Elevated temperature tensile behavior and microstructure evolution of Nb–5W–2Mo–1Zr alloy sheets

Niobium alloys possess several advantages, including a high melting point, low density, high specific strength at elevated temperatures, and good workability, making them promising candidate materials for aerospace structural components. Investigation into their high-temperature properties and fracture behavior is therefore essential. This study examines the tensile properties of 0.5 mm-thick Nb–5W–2Mo–1Zr alloy sheets over a temperature range of 400–1400 °C. Based on the experimental results, stress-strain curves and predictive equations for the temperature dependence of the alloy's mechanical properties are established. Furthermore, the deformation and fracture mechanisms of the alloy at various temperatures are elucidated. The results show that although the Nb–5W–2Mo–1Zr alloy exhibits excellent high-temperature mechanical properties—with tensile strength, yield strength, and elongation at 800 °C reaching 348.53 MPa, 183.5 MPa, and 36.73 %, respectively—its tensile strength at 1400 °C remains as high as 190.7 MPa. Nevertheless, the mechanical properties of this alloy are relatively sensitive to temperature, with strength decreasing as temperature increases. A marked reduction in tensile strength is observed when the testing temperature exceeds 400 °C, with a more pronounced decline above 1300 °C. Between 400 °C and 1200 °C, the primary tensile deformation mechanism is dislocation multiplication, and the dominant fracture mode is ductile transgranular fracture. At 1400 °C, grain rotation and grain boundary sliding become the main deformation mechanisms, and the fracture mode transitions from a mixed transgranular and intergranular type at 1300 °C to a typical intergranular fracture.