Titanium Alloy Sheet Manufacturing via Quasi-Isothermal Rolling
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Solution Overview
Problem
Current methods for manufacturing thin sheets of high-strength titanium alloys face challenges in producing big-sized semifinished products with homogeneous submicrocrystalline structure suitable for superplastic forming at temperatures below 800°C, due to difficulties in achieving the required grain size and maintaining mechanical properties, which leads to high tool wear and energy consumption.
Innovation Solution
A method involving the preparation of initial blanks with α-phase grain size not more than 2 μm through hot rolling and heat treatment, followed by rapid cooling, and subsequent hot rolling in quasi-isothermal conditions with directional changes to achieve a submicrocrystalline structure, allowing for the production of thin sheets with grain sizes of 1 μm or lower, suitable for superplastic forming at lower temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional hot rolling is used to produce thin sheets of high-strength titanium alloys, then the sheets can be produced, but the processing causes formation of microcracks and breaks in the material
Solution Approach 1:
The patent applies parameter changes by precisely controlling temperature and deformation rate parameters during hot rolling. The temperature is maintained within a specific range (730-757°C) and the deformation rate is controlled to be within 0.002-0.02 sec⁻¹, which transforms the processing conditions to avoid microcrack formation while maintaining manufacturability
Solution Approach 2:
The patent employs periodic action through multi-pass rolling with intermediate annealing treatments. The rolling process is divided into multiple passes with intermediate holding periods for annealing, which allows stress relaxation and prevents microcrack formation during continuous deformation
2Strength
If sheets are produced with grain size of 4 to 6 μm by conventional methods, then the required mechanical properties are achieved, but superplastic forming can only be performed at high temperatures (900-960°C)
Solution Approach 1:
The patent applies preliminary action by performing controlled hot rolling and annealing treatments before the final superplastic forming operation. The preliminary hot rolling at 730-757°C with specific deformation rates creates an optimized grain structure that enables subsequent SPF at lower temperatures
Solution Approach 2:
The patent utilizes phase transitions by controlling the material through the beta transus temperature range during hot rolling. The temperature range of 730-757°C is specifically chosen to be near the beta transus point, where phase transformation occurs, enabling grain refinement and creation of a microstructure suitable for low-temperature superplasticity
3Adaptability or versatility
If superplastic forming is performed at high temperatures (900-960°C), then articles of complex shape can be formed, but tool wear increases and energy consumption increases
Solution Approach 1:
The patent applies preliminary action by creating an optimized grain structure through controlled hot rolling and annealing before superplastic forming. This preliminary preparation enables the material to exhibit superplastic behavior at lower temperatures, reducing energy consumption while maintaining formability
Solution Approach 2:
The patent applies parameter changes by optimizing the grain size and microstructure through controlled thermal-mechanical processing. The grain size is controlled to be 4-6 μm through specific hot rolling parameters, which enables superplastic forming at lower temperatures (700-800°C) while maintaining the ability to form complex shapes
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 enables the production of thin sheets with improved mechanical properties and reduced anisotropy, suitable for superplastic forming at temperatures below 800°C, thereby extending tool life and decreasing energy consumption, while maintaining the required mechanical properties and grain size.
Implementation Method 1
heating the pack up to about 730-757° C. (from about 1345 to 1395° F.), hot rolling the pack
Implementation Method 2
annealing the pack
Implementation Method 3
maintaining optimum temperature-deformation conditions of the process... in the alpha-beta field of said metal
Data Source
AI summary
Disclosed is a method for manufacturing thin sheets of high-strength titanium alloys. The method includes the steps of preparing initial blanks, assembling the initial blanks into a pack within a sheath, and heating and hot rolling the pack of the initial blanks in the sheath. The method is characterized in that, in the step of preparing the initial blanks, blanks having an (α-phase grain size of not more than 2 μm are produced by hot rolling a forged or die-forged slab to a predetermined value of a relative thickness hB/hF, where hB is a thickness in mm of the initial blank before said pack hot rolling and hF is a final sheet thickness in mm, and by heat treating the initial blanks followed by rapidly cooling; and in that the step of pack hot rolling is conducted in quasi-isothermal conditions in longitudinal and transverse directions, while changing a rolling direction by about 90° after a predetermined total reduction in one direction is achieved. The method provides big-sized thin sheets made of high-strength titanium alloys and having homogeneous submicrocrystalline structure where an average grain size is less than 1 μm. The sheets have the required mechanical properties suitable for superplastic forming (SPF) at temperatures below 800° C.