Titanium Alloy Grain Refinement via High Strain Rate Multi-Axis 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, which includes press forging in multiple orthogonal directions with controlled strain rates and thermal management to achieve refined grain sizes without the need for custom equipment and reduced processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ultra-slow strain rate MAF process is used to produce ultrafine grain microstructure, then grain refinement is achieved, but processing time becomes excessive
Solution Approach 1:
The patent changes the strain rate parameter from ultra-slow (0.001 s^-1) to high (0.03 s^-1 and above), which dramatically reduces processing time while still achieving ultrafine grain microstructure through dynamic recrystallization. This parameter change resolves the contradiction by finding an optimal strain rate that balances grain refinement quality with production efficiency.
Solution Approach 2:
The patent employs periodic heating and cooling cycles during multi-axis forging to maintain dynamic recrystallization conditions. By periodically reheating the workpiece to austenite temperature between forging passes, the material undergoes continuous grain refinement without requiring excessively slow deformation rates, thus reducing total processing time while achieving ultrafine grain structure.
2Manufacturing precision
If ultra-slow strain rate MAF process is used for grain refinement, then dynamic recrystallization regime is maintained, but custom forging equipment is required
Solution Approach 1:
The patent changes the strain rate parameter from ultra-slow to high, which allows the use of conventional open die press forging equipment instead of custom-built ultra-slow strain rate equipment. The high strain rate process achieves grain refinement through different mechanisms (dynamic recrystallization at high strain rates) that are compatible with standard industrial forging machinery, eliminating the need for specialized custom equipment.
Solution Approach 2:
The patent makes the forging process universal by using conventional open die press equipment that can handle multiple alloy types and production volumes. The high strain rate multi-axis forging process can be performed on standard equipment already present in commercial foundries, making the ultrafine grain production method universally applicable rather than requiring dedicated custom equipment for each application.
3Manufacturing precision
If multiple reheats and forging steps are used to produce refined grain structures, then grain size control is achieved, but process complexity increases
Solution Approach 1:
The patent implements continuous high strain rate multi-axis forging without intermediate reheats, maintaining the material in the appropriate temperature range throughout the entire deformation process. This continuous action achieves grain refinement through cumulative plastic deformation and dynamic recrystallization, eliminating the need for multiple separate heating and cooling cycles, thus simplifying the process while maintaining grain size control.
Solution Approach 2:
The patent performs preliminary heating of the workpiece to the appropriate temperature range before forging, ensuring the material is in the optimal state for high strain rate deformation throughout the entire multi-axis forging sequence. This preliminary preparation eliminates the need for intermediate reheats during the forging process, reducing process complexity while maintaining the ability to achieve refined grain structures through controlled high strain rate deformation.
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 method effectively refines grain sizes in titanium alloys, such as Ti-6Al-2Sn-4Zr-6Mo and Ti-6Al-4V, to ultrafine grain structures with reduced processing time and without the need for custom equipment, improving efficiency and scalability.
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
beta annealing the workpiece
Implementation Method 3
heating the workpiece to a temperature above the beta transus temperature of the titanium alloy
Data Source
Figure 1
Figure 2a~2g
Figure 3~3(f)
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.