Glass-Ceramic Composite Joining for CTE-Homogeneous Structures
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Solution Overview
Problem
Existing methods for bonding glass-ceramic components, particularly for precision components in space applications, suffer from issues such as stress due to mismatched thermal expansion, require high surface quality, and are not suitable for large components, limiting the production of composite components with high CTE homogeneity and mechanical stability.
Innovation Solution
A process involving two-dimensionally pressing green glass-ceramic starting elements under pressure at a controlled temperature, allowing for monolithic bonding and ceramization, which includes using intrinsic weight, added weights, or vacuum to create a pressure, ensuring a coefficient of thermal expansion (CTE) homogeneity and mechanical stability, even for large components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If bonding materials such as adhesives and solders are used to join glass-ceramic components, then the joining process is simplified and can be applied to various component sizes, but the composite component exhibits stress and impaired stability due to mismatched thermal expansion coefficients
Solution Approach 1:
The patent uses homogeneous glass-ceramic material for both the starting elements and the bonding interface. The bonding is achieved through direct contact and ceramization of the green glass surfaces, ensuring identical material composition and thermal expansion properties throughout the composite component, thereby eliminating stress from CTE mismatch
Solution Approach 2:
The patent changes the physical and chemical parameters of the green glass material through controlled heating to the ceramization temperature range (900-1100°C). This transformation converts the green glass into glass-ceramic with matched thermal expansion properties, enabling stress-free bonding while maintaining manufacturing simplicity
2Strength
If contact bonding or LTB methods are used to bond glass-ceramic components, then bonding strength is improved, but high surface quality is required with gap sizes less than 10 μm, necessitating complex polishing and making the method inapplicable to large components
Solution Approach 1:
The patent changes the temperature parameter to the green glass softening range (600-900°C) during bonding, which increases the viscosity and flow properties of the glass material. This allows the material to self-level and fill surface irregularities, achieving strong bonding without requiring precision polishing or tight gap control
Solution Approach 2:
The patent utilizes the composite nature of green glass (unfired ceramic material with plastic properties) that combines the strength of ceramic with the formability of glass. This allows the green glass to be pressed and deformed under pressure to conform to bonding surfaces, eliminating the need for complex surface preparation
3Reliability
If very high heating rates of >5 K/min are employed for joining green glasses, then ceramization and joining are achieved at higher temperatures, but the process time increases and energy consumption rises
Solution Approach 1:
The patent applies pressure to the green glass components before heating, which promotes intimate contact between bonding surfaces and initiates the bonding process. This preliminary mechanical action reduces the required heating time and energy, as the material is already in optimal position for bonding when heating begins
Solution Approach 2:
The patent combines pressure application and heating into a continuous simultaneous process rather than sequential steps. The pressure is maintained throughout the heating and ceramization process, ensuring continuous bonding action and reducing total process time compared to methods that separate these operations
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 process achieves composite components with CTE homogeneity up to 4 m, low thermal hysteresis, and mechanical stability, reducing stress and deformation, suitable for precision components like mirrors and telescopes.
Implementation Method 1
creating a monolithic bond between the at least two starting elements by heating, under the action of pressure (P), the starting elements pressed to one another at a temperature TK at which ceramization of the green glass to the glass-ceramic takes place
Implementation Method 2
two-dimensionally pressing the surfaces of the at least two starting elements to be bonded to one another under the action of pressure (P)
Implementation Method 3
create a pressure on the bonding sites by virtue of the intrinsic weight of an upper starting element or create a pressure on the bonding sites by virtue of one or more added weights lying on an upper starting element
Implementation Method 4
bring about a tensile force on the starting elements by application of vacuum and hence create a pressure on bonding sites
Data Source
AI summary
The invention relates to a method for producing a glass-ceramic composite object, and a glass-ceramic composite object produced from at least two starting elements. In the method, respective surfaces of at least two starting elements consisting of the precursor glass of the glass-ceramic material are pressed flat and directly against one another with the application of pressure, and at a temperature at which the ceramisation of the glass-ceramic material takes place they are joined so as to create a monolithic bond between the at least two starting elements.