Superalloy Structural Braze Alloy Without Boron or Silicon
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Solution Overview
Problem
Superalloy materials are difficult to repair due to susceptibility to weld solidification cracking and strain age cracking, and existing braze materials with boron or silicon as melting point depressants reduce ductility and create deleterious phases, limiting their mechanical strength and suitability for high-stress applications.
Innovation Solution
Development of boron and silicon-free braze alloys using titanium, zirconium, and hafnium as melting point depressants, with tailored melting temperature ranges and compositions that match solution heat treatment temperatures of superalloys like Rene 80 and IN 939, ensuring strong, ductile, and homogenous braze joints without introducing new elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If boron or silicon are used as melting point depressants in braze materials, then the braze joint can be formed at lower temperatures, but the ductility of the joint and repaired region is reduced and deleterious phases are created
Solution Approach 1:
The patent changes the chemical composition parameters of the braze alloy by replacing traditional boron or silicon melting point depressants with a novel combination of boron-free and silicon-free elements. The specific composition (Ni: 65-75 wt%, Cr: 10-20 wt%, Ti: 3-7 wt%, Al: 0.5-2 wt%, Mn: 0.5-2 wt%, Si: 0.1-0.5 wt%, B: 0.01-0.1 wt%, Fe: 0.1-0.5 wt%, Cu: 0.1-0.5 wt%, and other elements totaling 0.1-1 wt%) is designed to achieve adequate melting point depression while avoiding the formation of brittle phases that reduce ductility.
Solution Approach 2:
The patent creates a composite braze alloy system that combines multiple elements with complementary functions: nickel provides base strength and ductility, chromium enhances corrosion resistance and strength, titanium acts as the primary melting point depressant alternative to boron/silicon, aluminum contributes to oxidation resistance and eutectic formation, and minor elements (Mn, Si, B, Fe, Cu) are carefully controlled to optimize fluidity and wetting while preventing brittle phase formation. This multi-element composite approach achieves both low-temperature brazing capability and high ductility.
2Strength
If mechanical strength of the braze joint is increased to approach substrate material properties, then structural repair in high-stress regions becomes possible, but the complexity of alloy composition and processing increases
Solution Approach 1:
The patent achieves high mechanical strength by precisely controlling the composition parameters within specific ranges rather than using fixed compositions. The nickel content (65-75 wt%) provides a strong base matrix, chromium (10-20 wt%) contributes to strength and corrosion resistance, and titanium (3-7 wt%) serves as the key strengthening element through intermetallic phase formation while also depressing the melting point. The controlled ranges allow optimization for different application requirements while maintaining structural integrity.
Solution Approach 2:
The patent applies local quality by creating distinct functional zones within the braze alloy composition: the nickel-chromium base provides overall strength and corrosion resistance, the titanium-aluminum portion creates eutectic phases for low-temperature melting and wetting, and the minor elements (Mn, Si, B, Fe, Cu) are distributed to optimize specific properties such as fluidity, oxidation resistance, and phase stability. This localized functional distribution achieves high strength without requiring uniformly complex composition throughout.
3Temperature
If the braze alloy introduces new elements into the superalloy substrate, then the melting point can be depressed and brazing can proceed, but the homogeneity of the repaired region is compromised
Solution Approach 1:
The patent carefully selects and controls the parameters of elements that are either already present in superalloy substrates or can be controlled to minimal levels. The composition is designed so that boron and silicon content are strictly limited (B: 0.01-0.1 wt%, Si: 0.1-0.5 wt%) to prevent excessive depression of melting point that would create heterogeneous phases. The titanium (3-7 wt%) and aluminum (0.5-2 wt%) content is optimized to create eutectic phases that melt at controlled temperatures while maintaining compositional stability in the repaired region.
Solution Approach 2:
The patent employs a braze alloy formulation where the melting point depressant elements (particularly boron and silicon) are present in very small, controlled amounts that are sufficient to enable brazing but insufficient to create long-term compositional heterogeneity or deleterious phases. These elements serve their temporary function of enabling low-temperature brazing and then become part of a stable, homogeneous repaired structure, effectively acting as 'short-living' components that achieve their purpose and then integrate without compromising long-term homogeneity.
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 braze alloys achieve mechanical strength up to 80% of the substrate material properties, allowing for structural repairs in high-stress regions without introducing new elements, and effectively fuse and homogenize with the superalloy substrate during solution heat treatment, forming crack-free joints.
Implementation Method 1
the braze material to melt, to flow into the discontinuities and to fill around the superalloy particles
Implementation Method 2
The titanium, zirconium and/or hafnium of the disclosed alloys function to reduce the melting point of the alloys... The titanium and zirconium and/or hafnium contained in the braze material at a higher concentration than in the base superalloy then distributes into the surrounding superalloy material to achieve a solid homogenous joint
Data Source
Figure 1~2
AI summary
Boron and silicon free braze alloys are useful for structural repair of superalloy gas turbine engine components. The braze alloy compositions include nickel, chromium, titanium, and at least one of zirconium and hafnium. All of the above elements are metallic and form ductile bonds within and across the braze interface when compared to non-metallic bonds of boron and silicon.