Prodn. of multilayered nitrated or nitride coating by reactive plasma spraying - in which successive layers are sprayed onto base layer with step increases of partial pressure of nitrogen in the plasma jet

摘要

A multilayered nitrated or nitride coating is produced by reactive plasma spraying, with supply of a reactive metal powder. It includes the following process steps: (a) a reactive metal base layer at least 30 micron thick is first applied to a preheated substrate with the use of a plasma gas free from reactive gases in an inert gas atmosphere in the spraying chamber, at a pressure of at least 30 mbar; and (b) several individual layers, each at least 30 micron thick, are then successively sprayed onto the base layer, with the partial pressure of nitrogen in the plasma jet (and thus in the vicinity of spray particles) increased stepwise from layer to layer. The partial pressure of nitrogen in the plasma jet is stepwise increased in such a way that the last layer consists of pure reactive metal nitride. The pressure in the spraying chamber is increased stepwise by appropriate increases in the nitrogen supply. Liquid nitrogen is used to cool at least temporarily the coatings produced. USE/ADVANTAGE - For production of multilayered coatings for various purposes (e.g. for sliding bearings).