Tungsten is a heavy, gray metal with bluish overtones

A thermal spray powder is formed as a mixture of tungsten carbide granules and chromium carbide granules. The tungsten carbide granules each consists essentially of tungsten carbide bonded with cobalt, and the chromium carbide granules each consists essentially of chromium carbide bonded with nickel-chromium alloy. The powder may be asmixed with self-fluxing alloy powder. The powder preferably is sprayed with a high velocity oxygen-fuel thermal spray gun.

Tungsten is a heavy, gray metal with bluish overtones. When mixed with black carbon, tungsten carbide is created.
The compound is made by heating pulverized tungsten with black carbon, when hydrogen is present. Temperatures range from 2,550 to 2,900 degrees F or 1,400 to 1,600 degrees C. A common method for making the compound was developed in the 1920s in Germany and involves mixing powered tungsten carbide with cobalt. This mixture is then made into the required shape and heated to 2,550 to 2,900 degrees F or 1,400 to 1,600 degrees C. This heat melts the tungsten carbide partially, working as a cement. These tungsten carbide-cobalt creations are known by the names Carboloy and hardmetal.

Wear resistance is a common requirement for thermal sprayed coatings, and carbide powders are frequently used, for example tungsten carbide. British patent specification No. 867,455 typifies cobalt bonded tungsten carbide powder admixed with a sprayweld self-fluxing powder for producing coatings. Often such coatings are subsequently fused. Self-fluxing alloys are nickel, cobalt or iron based alloys with chromium and with small amounts of boron, silicon and carbon which serve as fluxing agents and hardeners. Examples of self-fluxing alloys are disclosed in the aforementioned British patent specification and U.S. Pat. Nos. 3,743,533 and 4,064,608. Iron base alloys with molybdenum, boron and silicon are disclosed in U.S. Pat. No. 4,822,415.

The cobalt- tungsten carbide itself is also sprayed neat, i.e. without the self-fluxing ingredient, best results being with high velocity, particularly plasma spray or a high velocity oxygen-fuel (HVOF) gun or a detonation gun. The granules of a powder typically are formed of subparticles of tungsten carbide and cobalt, spray dried, sintered or fused, the result being crushed and classified into a powder of proper size for thermal spraying.

Another carbide is chromium carbide that is utilized for higher temperature applications. This carbide may be sprayed without any metal binder, but it usually is clad or bonded with nickel or nickel alloy, such as nickel-chromium alloy, such as described in U.S. Pat. Nos. 3,150,938 and 4,606,948.

Tungsten carbide manufacturer and chromium carbide have been combined together with nickel for the detonation process as taught in U.S. Pat. Nos. 3,071,489. In one aspect of this patent, the elemental ingredients are all mixed together, and then sintered and crushed into a powder. In another aspect, separate powders of tungsten carbide, chromium carbide and nickel are blended to form a powder mixture of the three ingredients. In this form there is a tendency for the carbide to lose carbon in the flame. The two carbides also have been combined together with cobalt (without nickel) in a powder formed by casting and crushing, or by sintering, as taught in U.S. Pat. No. 4,925,626. Cobalt does not have as high corrosion resistance as nickel.

The latter patent teaches a method for producing a coating material of WC-Co-Cr alloy for high velocity oxygen-fuel thermal spraying. A mixture is prepared of tungsten carbide, cobalt and chromium, the latter being in the form of chromium carbide. The mixture is alloyed by by spray drying followed by sintering and plasma densification.

U.S. Pat. No. 4,588,608 teaches a powder for the detonation process, in which the powder is a cast and crushed composition of tungsten carbides , chrominum and cobalt. Two proprietary coatings of this nature are LW-45 and LW-15 produced by Praxair, Inc., Danbury, Conn., by the detonation process. LW-45 nominally contains 8% cobalt 4% chromium and balance tungsten carbide. LW-15 nominally contains 84% tungsten, 8% cobalt, 3% chromium and 5% carbon. These coatings have been utilized in specified applications such as petrochemical gate valves.

The tungsten and carbon is made into a powder using a pulverizer. The materials are then placed into a crucible and heated using an arc of electricity. The two materials then combine creating the tungsten carbide.
A gray, inorganic material, tungsten carbide functions as a hardener in armor-piercing projectiles, the sharp edges of drills and saws, and cast iron. Besides industrial uses, it is also used to create jewelry due to its hardness and deduced risk of allergic reactions among those with sensitive skin, among other desirable properties.

An object of the present invention is to provide an improved powder of Tungsten Bar and chromium carbide for the thermal spray process. Another object is to provide improved corrosion resistance in wear resistant carbide coatings. Further objects are to provide improved impact and toughness in such coatings.

The foregoing and other objects are achieved by a thermal spray powder formed as a mixture of tungsten carbide granules and chromium carbide granules. The tungsten carbide granules each consist essentially of Tungsten Carbide Powder bonded with cobalt, and the chromium carbide granules each consist essentially of chromium carbide bonded with nickel-chromium alloy. The powder may be admixed with a self-fluxing alloy powder, advantageously iron based.

Objects are also achieved by a method of producing a carbide coating utilizing a thermal spray gun having a combustion chamber with an open channel for propelling combustion products into the ambient atmosphere at supersonic velocity. The method comprises preparing a substrate for receiving a thermal sprayed coating, feeding through the open channel a carbide powder, injecting into the chamber and combusting therein a combustible mixture of combustion gas and oxygen at a pressure in the chamber sufficient to produce a supersonic spray stream containing the powder issuing through the open channel, and directing the spray stream toward the substrate so as to produce a coating thereon. The carbide powder is formed as a mixture as set forth above.