WC-Fe-Cr Cemented Carbide for Fusion Neutron Shielding
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Solution Overview
Problem
The production of 100% dense blocks for fusion nuclear reactor walls using tungsten carbide (WC) is hindered by the inability to fabricate WC-Fe cemented carbides without inclusions of η-phase or free carbon, which are brittle and unsuitable for neutron shielding.
Innovation Solution
Alloying the binder phase with chromium (Cr) allows for the broadening of the W-C-Fe phase diagram, enabling the production of WC-Fe-Cr cemented carbides with a microstructure comprising WC grains, cementite grains, and dissolved Cr, W, and C in an Fe-based binder matrix, thus avoiding brittleness and porosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If WC-Fe cemented carbides are used for neutron shielding, then the material provides effective neutron absorption and moderation, but the narrow two-phase region leads to formation of brittle η-phase or free carbon inclusions
Solution Approach 1:
The patent changes the chemical composition parameters by adding chromium to the WC-Fe system, transforming the narrow two-phase region into a broader three-phase region (WC + cementite + Fe-based binder). This parameter change allows for a wider compositional window that avoids brittle η-phase and free carbon inclusions while maintaining neutron shielding effectiveness.
Solution Approach 2:
The invention creates a composite cemented carbide material system comprising WC, Fe, and Cr, where chromium acts as an alloying element in the binder phase. This composite approach broadens the stable two-phase region and enables production of fully dense blocks without harmful inclusions, resolving the manufacturing precision issue while preserving neutron shielding reliability.
2Ease of manufacture
If chromium is added to WC-Fe graded powders, then the two-phase region is broadened and production becomes feasible, but the binder phase composition becomes more complex
Solution Approach 1:
By introducing chromium as an additional compositional parameter, the patent transforms the phase diagram structure, broadening the manufacturable region. Although this adds compositional complexity, it simultaneously improves ease of manufacture by enabling production of fully dense blocks without brittle inclusions, making the process more robust and controllable.
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 addition of chromium expands the two-phase region in the WC-Fe system, facilitating the production of fully dense, η-phase and free carbon-free cemented carbides with improved hardness and fracture toughness, making them suitable for neutron shielding in fusion reactors.
Implementation Method 1
additions of powders of different chemical elements, in particular chromium, to WC—Fe graded powders in particular amounts as described herein allows broadening of the region of W—C—Fe phase diagram in which only the carbide phases, i.e. WC and cementite, and a metallic binder, i.e. Fe-based binder, are present in the equilibrium
Implementation Method 2
The most suitable material for this is known to be tungsten carbide (WC)... the resulting high-energy neutrons emitted from the plasma must be slowed (moderated) and captured (absorbed) in the walls of the containment vessel
Data Source
AI summary
A cemented carbide body for neutron shielding and a method of making the same, said cemented carbide body containing WC, Fe and Cr, wherein the Cr is present in an amount from approximately 1 wt. % to approximately 150 wt. % with respect to the Fe content, the cemented carbide body comprising WC grains, cementite grains and dissolved Cr, W and C in an Fe-based binder matrix material.