TiAl Alloy Billet Cladding for Crack-Resistant Hot Forging
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Solution Overview
Problem
TiAl alloys experience forging cracks during hot forging due to the propagation of cracks in the sheath material, which can lead to defects in the alloy.
Innovation Solution
A TiAl alloy material with a TiAl alloy substrate, an intermediate layer composed of β-TiAl and β-Ti layers, and a titanium layer is formed through hot isostatic pressing, preventing crack propagation by utilizing β-phases that are deformable at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the TiAl alloy is coated with a sheath material to be hot forged, then oxidation is prevented, but cracks may occur in the sheath material during hot forging which propagate to the TiAl alloy causing forging cracks
Solution Approach 1:
The coating structure is segmented into three distinct layers: an inner TiAl alloy layer, an intermediate layer with gradient composition, and an outer titanium layer. This segmentation allows each layer to perform its specific function - the inner layer provides oxidation resistance, the intermediate layer prevents crack propagation through its deformable β-phase structure, and the outer layer provides mechanical protection
Solution Approach 2:
The intermediate layer utilizes parameter changes in material phase structure by controlling the Al content to form β-TiAl phase at hot forging temperatures (1200-1350°C). This phase transformation enables the intermediate layer to be deformable at high temperature, absorbing stress and preventing crack propagation while maintaining oxidation resistance
2Object-affected harmful factors
If the TiAl alloy is coated with sheath material, then oxidation resistance is improved, but the complexity of the coating process and structure increases
Solution Approach 1:
The coating structure is designed to be self-service by utilizing the inherent properties of the TiAl alloy and titanium materials. The intermediate layer's β-phase deformability automatically absorbs stress during hot forging without requiring additional control mechanisms, and the gradient composition naturally forms through diffusion processes during hot isostatic pressing
Solution Approach 2:
The solution employs composite material structure combining TiAl alloy, intermediate layer with gradient composition, and titanium outer layer. This composite structure integrates multiple material properties - oxidation resistance from TiAl, crack resistance from β-phase deformability, and mechanical strength from titanium - creating a synergistic protective system
3Productivity
If high-speed hot forging is performed, then productivity is improved, but the risk of forging cracks increases
Solution Approach 1:
The intermediate layer acts as a beforehand cushioning layer that absorbs and dissipates stresses generated during high-speed hot forging. The β-TiAl phase in the intermediate layer provides a cushioning effect by being deformable at high temperature, preventing stress concentration that would otherwise lead to crack initiation and propagation
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 solution effectively suppresses forging cracks during high-speed hot forging, enhancing the alloy's forgeability and allowing for high-speed manufacturing of components like turbine blades.
Implementation Method 1
an intermediate layer forming step of applying hot isostatic pressing to the TiAl alloy substrate coated with the titanium material at a temperature range between 1200 °C or higher and 1275 °C or lower, at 150 MPa or more, for a hour range between 1 hour or longer and 5 hours or shorter so that the TiAl alloy substrate reacts with the titanium material
Implementation Method 2
the intermediate layer is formed of a first layer that is formed on a side of the TiAl alloy substrate and is formed of the TiAl alloy which becomes β-TiAl at a hot forging temperature range between 1200 °C or higher and 1350 °C or lower, and a second layer that is formed on a side of the titanium layer and is formed of a β-Ti material
Data Source
Figure 1~2
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AI summary
A TiAl alloy material (10) for hot forging includes a TiAl alloy substrate (12) formed of a TiAl alloy which contains 42 at% or more and 45 at% or less of Al, 3 at% or more and 6 at% or less of Nb, 3 at% or more and 6 at% or less of V, 0.1 at% or more and 0.3 at% or less of B, and the balance being Ti and inevitable impurities, an intermediate layer (14) formed on a surface of the TiAl alloy substrate, and a titanium layer (16) formed on a surface of the intermediate layer, wherein the intermediate layer is formed of a first layer (18) which is formed on a side of the TiAl alloy substrate and is formed of the TiAl alloy which becomes β-TiAl at a hot forging temperature range between 1200 °C or higher and 1350 °C or lower and a second layer (20) that is formed on a side of the titanium layer and is formed of a β-Ti material.