US2792657A - Gun barrel coated with tantalum - Google Patents

Description

E. E. SLOWTER Filed May 16, 1946 E liwurd E. EIlEIW ILET XMWMMW Illll' lltlilllhflll I IWIILkI May 21, 1957 GUN BARREL COATED WITH TANTALUM GUN BARREL COATED WITH TANTALUM Edward E. Slowter, Columbus, Ohio, assignor, by mesne assignments, to Battelle Development Corporation, Columbus, Ohio, a corporation of Delaware Application May 16, 1946, Serial No. 670,132

2 Claims. (CI. 42-76) This invention relates to methods for protecting surfaces exposed to high frictional heat and to chemical erosion from hot gases under great pressures, and to articles thus protected. More particularly, the invention relates to gun barrels having improved erosion-resistant properties produced by the application of a coating of a nonferrous metal to the bore surface thereof.

Many methods have been previously employed for treatment of the bore surface of firearm barrels in attempts to improve the erosion resistance of the bore surface and, hence, the life of the gun barrel. Most of these methods have been directed to the improvement of erosion resistance of barrel steel itself by utilization of special steels, heat treatments, and surface treatments. While some advantages have been obtained through such procedures, they have not solved the problem of bore erosion. example, an electrolytically deposited layer of pure iron has been attempted as a solution to this problem, but does not provide sufi-lcient protection.

An object of this invention is to provide an 1 Side having a surface which has greatly improved resistance to frictional erosion as well as to chemical erosion due to hot gases under great pressure.

Another object of this invention is to provide gun barrels having more surfaces thereof treated to withstand chemical erosion and high temperature effects.

A further object of this invention is to provide improved gun barrels having a coating of tantalum applied to the bore surface by a thermal diffusion process.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing wherein a longitudinal sectional view of a firearm barrel shows a coating of tantalum thermally diffused over the surface of the bore.

Before referring to the drawing, it is to be understood that the terms used herein are for purposes of description and not of limitation. For example, gun barrel relates to any body having for its purpose the directing of a projectile from a firearm, regardless of size.

In the accompanying drawing, the particular embodiment of the invention illustrated thereby represents a gun barrel 1 having a bore surface 2. The bore is preferably rifled by the provision of riding grooves 3-3. Over the interior bore surface a layer 4, a high-melting protective metal of the group consisting of tantalum, molybdenum, and tungsten, is applied by any suitable method. While such a layer is shown as extending the entire length of the barrel, it will be apparent that improved erosion resistance could nevertheless be obtained if the layer 4 covered merely the portion of the bore adjacent the chamber of the barrel, since the most severe erosion conditions generally occur at this point.

Although several methods are available for applying the protective metallic layer 4 to the bore surface 2, or similar surfaces, it is preferable to employ thermal deposition or diffusion methods in the application of such layers. A preferred embodiment of this invention utilizes For 2,792,657 Patented May 21, 1957 the thermal deposition of tantalum on the bore surface of gun barrels by the diffusion process of B. W. Gonser and E. E. Slowter as disclosed and claimed in the copending application for United States Letters Patent Serial No. 629,630, filed November 19, 1945, now Patent Number 2,604,395.

in general, one particular application of this method comprises heating the surface to be coated and contacting said surface with a mixture of hydrogen and a tantalum halide under such conditions as to cause deposition of substantially pure tantalum upon the heated surface. The hydrogen gas is passed through various drying means to free it from water vapor and other deleterious gases before it is directed into a furnace containing a tantalum halide such as tantalum chloride. The furnace containing the tantalum halide is heated above the boiling point of the tantalum halide employed which in no case need exceed 320 C., and is maintained below the decomposition temperature of this same halide when in contact with hydrogen, which is approximately 600 C. The rate at which the hydrogen gas is passed through the furnace containing the tantalum halide is preferably controlled so as to provide a. ratio of about l0 atoms of hydrogen to 1 atom of tantalum in the gas expelled therefrom and passed into a second furnace in which is positioned the gun barrel to be coated. This excess amount of hydrogen is apparently necessary for the successful completion of the process and is just equal to twice the theoretical amount required to react with the halide in the tantalum salt.

The mixture of hydrogen and tantalum halide gas is passed through the bore of the gun barrel to be plated while the barrel is heated to such temperatures as to cause rapid decomposition of the tantalum halide when in contact with the heated metal surface. While the temperature of the bore surface may range between 750 to 1300 C., optimum results have been obtained at temperatures between 850 to 1150 C. When sufficient tantalum has been deposited upon the bore surface to be coated, the heat is turned off from the first furnace containing the tantalum halide and the flow of gas therefrom is stopped before the removal of the treated gun barrel from the second furnace.

One remarkable feature of this particular method of applying tantalum to gun barrels is the fact that the tantalum apparently diffuses into the surface layer of the bore so as to produce an iron-tantalum alloy. For this reason, it is impossible to measure the exact thickness of the tantalum layer applied, although estimates thereof can be made. It is believed that the tenacity with which the tantalum plate adheres to the basis metal is due, at least in part, to the diffusion of tantalum into the surface of the basis metal. The strong adherence of the plate to the basis metal makes these tantalum coatings especially desirable for gun barrels.

A steel test gun barrel was coated in the manner above described with a layer of tantalum approximately .001 inch thick while the bore surfaces thereof were heated to a temperature of about 930 C. After firing 400 rounds from this barrel, only .008 gram of the barrel had been removed due to erosion and other factors, and no heat checks were apparent. Gun barrels of similar composition to that coated with tantalum, but having no coating upon the bore surfaces thereof, lost between .15 and .16 gram in weight during the firing of 400 rounds under similar conditions, and after the firing of 25 rounds heat checks appeared in every case. A molybdenumcoated barrel lost only .097 gram after 400 rounds of ammunition had been fired therefrom and did not show heat checks until rounds had been fired. Tungsten coatings have properties very similar to tantalum and molybdenum and may be deposited thermally as above described. However, an adherent coating of tungsten to steel is more difiicult to obtain than in the case of tantalum and molybdenum and its usefulness, therefore, is somewhat limited.

It is apparent from the foregoing description that this invention relates to methods of protecting the internal surfaces of gun barrels from frictional wear and chemical erosion comprising covering such surfaces with a layer of metal of the group consisting of tantalum, molybdenum, and tungsten. Gun barrels produced in accordance with this invention last longer and retain their accuracy longer than untreated barrels.

Variations and modifications of this invention as set forth in the above description will become apparent to those skilled in the art. For example, a molybdenum, tantalum, or tungsten tube may be produced by depositing a very thick layer of the given metal on a thin sleeve of steel and subsequently removing the steel by solution in strong acid. Such a tube of tantalum, molybdenum, or tungsten may be inserted into the gun barrel as means of protection rather than coating directly upon the bore surface itself.

What is claimed is:

1. A gun barrel comprising a basis metal of steel having a bore, the metal adjacent said bore being composed of an alloy of tantalum and the basis metal, and a layer of tantalum covering said alloy to define the surface of said bore.

2. A steel gun barrel having a bore surface alloyed with tantalum and an adherent layer of tantalum coating said alloyed surface.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. 2. A STEEL GUN BARREL HAVING A BORE SURFACE ALLOYED WITH TANTALUM AND AN ADHERENT LAYER OF TANTALUM COATING SAID ALLOYED SURFACE.

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