TiAl Alloy Cellular Structure Strength Toughness
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Solution Overview
Problem
Existing TiAl-based alloys face challenges in simultaneously achieving high strength, ductility, and fracture toughness, as refinement of crystal grain diameter or grain boundary precipitate phases typically compromise one or more of these properties.
Innovation Solution
A TiAl-based alloy with specific compositions and a two-stage heat treatment process to form a (α2/γ) lamellar grains and a cellular structure at (α2/γ) lamellar grain boundaries, with a controlled volume fraction of the cellular structure between 10 vol% and 70 vol%, comprising β-stabilizing elements like Cr, Nb, V, Mn, or Mo, and controlled heat treatment temperatures and times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If crystal grain diameter is refined or grain boundary precipitate phases are formed, then strength and ductility are improved, but fracture toughness deteriorates
Solution Approach 1:
The invention applies local quality by creating a dual-phase microstructure where (α2/γ) lamellar grains provide strength while cellular structures at grain boundaries provide fracture toughness. The cellular structures are specifically located at prior-α grain boundaries, creating local structural differentiation that resolves the contradiction between strength and fracture toughness.
Solution Approach 2:
The invention creates a composite microstructure combining two distinct phases: (α2/γ) lamellar grains and cellular structures. This composite approach allows the material to simultaneously exhibit properties of both phases - the lamellar structure provides strength while the cellular structure at boundaries enhances fracture toughness.
2Ease of operation
If grain boundary precipitate phases are formed, then ductility is improved, but fracture toughness deteriorates
Solution Approach 1:
The cellular structures are specifically positioned at prior-α grain boundaries, creating local structural quality that differs from the interior of grains. This localized placement allows the boundary regions to provide fracture toughness while the grain interiors maintain strength and ductility characteristics.
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 alloy achieves improved strength, ductility, and fracture toughness, with the cellular structure enhancing yield strength and high-temperature ductility while maintaining fracture toughness.
Implementation Method 1
the TiAl-based alloy is held for a predetermined period of time at a first temperature in an (α+γ) two-phase region, an α single-phase region, a (β+α) two-phase region, or a (β+α+γ) three-phase region, then the TiAl-based alloy is quenched... and the quenched TiAl-based alloy is held for a predetermined period of time at a second temperature in a (β+γ) two-phase region or a (β+α2+γ) three-phase region to form a metal structure comprising (α2/γ) lamellar grains and a cellular structure
Implementation Method 2
the TiAl-based alloy is quenched at a cooling rate equal to or higher than air cooling
Data Source
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AI summary
The present disclosure provides a TiAl-based alloy that combines desirable strength, ductility, and fracture toughness and method for producing the same. The TiAl-based alloy according to the present disclosure comprises, in atomic%, Al: 41% to 46 %, β-stabilizing elements: 3% to 11%, Ni: ≤ 1.0%, C: ≤ 0.6%, Si: ≤ 0.5%, O: ≤ 1.5%, the balance being Ti and inevitable impurities, in which the β-stabilizing elements are any of Cr, Nb, V, Mn and Mo or a combination thereof, a metal structure comprises (α2/γ) lamellar grains and a cellular structure precipitated at (α2/γ) lamellar grain boundaries, a volume fraction of the cellular structure is 10 vol% or more and 70 vol% or less, and the cellular structure is a (β/γ) cellular structure or an (α2/γ/β) cellular structure.