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The main strengthening pathways for niobium are solid solution, precipitation and deformation heat treatment.

In niobium alloys, the alloying elements tungsten and molybdenum can significantly improve its high-temperature and low-temperature strength, but too much content will reduce the alloy process performance. Tantalum is a moderate strengthening element and can reduce the plasticity-brittleness transition temperature of the alloy.

Another way to strengthen niobium alloys is to add titanium, zirconium and hafnium and a certain proportion of carbon to form a dispersed carbide phase for precipitation strengthening. In addition, these active elements can also improve other properties. For example, titanium can significantly improve the oxidation resistance and process performance of the alloy; hafnium and zirconium can improve the alloy’s resistance to molten alkali metal corrosion; hafnium can significantly improve the oxidation resistance and welding performance of the alloy. .

High-strength niobium alloys generally contain a large amount of solid solution elements (tungsten, molybdenum, tantalum, etc.) for solid solution strengthening. At the same time, precipitation strengthening is also used to make the alloy have high strength (see strengthening of metals). Plastic processing of these alloys is difficult and requires strict control of deformation process parameters. Except for the Nb-10W-1Zr-0.1C alloy, which contains a carbide precipitation strengthening phase, other varieties of medium-strength alloys add moderate contents of solid solution strengthening elements to ensure excellent comprehensive properties.

Low-strength alloys can ensure excellent processing properties by adding appropriate amounts of titanium, zirconium and hafnium.

Niobium has poor high-temperature oxidation resistance and begins to oxidize rapidly at around 600°C. Although high-strength niobium alloys with certain anti-oxidation properties such as WC-3015 (Nb-15W-4Ta-28Hf-2Zr-0.1C) have been developed, they are far from meeting actual requirements and still need to rely on high-temperature anti-oxidation coatings for protection. . The coatings that are better at protecting niobium alloys are Si-Cr-Fe, Cr-Ti-Si and Al-Cr-Si coatings.