CMC Braze Alloy Composition for High-Temperature Joint Stability
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Solution Overview
Problem
Traditional braze alloys for ceramic matrix composites in gas turbine engines have low melting temperatures and form low-melting point eutectic phases, leading to susceptibility to failure and oxidation at high temperatures, and the brazing process can jeopardize the microstructural integrity and mechanical strength of the components.
Innovation Solution
A braze alloy composition with silicon at 48-66 at.%, titanium at 1-35 at.%, and additional elements like aluminum, cobalt, vanadium, nickel, or chromium, with a melting temperature below 1300°C, allowing for lower temperature brazing without compromising mechanical properties or high-temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional nickel- or gold-based braze alloys are used, then the brazing process is simple, but the braze joints have low melting temperatures and form low-melting point eutectic phases that are susceptible to failure and oxidation at high temperatures
Solution Approach 1:
The patent changes the chemical composition parameters of the braze alloy by replacing traditional nickel- or gold-based compositions with a silicon-titanium-based alloy system. This compositional parameter change raises the melting temperature from below 400°C (gold-silicon eutectic) to above 1000°C, enabling the braze joint to withstand high temperature gas turbine engine operations without forming low-melting point eutectic phases
Solution Approach 2:
The patent creates a composite braze alloy system combining silicon, titanium, and reactive elements (aluminum, cobalt, vanadium, nickel, or chromium) that work synergistically. The silicon-titanium base provides high temperature stability, while the reactive elements control interfacial reactions with the SiC/SiC composite, forming a composite material structure that achieves both high melting point and compatibility with the ceramic matrix composite
2Reliability
If high temperature braze alloys are used, then the braze joint has high temperature stability, but the brazing temperature approaches the melting point of silicon in the CMC matrix, potentially jeopardizing microstructural integrity
Solution Approach 1:
The patent optimizes the brazing temperature parameter to fall within 1050°C to 1250°C, which is below the silicon melting point of 1414°C. This parameter optimization ensures that the brazing process occurs at a temperature sufficient to melt the silicon-titanium-based braze alloy (melting point >1000°C) while maintaining a safety margin that prevents melting or degradation of the silicon matrix in the SiC/SiC composite, thereby preserving microstructural integrity
3Strength
If the braze alloy reacts with free silicon in the CMC component, then bonding occurs, but low-melting point eutectic phases form that reduce joint reliability
Solution Approach 1:
The patent changes the chemical composition parameters by incorporating reactive elements (aluminum, cobalt, vanadium, nickel, or chromium) alongside silicon and titanium. These compositional changes modify the reaction products formed during brazing, promoting the formation of high-melting point intermetallic compounds and stable reaction layers instead of low-melting point eutectic phases, thereby maintaining both bonding strength and joint reliability at high temperatures
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 new braze alloy achieves high shear strength and stability in brazed joints, with suitable flow properties and wettability, enabling effective bonding of ceramic matrix composite components in gas turbine engines at reduced temperatures.
Implementation Method 1
heating the braze alloy to a predetermined brazing temperature, which is equal to or greater than a melting temperature thereof
Implementation Method 2
After the heating, the braze alloy is cooled to form a brazed joint between the first component and the second component
Implementation Method 3
The new braze alloy achieves high shear strength and stability in brazed joints, with suitable flow properties and wettability
Data Source
AI summary
A braze alloy for joining or repairing ceramic matrix composite (CMC) components comprises a braze composition including silicon at a concentration from about 48 at. % to about 66 at. %, titanium at a concentration from about 1 at. % to about 35 at. %, and an additional element selected from aluminum, cobalt, vanadium, nickel, and chromium. The braze composition comprises a melting temperature of less than 1300° C.