Reactor design for chemical vapor deposition of tungsten carbide coatings

Abstract

A chemical vapor deposition (CVD) technique has been developed to deposit hard tungsten carbide coatings at low temperatures onto a variety of metal substrates by hydrogen reduction of tungsten hexafluoride (WF 6) in the presence of dimethyl ether (DME). These coatings exhibit excellent erosion and wear-resistance properties when deposited onto parts with uniform composition and thickness. They were deposited onto three-dimensional parts with uniform chemical composition by carefully controlling the deposition temperature and reagent partial pressures, but attempts to deposit them with uniform thickness and properties in a conventional tubular CVD reactor were not successful. The non-uniform deposition of these coatings had been thought to be caused by poor distribution of gas flow and temperature in the reactor. Therefore, a program was undertaken to develop a pilot-scale CVD reactor to deposit these coatings with uniform thickness and properties. The program involved devising a method to control fluid flow and temperature profiles in the reactor by iterative interaction between computerized flow and temperature simulation and experimentation. This led to the development of specially designed reactor internals to deposit coatings with uniform thickness and properties. This paper discusses efforts involved in developing a reactor design to deposit tungsten carbide coatings with uniform thickness and properties.