# US 8,465,847 B2 · Manufacture of shape-memory alloy cellular materials and structures by transient-liquid reactive joining

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- Number: US 8,465,847 B2
- Document ID: US8465847B2
- Status: Granted
- Kind: B2
- Application number: 12/852,456
- Filed: 2010-08-07
- Published: 2011-01-13
- Granted: 2013-06-18
- Earliest claimed: 2004-10-01
- Assignees: The Regents of the University of Michigan; Board of Trustees of Michigan State University
- Applicants: John A. Shaw; David S. Grummon
- Inventors: John A. Shaw; David S. Grummon
- Web page: https://patentgrep.com/patent/US8465847B2

## CPC

- B23K 1/0008: {specially adapted for particular articles or work}
- B23K 2101/06: Tubes
- B23K 2101/18: Sheet panels
- Y10T 428/12333: Helical or with helical component
- Y10T 428/1234: Honeycomb, or with grain orientation or elongated elements in defined angular relationship in respective components [e.g., parallel, inter- secting, etc.]
- Y10T 428/12361: having aperture or cut
- Y10T 428/12479: Porous [e.g., foamed, spongy, cracked, etc.]
- Y10T 428/125: Deflectable by temperature change [e.g., thermostat element]
- Y10T 428/12507: More than two components
- Y10T 428/12618: Plural oxides
- Y10T 428/12778: Alternative base metals from diverse categories
- Y10T 428/12819: Group VB metal-base component
- Y10T 428/12861: Group VIII or IB metal-base component
- Y10T 428/192: Sheets or webs coplanar
- Y10T 428/24149: Honeycomb-like
- Y10T 428/24711: Plural corrugated components
- Y10T 428/31678: Of metal
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

This invention discloses a method, using pure niobium as a transient liquid reactive braze material, for fabrication of cellular or honeycomb structures, wire space-frames or other sparse builtup structures or discrete articles using Nitinol (near-equiatomic titanium-nickel alloy) and related shape-memory and superelastic alloys. Nitinol shape memory alloys (SMAs), acquired in a form such as corrugated sheet, discrete tubes or wires, may be joined together using the newly discovered joining technique. Pure niobium when brought into contact with nitinol at elevated temperature, liquefies at temperatures below the melting point and flows readily into capillary spaces between the elements to be joined, thus forming a strong joint.

## Claims

### Claim 1

A cellular structure having improved shape memory compression and improved elasticity comprising:
a nickel and titanium containing shape memory alloy (SMA) form comprising a plurality of SMA surfaces;
a first SMA surface arranged adjacent to a second SMA surface; and
a solidified eutectic liquid joint containing nickel, titanium, and niobium, having about equiatomic amounts of Ni and Ti, joining adjacent SMA surfaces.

### Claim 2 (depends on 1)

The cellular structure of claim 1 further comprising a plurality of SMA forms joined by a plurality of joints.

### Claim 3 (depends on 1)

The cellular structure of claim 1, wherein the joint was formed by a method comprising:
positioning a reactive metal adjacent to the adjacent SMA surfaces;
heating the adjacent SMA surfaces and the reactive metal to a reaction temperature insufficient to melt either the SMA form or the reactive metal but sufficient to form a eutectic liquid; and then
cooling the SMA form and the eutectic liquid sufficiently to solidify the eutectic liquid before 10% by weight of the reactive metal is diffused into the SMA form.

### Claim 4 (depends on 3)

The cellular structure of claim 3, wherein the reactive metal comprises niobium.

### Claim 5 (depends on 1)

The cellular structure of claim 1, wherein each SMA form is a NiTi alloy.

### Claim 6 (depends on 1)

The cellular structure of claim 1, wherein the adjacent SMA surfaces are arranged as a honeycomb or tube bundle.

### Claim 7 (depends on 1)

The cellular structure of claim 1, wherein the adjacent SMA surfaces are arranged as a mesh.

### Claim 8 (depends on 1)

The cellular structure of claim 1 further comprising an uncompressed density of less than 10%, measured as a surface to volume ratio.

### Claim 9 (depends on 8)

The cellular structure of claim 8 further comprising an uncompressed density of less than 5%, measured as a surface to volume ratio.

### Claim 10 (depends on 1)

The cellular structure of claim 1 further comprising a strain recovery greater than 50%.

### Claim 11 (depends on 1)

The cellular structure of claim 1, wherein the structure has a regular cell structure.

### Claim 12

An article comprising:
a nickel and titanium containing shape memory alloy form having a first surface;
a material having a second surface adjacent to the first surface; and
a solidified eutectic liquid that comprises nickel, titanium, and niobium, having approximately equiatomic stoichiometic amounts of nickel and titanium, joining the first surface to the second surface.

### Claim 13 (depends on 12)

The article of claim 12, wherein the solidified eutectic liquid was formed by a method comprising:
positioning a reactive metal adjacent to the first and the second surfaces;
heating the surfaces and the reactive metal to a reaction temperature insufficient to melt the SMA form, the material, or the reactive metal but sufficient to form the eutectic liquid; and then
cooling the SMA form, the material, and the eutectic liquid sufficiently to solidify the eutectic liquid before 10% by weight of the reactive metal is diffused into the SMA form.

### Claim 14 (depends on 13)

The article of claim 13, wherein the reactive metal comprises niobium.

### Claim 15 (depends on 12)

The article of claim 12, wherein the solidified eutectic liquid is a quasibinary (NiTi)—Nb eutectic solid that contains two phases, an ordered metallic structure of NiTi and a disordered body-centered cubic solid solution of Nb, Ti, and Ni.

### Claim 16 (depends on 12)

The article of claim 12, wherein the SMA form is a NiTi alloy.

### Claim 17 (depends on 12)

The article of claim 12, wherein the material having the second surface is selected from the group consisting of NiTi alloy, metals, and ceramics.

### Claim 18 (depends on 17)

The article of claim 17, wherein the material having the second surface is a metal other than a NiTi alloy.

### Claim 19 (depends on 17)

The article of claim 17, wherein the material is a ceramic.

### Claim 20 (depends on 12)

The article of claim 12, wherein the first surface and the second surface individually comprise metal oxides.

### Claim 21

An article comprising:
a joint comprising a niobium containing solidified eutectic liquid fixing a first shape memory alloy form and a second shape memory alloy form relative to each other, wherein the solidified eutectic liquid is a quasibinary (NiTi)—Nb eutectic solid that contains two phases, an ordered metallic structure of NiTi and a disordered body-centered cubic solid solution of Nb, Ti, and Ni, having approximately equiatomic stoichiometic amounts of nickel and titanium.

### Claim 22 (depends on 21)

The article of claim 21, wherein the first form is separate from the second form.

### Claim 23 (depends on 21)

The article of claim 21 further comprising a plurality of joints fixing a plurality of forms relative to each other.

### Claim 24 (depends on 21)

The article of claim 21, wherein the forms provide an article architecture selected from the group consisting of tube bundles; multilayer corrugated sheets; spaceframes; bundles of helically wrapped NiTi strip; auxetic forms; shafts manufactured from multiple tubes; flexible couplings; bellows; honeycombs; joined wire, strips and sheets; lap joints; butt joints; and mixtures thereof.

### Claim 25 (depends on 21)

The article of claim 21, wherein the article is selected from the group consisting of a bone replacement material; an airframe component; an energy absorbing structure; a medical device; armor; an acoustic damping material; eyeglass frames; a cell phone antenna; a surgical tool; a safety device; a toy; and an actuator.

### Claim 26 (depends on 21)

The article of claim 21, wherein the solidified eutectic liquid is solidified before 10% of the Niobium therefrom is diffused into the shape memory alloy form.