Apparatus and method for subsurface structural modification of materials at reduced temperatures

Abstract

Nanostructured or ultra-fine grained metallic systems according to embodiments of the invention may be formed of: pure Cu, pure Fe, or pure Ti, with grain sizes of less than 140 nm, 348 nm, or 59 nm, respectively. The metallic systems demonstrate a monotonically increasing grain size dependence from a minimum value attained at the surface; and a converse relation of microhardness, decreasing from 160 kg/mm 2 , 265 kg/mm 2 , or 320 kg/mm 2 , respectively. The grain refinement process at cryogenic conditions relies on the suppression of room temperature dislocation-mediated deformation mechanisms which facilitate grain restructuring, relaxation, and reorientation. At the cryogenic conditions, alternative mechanism for grain refinement, such as shear localization or dynamic recrystallization may be more dominant. Processes for refining the grain size of these metallic systems may include: subjecting metal plates to a high-energy milling process using a high-energy milling device to impart high impact energies to its surface. Due to the high-efficiency of this attrition process, these metallic systems are ideal candidates for improved corrosion and wear resistance.

1 . A surface mechanical attrition treatment process for a metal part comprising:
 providing at least one metal part that is formed from a first metal composition;   providing a plurality of metal fragments that are formed from a second metal composition wherein said metal fragments have a size that is significantly smaller than the size of the at least one metal part;   reducing the temperature of the at least one metal part and the plurality of metal fragments;   impacting the at least one metal part with the plurality of fragments at a reduced temperature (T r ), for an impact processing time (t i );   wherein, the at least one metal part is subjected to bombardment by the plurality of metal fragments at a reduced temperature (T r ), resulting in the as-received grain size of the at least one metal part to be reduced, by several orders of magnitude, and possessing a gradient structure from the impact surface of the at least one metal part into the interior of the bulk of the at least one metal part.   
     
     
         2 . The surface mechanical attrition treatment process of  claim 1 , wherein the reduced temperature (T r ) is not greater than about −50° C. 
     
     
         3 . The surface mechanical attrition treatment process of  claim 1 , wherein the reduced temperature (T r ) is not greater than about −100° C. 
     
     
         4 . The surface mechanical attrition treatment process of  claim 1 , wherein the reduced temperature (T r ) is not greater than about −150° C. 
     
     
         5 . The surface mechanical attrition treatment process of  claim 1 , wherein the reduced temperature (T r ) is not greater than about −196° C. 
     
     
         6 . The surface mechanical attrition treatment process of  claim 1 , wherein the refined grain size of the metallic system at its surface is about 1000 nm or less. 
     
     
         7 . The surface mechanical attrition treatment process of  claim 3 , wherein the room temperature refined grain size of the metallic system at its surface is about 355 nm or less. 
     
     
         8 . The surface mechanical attrition treatment process of  claim 3 , wherein the cryogenic refined grain size of the metallic system at its surface is about 140 nm or less. 
     
     
         9 . The surface mechanical attrition treatment process of  claim 3 , wherein the room temperature processed metallic system has a surface Vickers microhardness of about 110 kg/mm 2  or more at room temperature. 
     
     
         10 . The surface mechanical attrition treatment process of  claim 3 , wherein the cryogenic temperature processed metallic system has a surface Vickers microhardness of about 150 kg/mm 2  or more at cryogenic temperature. 
     
     
         11 . The surface mechanical attrition treatment process of  claim 4 , wherein the room temperature refined grain size of the metallic system at its surface is about 635 nm or less. 
     
     
         12 . The surface mechanical attrition treatment process of  claim 4 , wherein the cryogenic refined grain size of the metallic system at its surface is about 350 nm or less. 
     
     
         13 . The surface mechanical attrition treatment process of  claim 4 , wherein the room temperature processed metallic system has a surface Vickers microhardness of about 230 kg/mm 2  or more at room temperature. 
     
     
         14 . The surface mechanical attrition treatment process of  claim 4 , wherein the cryogenic temperature processed metallic system has a surface Vickers microhardness of about 260 kg/mm 2  or more at room temperature. 
     
     
         15 . The surface mechanical attrition treatment process of  claim 5 , wherein the room temperature refined grain size of the metallic system at its surface is about 155 nm or less. 
     
     
         16 . The surface mechanical attrition treatment process of  claim 5 , wherein the cryogenic refined grain size of the metallic system at its surface is about 60 nm or less. 
     
     
         17 . The surface mechanical attrition treatment process of  claim 5 , wherein the room temperature processed metallic system has a surface Vickers microhardness of about 280 kg/mm 2  or more at room temperature. 
     
     
         18 . The surface mechanical attrition treatment process of  claim 5 , wherein the cryogenic temperature processed metallic system has a surface Vickers microhardness of about 320 kg/mm 2  or more at room temperature. 
     
     
         19 . The surface mechanical attrition treatment process of  claim 1 , wherein the impact processing time (t i ) is at least about 5 minutes. 
     
     
         20 . The surface mechanical attrition treatment process of  claim 1 , wherein the impact processing time (t i ) is at least about 10 minutes. 
     
     
         21 . The surface mechanical attrition treatment process of  claim 1 , wherein the impact processing time (t i ) is at least about 20 minutes. 
     
     
         22 . The surface mechanical attrition treatment process of  claim 1 , wherein the impact processing time (t i ) is at least about 40 minutes. 
     
     
         23 . The surface mechanical attrition treatment process of  claim 1 , wherein the impact processing time (t i ) is at least about 60 minutes. 
     
     
         24 . A method of modifying the surface of a metal part, the method comprising the steps of:
 providing at least one metal part t;   providing a plurality of metal fragments wherein said metal fragments have a size that is significantly smaller than the size of the at least one metal part;   reducing the temperature of the at least one metal part and the plurality of metal fragments; and   impacting the at least one metal part with the plurality of fragments at a reduced temperature (T r ), for an impact processing time (t i ).