Superelastic Nitinol Wires Grain Size and Heat Treatment
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Solution Overview
Problem
Current nickel-titanium alloys used in medical devices have limited superelasticity, which restricts their ability to be compactly delivered and expanded to functional configurations, necessitating enhanced material properties and manufacturing processes to achieve greater than 6% superelasticity while maintaining or improving existing properties.
Innovation Solution
The development of nickel-titanium alloys with specific grain sizes between 0.2 and 10 microns, combined with shape set heat treatments at temperatures between 225° C. and 350° C. for 20-240 minutes, and partial annealing at 550° C. to 700° C. for up to 60 minutes, to achieve increased recoverable strain, upper plateau length, and elongation at fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nickel-titanium alloys are used, then manufacturing process is simple, but superelasticity is limited to 6% or less
Solution Approach 1:
The patent applies parameter changes by precisely controlling grain size (0.2-10 microns) and implementing multi-stage heat treatments at specific temperatures (550-700°C for partial annealing, 225-350°C for shape set) to achieve superelasticity beyond 6%. This systematic parameter optimization transforms the material properties while maintaining manufacturability through established thermal processing techniques.
Solution Approach 2:
The patent employs preliminary action by performing partial annealing at 550-700°C for 1-60 minutes before the shape set heat treatment. This preliminary thermal processing prepares the microstructure by controlling grain growth and phase distribution, enabling the subsequent shape set treatment to achieve enhanced superelasticity without requiring overly complex manufacturing steps.
2Reliability
If grain size is reduced to enhance superelasticity, then recoverable strain increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent establishes a specific grain size range of 0.2-10 microns through controlled heat treatment parameters. By defining this precise range rather than targeting a single value, the patent achieves enhanced recoverable strain (>9%) while maintaining manufacturable precision levels. The grain size control is achieved through standard thermal processing techniques rather than requiring cutting-edge precision manufacturing.
3Reliability
If heat treatment time is extended to improve material properties, then superelasticity increases, but production time increases
Solution Approach 1:
The patent applies partial annealing at 550-700°C for 1-60 minutes, which is a controlled partial heat treatment rather than full annealing. This partial action is sufficient to achieve the desired grain size and phase distribution for enhanced superelasticity, avoiding the excessive time consumption of complete annealing processes while still obtaining the necessary material property improvements.
Solution Approach 2:
The preliminary partial annealing step at 550-700°C prepares the microstructure in advance, making the subsequent shape set heat treatment at 225-350°C more efficient. This preliminary action reduces the overall time required for achieving enhanced superelasticity compared to performing only extensive heat treatments without the preparatory step.
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
These processing methods result in nickel-titanium alloys with enhanced superelastic properties, including recoverable strains greater than 9%, upper plateau lengths greater than 6%, and elongation at fracture greater than 15%, suitable for improved performance in medical devices.
Implementation Method 1
Key to exploiting the performance of nitinol alloys is the phase transformation in the crystalline structure that transitions between an austenitic phase and a martensitic phase
Implementation Method 2
applying a shape set heat treatment to the nickel-titanium alloy. The heat treatment includes applying heat at a temperature between 225° C. and 350° C. for a period of time between 20 and 240 minutes
Implementation Method 3
applying a partial annealing heat treatment at a temperature between 550° C. and 700° C. for a period of time up to 60 minutes
Data Source
AI summary
A nickel-titanium alloy with an average grain size of between 0.2 and 10 microns and a recoverable strain of greater than 9% is disclosed herein, in which the alloy is formed using a method which involves applying a shape set heat treatment to the nickel-titanium alloy. The heat treatment includes applying heat at a temperature between 225° C. and 350° C. for a period of time between 20 and 240 minutes.