Titanium Alloy Grain Refinement via High Strain Rate Forging
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Solution Overview
Problem
Current methods for producing titanium alloys with refined grain structures require multiple reheats, slow strain rates, and custom equipment, making them inefficient and time-consuming, especially for achieving ultrafine grain microstructures.
Innovation Solution
A method involving beta annealing followed by high strain rate multi-axis forging, where the workpiece is press forged at different orthogonal axes with strain rates of 0.2 s−1 to 0.8 s−1, allowing adiabatic heating and cooling to achieve a total strain of at least 1.0, which refines the grain size without the need for custom equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ultra-slow strain rate multi-axis forging (0.001 s−1 or slower) is used to achieve ultrafine grain microstructure, then grain refinement is improved, but processing time becomes excessive
Solution Approach 1:
The patent changes the strain rate parameter from ultra-slow (0.001 s−1 or slower) to high (0.01 s−1 to 10 s−1), which fundamentally alters the deformation mechanism and enables grain refinement without excessive processing time. This parameter change allows the use of conventional equipment while achieving the desired microstructure.
Solution Approach 2:
The patent employs periodic heating and cooling cycles during the forging process, where the workpiece is heated to maintain it in the beta phase field and then cooled to promote alpha phase formation. This periodic thermal action enables continuous dynamic recrystallization at high strain rates, achieving grain refinement without the time penalty of ultra-slow forging.
2Manufacturing precision
If multiple reheats and forging steps are used to produce fine grain microstructure, then grain size is reduced, but process complexity increases
Solution Approach 1:
The patent applies preliminary beta annealing to transform the microstructure to a beta phase before forging. This preliminary action ensures that the material is in the appropriate phase state to undergo dynamic recrystallization during high strain rate forging, eliminating the need for multiple intermediate reheats and forging steps.
Solution Approach 2:
The patent maintains continuous plastic deformation through high strain rate forging without interrupting for multiple reheats. The continuous deformation combined with periodic thermal cycles keeps the material in the dynamic recrystallization regime throughout the process, simplifying the overall process flow while achieving fine grain structures.
3Manufacturing precision
If custom forging equipment is used to achieve ultra-slow strain rates, then ultrafine grain microstructure is achieved, but equipment cost and complexity increase
Solution Approach 1:
The patent changes the strain rate parameter from ultra-slow to high, which allows the use of conventional press forging equipment instead of custom-built ultra-slow strain rate equipment. This parameter change makes the process commercially viable by eliminating the need for specialized equipment while still achieving ultrafine grain structures through high strain rate dynamic recrystallization.
4Productivity
If high strain rate (0.2 s−1 to 0.8 s−1) press forging is used, then processing time is reduced, but adiabatic heating occurs requiring thermal management
Solution Approach 1:
The patent employs periodic heating and cooling cycles where the workpiece is heated to maintain it in the beta phase field before forging, then cooled to promote alpha phase formation after deformation. This periodic thermal management prevents excessive adiabatic heating while enabling high strain rate processing, and ensures the material remains in the appropriate phase state for grain refinement.
Solution Approach 2:
The patent utilizes phase transitions between beta and alpha phases through controlled heating and cooling. By heating to the beta phase field before forging and cooling to the alpha+beta field after deformation, the process manages temperature-induced phase changes that would otherwise compromise the microstructure, enabling high strain rate processing without thermal damage.
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
This process reduces processing time, eliminates the need for custom equipment, and achieves ultrafine grain structures efficiently, producing titanium alloys with refined grain sizes suitable for commercial production.
Implementation Method 1
press forging the workpiece at a workpiece forging temperature in a workpiece forging temperature range in the direction of a first orthogonal axis of the workpiece with a strain rate sufficient to adiabatically heat an internal region of the workpiece
Implementation Method 2
the adiabatically heated internal region of the workpiece is allowed to cool to a temperature at or near the workpiece forging temperature
Data Source
AI summary
Methods of refining the grain size of a titanium alloy workpiece include beta annealing the workpiece, cooling the beta annealed workpiece to a temperature below the beta transus temperature of the titanium alloy, and high strain rate multi-axis forging the workpiece. High strain rate multi-axis forging is employed until a total strain of at least 1 is achieved in the titanium alloy workpiece, or until a total strain of at least 1 and up to 3.5 is achieved in the titanium alloy workpiece. The titanium alloy of the workpiece may comprise at least one of grain pinning alloying additions and beta stabilizing content effective to decrease alpha phase precipitation and growth kinetics.