TiAl Alloy Transient Liquid Phase Bonding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional joining techniques for titanium aluminide alloys, such as diffusion bonding and fusion bonding, face challenges like high machining precision requirements, low service temperature of brazing joints, and heat-sensitive cracking, while existing transient liquid phase (TLP) bonding methods using Ti foils with Cu or Fe foils are not suitable for achieving strong and ductile joints or repairing cracks effectively.
Innovation Solution
A method involving the application of a braze material with a composition of 10-35 at.% aluminum and 5-30 at.% iron or nickel, optionally including other alloying elements, at the faying surface of γ-TiAl alloy substrates, subjected to an elevated temperature above the braze's melting point but below the γ-solvus temperature of the alloy, facilitating transient liquid phase bonding for improved strength and ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If diffusion bonding is used to join titanium aluminide substrates, then joint strength can be achieved, but high machining precision of mating surfaces is required and bonding time is extended
Solution Approach 1:
A braze alloy layer serves as an intermediary material between the two titanium aluminide substrates. This intermediate layer facilitates bonding by providing a eutectic reaction that creates a liquid phase at lower temperatures, enabling joint formation without requiring the high machining precision and extended times associated with direct diffusion bonding of the substrates themselves.
Solution Approach 2:
The invention changes the bonding parameters by introducing a braze alloy with specific composition (Ti-25Al-25Fe-5Cr-2B in at.%) that undergoes eutectic reaction at 1020°C. This parameter change allows bonding to occur at lower temperatures and shorter times compared to conventional diffusion bonding, while also reducing the stringency of surface preparation requirements.
2Ease of manufacture
If conventional brazing is used, then joining can be achieved, but the service temperature of the brazing joint is limited
Solution Approach 1:
The braze alloy composition is specifically designed with a eutectic point at 1020°C, which is below the γ-solvus temperature of the titanium aluminide substrate. This parameter change ensures that the brazing joint can service at high temperatures while the bonding process occurs at controlled lower temperatures, resolving the contradiction between ease of manufacturing and service temperature capability.
3Ease of manufacture
If fusion bonding is used, then joining can be achieved, but heat-sensitive cracking occurs during the process
Solution Approach 1:
The invention utilizes phase transitions of the braze alloy, specifically the eutectic reaction that occurs at 1020°C. The braze alloy transforms from solid to liquid phase during bonding, then solidifies to form a strong joint. This controlled phase transition allows joining to proceed at lower temperatures than fusion bonding, avoiding the heat-sensitive cracking that plagues conventional fusion bonding of titanium aluminide substrates.
4Ease of manufacture
If existing TLP bonding methods using Ti foils with Cu or Fe foils are used, then joining can be achieved, but strong and ductile joints and effective crack repair are not obtained
Solution Approach 1:
The braze alloy represents a composite material system combining multiple elements (Ti, Al, Fe, Cr, B) in specific proportions. This composite composition creates a eutectic system with melting point of 1020°C, which is optimized for bonding titanium aluminide substrates. The multi-element composition provides both the liquid phase formation capability and the structural properties needed to achieve strong, ductile joints and effective crack repair, overcoming the limitations of simpler Ti-Cu or Ti-Fe foil systems.
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 produces joints with strengths and ductility similar to the base metal, suitable for both joining and repairing γ-TiAl alloy substrates, offering enhanced structural homogeneity and overcoming the limitations of previous techniques.
Implementation Method 1
subjecting the substrates and the braze material to an elevated temperature above the melting point of the braze material
Implementation Method 2
several single phase layers were formed within the filler alloy due to the solid state interdiffusion of Ti and Ni atoms
Implementation Method 3
followed by solidification, even during an isothermal heat treatment
Data Source
Figure 1
Figure 2~3
AI summary
The present invention relates to a method of bonding two substrates of γ-titanium aluminide alloy at a faying surface, comprising the steps of applying a braze material of a titanium alloy consisting of from 10 to 35 at.% aluminum, from 5 to 30 at.% iron and/or nickel, and optionally other alloying elements present in the substrate material in quantities (at.%) up to their content in the substrate material, the remainder being titanium, at the faying surface of the substrates, and subjecting the substrates and braze material to an elevated temperature above the melting point of the braze material and below γ-solvus temperature of the γ-titanium aluminide alloy, and joining the substrates by transient liquid phase bonding.