Grain boundary engineering of polycrystalline shape memory alloys by phase manipulation for enhanced mechanical ductility and application fatigue life

Patent metadata

Field	Value
Publication number	US-2018274071-A1
Application number	US-201515525128-A
Country	US
Kind code	A1
Filing date	Nov 6, 2015
Priority date	Nov 6, 2014
Publication date	Sep 27, 2018
Grant date	—

Abstract

Provided is a method of making a polycrystalline shape memory alloy (SMA) by forming an alloy with grains and boundaries between them, exposing the alloy to a two-phase temperature range at which a two-phase equilibrium is achieved in the alloy, converting grains to an austenite phase, and precipitating a face-centered-cubic crystal structure solid solution phase at grain boundaries, then quenching the alloy. Also provided is a polycrystalline SMA with a dual-phase microstructure having grains mostly in an austenite phase, a martensite phase, or in transition between an austenite phase and a martensite phase and grain boundaries containing a face-centered-cubic crystal structure solid solution phase.

First claim

What is claimed is:

1 . A method of making a polycrystalline shape memory alloy comprising:
forming an alloy wherein the forming comprises combining a plurality of metals and the alloy comprises a matrix of grains and a plurality of grain boundaries, wherein the plurality of grain boundaries comprise a plurality of interfaces between adjacent grains; exposing the alloy to a two-phase temperature range wherein the alloy comprises a two-phase equilibrium when heated to within the two-phase temperature range; exposing the alloy to a dwell temperature within the two-phase temperature range for a duration of time; converting at least most of the matrix of grains to an austenite phase; precipitating a face-centered-cubic crystal structure solid solution phase at the plurality of grain boundaries; and quenching the alloy.

2 . The method of claim 1 wherein the plurality of metals are selected from a group consisting of cobalt, nickel, copper, iron, aluminum, zinc, manganese, gallium, titanium, tin, beryllium, silicon, and any combination of two or more of the foregoing.

3 . The method of claim 2 wherein the alloy comprises combinations of metals and the combinations are selected from the group consisting of copper-zinc-aluminum, copper-zinc-tin, copper-zinc-gallium, copper-zinc-silicon, copper-aluminum-nickel, copper-aluminum-beryllium, copper-aluminum-manganese, cobalt-nickel-aluminum, cobalt-nickel-gallium, nickel-aluminum, nickel manganese gallium, nickel-manganese-aluminum, nickel-iron-gallium, iron-manganese-aluminum-nickel, iron-nickel-cobalt-titanium, iron-nickel-cobalt-aluminum, and nickel-titanium.

4 . The method of claim 1 wherein forming the alloy comprises combining a relative weight proportion of the plurality of metals, the two-phase temperature range comprises a low temperature and a high temperature, and the dwell temperature is above the low temperature by between approximately 50% to approximately 95% of a difference between the low temperature and the high temperature.

5 . The method of claim 4 wherein the dwell temperature is above the low temperature by between approximately 50% to approximately 80% of the difference.

6 . The method of claim 5 wherein the dwell temperature is above the low temperature by between approximately 50% to approximately 60% of the difference.

7 . The method of claim 1 wherein forming the alloy comprises combining a relative weight proportion of the plurality of metals, the two-phase temperature range comprises a low temperature and a high temperature, and the dwell temperature is above the low temperature by between approximately 10% to approximately 50% of a difference between the low temperature and the high temperature.

8 . The method of claim 1 wherein the duration of time is between approximately 1 hr and 10 hr.

9 . The method of claim 8 wherein the duration of time is between approximately 1 hr and 8 hr.

10 . The method of claim 9 wherein the duration of time is between approximately 1 hr and 4 hr.

11 . The method of claim 1 further comprising exposing the alloy to a temperature above the dwell temperature and ramping down to the dwell temperature.

12 . The method of claim 11 wherein the temperature above the dwell temperature is above the two-phase temperature range.

13 . The method of claim 11 wherein the alloy is exposed to the temperature above the dwell temperature for between approximately 1 hr to 2 hr.

14 . The method of claim 11 wherein ramping down comprises lowering a temperature to which the alloy is exposed from the temperature above the dwell temperature to the dwell temperature by between approximately 0.8° C./min and 2.5° C./min.

15 . The method of claim 1 wherein the alloy comprises Co x Ni y Al z , x, y, and z comprise weight percentages wherein x+y+z=100%, 37≤x≤48, 12≤z≤22, and the dwell temperature is between approximately 1150° C. and approximately 1375° C.

16 . The method of claim 1 wherein the alloy comprises Cu x Zn y Al z , x, y, and z comprise weight percentages wherein x+y+z=100%, 10≤y≤40, 1≤z≤12.5, and the dwell temperature is between approximately 550° C. and approximately 750° C.

17 . The method of claim 1 wherein the alloy comprises Cu x Al y Ni z , x, y, and z comprise weight percentages wherein x+y+z=100%, 5≤y≤15, 1≤z≤10, and the dwell temperature is between approximately 600° C. and approximately 900° C.

18 . A polycrystalline shape memory alloy comprising:
an alloy comprising a plurality of metals; a dual-phase microstructure within the alloy comprising a matrix of grains and a plurality of grain boundaries wherein: the matrix of grains comprises a plurality of grains that are at least mostly in an austenite phase, at least mostly in a martensite phase, or at least mostly transitioning between an austenite phase and a martensite phase; and the plurality of grain boundaries comprises a face-centered-cubic crystal structure solid solution phase at a plurality of interfaces between adjacent grains.

19 . The shape memory alloy of claim 18 wherein the plurality of metals are selected from a group consisting of cobalt, nickel, copper, iron, aluminum, titanium, zinc, manganese, gallium, tin, beryllium, silicon, and any combination of the foregoing.

20 . The shape metal allow of claim 18 comprising an article wherein the article is selected from the group consisting of a rod, a bar, a wire, a wire cloth, a woven fabric, a foil, a ribbon, a sheet, a porous alloy, a foam, a tube, and any combination of two or more of the foregoing.

Assignees

• Rensselaer Polytech Inst

Inventors

• Chen Ying
• Dar Rebecca

Classifications

• C22C19/07

  based on cobalt · CPC title

• C22F1/006 Primary

  Resulting in heat recoverable alloys with a memory effect · CPC title

• C22C9/01

  with aluminium as the next major constituent · CPC title

• C22F1/10

  of nickel or cobalt or alloys based thereon · CPC title

• C22F1/08

  of copper or alloys based thereon · CPC title