Ceramic-to-Ceramic Joint via Solid-State Sintering
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Solution Overview
Problem
Existing methods for joining sintered bodies, particularly those with perovskitic or fluoritic crystal structures, face challenges such as requiring high pressures, special atmospheres, or leaving behind interfacial phases with inferior mechanical and thermal properties, which can lead to joint instability and incompatibility with the materials being joined.
Innovation Solution
A method involving a green ceramic joint material composed of ceramic particles and organic components, where the ceramic particles constitute 40-75 vol% of the joint material and include elements from the sintered bodies, applied under pressures of 1 kPa to 5 MPa, and heated to conform and join the bodies below their sintering temperature without forming a liquid phase, allowing for solid-state sintering and forming a compatible, refractory joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic-metal eutectics are used for joining sintered bodies, then the joint can be formed, but special reducing atmospheres are required which cause decomposition of the sintered bodies
Solution Approach 1:
The invention removes the metal component from the joining material, extracting only the ceramic particles and organic binder. This eliminates the need for reducing atmospheres while maintaining joining capability through solid-state sintering of the ceramic-organic composite.
Solution Approach 2:
The invention changes the chemical composition parameters of the joining material by replacing metallic components with organic binders and ceramic particles. This parameter change allows joining to proceed in oxidizing atmospheres without decomposition, as the organic binder decomposes to leave behind only ceramic material compatible with the sintered bodies.
2Reliability
If very high pressures are applied during joining of sintered bodies using nanocrystalline interlayers, then the joint can be formed, but the parts to be joined are damaged due to creep or fracture
Solution Approach 1:
The invention changes the pressure parameter from very high pressures to moderate pressures (0.1-10 MPa). This parameter change is sufficient because the organic binder provides plasticity and conformability at lower pressures, and the ceramic particles sinter effectively at these reduced pressures to form strong joints without damaging the parts.
Solution Approach 2:
The invention uses a composite joining material consisting of ceramic particles dispersed in an organic binder matrix. This composite structure allows the organic phase to provide plasticity and conformability under low pressure, while the ceramic phase provides structural integrity and sintering capability, eliminating the need for very high pressures.
3Reliability
If brazes or glasses are used for joining sintered bodies, then the joint can be formed, but an interfacial phase with inferior properties is left behind which reduces thermal cycling stability
Solution Approach 1:
The invention uses ceramic particles with the same composition and crystal structure as the sintered bodies being joined. This homogeneity ensures that the joint material has identical thermal expansion coefficients and chemical compatibility, eliminating interfacial phase issues and improving thermal cycling stability. The organic binder decomposes to leave behind only the matching ceramic material.
Solution Approach 2:
The organic binder serves as a temporary, disposable component that facilitates joining at low temperatures and then decomposes completely during or after the joining process. This disposable organic phase enables the formation of a pure ceramic joint without leaving behind any harmful interfacial residues, as it is intentionally designed to be consumed during processing.
4Shape
If joining is performed at high temperatures above glass transition temperature, then the joint material can flow and conform, but the glass joint softens and flows excessively causing loss of mechanical integrity
Solution Approach 1:
The invention changes the temperature parameter to remain below the glass transition temperature of any potential glassy phase. Instead, the organic binder is heated to its decomposition temperature (typically 200-400°C), where it decomposes and leaves behind ceramic particles that sinter at moderate temperatures. This parameter change avoids the excessive softening and flowing that occurs when glasses are heated above their glass transition temperature.
Solution Approach 2:
The organic binder is designed as a temporary, consumable component that decomposes at relatively low temperatures to enable ceramic particle sintering. This disposable organic phase provides the necessary plasticity and conformability during joining, then decomposes completely to leave behind only the ceramic structure, avoiding the problems of excessive softening and flow associated with glassy materials heated above their glass transition temperature.
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
This approach enables the formation of joints with mechanical and thermal properties matching the sintered bodies, maintaining integrity and gas-tightness, even under severe operating conditions, without the need for high pressures or special atmospheres, and results in joints with low leak rates and enhanced stability.
Implementation Method 1
heating the assembly to a conforming temperature sufficient to allow the joint material to conform to the joining surfaces
Implementation Method 2
further heating the assembly to a joining temperature below a minimum sintering temperature of the first and second sintered bodies, whereby the at least two sintered bodies are joined by the joint material
Implementation Method 3
applying a pressure to the joining surfaces of at least 1 kPa and less than 5 MPa to provide an assembly... heating the assembly to a conforming temperature sufficient to allow the joint material to conform to the joining surfaces
Data Source
AI summary
A method of joining at least two sintered bodies to form a composite structure, includes: providing a joint material between joining surfaces of first and second sintered bodies; applying pressure from 1 kP to less than 5 MPa to provide an assembly; heating the assembly to a conforming temperature sufficient to allow the joint material to conform to the joining surfaces; and further heating the assembly to a joining temperature below a minimum sintering temperature of the first and second sintered bodies. The joint material includes organic component(s) and ceramic particles. The ceramic particles constitute 40-75 vol. % of the joint material, and include at least one element of the first and/or second sintered bodies. Composite structures produced by the method are also disclosed.