Fatigue Resistant Nanograin Wire via Cold Work and Annealing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional wire manufacturing methods do not effectively produce metal or metal alloy wires with improved fatigue damage resistance, particularly for fine diameters less than 1.0 mm, as existing methods are not suitable for high surface quality continuous wires with submicron or nanograin structures.
Innovation Solution
A method involving cold work conditioning followed by nano-recrystallization to achieve a submicron-scale or nanograin microstructure in metal or metal alloy wires, specifically through processes like cold drawing and annealing, to enhance fatigue damage resistance properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wire drawing and annealing processes are used, then manufacturing process is simple and cost-effective, but the wire achieves only micron-scale grain size (3-12 μm) with limited fatigue damage resistance
Solution Approach 1:
The patent applies severe plastic deformation (SPD) techniques such as high pressure torsion (HPT) and equal channel angular pressing (ECAP) to fundamentally change the deformation parameters beyond conventional wire drawing. These processes impose extreme shear strains (typically ε≥1.0, often ε≥2.0) that conventional drawing cannot achieve, resulting in nanograin formation with mean grain sizes of 100-500 nm compared to conventional 3-12 μm grains. This parameter change in deformation intensity directly resolves the contradiction by achieving superior fatigue damage resistance through refined microstructure.
Solution Approach 2:
The patent utilizes dynamic recrystallization as a phase transition mechanism during severe plastic deformation. The extreme deformation conditions trigger continuous grain refinement and phase transformations that convert the conventional micrometer-scale crystalline structure into nanometer-scale grains. This dynamic phase transition during SPD processing enables the material to achieve a stable nanograin microstructure that provides enhanced fatigue damage resistance, directly addressing the grain size control limitation of conventional processes.
2Reliability
If severe plastic deformation processes like HPT or ECAP are applied, then nanograin microstructure with improved fatigue resistance is achieved, but the method is not suitable for continuous fine diameter wire production
Solution Approach 1:
The patent segments the severe plastic deformation process into multiple sequential drawing passes with intermediate annealing steps. Instead of attempting single-pass extreme deformation that would be impractical for continuous wire production, the total strain is divided into manageable increments (e.g., multiple draws with true strains of 0.2-0.5 each, with annealing in between). This segmentation makes the nanograin formation process compatible with continuous wire manufacturing while still achieving the required cumulative deformation for nanocrystalline structure development.
Solution Approach 2:
The patent applies preliminary cold work conditioning to the wire before final nanograin formation processing. This preliminary deformation prepares the microstructure by introducing dislocations and subgrain structures that serve as precursors for subsequent dynamic recrystallization during the nanograin formation stage. This preliminary action facilitates the transition to nanograin structure and improves the efficiency of the overall manufacturing process for continuous wire production.
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
The method results in wires with improved fatigue endurance, ultimate strength, ductility, and recoverable strain, suitable for medical devices and high-end applications, with fatigue endurance exceeding 0.35% strain amplitude at one million cycles and axial ductility greater than 6% strain to rupture.
Implementation Method 1
subjecting the wire to cold work conditioning to impart 50% and 99.9% cold work and 0.69 and 6.91 units of true strain by drawing the wire
Implementation Method 2
annealing the wire to create a crystal structure having a mean grain size of less than 500 nanometers
Data Source
AI summary
Fatigue damage resistant metal or metal alloy wires have a submicron-scale or nanograin microstructure that demonstrates improved fatigue damage resistance properties, and methods for manufacturing such wires. The present method may be used to form a wire having a nanograin microstructure characterized by a mean grain size that is 500 nm or less, in which the wire demonstrates improved fatigue damage resistance. Wire manufactured in accordance with the present process may show improvement in one or more other material properties, such as ultimate strength, unloading plateau strength, permanent set, ductility, and recoverable strain, for example. Wire manufactured in accordance with the present process is suitable for use in a medical device, or other high end application.