Plasma Spraying

Tungsten layers can be sprayed with suitable guns on different base materials. Easily flowing tungsten powder is used as spraying material Ar or Ar-N2 mixtures are preferred as protective atmosphere in closed chambers. Besides coatings, tungsten parts can be produced by spraying tungsten layers on an adequately formed nucleus until the desired thickness is reached.

One may distinguish between three basic types of substrates:

Expendable substrates are removed after spraying by selective chemical etching, melting, etc;

Reusable substrates are used for mass production;

Permanent substrates become an integral part of the article.

Density ranges from 50—95% of the theoretical value. Higher density is attained by uniform substrate temperature and Iow deposition rate. Density and strength might be increased by post-sinterning in hydrogen. Low-pressure plasma spraying is mainly used for producing intricate shapes, which otherwise cannot be manufactured.