Niobium alloy formed by adding a certain amount of hafnium and other elements to the niobium base. On a binary phase diagram, niobium and β-Hf form a replacement solid solution. Hafnium is a kind of active element, which is combined with oxygen and carbonation in niobium to form HfO2 and HfC compounds. It plays a diffusion strengthening role, reduces the harmful effects of interspace elements, and improves the weldability and coating performance of niobium alloy. Niobium hafnium alloy is the most important niobium alloy in aerospace engineering and technology. In 1965, the United States successfully developed Nb-10Hf-1Ti alloy, and it was used in the Apollo manned Lunar module descent stage rocket engine nozzle extension section in 1969. In 1975, China successfully developed NbHf10Ti1Zr0.7 niobium alloy.
Niobium and hafnium alloys can be divided into two types according to strengthening methods: solid solution strengthening alloy and solid solution strengthening and dispersion strengthening alloy.
Preparation methods and processing techniques include ingot preparation and plastic processing, welding, heat treatment and coating.
Billet preparation and plastic processing niobium hafnium alloy usually adopts electron beam smelting and vacuum consumable arc smelting combined to prepare billet, and then at 1200℃ above the temperature of extrusion or forging, rolling and drawing below the temperature of 500℃, can be made into plates, belts, bars, lines and forgings and other products.
Welding niobium hafnium alloy has good weldability, usually using tungsten argon protection welding and electron beam fusion welding method to achieve the connection of the parent metal, but also can use these two welding methods to complete niobium hafnium alloy with titanium and titanium alloy welding. The quality of welding seam is related to the purity and vacuum degree of argon. Generally, the higher the purity of argon, the lower the residual atmospheric pressure, the better the welding seam quality.
Generally, vacuum or inert gas protection annealing treatment and solid solution aging treatment are used for heat treatment.
Cr-Ti-Si and Cr-Fe-Si systems are usually used as anti-oxidation coatings. The antioxidant life of niobium hafnium alloy coated with these two kinds of coatings is more than 150h at 1371℃.
It is mainly used for liquid rocket engine radiation cooling nozzle extension section and thrust chamber body, space power generation system fused sodium and sodium potassium alloy pressure tube, turbo pump, jet engine high-temperature structural parts, etc.
