Speaker
Description
Tungsten has many advantageous features; however, it is rather susceptible to oxidation at temperatures above 500 °C. By the addition of various oxide-forming elements to tungsten, self-passivation is induced. During exposure of the alloy to air, a passivation layer is formed on its surface, thereby preventing further tungsten oxidation, material degradation and related radiation spreading. Currently, the most promising result has been achieved using W-Cr solid solution with a small addition of yttrium prepared by mechanical alloying and Field Assisted Sintering.
The aim of the present study is to explore the feasibility of two large-scale technologies that are either already available in the industry or technologies where the laboratory experiences can be easily translated to industrial production. Both methods can fabricate the plasma-facing layer directly on the structural part, without the need for joining. The following technologies were applied to deposit W-Cr coatings:
Cold Spray is a coating deposition method that offers a huge versatility and material throughput without the necessity for any special substrate surface pre-treatment. Using kinetic energy in lieu of thermal input, the method is particularly good for deposition of metals or metallic blends. Low temperatures involved in this process prevent material oxidation.
Radiofrequency plasma spraying is a coating deposition method that operates in a controlled atmosphere (inert gas, reactive gas or vacuum), effectively eliminating oxidation of the molten metal. The temperatures involved in this process are high enough to melt tungsten and ensure its proper deposition
The first results clarify the capabilities and limits of these technologies with respect to production of W-Cr solid solution deposits. Basic questions were answered, e.g. whether a specific powder treatment is necessary prior to the deposition, what is the most suitable powder size for production of the solid solution or whether a post-treatment of the deposits is necessary.
