Single-Crystal SMA Components for Large Recoverable Strain

Solution Overview

Problem

Conventional polycrystalline shape memory alloys (SMAs) exhibit limited recoverable strain and superelasticity, leading to reduced performance in mechanical devices due to grain boundary restrictions and lower deformation capabilities compared to single crystal SMAs.

Innovation Solution

The use of single crystal shape memory alloys, such as CuAlNi, which enable hyperelastic properties with up to 24% repeatable strain recovery, offering greater strength, fatigue life, and thermally induced phase transformations, along with stress-induced transitions, for applications requiring large recoverable distortions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If polycrystalline shape memory alloys are used, then the material can be easily manufactured and processed, but the recoverable strain and superelasticity are limited due to grain boundary restrictions

Engineering Contradiction:

Improveease of manufactureVSAvoidrecoverable strain

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the microstructural parameter from polycrystalline to single crystal, eliminating grain boundaries and enabling recoverable strains up to 24% compared to limited strains in polycrystalline materials, while maintaining manufacturability through controlled crystal growth processes

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If polycrystalline shape memory alloys are used, then conventional manufacturing processes can be applied, but the superelasticity and strain recovery are reduced

Engineering Contradiction:

Improveease of manufactureVSAvoidsuperelasticity

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

The patent changes the microstructural parameter from polycrystalline to single crystal, eliminating grain boundaries and enabling recoverable strains up to 24% compared to limited strains in polycrystalline materials, while maintaining manufacturability through controlled crystal growth processes

Inventive Principle:

Principle #35Parameter changes

3Reliability

If single crystal shape memory alloys are used, then large recoverable distortions and hyperelastic properties are achieved, but the manufacturing complexity increases

Engineering Contradiction:

Improvestrain recoveryVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the microstructural parameter from polycrystalline to single crystal, eliminating grain boundaries and enabling recoverable strains up to 24% compared to limited strains in polycrystalline materials, while maintaining manufacturability through controlled crystal growth processes

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Single crystal SMAs provide enhanced strain recovery, true constant force deflection, narrow loading-unloading hysteresis, and ultra-low yield strength, enabling more efficient actuation and deployment in devices like booms, antennae, and medical instruments with improved reliability and energy efficiency.

Implementation Method 1

Superelasticity results from stress-induced conversion from austenite to martensite as stress is increased beyond a critical level, and reversion from martensite to austenite as stress is reduced below a second (lower) critical level.

Methodology Applied

Scientific EffectStress-induced phase transformation: Phase Change

Implementation Method 2

Such an SMA material will undergo a crystalline phase transformation from martensite to austenite when heated through the material s phase change temperature.

Methodology Applied

Scientific EffectThermal phase transformation: Phase Change

Data Source

PatentUS7632361B2Single crystal shape memory alloy devices and methods

Publication Date: 2009.12.15 ENSIGN BICKFORD AEROSPACE & DEFENSE CO

AI summary

Devices and methods of making devices having one or more components made of single crystal shape memory alloy capable of large recoverable distortions, defined herein as “hyperelastic” SMA. Recoverable Strains are as large as 9 percent, and in special circumstances as large as 22 percent. Hyperelastic SMAs exhibit no creep or gradual change during repeated cycling because there are no crystal boundaries. Hyperelastic properties are inherent in the single crystal as formed: no cold work or special heat treatment is necessary. Alloy components are Cu—Al—X where X may be Ni, Fe, Co, Mn. Single crystals are pulled from melt as in the Stepanov method and quenched by rapid cooling to prevent selective precipitation of individual elemental components. Conventional methods of finishing are used: milling, turning, electro-discharge machining, abrasion. Fields of application include aerospace, military, automotive, medical devices, microelectronics, and consumer products.