Blog

The "High-Temperature Potential" of Dual-Phase Strengthening: Performance Breakthroughs of Niobium-Ti in High-Temperature Structural Materials

When niobium-titanium (NbTi) materials are mentioned, people often think of its superconducting properties first. However, in reality, niobium-titanium is equally valuable as a strengthening element in high-temperature structural alloys. In nickel-based superalloys, niobium and titanium form a dual-phase strengthening phase, significantly improving the alloy's high-temperature strength, creep resistance, and oxidation resistance, making it a key material in high-temperature fields such as aerospace and nuclear power. This performance advantage in application dimension perfectly complements its superconducting applications.

The core role of niobium-titanium in high-temperature alloys is to achieve γ''/γ' dual-phase synergistic strengthening. Taking a typical 2.4618 nickel-based alloy as an example, its composition system has nickel as the matrix (58%-62%), with 3%-4% niobium and 1.5%-2.5% titanium added. After specific heat treatment, two strengthening phases will precipitate uniformly in the matrix: the γ'' phase (Ni₃Nb) and the γ' phase (Ni₃Ti). The crystal structures of these two strengthening phases exhibit excellent compatibility with the face-centered cubic structure of the nickel matrix, with lattice mismatch controlled at 1.2%-1.5%. This effectively hinders dislocation movement, enhancing alloy strength without causing brittle fracture due to stress concentration.

Specifically, the γ'' phase, distributed in a disk-like pattern with a size of approximately 50-80 nm, primarily provides strength support in the room temperature to 650°C range. The γ'' phase, dispersed in a spherical pattern with a smaller size (20-30 nm), dominates high-temperature strengthening in the 650-800°C range. This dual-phase synergistic mechanism enables the alloy to maintain high hardness and strength over a wide temperature range. After solution treatment at 980°C followed by aging at 720°C, its yield strength is increased by 80% compared to the solution-treated state, and its tensile strength at 700°C still exceeds 850 MPa, far superior to high-temperature alloys with a single strengthening phase. Compared to traditional nickel-based alloys without niobium and titanium, such as Inconel 600, whose tensile strength at 700℃ is only around 600MPa and exhibits poor creep resistance (less than 50 hours of creep rupture life at 800℃ under 100MPa stress), the 2.4618 alloy containing niobium and titanium achieves a creep rupture life exceeding 150 hours under the same conditions, representing a more than 40% improvement in creep resistance.

In terms of oxidation and corrosion resistance, the addition of niobium and titanium also significantly optimizes the performance of high-temperature alloys. Niobium and titanium synergistically work with elements such as chromium and aluminum in the alloy to form a dense oxide film (mainly composed of TiO₂, Nb₂O₅, and Cr₂O₃) at high temperatures. This oxide film effectively prevents oxygen and corrosive media from penetrating the alloy, slowing down the oxidation and corrosion process. Experimental data shows that the 2.4618 alloy, after continuous operation in static air at 700℃ for 1000 hours, exhibits an oxidation weight gain of only 0.3 g/m², far superior to traditional 310 stainless steel (approximately 2.5 g/m²). After three years of operation in the high-pressure steam environment of nuclear power equipment, no oxidation spalling occurred on the pipe wall, and the mechanical properties were retained at 90%.

Compared to other high-temperature strengthening elements, the niobium-titanium combination offers unique advantages. For example, while niobium alone can form a stable γ'' phase, the precipitated phase size tends to coarsen with increasing temperature, leading to a decline in long-term high-temperature performance. Titanium alone results in an unstable γ' phase that easily decomposes above 750℃. However, the synergistic addition of niobium and titanium allows for precise control of the size and distribution of both strengthening phases through compositional adjustments, significantly improving the high-temperature stability of the strengthening phase. Compared to refractory strengthening elements such as molybdenum and tungsten, niobium-titanium alloys have lower densities (niobium density 8.57 g/cm³, titanium density 4.51 g/cm³, molybdenum density 10.2 g/cm³), allowing for increased strength while reducing overall alloy weight, which is crucial for weight reduction requirements in the aerospace field.

In practical applications, niobium-titanium strengthened high-temperature alloys have become core materials for gas turbine blades, hot-end components of industrial furnaces, and intermediate heat exchangers in nuclear reactors. A heavy-duty gas turbine manufacturer used 2.4618 alloy to manufacture first-stage moving blades. After 8000 hours of operation at 750℃ and 200 MPa centrifugal stress, the blade deformation was only 0.1 mm, and metallographic analysis showed no significant coarsening of the strengthening phase. In contrast, blades made with traditional alloys showed a deformation of 0.5 mm after 4000 hours under the same conditions, rendering them unusable. This fully verifies the reliable performance of niobium-titanium strengthened high-temperature alloys and highlights their irreplaceable role in the field of high-temperature structural materials. AlloyHit specializes in producing Niobium-Titanium products in various specifications, such as Nb53-Ti47, Nb50-Ti50.