Microstructural evolution and mechanical properties of hundred-kilometer-scale ultra-fine tungsten wires during the forming process

Abstract

In response to the demand for hundred-kilometer-scale ultra-fine and high-strength tungsten wires in the photovoltaic industry for silicon wafer cutting, W-0.5 wt%La₂O₃ alloy billets (φ23mm) were prepared by powder metallurgy. Subsequently, through forging and multiple drawing processes, ultrafine tungsten wires with diameters of 33–35 μm were obtained. The changes in microstructure and mechanical properties of the tungsten wire during the thermal processing were investigated. Electron backscatter diffraction (EBSD) was employed to characterize the microstructure after deformation. The average grain size of the sintered tungsten matrix was approximately 20.11 μm, while the equivalent circular diameter of La₂O₃ was about 2.965 μm. When the wire diameter was 0.035 mm, the fiber width of tungsten grains was approximately 25–55 nm, and the length and width of lanthanum oxide were refined to approximately 44.3 nm and 3 nm. The tensile strength of the tungsten wire reached 5706.82 MPa. The <111> texture gradually formed during plastic deformation, with the orientation intensity increasing progressively. The dislocation density also increased with the increase in deformation. Transmission electron microscopy (TEM) was used to explore the strengthening mechanisms of the alloy wire during the cumulative strain process. When the tungsten wire diameter was less than 0.6 mm, the W-0.5 wt%La₂O₃ alloy maintained a relatively constant fibrous structure, which increased the grain boundary area and dislocation density. Meanwhile, La₂O₃ transformed into strip-like structures parallel to the tungsten matrix with increasing deformation, residing at grain boundaries. The interface between La₂O₃ and the tungsten matrix evolved from a non-coherent to a coherent interface. Grain boundary strengthening is an important mechanism for the reinforcement of W-0.5 wt%La₂O₃ alloy wire. The strengthening mechanism of the alloy wire during the cumulative strain process was analyzed, and a predictive formula for the strength of tungsten alloy wire was derived, with an error margin within 7 %.