A method as claimed in  claim 11  further comprising the vibratory process being an abrasive polishing process including loading the article into a bed of paste including abrasive particles and oscillating the bed across and around the article.  
   
   
       19 . A method as claimed in  claim 11  further comprising the bare laser shock peening including providing a confining medium over the bare metallic surface and firing a laser beam through the confining medium onto the bare surface with sufficient power to vaporize material of the substrate to form the pre-stressed region having deep compressive residual stresses imparted by laser shock peening extending into the article and the recast layer above the pre-stressed region.  
   
   
       20 . A method as claimed in  claim 1  further comprising a preliminary abrasive grinding process to pre-clean the laser shock peened surface of the article after the bare laser shock peening and prior to the removing just the recast layer with an abrasive vibratory process.  
   
   
       21 . A method as claimed in  claim 20  wherein the preliminary abrasive grinding process includes using a flexible abrasive wheel to pre-clean the laser shock peened surface.  
   
   
       22 . A method as claimed in  claim 11  further comprising: 
 a preliminary abrasive grinding process to pre-clean the laser shock peened surface of the airfoil after the bare laser shock peening and prior to the removing just the recast layer with an abrasive vibratory process,    the preliminary abrasive grinding process including running the laser shock peened surface along the leading edge of the airfoil between two slightly spaced apart and spinning flexible abrasives wheels to pre-clean the laser shock peened surface on both the pressure and suction sides of the airfoil.    
   
   
       23 . A laser shock peened article comprising: 
 a laser shock peened surface of a substrate of the article,    a pre-stressed region having deep compressive residual stresses imparted by laser shock peening extending into the article from the laser shock peened surface,    the laser shock peened surface and the pre-stressed region having been formed using bare laser shock peening,    the bare laser shock peening a bare metallic surface of a substrate of the article without using an ablative coating on the metallic surface and forming a pre-stressed region having deep compressive residual stresses imparted by laser shock peening extending into the article and a recast layer above the pre-stressed region, and    removing just the recast layer with an abrasive vibratory process with an abrasive media.    
   
   
       24 . An article as claimed in  claim 23  wherein the vibratory process includes one or more of the following processes: 
 an abrasive tumbling process including packing the article within a bed of abrasive particles and shaking the article within the bed during a tumbling cycle for a period of time,    a mechanical peening process including peening the article is with small particles which either abrade and/or shatter a brittle surface of the recast layer, and    an abrasive polishing process including loading the article into a bed of paste including abrasive particles and oscillating the bed across and around the article.    
   
   
       25 . An article as claimed in  claim 23  further comprising the laser shock peened surface being located along a leading edge of a gas turbine engine airfoil.  
   
   
       26 . An article as claimed in  claim 25  wherein the vibratory process includes one or more of the following processes: 
 an abrasive tumbling process including packing the article within a bed of abrasive particles and shaking the article within the bed during a tumbling cycle for a period of time,    a mechanical peening process including peening the article with small particles which either abrade and/or shatter a brittle surface of the recast layer, and    an abrasive polishing process including loading the article into a bed of paste including abrasive particles and oscillating the bed across and around the article.