TiAl Single Crystal Solidification for Lamellar Orientation
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Solution Overview
Problem
Current methods for controlling the lamellar orientation of TiAl alloys during directional solidification are inadequate, leading to poor room-temperature brittleness and limited high-temperature performance, as they fail to achieve a fully lamellar structure with lamellar orientation parallel to the growth direction, and are plagued by alloy pollution and complex processes.
Innovation Solution
A method involving Bridgman directional solidification with controlled temperature gradient and growth rate to ensure a β phase primary phase, followed by vacuum heat treatment to eliminate segregation, allowing for the growth of TiAl single crystals with lamellar orientation completely parallel to the growth direction, thereby improving mechanical properties and simplifying the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If seeded method is used to control lamellar orientation, then lamellar orientation parallel to growth direction is achieved, but alloy composition becomes uneven and preparation process becomes complex
Solution Approach 1:
The invention removes the seed crystal from the preparation process entirely, using instead a controlled directional solidification method with specific temperature gradients and growth rates to achieve the desired lamellar orientation parallel to the growth direction, thereby eliminating the complexity associated with seed crystal preparation and composition matching
Solution Approach 2:
The invention controls the solidification process by adjusting key parameters including temperature gradient (G), growth rate (V), and their ratio (G/V), along with alloy composition (Ti-45Al-8Nb), to achieve complete lamellar orientation parallel to growth direction without requiring seed crystals
2Productivity
If conventional directional solidification is used, then TiAl alloy is produced, but room-temperature brittleness remains poor due to inadequate lamellar orientation control
Solution Approach 1:
The invention optimizes specific process parameters including temperature gradient (5-10℃/cm), growth rate (0.5-2mm/h), and their ratio (G/V), combined with Ti-45Al-8Nb alloy composition, to achieve fully lamellar structure with lamellae parallel to growth direction, simultaneously improving room-temperature ductility to 6.9% and high-temperature strength to 637 MPa at 900℃
Solution Approach 2:
The invention creates a composite microstructure consisting of fully lamellar TiAl phase with specific orientation, where the controlled microstructural architecture enables both improved room-temperature ductility and high-temperature strength
3Temperature
If working temperature is increased to improve high-temperature performance, then creep resistance improves, but material becomes more brittle at higher temperatures
Solution Approach 1:
The invention develops a TiAl-Nb intermetallic compound single crystal with fully lamellar structure where Nb elements (8 at%) strengthen the matrix and the controlled lamellar orientation parallel to growth direction provides optimal creep resistance, enabling reliable operation at 900℃ with 637 MPa yield strength and 8.1% elongation
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 achieves significant improvements in room-temperature ductility and high-temperature strength, with a TiAl alloy exhibiting 6.9% tensile ductility at room temperature and 637 MPa yield strength at 900°C, while avoiding alloy pollution and simplifying the production process.
Implementation Method 1
Bridgman directional solidification with controlled temperature gradient and growth rate to ensure a β phase primary phase
Implementation Method 2
controlled temperature gradient and growth rate
Implementation Method 3
followed by vacuum heat treatment to eliminate segregation
Data Source
Figure 1~2(b)
Figure 3~5
Figure 6(a)~7
AI summary
A TiAl intermetallic compound single crystal material and a preparation method therefor are disclosed. The alloy composition of the material comprises TiaAlbNbc(C, Si)d, wherein 43≤b≤49, 2≤c≤10, a+b+c=100, and 0≤d≤1 (at. %).