Abstract
The influence of the distribution of components in vanadium alloys on the probability of hydrogen embrittlement of filters is analysed. Examining V-15Ni and V-15(Fe-Co-Cr-Ni) alloys with dendritic structures formed by solidification, it was demonstrated that microvolumes with vanadium concentrations as high as 91 at.% were present, exceeding the average value of 85 at.%. The equilibrium hydrogen solubility in such microvolumes is higher than average in the alloy. Therefore, even if the average hydrogen concentration in the alloy does not exceed the ductile-to-brittle transition concentration (DBTC), H / M = 0.2, this “safety” criterion will be violated locally in microvolumes with a higher vanadium content, increasing the probability of failure. To preserve the integrity of membrane filters, we propose a stricter criterion: the membrane operating parameters (pressure and hydrogen concentration at a constant temperature) must satisfy Sieverts’ law. Even if the elements in the alloy are distributed unevenly, the probability of exceeding the local DBTC remains low. However, alloys that have a uniform distribution of components are preferred. Non-hydride-forming metals that are completely soluble in vanadium should be selected as alloying elements, and the alloy should solidify in a narrow temperature range. Chromium is one of such elements. Indeed, no microsegregation is observed in experimental V-23Cr alloy ingots after solidification.
Funding
1. Russian Science Foundation - 22-12-00360-П
2. Institute for Metals Superplasticity Problems of the Russian Academy of Sciences -
3. Vatolin institute of metallurgy of the Ural branch of the Russian Academy of sciences -