Process for preparing metal powders having low oxygen content, powders so-produced and uses thereof

Abstract

The present invention is directed to a process for the preparation of a metal powder having a purity at least as high as the starting powder and having an oxygen content of 10 ppm or less comprising heating said metal powder containing oxygen in the form of an oxide, with the total oxygen content being from 50 to 3000 ppm, in an inert atmosphere at a pressure of from 1 bar to 10⁻⁷ to a temperature at which the oxide of the metal powder becomes thermodynamically unstable and removing the resulting oxygen via volatilization. The metal powder is preferably selected from the group consisting of tantalum, niobium, molybdenum, hafnium, zirconium, titanium, vanadium, rhenium and tungsten. The invention also relates to the powders produced by the process and the use of such powders in a cold spray process.

Description

BACKGROUND OF THE INVENTION[0001]Passive oxide layers are inherent to all metal powders. In general, the presence of such oxides has an adverse effect on one or more of the properties of the products made from such powders.[0002]For example, due to the high melting point of tantalum, its purification method yields a metal powder. When exposed to air, tantalum oxidizes and forms an oxide layer, which protects it from further oxidation. In order to make metal parts, this powder must be consolidated to solid form. Due to the inherent stability of this oxide layer, when pressed and sintered into a powder metallurgy form, the oxygen is conserved, yielding a lower quality product. Therefore the oxygen removal becomes a primary objective for tantalum refining.[0003]The operation of oxygen removal is called deoxidation. There is quite a bit of art teaching various ways of removing oxygen. One way to avoid this oxygen is to electron beam melt the powder, vaporizing the oxygen, resulting in a...

AI Technical Summary

Problems solved by technology

In general, the presence of such oxides has an adverse effect on one or more of the properties of the products made from such powders.

However, since excess carbon is used for reduction, tantalum, carbides result as a contaminant.

Another potential contaminant, which may result during this process, is magnesium.

Other refractory metals such as molybdenum, hafnium, zirconium, and particularly tungsten are considered brittle, and therefore cannot plastically deform and adhere upon impact during cold spray.

Oxygen and carbon are notoriously deleterious to the ductility.

Since the cold-spray process requires metals powders as a raw material, it makes the use of high DBTT refractory metals prohibitive, with the exception of tantalum and niobium, which have lower DBTT.