Shape Memory Alloy Wire With Controlled Energy Damping

Abstract

There is provided a shape memory alloy wire with a length of polycrystalline shape memory alloy having an alloy composition including at least one member selected from the group consisting of Cu in at least 10 wt. %, Fe in at least 5 wt. %, Au in at least 5 wt. %, Ag in at least 5 wt. %, Al in at least 5 wt. %, In in at least 5 wt. %, Mn in at least 5 wt. %, Zn in at least 5 wt. % and Co in at least 5 wt. %, and having a martensite crystal structure consisting of one of 2H, 18R 1 , M18R, and 6R. The length of polycrystalline shape memory alloy has a cross sectional wire diameter greater than 1 micron and less than 500 microns, an oligocrystalline morphology including polycrystalline grains that span the wire diameter and a wire surface with a surface roughness that is no greater than about 100 nanometers.

We claim: 
     
         1 . A shape memory alloy wire comprising:
 a length of a polycrystalline shape memory alloy having an alloy composition including at least one member selected from the group consisting of Cu in at least about 10 wt. %, Fe in at least about 5 wt. %, Au in at least about 5 wt. %, Ag in at least about 5 wt. %, Al in at least about 5 wt. %, In in at least about wt. %, Mn in at least about 5 wt. %, Zn in at least about 5 wt. % and Co in at least about 5 wt. %, the shape memory alloy composition having a martensite crystal structure consisting of one of 2H, 18R 1 , M18R, and 6R;   the length of a polycrystalline shape memory alloy having a cross sectional wire diameter greater than about 1 micron and less than about 500 microns;   the length of a polycrystalline shape memory alloy having an oligocrystalline morphology including polycrystalline shape memory alloy grains that span the cross sectional wire diameter; and   the length of a polycrystalline shape memory alloy having a wire surface with a surface roughness no greater than about 100 nanometers.   
     
     
         2 . The shape memory alloy wire of  claim 1  wherein the cross sectional wire diameter has an extent that causes energy dissipation by the shape memory alloy wire during a martensitic phase transformation to be dominated by surface roughness of the oligocrystalline shape memory alloy wire. 
     
     
         3 . The shape memory alloy wire of  claim 1  wherein the shape memory alloy wire cross sectional diameter is less than about 250 microns. 
     
     
         4 . The shape memory alloy wire of  claim 1  wherein the shape memory alloy wire cross sectional diameter is less than about 100 microns. 
     
     
         5 . The shape memory alloy wire of  claim 1  wherein the shape memory alloy wire cross sectional diameter is greater than about 10 microns. 
     
     
         6 . The shape memory alloy wire of  claim 1  wherein the shape memory alloy wire cross sectional diameter is greater than about 100 microns. 
     
     
         7 . The shape memory alloy wire of  claim 1  wherein the shape memory alloy composition comprises Cu—Zn—Al. 
     
     
         8 . The shape memory alloy wire of  claim 1  wherein the shape memory alloy composition comprises Cu-14Al-4Ni (wt. %). 
     
     
         9 . The shape memory alloy wire of  claim 1  wherein the shape memory alloy cross sectional wire diameter is greater than about 20 microns and less than about 250 microns. 
     
     
         10 . The shape memory alloy wire of  claim 1  wherein the length of polycrystalline shape memory alloy has a surface roughness characterized by an arithmetic average surface roughness, R a , no greater than about 80 nanometers.