Tantalum and Niobium application in thermal strength alloys

Niobium is an alloy additive of nickel, cobalt and other thermo-strong alloys. The basic components of these alloys are nickel, cobalt, and chromium. Alloy additives are titanium, tungsten, molybdenum, aluminum, iron. These alloys are used to make parts for aircraft generators, blades for gas turbines, etc. These alloys work well at 800-100℃.The alloy has good thermal strength, thermal resistance and machining properties.

In thermally strong nickel-based alloys, niobium additive is mainly distributed in two phases: the multiple nickel-based 'solid solution and the strengthening phase γ' (Ni3Al).In addition, niobium also enters the carbide phase Me(C, N), which is titanium, zirconium, niobium and other refractory alloying elements. These elements prevent the development of intercrystalline slip process and have a good effect on the properties of the alloy.

In thermally strong cobalt alloy, the main function of alloying element niobium is to form carbide phase which has good influence on microstructure stability and can improve thermally strong performance at high temperature. Other thermal-strength alloys are α-Ti, molybdenum and tungsten based alloys, and niobium - tantalum based alloys.

Niobium is a stabiliser used in titanium alloys for alloying thermal strength alloys (alloy BT18 and its variants). The main purpose of adding niobium to these alloys is to alloying the alpha phase to improve its strength and thermal strength.

The main purpose of adding a small amount of niobium into the thermal-strength alloys of molybdenum and tungsten is to improve the strength and thermal-strength properties of these materials at high temperature without significantly reducing the low temperature plasticity of the alloys. Adding a small amount of Niobium (0. 15% ~ 0.25%) to the high strength molybdenum alloy (Mo-Zr-C series) can obviously reduce the transition temperature of the brittle state of the alloy, increase the starting temperature of the recrystallization of the alloy, and improve the strength and thermal strength performance at 1100-1150℃.The good effect of alloying element Niobium is related to the refinement of carbide phase (Zr, Nb)C and its uniform distribution in solid solution grains. Niobium based thermal strength alloy is suitable for working at 1100-1250℃.

The niobium alloy containing 15%(W+Mo), 1.5%Zr and 0.12%C has the highest thermal strength. The thermal strength niobium alloy is used in the thermal stress structure of high speed aircraft, missile, space vehicle and the blade of gas turbine. Tantalum - based thermal-strength alloys are also used in these fields, but their use is limited due to their scarcity and high cost. The alloy additives to improve the thermal strength of tantalum include tungsten, molybdenum, hafnium and rhenium. If the developed alloy has Ta+10% W +1 2.5%Mo; Ta+8%W+2%Hf, etc., operating temperature is 1300-1650℃ or higher. Niobium is mainly used as an alloying element in tantalum base alloys. Compared with other refractory metals, niobium has lower corrosion resistance and process plasticity.