Nb3Sn Strand Heat Treatment via Cu Diffusion Plateau
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Solution Overview
Problem
Existing heat treatment processes for Nb3Sn superconducting strands often result in disconnected Nb3Sn due to Nausite membrane growth, limiting critical current density.
Innovation Solution
A heat treatment process involving a Cu diffusion plateau at 350°C to 380°C for 100 to 400 hours, followed by a Nb3Sn reaction plateau between 620°C and 750°C, focuses on inhibiting Nausite membrane growth to enhance Cu diffusion and prevent liquefaction, thereby maximizing critical current density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If traditional heat treatment with multiple temperature holds is used, then homogenization of Cu-Sn mix is achieved, but Nausite membrane growth causes disconnected Nb3Sn and limits critical current density
Solution Approach 1:
The patent applies preliminary action by performing a low-temperature Cu diffusion plateau (350-380°C for 100-400 hours) before the high-temperature Nb3Sn reaction plateau. This preliminary Cu diffusion step pre-homogenizes the Cu-Sn mix and reduces Nausite membrane thickness before the main reaction, preventing the formation of disconnected Nb3Sn regions and maximizing critical current density in the final product.
2Stability of the object's composition
If longer heat treatment time is used to homogenize Cu-Sn mix, then composition uniformity improves, but production time and cost increase
Solution Approach 1:
The patent segments the heat treatment process into two distinct plateaus: a low-temperature Cu diffusion plateau (350-380°C for 100-400 hours) and a high-temperature Nb3Sn reaction plateau (620-750°C for 24-400 hours). This segmentation allows Cu diffusion to occur at lower temperatures over an extended period without causing excessive Nausite growth, achieving homogenization more efficiently than traditional single-stage high-temperature treatment.
3Reliability
If high temperature heat treatment is used to form Nb3Sn, then superconducting properties are activated, but Nausite membrane growth increases and disconnects Nb3Sn regions
Solution Approach 1:
The patent performs preliminary Cu diffusion at low temperature (350-380°C) before the high-temperature Nb3Sn reaction. This preliminary action reduces Nausite membrane thickness and pre-homogenizes the Cu-Sn mix, ensuring that when the high-temperature reaction occurs, Nb3Sn forms as continuous connected regions rather than disconnected islands, maintaining both superconducting properties and structural continuity.
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 process reduces Nausite membrane thickness, increases Cu content in the core, and enhances critical current density by 27% at 16 T, with improved wire performance demonstrated in distributed barrier RRP strands.
Implementation Method 1
a Cu diffusion plateau between 350°C and 380°C is provided for 100 to 400 hours
Implementation Method 2
designed to homogenize the Cu-Sn mix before going through phase transitions
Data Source
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AI summary
A new heat treatment for Internal-Tin Nb3Sn strands is described. The heat treatment uses Nausite membranes to decrease the volume fraction of the η phase and therefore minimize its liquefaction-ultimately resulting in better connected Nb3Sn. The heat treatment requires only one stage aside from the final Nb3Sn reaction stage. This heat treatment enables an increase in critical current density (at 16 T) of 28%.