Cerium Containing Copper Based Shape Memory Alloy

Abstract

Embodiments of the present disclosure relate to a copper-based shape memory alloy (Cu-SMA) having improved shape memory properties. Cu-SMAs, especially in the Cu—Al—Mn family, have low cost, excellent ductility, and a wide range of tunable phase transformations and the associated physical properties. However, the transformation stress of the commonly developed Cu-SMA is low, limiting its application for high load conditions. Alloying Cu-SMAs with transition and/or rare earth metals may effectively increase the transformation stress by forming fine precipitates of intermetallics in the Cu—Al—Mn matrix. For example, 0.5 at % Ce addition can result in increases of 71.4%, and 78.6% in the room temperature transformation stress and peak stress, respectively. When the properly distributed Ce-containing precipitation combined with the additional alloying elements to engineer phase transformation temperature, the obtained Cu-SMAs can offer a wide range of tunable mechanical properties in a wide temperature range.

What is claimed is: 
     
         1 . A shape memory alloy, comprising:
 from about 5 at % to about 30 at % aluminum,   from about 0.05 at % to about 30 at % manganese,   from about 0.05 at % to about 10 at % of a rare earth element,   from 0 at % to about 10 at % of a transition metal element, and   balance copper.   
     
     
         2 . The shape memory alloy of  claim 1 , wherein the rare earth element increases a strength of the shape memory alloy. 
     
     
         3 . The shape memory alloy of  claim 1 , wherein the rare earth element is selected from a group consisting of cerium, lanthanum, yttrium, scandium, or a combination of two or more thereof. 
     
     
         4 . The shape memory alloy of  claim 1 , comprising at least 0.05 at % of the transition metal element, wherein the transition metal changes the phase transformation temperature and ductility of the shape memory alloy. 
     
     
         5 . The shape memory alloy of  claim 4 , wherein the transition metal element is selected from a group consisting of tin, nickel, silver, zinc, iron, cobalt, chromium, vanadium, titanium, calcium, or a combination of two or more thereof. 
     
     
         6 . The shape memory alloy of  claim 1 , comprising a transformation stress for the induced martensite transformation of at least 150 MPa. 
     
     
         7 . The shape memory alloy of  claim 1 , comprising a peak stress of at least 170 MPa. 
     
     
         8 . The shape memory alloy of  claim 1 , wherein a microstructure of the shape memory alloy comprises intermetallic compounds of aluminum and cerium at grain boundaries. 
     
     
         9 . The shape memory alloy of  claim 8 , wherein the intermetallic compounds comprise at least one of Al 3 Ce and Al 11 Ce 3 . 
     
     
         10 . The shape memory alloy of  claim 1 , comprising an austenite start temperature and an austenite finish temperature both within a range from −40° C. to 0° C. 
     
     
         11 . A device comprising the shape memory alloy according to  claim 1 , the device being an elastocaloric heat pump, a smart structure, or an actuator. 
     
     
         12 . A device comprising the shape memory alloy according to  claim 1 , the device being an elastocaloric refrigerant, a non-pneumatic tire, anti-earthquake rebar, or robotic muscle. 
     
     
         13 . A thermomechanical process to optimize microstructure and shape memory properties of the shape memory alloy according to  claim 1 , the thermomechanical process comprising:
 solution treating an ingot of the shape memory alloy at a temperature in a range of 750° C. to 950° C. for a time in a range of 0.5 hours to 5 hours followed by cooling.   
     
     
         14 . The thermomechanical process of  claim 13 , wherein the cooling comprises water quenching. 
     
     
         15 . The thermomechanical process of  claim 13 , further comprising:
 hot deforming the ingot, after solution treating, to reduce defects and obtain uniform microstructure; and   quenching the hot deformed ingot.   
     
     
         16 . The thermomechanical process of  claim 15 , further comprising:
 tempering the ingot, after hot deforming, at a temperature in a range of 150° C. to 350° C. for a time in a range of 15 minutes to 60 minutes; and   quenching the tempered ingot to achieve a disorder state and improved ductility.   
     
     
         17 . The thermomechanical process of  claim 16 , further comprising:
 cold working the ingot to improve a stress plateau of the shape memory alloy and to adjust phase transformation temperature.   
     
     
         18 . The thermomechanical process of  claim 16 , further comprising:
 isothermal, thermomechanically stabilizing the ingot to improve a stress plateau of the shape memory alloy.   
     
     
         19 . The thermomechanical process of  claim 17 , further comprising:
 hot deforming and tempering the ingot one or more additional times.   
     
     
         20 . The thermomechanical process of  claim 13 , wherein the shape memory alloy comprises <1 at % of the rare earth element.