Superelastic Alloy Structural Geometry for Ultrahigh Mechanical Damping

Abstract

A mechanical structure is provided with a crystalline super alloy that is characterized by an average grain size and that exhibits a martensitic phase transformation resulting from a mechanical stress input greater than a characteristic first critical stress. A configuration of the superelastic alloy is provided with a geometric structural feature of the alloy that has an extent that is no greater than about 200 micrometers and that is no larger than the average grain size of the alloy. This geometric feature undergoes the martensitic transformation without intergranular fracture of the geometric feature.

We claim:  
     
         1 . A mechanical structure comprising:
 a crystalline superelastic alloy characterized by an average grain size and exhibiting a martensitic phase transformation resulting from a mechanical stress input greater than a characteristic first critical stress; and   a configuration of the superelastic alloy providing a geometric structural feature of the alloy having an extent that is no greater than about 200 micrometers and that is no larger than the average grain size of the alloy, the geometric feature undergoing the martensitic transformation without intergranular fracture of the geometric feature.   
     
     
         2 . The structure of  claim 1  wherein the characteristic first critical stress for causing the martensitic phase transformation is less than a plastic deformation stress that would plastically deform the structure. 
     
     
         3 . The structure of  claim 1  wherein the geometric structural feature extent is less than an extent of a martensitic domain of the superelastic alloy. 
     
     
         4 . The structure of  claim 1  wherein an individual grain of the alloy extends to more than one free surface edge of the geometric structural feature. 
     
     
         5 . The structure of  claim 1  wherein the superelastic alloy further exhibits an austenitic phase transformation resulting from a reduction in mechanical stress input below a characteristic second critical stress, with a difference between the first critical stress and the second critical stress in the geometric structural feature being at least about 20 MPa. 
     
     
         6 . The structure of  claim 1  wherein the superelastic alloy comprises a shape memory alloy. 
     
     
         7 . The structure of  claim 1  wherein the superelastic alloy grain structure is monocrystalline. 
     
     
         8 . The structure of  claim 1  wherein the superelastic alloy grain structure is polycrystalline. 
     
     
         9 . The structure of  claim 1  wherein the superelastic alloy is characterized by an austenitic phase at room temperature. 
     
     
         10 . The structure of  claim 1  wherein the superelastic alloy comprises copper. 
     
     
         11 . The structure of  claim 1  wherein the superelastic alloy comprises aluminum. 
     
     
         12 . The structure of  claim 1  wherein the superelastic alloy comprises nickel. 
     
     
         13 . The structure of  claim 1  wherein the geometric structural feature of the alloy has an extent that is greater than about 2 micrometers. 
     
     
         14 . The structure of  claim 1  wherein the geometric structural feature of the alloy has an extent that is no greater than about 100 micrometers. 
     
     
         15 . The structure of  claim 1  wherein the geometric structural feature of the alloy has an extent that is no greater than about 50 micrometers. 
     
     
         16 . The structure of  claim 1  wherein the configuration of the superelastic alloy includes a pillar of the alloy providing the geometric structural feature as a diameter of the pillar. 
     
     
         17 . The structure of  claim 1  wherein the configuration of the superelastic alloy includes a wire of the alloy providing the geometric structural feature as a diameter of the wire. 
     
     
         18 . The structure of  claim 17  wherein the wire comprises grains arranged in a bamboo grain structure in which grains extend across the wire diameter, the wire undergoing the martensitic transformation without intergranular fracture of the wire. 
     
     
         19 . The structure of  claim 1  wherein the configuration of the superelastic alloy structure includes a ribbon of the alloy providing the geometric structural feature as a thickness of the ribbon. 
     
     
         20 . The structure of  claim 20  wherein the fiber is characterized by a bamboo grain structure in which grains extend across the fiber diameter.