In niobium alloy, the high and low temperature strength of Nb alloy can be significantly improved by containing tungsten and molybdenum, but too much will reduce the technological properties of Nb alloy.
Tantalum is a medium strengthening element and can reduce the plasticity-brittle transition temperature.
Another way to strengthen Nb alloy is to add titanium, zirconium, hafnium and a certain proportion of carbon to form a diffuse carbide phase for precipitation strengthening.
In addition, these active elements can also improve other properties, such as titanium can significantly improve the oxidation resistance and process properties of the alloy; Hafnium and zirconium can improve the corrosion resistance of molten alkali metal. Hafnium can significantly improve the oxidation resistance and welding property of the alloy.
The high strength niobium alloy generally contains a large number of solid solution elements (tungsten, molybdenum, tantalum, etc.) for solid solution strengthening, and precipitation strengthening is also used to make the alloy have high strength (see metal strengthening). The plastic processing of these alloys is difficult and the deformation parameters need to be strictly controlled.
In addition to Nb-10W-1Zr-0.1C alloy containing carbide precipitation strengthening phase, the other varieties are added with medium content of solid solution strengthening elements to ensure that they have excellent comprehensive properties.
As long as proper amount of titanium, zirconium and hafnium is added to the low strength alloy, it can ensure that the alloy has excellent processing properties.
Niobium has poor oxidation resistance at high temperature and begins to oxidize rapidly at about 600℃. Although the high strength niobium alloy such as WC-3015 (Nb-15W-4Ta-28Hf-2Zr-0.1C) with certain oxidation resistance has been developed, it is far from meeting the practical requirements and still needs to rely on high temperature oxidation resistance coating to protect. The coatings of Si-Cr-Fe, Cr-Ti-Si and Al-Cr-Si series have better protective effect on Nb alloy.
