In the fabrication of high-temperature superconducting (HTS) substrates, the surface quality and thickness precision of the metallic base tape directly determine the performance of the final superconducting tape. To meet the stringent requirements for epitaxial growth of the superconducting layer, the substrate must simultaneously achieve two critical characteristics: “ultra-thin” dimensions and a “mirror-like” surface finish. The patent filed by Ningbo Yongcheng Metal Materials Technology Co., Ltd.—“A Mirror-Finish Rolling Process for Hastelloy Ultra-Thin Strips Used in Second-Generation High-Temperature Superconducting Substrates” (Publication No. CN 119489092 A)—reveals the core technology behind this breakthrough.
According to public records from China’s National Intellectual Property Administration, this patented process specifically addresses the challenges of processing ultra-thin Hastelloy strips. Hastelloy C276 is the preferred substrate material for second-generation HTS tapes due to its exceptional strength, ductility at cryogenic temperatures, and outstanding corrosion resistance. However, reducing this notoriously difficult-to-deform alloy from an initial thickness of 0.6–0.8 mm down to an ultra-thin gauge of just 0.03–0.045 mm—thinner than a human hair—while maintaining a width of 280–300 mm, presents formidable technical hurdles in rolling technology.
The core innovation of this patent lies in a multi-stage asynchronous rolling process. Conventional rolling methods often suffer from low thinning efficiency, poor flatness control, and high surface roughness when producing ultra-thin strips. Yongcheng Metal’s approach ingeniously divides the rolling sequence into three distinct phases: rough rolling, intermediate rolling, and finish rolling.
Balancing Thinning and Flatness: During the rough and intermediate rolling stages, the primary focus is on achieving significant thickness reduction while managing internal stresses to prevent strip fracture during high-speed rolling. Multiple passes across these stages gradually relieve work-hardening-induced stresses.
Achieving Mirror Finish: In the finish rolling stage, asynchronous rolling is employed. This technique uses upper and lower work rolls rotating at different surface speeds. The resulting speed differential generates intense shear deformation in the roll gap—not only aiding further thinning but, more importantly, effectively transferring the high surface polish of the work rolls onto the strip. This dramatically reduces surface roughness.
Surface Quality Control: Integrated between each rolling stage are cleaning and mechanical polishing steps. These not only remove oils and oxides but also eliminate micro-defects potentially introduced during rolling, ensuring the final product meets the stringent surface smoothness required for epitaxial growth of the superconducting layer.
This staged-control methodology enables precise regulation of surface roughness, ultimately realizing true “mirror-finish rolling.” For HTS substrates, surface roughness directly impacts the texture quality of the buffer layer. Micron-scale protrusions or depressions on the substrate can disrupt the biaxial texture of the superconducting layer, leading to a significant drop in critical current density.
Yongcheng Metal’s patented technology not only enhances the thinning efficiency of Hastelloy ultra-thin strips but also achieves a breakthrough in the most critical metric—surface quality. This advancement provides a high-performance, domestically produced substrate solution for subsequent superconducting tape manufacturing, breaking long-standing reliance on imported materials and showcasing the technical prowess of Ningbo-based enterprises in high-end manufacturing.
