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.
Coating.heat-resistant alloy is the first system developed for niobium alloy coating, which mainly includes iron. Metals and alloys of the nickel and cobalt classes. The researchers explored a variety of coating preparation methods: electroplating. However, no satisfactory results were obtained in hot dipping, infiltrating deposition, spraying, molten salt deposition and electrophoresis fruit. In 1970, the US National Advisory Committee published a work on heat-resistant alloy coatings. It was concluded and evaluated that the adhesion between the coating and niobium substrate was poor and subjected to high temperature erosion is easy to flake off; The porosity of the coating provides a large number of diffusion channels for oxygen atoms. Rapid oxidation occurs when the temperature is above 900 ℃, resulting in matrix failure, such coating due to the defects of its composition, it is not suitable for high-temperature anti-oxidation protection of niobium alloy.
Precious metals are not only good corrosion resistance, but also ductile and adaptable
Stress deformation caused by elastic-plastic deformation or high-temperature creep of the matrix. Platinum can be used as a metal. But a lot of mutual diffusion occurs between niobium substrate and coating material, which leads to coating loss. Iridium has low oxygen permeability and diffusivity, making it an ideal oxygen diffusion barrier, but its oxide vapor pressure is high and cannot be directly exposed to high temperature atmosphere. A coating of other ingredients is required. Many precious metals have higher melting points low, as the main coating, the use temperature is too low and the cost is too high, by the practical application limited, so consider it as an addition or modification of other coatings.
