Titanium Alloy Basketweave Microstructure via Controlled Cooling
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Solution Overview
Problem
The high material and processing costs of titanium alloys, particularly due to the need for tightly controlled minor elements like iron and oxygen, and the costly machining processes, limit their application in industries such as aerospace, defense, and energy, where low-weight, corrosion-resistant structures are required.
Innovation Solution
A titanium alloy composition with specific ranges of aluminum, vanadium, molybdenum, chromium, iron, oxygen, and incidental elements, processed using near-net shape casting and cooling techniques to achieve a basketweave microstructure, reducing the need for hot working and allowing for additive manufacturing without damaging the alloy's physical and structural properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If titanium alloys are wrought and hot worked to achieve near-net shape, then mechanical properties and strength are improved, but processing costs and material waste increase significantly
Solution Approach 1:
The invention utilizes phase transition during cooling from beta phase to alpha phase to achieve basketweave microstructure directly in the as-cast state, eliminating the need for subsequent hot working operations. The controlled cooling rate (0.03°C/s to 10°C/s) from the beta transus temperature transforms the microstructure in situ, providing both strength and eliminating costly machining operations.
Solution Approach 2:
The alloy composition is specifically designed during the melting stage to enable direct formation of the desired basketweave microstructure upon cooling, without requiring subsequent hot working or machining operations. The preliminary alloy design with controlled Fe and O content allows the material to self-organize into the strength-providing microstructure during the cooling process itself.
2Stability of the object's composition
If iron and oxygen content are tightly controlled in the melt stock, then non-uniform mechanical properties due to segregation are eliminated, but material cost increases
Solution Approach 1:
The invention changes the parameter thresholds for iron and oxygen content from the conventional ELI grade limits (Fe≤0.25%, O≤0.13%) to higher permissible limits (Fe≤0.55%, O≤0.35%). This parameter change allows the use of lower-quality, cheaper scrap materials while still achieving uniform mechanical properties through the basketweave microstructure that forms during controlled cooling, which suppresses segregation effects.
Solution Approach 2:
The invention converts what would normally be harmful impurities (iron and oxygen at higher levels) into acceptable constituents by changing the processing conditions. The controlled cooling rate and specific alloy composition transform the potential harm of higher Fe/O content into a benefit by forming a microstructure that is inherently more uniform and less susceptible to segregation, thereby allowing cheaper materials to be used.
3Ease of manufacture
If conventional titanium alloys are used with standard cooling rates, then processing is simpler, but the resulting microstructure lacks the interlocking basketweave morphology needed for optimal strength and toughness
Solution Approach 1:
The invention identifies and applies a specific cooling rate parameter range (0.03°C/s to 10°C/s) that transforms the microstructure into the desired interlocking basketweave morphology. This parameter change in cooling rate, combined with the specific alloy composition and cooling from above the beta transus temperature, produces the optimal microstructure for strength and toughness while maintaining industrial feasibility.
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 approach results in a combination of high strength and toughness at a lower cost, enabling the use of lower-quality scrap materials and reducing manufacturing costs by eliminating the need for forging and rapid cooling, while maintaining excellent mechanical properties.
Implementation Method 1
cooling the alloy from the beta phase at a cooling rate so as to form a microstructure comprising alpha phase laths in a basketweave morphology
Implementation Method 2
cooling the alloy with a gas pressurized to about 2 atm
Data Source
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AI summary
Provided herein are titanium alloys that can achieve a combination of high strength and high toughness or elongation, and a method to produce the alloys. By tolerating iron, oxygen, and other incidental elements and impurities, the alloys enable the use of lower quality scrap as raw materials. The alloys are castable and can form α-phase laths in a basketweave morphology by a commercially feasible heat treatment that does not require hot-working or rapid cooling rates. The alloys comprise, by weight, about 3.0% to about 6.0% aluminum, 0% to about 1.5% tin, about 2.0% to about 4.0% vanadium, about 0.5% to about 4.5% molybdenum, about 1.0% to about 2.5% chromium, about 0.20% to about 0.55% iron, 0% to about 0.35% oxygen, 0% to about 0.007% boron, and 0% to about 0.60% other incidental elements and impurities, the balance of weight percent comprising titanium. There exists an unmet need to produce titanium alloys for use in aerospace applications which have a refined equiaxed grain structure. This can be beneficial for fatigue critical applications. The technology developed by QuesTek describes a titanium alloy and manufacturing methods thereof to obtain equiaxed grains on the order of 300 microns and corresponding UTS of approximately 170 ksi. In addition, various forms of the alloys are disclosed including ingots, billets, powders and wire in accord with the described microstructure and physical characteristics.