Hot Stretch Straightening High Strength Alpha Beta Titanium
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Solution Overview
Problem
High strength titanium alloys aged in the α+β phase field are difficult to straighten without affecting their mechanical properties, as conventional straightening methods can cause distortion and shattering due to high room temperature strength and limited available straightening temperatures.
Innovation Solution
A method involving heating the solution treated and aged titanium alloy to a straightening temperature within the α+β phase field, applying elongation tensile stress to straighten the alloy, and simultaneously cooling it with a tensile stress to balance thermal stresses, maintaining minimal deviation from straightness and preserving mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional straightening methods are used on solution treated and aged β-titanium alloy bar, then the bar can be straightened at room temperature, but the bar will shatter due to high strength (200 ksi ultimate tensile strength)
Solution Approach 1:
The patent applies parameter changes by heating the alloy to elevated temperatures (below aging temperature) to reduce its strength and increase ductility, enabling straightening operations that would otherwise cause shattering at room temperature. The temperature parameter is specifically controlled to remain below the aging temperature to prevent mechanical property changes.
Solution Approach 2:
The patent introduces a temperature dimension to the straightening process, transitioning from isothermal room temperature straightening to thermally-assisted straightening. This adds thermal energy as another dimension to overcome the strength barrier without affecting the final mechanical properties.
2Ease of operation
If straightening is performed at temperatures above aging temperature, then the alloy becomes more ductile and easier to straighten, but significant changes in mechanical properties occur
Solution Approach 1:
The patent carefully controls the temperature parameter within a specific range (below aging temperature) to achieve sufficient ductility for straightening while preventing the precipitation of strengthening phases that would alter mechanical properties. This constrained parameter change resolves the contradiction between workability and property preservation.
3Manufacturing precision
If vertical solution heat treating and aging is used for α+β titanium alloys, then distortion is minimized, but the process is expensive and not available at all manufacturers
Solution Approach 1:
The patent applies preliminary straightening after solution treating but before aging, when the alloy is still relatively soft and easy to form. This preliminary action addresses distortion early in the process sequence, eliminating the need for complex vertical aging equipment while achieving similar distortion control results.
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 effectively straightens titanium alloys with minimal deviation and maintains their tensile strengths, reducing the risk of distortion and shattering, while allowing for precise control of straightening temperatures to prevent mechanical property changes.
Implementation Method 1
heating the solution treated and aged titanium alloy to a straightening temperature within the α+β phase field
Implementation Method 2
applying elongation tensile stress to the solution treated and aged titanium alloy for a time sufficient to elongate and straighten the alloy
Implementation Method 3
cooling the alloy while applying a tensile stress sufficient to balance the thermal stresses in the alloy
Data Source
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AI summary
A method for straightening a solution treated and aged (STA) titanium alloy form includes heating an STA titanium alloy form to a straightening temperature of at least 25°F below the age hardening temperature, and applying an elongation tensile stress for a time sufficient to elongate and straighten the form. The elongation tensile stress is at least 20% of the yield stress and not equal to or greater than the yield stress at the straightening temperature. The straightened form deviates from straight by no greater than 0.125 inch over any 5 foot length or shorter length. The straightened form is cooled while simultaneously applying a cooling tensile stress that balances the thermal cooling stress in the titanium alloy form to thereby maintain a deviation from straight of no greater than 0.125 inch over any 5 foot length or shorter length.