Aging Effect on the Microstructure and Creep Behavior of Dy-Doped Ti–Nb Alloys

The microstructure and mechanical properties of Ti–Nb-based alloys are often influenced by alloying elements and heat treatment. In the present work, Ti–22Nb–xDy alloys with different Dy contents (x = 0, 0.5, 1.0, 2.0 at %) are prepared by non-consumable vacuum arc melting. The effects of in situ aging temperature on the microstructural evolution and creep properties of the alloys are investigated by in situ X‑ray diffraction, scanning electron microscopy, and nanoindentation tests. It is found that Dy doping in the Ti-Nb alloys leads to grain refinement and contributes to the aging precipitation of α, ω, and rare-earth phases. As the aging temperature is raised from 250 to 550°C, the phases of the Ti–Nb–Dy alloys change as α" → β → α + β → ω + α + β. In addition, rare-earth precipitates are aggregated and distributed along grain boundaries and in the matrix. Furthermore, Dy doping and aging temperature have great effects on the nanohardness, elastic modulus and creep resistance of the Ti–Nb–Dy alloys. When the in situ aging temperature is 400°C, the Ti–22Nb–2Dy alloy has the largest nanohardness and elastic modulus and better creep resistance.