Oxide dispersion strengthened and oxidation resistant vanadium alloys

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Vanadium-base alloys are promising candidates for the development of novel high temperature materials due to, among others, their highly specific mechanical strength. This can be achieved by alloying with elements that cause precipitation hardening (such as Si and B) or with oxide particles, so-called ODS particles (oxide dispersoids). However, optimal mechanical properties require a V solid solution matrix in the materials microstructure. This matrix in turn is extremely vulnerable in oxidising environments. The reason is that the formation of V2O5, which – in contrast to the pure metal (Ts (Vanadium) = 1919 °C) – is liquid at temperatures above ca. 690°C. This oxidation behaviour is the reason why vanadium-base alloys have not been considered for high temperature application until now. To make matters worse, vanadate changes very easily between different oxidation states, which extremely accelerates the high temperature corrosion of Ni-, Co- or Fe-base materials, especially if it is present in a molten form. This also excludes an application of currently available vanadium alloys in combination with these materials.In order to make vanadium alloys applicable at high temperatures, a completely new approach of oxidation protection is proposed with simultaneous oxide particle strengthening: Using Mg- and Ca-containing oxide particles to produce oxidation-resistant ODS-V-Si alloys. Introduced in sufficient amounts, the ODS particles are expected to prevent the formation of liquid phase at high temperatures. At the same time we expect a strengthening effect of the particles, which is to be quantified in the potential application range of such alloys from ambient temperature to 1100°C.The purpose of the project is to clarify (1) up to which volume fraction of MgO, CaO or magnesium orthosilicate particles homogeneous microstructures can be formed in vanadium materials, (2) which concentration of MgO, CaO or magnesium orthosilicate is required to prevent liquid phase formation or to trigger a self-protecting mechanism, (3) how much of a strengthening effect can be achieved by adding oxide dispersoids and how the ODS particles affect the creep behaviour of vanadium alloys. Accompanying investigations are planned in order to systematically characterise the powder and alloy systems in terms of their composition and their microstructure and, subsequently, their oxidation behaviour. The main focus lies on determining the optimal ratio between ODS particles and vanadium solid solution in relation to oxidation resistance and mechanical properties. Thus, a completely new approach of alloy design is taken in order to improve oxidation resistance and mechanical properties at the same time.