Coated Metal Substrates That Are Susceptible to Wear, and Method for the Manufacture Thereof

Abstract

The use of tungsten, molybdenum, tungsten or molybdenum alloys for coating metal substrates using a single-wire arc spraying method results in coatings that are characterized in particular by an increased Vickers hardness (VH).

Claims

1.-7. (canceled)

8. A metal substrate whose surface is entirely or partially coated with tungsten, molybdenum, tungsten alloys or molybdenum alloys applied by arc-spraying.

9. The metal substrate according to claim 8, wherein the coated surface is an inner surface of a filling chamber or of a filling chamber insert of a pressure die casting machine.

10. A pressure die casting machine, comprising the filling chamber or the filling chamber insert according to claim 9.

11. The pressure die casting machine according to claim 10, wherein it is an aluminum pressure die casting machine.

12. A method for coating a surface of a metal substrate, comprising: arc-spraying tungsten, molybdenum, a tungsten alloy or a molybdenum alloy onto the surface.

13. (canceled)

14. The method according to claim 12, wherein the arc spraying is a single-wire method.

15. The method according to claim 12, wherein air is used as the atomizing gas.

16. The method according to claim 12, wherein the tungsten alloy is an alloy containing more than 50% by weight of tungsten.

17. The method according to claim 12, wherein the tungsten alloy is a WNiFe alloy with more than 50% by weight of tungsten or a WMoNiFe alloy in which the sum of the portions of tungsten and molybdenum amounts to more than 50% by weight.

18. The method according to claim 12, wherein the molybdenum alloy is TZM molybdenum, consisting of 0.5% by weight of titanium, 0.08% by weight of zirconium, 0.01% to 0.04% by weight of carbon and the remainder consists of 100% by weight of molybdenum.

19. The method according to claim 12, wherein the metal substrate comprises areas of a metal casting system that are susceptible to wear, or surfaces of forming tools, pistons, camshafts or shunts.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0040] The following is shown, at times schematically:

[0041] FIG. 1 is the spraying head of a single-wire device in schematic view.

DETAILED DESCRIPTION

[0042] Below, the preferred coating or spraying method will be described in greater detail by way of an example making reference to FIG. 1, without restricting the subject matter of the present invention in this process. Here, FIG. 1 shows the spraying head of a single-wire device in a schematic view. Here, the electrode 4 (tungsten electrode) is installed so as to be rotatable around the wire.

[0043] In the two-wire method as shown in FIG. 1, the arc is ignited between two wires, and in the single-wire method, the arc is ignited between the tungsten electrode 1 and the spraying wire 7. Here, the emitted electrons, that is to say, the arc, first pass through the shielding gas 2, in this case argon or an argon-hydrogen mixture, and subsequently through the gas mixture consisting of shielding gas 2 and atomizing gas 5 consisting of N.sub.2 or air, thereby ionizing the gas into plasma 4 and heating it to approximately 15,000° C. The plasma 4 consists of a gas mixture consisting of shielding gas 1, in other words, argon or argon/hydrogen (Ar/ArH.sub.2) together with atomizing gas 3 [sic, 5]. Exclusively shielding gas 2 remains flowing around the electrode 1, thus shielding it. In this process, the arc 4 melts the spraying wire 7 before the atomizing gas 5 atomizes the melted droplets of the spraying wire 7 at a very high pressure or at a very high speed. The atomized spraying wire with atomizing gas and shielding gas is designated by the reference numeral 8. The atomizing gas stream does not have to flow annularly around the shielding gas 2 as is the case with plasm welding, but rather, it can also be made to flow in through nozzles. In this case, the atomizing gas nozzle 6 shown in FIG. 1 would be eliminated and replaced by individual nozzles.

[0044] The spatial separation between the electrode 1 and the wire 7, whereby the electrode 1 can rotate around the wire 7, makes it possible to use less expensive nitrogen gas instead of noble gases. In this manner, an increase in hardness to approximately 600 HV can be attained in comparison to approximately 300 HV in the case of the starting material. It has been found that, with air as the atomizing gas 5, an additional and substantial increase in hardness to approximately 900 HV can be attained. Currents preferably in the range from 60 A to 159 A are used for single-wire spraying with wire made of tungsten or tungsten alloys.

[0045] The present invention especially translates into in a longer service life for the highly stressed filling chambers and thus also into a longer service life of a corresponding pressure die casting system, and the invention encompasses a coated filling chamber or a corresponding insert, a method for coating these components, the correspondingly equipped pressure die casting system and the use of tungsten or tungsten alloys for (entirely or partially) coating the filling chamber or the filling chamber insert. These statements apply correspondingly when it comes to metal substrates that are coated according to the invention.

[0046] In this context, the following must be pointed out:

[0047] tungsten/tungsten alloys are less brittle in comparison to molybdenum (Mo) or a molybdenum alloy and they are also less susceptible to oxidation. The thermal spraying that is preferred according to the invention makes it possible not only to protect an insert but also the entire filling chamber.

[0048] Owing to the spraying, the materials harden a great deal, as a result of which there is not only an improvement in terms of the dissolution caused by the liquid melt, but also at the same time, an improvement against mechanical wear and tear. Thus, the hardness of tungsten or of a typical tungsten alloy increases, for example, from 250-300 HV to more than 800 HV (e.g. 900 HV) for a sprayed-on coating (HV=Vickers hardness). Such hardening is remarkable and it does not occur, for example, with the iron or nickel alloys otherwise used. The method of thermal spraying also permits very simple repair of worn-out inserts of filling chambers. In this context, they do not need to have originally been provided with a coating.

[0049] Moreover, the following embodiments and application forms have been found which are likewise encompassed by the present invention.

[0050] Aside from the thermal spraying, the welding or the welding-on of a tungsten/tungsten alloy onto the substrate that is to be protected also brings about an improvement of the thermal, chemical and mechanical properties of the (coated) surface. The hardness of the welded-on tungsten/tungsten alloy is likewise markedly improved in comparison to the standard value, but generally does not reach the values that can be attained by thermal spraying. The welding-on is carried out with conventional welding processes such as TIG, MIG and MAG welding.

[0051] Thermal spraying or welding onto a substrate surface—as described for tungsten/tungsten alloys—also achieves a marked improvement of the thermal, chemical and mechanical properties (hardness) in the case of molybdenum or molybdenum alloys. For this reason, the coating of metal substrate surfaces by means of thermal spraying or welding-on of molybdenum or molybdenum alloys of the type described, for example, in European patent application EP 3 184 203 A1 (see paragraphs [0009] through [0012] there) and to which reference is hereby made explicitly for purposes of the disclosure, is likewise encompassed by the present invention for the purposes according to the invention.

[0052] Finally, the application according to the invention of tungsten/tungsten alloys or molybdenum of molybdenum alloys, whereby tungsten/tungsten alloys are preferred, is not limited only to the coating of the inner surfaces of filling chambers and filling chamber inserts of pressure die casting machines, but rather relates to all areas that are susceptible to wear and tear during casting, for example, of aluminum, zinc and copper as well as of the corresponding alloys. Therefore, the use of the coatings applied according to the invention encompasses all of the claimed components during the casting process and their use likewise encompasses all other conceivable wear and tear applications such as, for example, coatings for forming tools for aluminum, copper and steel, for camshafts, shunts, pistons and comparable areas of application. As set forth in the present invention, these are examples of metal substrates that are susceptible to wear.

LIST OF REFERENCE NUMERALS

[0053] 1 cathode (tungsten electrode)
2 shielding gas argon or argon/hydrogen
3 shielding gas nozzle
4 arc (plasma consisting of shielding gas Ar/ArH.sub.2)
5 atomizing gas (N.sub.2 or air)
6 atomizing gas nozzle
7 spraying wire
8 atomized spraying wire (with atomizing gas and shielding gas)