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Mechanism of Niobium-Titanium Alloy Maintaining Strength under High Temperature Conditions

The mechanism of Niobium-Titanium Alloy maintaining strength under high temperature conditions is mainly reflected in three aspects: multi-element synergistic strengthening, phase structure stabilization and process optimization. The following is a specific mechanism analysis:

1. Multi-element synergistic solid solution strengthening
Niobium-Titanium alloy forms a composite solid solution by adding elements such as Al, Nb, Ta, and Si, which significantly improves high-temperature performance:
• α-phase stabilizing elements (Al, Ga): Al is the core element of high-temperature titanium alloys. It is dissolved in the α phase and improves creep resistance and endurance strength by inhibiting dislocation movement. Patent CN107058804A points out that controlling the Al content at 4.0%-5.0% can avoid the precipitation of brittle Ti3Al phase and balance strength and plasticity.
• β-phase stabilizing elements (Nb, Ta): The addition of niobium and tantalum not only improves oxidation resistance, but also improves the stability of the β phase through solid solution strengthening. Studies have shown that niobium occupies Ti or Al sub-lattice positions in Ti-Al alloys, forming a short-range ordered structure that hinders dislocation sliding, and this effect is still effective at high temperatures.
• Neutral elements (Sn, Zr): Supplement and strengthen the α phase, delay the formation of harmful phases (such as ω phase), and optimize thermal stability.

2. Dispersed phase and precipitation strengthening
High-temperature creep resistance is enhanced by forming high-melting point dispersed phases through alloying elements:
• Silicide (S2-type silicide): Si element (0.1%-0.5%) generates dispersed silicide particles at high temperatures, hindering dislocation climbing and grain boundary sliding, and significantly improving creep resistance. Experiments show that the endurance life of Si-containing alloys at 600℃/450MPa can reach more than 30 hours.
• Bismuth (Bi): The addition of Bi (0.1%-0.35%) can refine the grains and form a strengthening phase, further inhibit high-temperature deformation, and improve process plasticity.

3. Phase stability and oxidation resistance optimization
• Thermal stability control: By balancing the α and β phase stabilizing elements (such as Al equivalent formula: %Al + 1/3%Sn + 1/6%Zr ≤8%), the precipitation of harmful phases (such as Ti3Sn) at high temperatures is avoided to maintain the stability of the organization.
• Anti-oxidation coating technology: When the high niobium Ti-Al intermetallic compound coating is cyclically oxidized at 950℃, the oxidation kinetic curve is parabolic, and the oxidation rate is only 1/20 of the titanium alloy substrate. The continuous and dense oxide layer (such as Al2O3, Nb2O5) formed on the coating surface effectively isolates oxygen erosion.

4. Advanced process strengthening
• Heat treatment and hot isostatic pressing: Patent CN107058804A uses 990℃/130MPa hot isostatic pressing treatment to eliminate internal defects and improve density; 760℃ vacuum annealing optimizes the grain boundary structure, so that the alloy still maintains excellent mechanical properties at 650-750℃.
• Dynamic recrystallization inhibition: At high temperatures, niobium alloys slow down diffusion creep and grain boundary sliding through grain boundary strengthening and second phase pinning (such as Zr) to maintain strength.

Summary
The high-temperature strength of niobium-titanium alloys comes from the combined effects of multi-element solid solution strengthening, dispersed phase pinning dislocations, phase stability design, and process optimization. For example, the addition of Nb and Ta not only improves oxidation resistance, but also strengthens the matrix through short-range ordered structures; the dispersed phases of Si and Bi significantly inhibit high-temperature creep. These mechanisms jointly ensure the high thermal strength of niobium-titanium alloys in short-term use scenarios at 650-750℃, providing a material basis for high-temperature components in aerospace.