According to the oxidation mechanism of niobium, the methods of alloying can be considered from several the anti - oxidation properties of niobium were improved.
(1) Add the alloy in Nb2O5 to form a solid solution, the valence number of solute element ions and ionic radius obviously affect the crystal defect structure and volume of Nb2O5.
The addition of ions can be expected to change the diffusion characteristics of the shell and reduce the expansion of oxygen ions speed.
(2) The alloying elements added exceed the solid solubility in Nb2O5 to generate other oxygen. The oxide phase, or the low - cost oxide, or the amorphous surface layer, gives the oxide layer a variety of properties produce favorable changes.
(3) To improve the strength and creep property of the oxide layer, release the internal stress slowly, and reduce the crack is generated.
(4) Densify the surface layer, reduce the voidness, and block the oxygen to the interior of the matrix to spread. Most niobium alloys rely mainly on self-generated protective oxidation on their surfaces content layer, to achieve antioxidant function. Many researchers recognize the major role of alloying instead of modifying Nb2O5, it produces a protective oxide layer. Namely in a certain article the Al, Si, B and other elements in niobium alloy were selectively oxidized to form aluminum on the surface of the matrix compounds, silicides, or borides, but in these cases the tough niobium group cannot be obtained alloy.
The anti-oxidation properties of niobium and niobium alloys were improved by alloying
The amount of aurified elements must exceed a critical value in order to protect the matrix
In this way, it is bound to affect other properties, especially the high-temperature mechanical properties of the matrix. It can be seen that the alloying method has its own limitations. Surface coating protection is a practical and effective way to give consideration to the high-temperature mechanical properties and anti-oxidation properties of niobium alloy. From the orders, the previous studies show that niobium and its niobium alloy surface high temperature anti-oxidation coating materials are the main. It is divided into several systems: heat resistant alloy coating, aluminate coating, precious metal coating, silicide coating.
