超高强奥氏体不锈钢微丝是光伏电池丝网印刷的核心材料，其性能取决于冷拉拔过程中超大塑性变形引起的组织演变。然而，在超大塑性变形冷拉拔过程中，微丝的微观组织演变复杂，对其强-塑性协同影响的内在机制尚不完全清晰。本工作以304不锈钢为研究对象，通过多尺度表征(XRD、EBSD/TKD、TEM)，系统研究其直径从100.0 μm冷拉拔至10.0 μm (真应变(ε)从0到4.61)过程中的微观组织演变、形变诱导γ→α¢马氏体相变及晶体取向演变规律，旨在阐明超大塑性变形条件下的形变机制演化规律及其对强-塑性协同的作用机制，为超高强金属微丝的组织调控与性能优化提供理论依据。结果表明，随ε增加，材料经历“位错滑移→形变孪晶协同→马氏体相变→纳米晶形变”的阶段性演变。当ε = 1.93时，奥氏体基本转变为马氏体，形成沿拉拔方向的板条状组织，马氏体变体从初始择优选择(Bain 3组主导)转向多变体协同(Bain 1/Bain 2/密排面平行组均衡分布)；当ε = 4.61时，组织细化为尺寸为(26.9 ± 10.1) nm的板条马氏体，形成强bcc结构<110>//拉拔方向的丝织构，取向演变由马氏体自身塑性变形与晶格旋转主导。力学测试结果表明，直径10 μm的冷拉拔微丝抗拉强度达(3199 ± 19) MPa，其超高强度源于形变诱导马氏体相变、纳米级晶粒细化及高位错密度的协同强化作用。
Ultrahigh-strength
austenitic stainless steel ultrafine wires are critical materials in
next-generation photovoltaic technologies, particularly in screen-printing
electrodes requiring a synergistic balance of high strength and adequate
ductility to support the mechanical demands of advanced manufacturing and the
functional requirements of device performance. However, the underlying
mechanisms of microstructural evolution and their direct link to the
exceptional mechanical properties achieved via severe plastic deformation are
incompletely understood. Specifically, the intricate interplay between
dislocation slip, deformation twinning, and martensitic transformation, and how
these deformation mechanisms drive the microscale development of
crystallographic texture and hierarchical nanostructures, have not been
comprehensively characterized, especially under extreme processing conditions.
Herein, we comprehensively evaluate the microstructural evolution of 304
austenitic stainless steel ultrafine wires subjected to systematic cold drawing
from an initial diameter of 100 μm to a final diameter of 10 μm, corresponding
to true strains from 0 to 4.61. At each deformation stage, the wires are
characterized using XRD, EBSD, transmission Kikuchi diffraction, and TEM.
Through tensile tests and fractographic analysis, we systematically correlate
the mechanical properties with the microstructural features, establishing a
direct link between processing, microstructure, and performance. Integrated
multiscale analysis reveals a clearly defined hierarchical pathway of
microstructural transformation under extreme deformation: pervasive dislocation
slip, followed by activation of deformation twinning that subsequently
progresses to nucleation and rapid growth of strain-induced martensite. At an
intermediate true strain (ε = 1.93), the austenite matrix is almost
completely transformed into lath martensite; meanwhile, the martensite variant
selection evolves significantly
from Bain3 dominance to a complex, multivariant distribution of Bain1, Bain2,
and close-packed plane parallel orientations. At the highest strain (ε =
4.61), the microstructure exhibits ultrafine lath martensite grains with
average widths of 26.9 ± 10.1 nm and a sharp body-centered cubic <110>
texture aligned with the drawing direction. This extreme refinement is further
characterized by substantial lattice rotation and reorientation processes,
driven by continued martensite plasticity and high defect density. Importantly,
these multiscale microstructural transformations culminate in extraordinary
mechanical properties. The processed 10-μm-diameter ultrafine wires reach an
ultimate tensile strength of 3199 ± 19 MPa while maintaining sufficient
ductility for processing, manufacturing, and integration into photovoltaic
modules. This extended analysis elucidates the synergistic strengthening
contributions of deformation-induced martensitic transformation, progressive
nanoscale grain refinement, and sustained high dislocation density, providing a
comprehensive mechanistic framework for understanding and optimizing the
performance of ultrafine austenitic stainless steel wires. These findings not
only advance fundamental knowledge of hierarchical microstructure development
under severe plastic deformation but also establish clear design principles for
next-generation high-performance materials in photovoltaics and beyond.
