DE3590390T1 - Process for applying hard coatings and the like to metals and the product obtained thereby - Google Patents

Description

The invention relates to the coating of metals (hereinafter referred to as substrates or substrate metals are) with coatings that form hard surfaces, chemically resistant coatings, etc.

Hard coatings are designed to have a combination of high performance properties such as friction, wear and tear Maintain corrosion resistance for cheaper metal components. Previous processes used in applying these coatings based on the surface treatment of metallic substrates by diffusion of carbon, Nitrogen, boron or silicon, so that the hard materials were formed directly on the substrate surface. Both Most newer techniques use a hard coat as the outer coating. Examples of such techniques are Gas phase deposition using chemical processes or CVD processes, PVD processes, laser fusion, sputtering, flame or Plasma spray and the coating gun. With the possible exception of CVD processes, these techniques are expensive and limited to the line of sight, resulting in different thickness and uneven coating especially at corners, openings and can lead to complex shapes.

The object of the invention is to provide an improved method for applying coatings of M ₁ X to substrate _{metals, where M 1 is} the metal whose compound is to be applied to the substrate, X is an element such as nitrogen, carbon, boron or silicon and η is a number which indicates the atomic ratio of X to M.

Coated substrate metals are also to be specified, the coatings M ₁ X given above being uniform and adhering to the substrate.

These and other objects and objects of the invention will become apparent from the following description and the accompanying one Claims.

According to the invention, an alloy or a physical metal mixture is provided, consisting of two metals M ₁ and M ₂ , which are selected according to the criteria given below. This alloy or mixture of metals is then melted to form a uniform melt which is applied to a metal substrate by dipping it into the melt. Alternatively, the metal mixture or alloy is reduced in a finely divided state and the finely divided metal is placed in a volatile solvent to form an emulsin which is applied to the metal substrate by spraying or brushing. The resulting coating is heated in a protective gas atmosphere in order to evaporate the volatile solvent and to melt the alloy or the metal mixture onto the substrate surface. (If physical mixtures of metals are employed, they are either converted into an alloy by melting, or they are alloyed or fused in situ as in the emulsion method outlined above.) In certain circumstances, e.g. B. the alloy melts at high temperature so that the substrate metal by melting an alloy coating

could be adversely affected, the alloy can be applied by plasma spraying.

The metals M ₁ and M ₂ are selected according to the following criteria: M. forms a heat-resistant compound with X (ie a nitride, a carbide, a boride or a silicide) when it is exposed to an atmosphere at a high temperature which is low Concentration of X or a dissociable molecule or compound of X contains. The stable compound that M- forms with X can be represented as M ₁ X, where η denotes the atomic ratio of X to M _1.

The metal M_ does not form a stable compound with X under these conditions and remains either completely or essentially completely in the metallic form. Furthermore, M ₂ is compatible with the substrate metal in that it is in an intermediate _{layer between the outer M 1} X layer (as a result of the

in

Reaction with X) and the substrate results, this intermediate _{layer serving to attach the M 1} X layer to the substrate

ι η

tie. Mutual diffusion of M ₂ and the substrate metal supports this binding effect.

It should be noted that M _{1 can be} a mixture or an alloy of two or more metals which _{meets the requirements for M 1} , and that M _{2 can} also be a mixture or an alloy of two or more metals which meets the requirements for M _2.

The coating so formed and applied is then preferred subjected to an annealing process. Annealing can be omitted if annealing takes place under operating conditions.

If a coating of suitable thickness is applied to the substrate alloy by the dip-coating process described or the emulsion process (in the latter case after the solvent has evaporated and the M ₁ M ~ alloy or the

Mixture has melted onto the substrate surface) or Applied by any other suitable method, the surface will be in a selectively reactive atmosphere suitably high temperature outsourced.

To form a nitride, carbide, boride or silicide layer on the substrate metal, a suitable, thermally dissociable Compound or a molecule of nitrogen, carbon, boron or silicon can be used. Examples of suitable ones gaseous media are given in the following Table I, which indicates the media, where X = nitrogen etc.

TABLE

Gaseous media for the formation of nitrides, carbides, borides and suicides

X Gaseous media

NN ₂ , NH ₃ or mixtures thereof

C methane, acetylene

B borane, diborane, boron halides

Si silane, trichlorosilane, tribromosilane, Silicon tetrachloride

If a very low partial pressure of the reactive species is required, this can be achieved with an inert gas, e.g. B. argon, be diluted. If the active species results from a gaseous reaction of two precursor species, the concentration may the active species can be controlled by adjusting the ratio of the precursor species.

This process results in a structure as shown in FIG. 1.

1 shows a cross section through a substrate alloy 10 which is covered with a laminar coating 11. The laminar coating 11 consists of a metallic intermediate _{layer 12 and an outer M 1} X layer 13. The rela-

i η

tive thicknesses of layers 12 and 13 are shown exaggerated. The substrate layer 10 is as thick as is necessary for the respective application.

The layers 12 and 13 together typically have a thickness of approx. 300-400 μm, the thickness of the layer 12 being approx. 250 pm and that of the layer 13 is approx. 150 pm. It should be noted that the layer 12 has a thickness sufficient for formation a firm connection to the substrate is sufficient, and that the thickness of the layer 13 is adapted to its intended use.

Figure 1 is a simplified representation of the coating and substrate. A more detailed illustration is shown in FIG. 1A, the substrate 10 and the outer layer MX corresponding to the description given for FIG. 1. However, a diffusion zone D is present, which can be an alloy of one or more substrate metals and the metal M ₂ or an interdiffusion layer resulting from a diffusion of substrate _{metal away from the substrate and from M 2} inward into the substrate. There is also an intermediate zone I, which can be a cermet which is formed as a composite layer _{from MX and M 2.}

The metals M and M ₂ are selected according to the desired application. The following Table II lists metals that are useful as M- and Table III lists metals that are useful as M ₂ . Not every metal in Table II can be used with every metal in Table III; in every M- / M ₂ ~ pair M ₂ must be nobler than M-. A white

The other factor is the intended use, e.g. B. whether a hard surface or a surface resistant to aqueous environments, a surface acting as a lubricant, etc. is desired. The nature of the substrate should also be taken into account. It can be seen that some metals are listed in both tables; that is, a metal M- listed in Table II can be used with a less noble metal M. from Table III than M ₂ (the more noble metal).

TABLE

Actinium Aluminum Barium Beryllium Calcium Cer

Chromium Dysprosium Erbium Europium Gadolinium Hafnium Holmium Lanthanum Lithium Magnesium Molybdenum

Neodymium niobium

Praseodymium Samarium Scandium S i1i ζ i um Tantalum Terbium Thorium Thulium Titanium Tungsten Vanadium Ytterbium Yttrium Zirconium

TABLE III

(M ₂ )

Cobalt copper gold

Iridium iron

Manganese Molybdenum Nickel Osmium

Palladium Platinum Rhenium Rhodium Rubidium Ruthenium silver tin

zinc

It should be noted that two or more metals from Table II and two or more metals from Table III can be used to form the coating alloy or the coating mixture. Examples of suitable M ../ M ₂ metal pairs, including mixtures of two or more M .. metals and two or more M ₂ metals, are listed in Table IV.

TABLE

IV

Hi ' -2 Th Ü2 Ti Ni Th Ni Ti Fe Th Fe Ti Co Th Co Ti Cu «9 * Ti Pd Ti + Nb Ni Th Ti + Zr Co Th Cu Ti + Zr Fe S * Al Ti + Zr Cu Al Zr Fe Sc Zr. Co Sc Cu Zr Cu Fe Zr Pd Sc Zr Pt Sc Pd Zr Rh Y Ru Zr + Y Ni Y Al Zr + Y Co ** ·. Co Zr + Y Fe Y Zr + Y Pd Y Cu Fe Zr + Nb Ni Y Zr + Hf .. Ni Y Ni Hf Ni Y Pd Hf Cu Ru Si Nb Si Co Si Fe Si Mon Si "Si Si Pd Si Pt Cr Ni Cr Pd Si Ru

Of course, not every metal pair is suitable for every purpose. If z. B. M silicon, the coating tends to to brittleness; some pairs are better suited for hardship, others for use as heat barriers, still others for the Oxidation and corrosion resistance etc.

Examples of eutectic alloys are given in Table V. It should be noted that not all of the alloys listed can be used on all substrates. In some cases the melting points are approximate. The numbers indicate the approximate mass percentage of M ₂ .

TABLE V

Ti - 28.5 Ni 942

Ti - 32 Fe 1085

Ti - 28 Co 1025

Ti - 50 Cu 955

Ti - 72 Cu 885 Ti - 48 Pd * '1080

Zr-17 Ni 960

Zr - 27 Ni 1010

Zr - 16 Fe 934 Zr - 27 Co ** 1061

Zr- 54 Cu 885

Zr- 27 Pd 1030

Zr - 37 Pt 1185

Zr - 25 Rh 1065

Hf - 72 Ni 1130

Hf - 38 Cu 970

Th - 36 Ni. 1037

Th- 17 Fe * 875

Th - 30 Co Th - 22, , 5 Cu Th - 75 Al Sc - 45 Al Sc - 77 Cu Sc - 24 Fe Sc - 22 Pd Sc - 17th Ru Y - 93 Al Y -19 Al Y - V 5 Al Y .- 28 Co Y - 88 Cu Y - 66 Cu Y - 50 Cu Y - 27 Cu Y - 25th Fe Y - 47 Ni Y - 25th Ni Y - 34 Pd Y - 28 Pd Y - 17th Ru Nb ι- 76 , 5 Ni Nb - 48 _f 4 Ni Si - 88 _f 3 Al Si - 37 _} B Co Si - 84 Cu Si - 42 Fe Si - 12 Mon Si - 62 Ni Si - 74 Pd Si - 77 Pt

975

880

632 1150

875

910 1000 1100

640 1100

960

725

890

840

830

760

900

950

802

903

907 1080 1270 1175

577 1259

802 1200 1410

964

870

979

Table VA identifies certain tertiary alloys which are useful in practicing the invention.

TABLE VA

55.18 Ti - 23.13 Nb - 21.69 Ni 40.38 Ti - 43.52 Zr - 16.10 Ni 40.07 Ti - 44.35 Zr - 15.58 Co 25.37 Ti - 65.69 Zr - 11.94 Pe 17.36 Ti - 38.01 Zr - 44.63 Cu 69.65 Zr - 16.07 Y - 14.26 Ni 55.96 Zr - 23.34 Y - 20.70 Ni 43.0β Zr - 40.98 Y - 15.94 Co 56.76 Zr - 32.43 Y - 10.81 Pe 47.89 Zr - 34.39 Y - 17.72 Pd 56.68 Zr - 22.35 Nb - 20.97 Ni 49.33 Zr - 32.43 Hf - 43.94 Ni 24.20 Zr - 48.51 Hf - 27.29 Ni

Yttrium, calcium and magnesium are _{particularly advantageous in zirconium precious metal (M 2} ) alloys because they stabilize zirconium in the cubic form. Examples of such ternary alloys are given below:

Zr Y Ca Ma Ni

76 8 16

77. '■ · "7 16
79. 5 16

Table VI shows examples of metal substrates to which the metal pairs can be deposited.

TABLE VI Superalloys

Nickel-based cast alloy, ζ. B. IN 738 cobalt-based cast alloy, e.g. B. MAR-M509 Nickel-based wrought alloy, e.g. B. Rene 95 wrought cobalt-based alloy, e.g. B. Haynes alloy No. 188

Wrought iron-based alloy, e.g. B. Discaloy Hastalloy X
RSR 185
Incoloy 901

Coated superalloys (corrosion-resistant coated) Superalloys coated with Co (or Ni) -Cr-Al-Y alloy, e.g. B. 15-25% Cr, 10-15% Al, 0.5% Y, the remainder Co or Ni

Steels

Tool steels (forged steel, cast steel or powder metallurgical steel)
E.g. AISIM2; AISIW1

Stainless steels

Austenitic steel 304
Ferrite steel 430
Martensitic steel 410

Carbon steels
AISI 1018

Alloy steels
AISI 4140
Maraging 250

Cast iron

Gray cast iron, spheroidal graphite cast iron, malleable cast iron, alloyed cast iron

UNSF 10009

Non-ferrous metals

Titanium and titanium alloys, e.g. B. ASTM Grade 1; T1-6A1-4V

Nickel and nickel alloys, e.g. B. Nickel 200, Monel 400 Cobalt

Copper and its alloys, e.g. B. C10100; C 17200; C26000; C 95200

Refractory metals and alloys Molybdenum alloys, e.g. B. TZM
Niobium alloys, e.g. B. FS-85
Tantalum alloys, e.g. B. T-111
Tungsten alloys, ζ. B. W-Mo alloys

Cemented carbides

Ni and cobalt bonded carbides, e.g. B. WC-3 to 25 Co steel bonded carbides, e.g. B. 40-55 vol .-% TiC, remainder steel; 10-20% TiC - the rest steel

The ratio of M ₁ to M ₂ is very different and depends on factors such as the choice of M ₁ and M ₂ , the nature of the substrate metal, the selected reactive gaseous species, the transition temperature, the intended use of the coating (e.g. whether it is . to serve as a thermal barrier or as a hardened surface), etc.

The dip coating method is preferred. It's easy to do, and the alloy melt removes surface oxides (which can cause chipping). In this process, a M ../ M ₂ alloy melt is produced and the substrate alloy is immersed in a bath of the coating alloy. The temperature of the alloy and the dwell time,

while the substrate is held in the alloy melt, determine the thickness and smoothness of the coating. When making an aerodynamic surface or cutting edge, a smoother surface is needed than for some other purposes. The thickness of the applied coating can be between a fraction of 1 μm and several mm. A coating with a thickness of approx. 300-400 μm is preferably applied if a heat barrier is to be provided. A hard surface doesn't need to be that thick. Of course, the coating thickness is selected according to the requirements of a special application.

The emulsion melting process offers the advantage that the coating alloy or the coating metal mixture is diluted and therefore the thickness of the coating applied to the substrate can be more easily controlled. Furthermore, complex shapes can also be coated and the process is repeatable so that a coating of a desired thickness is built up. Typically the emulsion melting process is used as follows: A powdery alloy of M ₁ and M2 is mixed with a mineral spirits and an organic binder such as Nicrobraz 500 (Well Colmonoy Corp.) and MPA-60 (Baker Caster Oil Co.). Typical proportions of the emulsion are: coating alloy 45% by weight, mineral spirits 10% by weight and organic binder 45% by weight. This mixture is then z. B. ground in a ceramic ball mill using aluminum oxide balls. After separating the resulting emulsion from the alumina spheres, the mixture is applied to the substrate surface (while it is kept agitated to ensure even distribution of the alloy particles in the liquid medium) and the solvent is e.g. B. evaporated in air at ambient temperature or slightly higher temperature. The residue consisting of alloy and binder is then melted onto the surface by being placed in a protective gas atmosphere, e.g. B. in argon, which is used for oxygen gettering

hot calcium chips was passed to a suitable temperature is heated. The binder decomposes, and so do the decomposition products are evaporated.

When the alloy of M .. and M2 has such a high melting point has that this either exceeds the melting point of the substrate or comes very close to this, the alloy can be applied by sputtering, vapor deposition or some other method will.

It is advantageous to use M ₁ and M ₂ in the form of an alloy which is either a eutectic or almost eutectic mixture. This offers the advantage that a coating of a definite predictable composition is applied evenly. Furthermore, eutectic and near-eutectic mixtures have lower melting points than non-eutectic mixtures. Hence, refractory alloys are less likely than refractory alloys to adversely affect the substrate metal and are easier to sinter than refractory alloys.

The following examples serve to illustrate the invention.

example 1

The substrate metal was tool steel in the form of a rod. The coating alloy was a eutectic alloy containing 71.5% Ti and 28.5% Ni. This eutectic has a melting point of 942 ⁰ C. The rod was in this alloy at 1000 ^e C for a period of 10 s immersed, removed and 5 annealed at 800 ° C. It was then stored in oxygen-free nitrogen ^{at 800 ° C. for 15 h.} The nitrogen was slowly passed over the rod at atmospheric pressure. The resulting coating was continuous and adherent. The composition of the titanium nitride TiN depends on the temperature and the nitrogen pressure.

Example 2

Example 1 was repeated using mild carbon steel as the substrate. It became a titanium nitride layer upset.

The coatings of Examples 1 and 2 are useful because the surface treated is hard. This is special advantageous for soft unalloyed steel, since it is inexpensive, but soft. So there is the possibility obtain an inexpensive metal with a hard surface.

Example 3

It was as in Example 1, but at a temperature of 650 ° C proceeded. The coating with a thickness of 2 ι was lighter than the coating of Example 1.

Darker colors obtained at higher temperatures indicate a stoichiometric composition of TiN.

Similar coatings have been applied to stainless steel.

Example 4

A eutectic alloy with 83% Zr and 17% Ni (melting point 961 ^° C.) was used. The substrate metal (tool steel) is dip coated at 1000 ⁰ C for 3 h at 1000 ⁰ C

rf -

annealed and as paged in Examples 1 and 3 in nitrogen at 800 ⁰ C. A uniform, adherent coating of 2-3 µm resulted.

Example 5

There was a eutectic alloy of 48% Zr and 52% of Cu having a melting point of 885 ⁰ C. Tool steel was dipped for 10 s in the alloy at 1000 ° C, removed and annealed for 5 hours at 1000 ⁰ C. It was then outsourced in nitrogen at a pressure of 0.98 bar for 50 h at 800 ⁰ C. A uniform adhesive coating resulted.

An advantage of copper as the metal M ₂ is that it is a good conductor of heat, which is useful for dissipating heat (into the tool body) during cutting operations.

Example 6

A eutectic alloy with 77% Ti and 23% Cu with a melting point of 875 ^° C. was used. Hot dipping was carried out at 1027 ⁰ C for 10 s; Annealing took place at 900 ^° C. for 5 h; Aging in N2 took place at 900 ^° C. for 100 h. An adherent, continuous coating resulted. The substrate metal was high speed steel.

Example 7

Tool steel was coated with a Ti-Ni alloy and annealed as in Example 3. The reactive gas was methane, that can be used with or without an inert gas diluent such as argon or helium. The coated steel rod was in methane

- * β

aged at 1000 ^° C. for 20 h. A hard, adherent titanium carbide coating resulted.

Example 8

The method according to Example 7 can be carried out using BH ₃ as the reactive gas at a temperature above 700 ^° C., e.g. B.> 700 ⁰ C to 1000 ⁰ C, be repeated for 10-20 h. A hard and adhesive titanium boride coating is formed in the process.

Example 9

The procedure of Example 7 was repeated using silane SiH- as the reactive gas, with or without a diluting inert gas such as argon or helium. The temperature and aging time can> 700 ⁰ C to 1000 ° C and amount to 10-20 h. A hard and adhesive titanium silicide coating was formed.

Among other things, the following considerations must be observed:

The metal M2 should be compatible with the substrate. It should e.g. B. do not form a brittle intermetallic compound with metals of the substrate. It preferably does not change the mechanical properties of the substrate noticeably and has a wide range of solubility in the solid state in the substrate. Furthermore, it preferably forms a low-melting eutectic with M-. It should also not form a highly stable carbide, nitride, boride or silicide. If z. B. M _{1 is to be converted} into a nitride, M _{2 should} not form a stable nitride under the conditions that are used to form the M-nitride.

In the hot dipping process for applying an M / M ₂ alloy, uneven application to the surface can be avoided or reduced by rapid turning and / or wiping.

The annealing after the application of the alloy or the mixture of M and M ₂ should take place in order to achieve a good bond between the alloy and the substrate.

The conversion of the alloy coating to the end product is preferably carried out by aging in a slowly flowing stream of reaction gas at a temperature and a pressure which are """sufficient to convert the reactive gaseous molecule or the compound with M ₁ , but which are not so high that a reaction _{takes place with M 2.} It is also advantageous to use a temperature slightly above the melting point of the coating alloy, for example slightly above the eutectic melting point of the alloy The presence of a liquid phase supports the migration of M- to the surface and displacing M ₂ in the outer layer.

When the temperature is below the melting point of the coating alloy, and when the compound formed by M and the reactive gas grows rapidly, M ₂ becomes trapped in the growing compound, thereby binding the particles of MX. In this case, a cermet is formed, which can offer advantages, e.g. B. a W or Nb carbide bound by cobalt or nickel.

It can thus be seen that a new and advantageous method for applying an M-X coating to a metal substrate as well as new and advantageous products are indicated.

Claims (23)

Telephone: (0 89) 4 70 60 55/56 Telex: 5 23016 Telegram / cable: Zetapatent® Munich PO Box SO 13 69 Lucile-Grahn-Straße 38 D-8000 Munich 80 Hans-Jürgen Müller Gerhard D. Schupfner Hans-Peter Gauger Patentanwälte European Patent Attorneys Mandataires en brevets europeens Process for applying hard coatings and the like to metals and resulting product patent claims 1. A method for coating a metal substrate with a Protective coating, marked by (a) Provision of a substrate metal to be coated, (b) Production of an alloy or a mixture of at least one metal M and at least one further metal M ₂ , which are selected according to the following criteria: (1) MJ is reactive with a reactive gaseous species of an element X (where X is nitrogen, carbon, boron, or silicon) to form a stable compound of M ₁ and X at a selected temperature and pressure of such reactive species, (2) M ₂ does not form a stable bond with X under such conditions and bonds with the substrate upon heat treatment of the coated material; (c) Applying such an alloy or such a mixture to a surface of the substrate with formation a coating and (d) bringing about a selective conversion of M- with the gaseous species at high temperature under conditions that lead to the formation of a compound of M- and X. and prevent or minimize the formation of a connection between M n and X. 2. The method according to claim 1, characterized in that that subsequent to step (c) the coating is annealed, 3. The method according to claim 1, characterized in that that the substrate metal is an iron alloy. 4. The method according to claim 1, characterized in that the substrate metal is a non-ferrous alloy. 5. The method according to claim 1, characterized in ei c h net, that X is nitrogen. 6. The method according to claim 1, characterized in that X is carbon. 7. The method according to claim 1, characterized in that X is boron. 8. The method according to claim 1, characterized in that X is silicon. 9. The method according to claim 1, characterized in that M ₁ is selected from the lanthanide metals. 10. The method according to claim 1, characterized in that M. is selected from the actinide metals. 11. The method according to claim 1, characterized in that M _{2 is} nickel, cobalt, aluminum, yttrium, chromium or iron. 12. The method according to claim 1, characterized in that M _{1 is} titanium and M _{2 is} cobalt or nickel. 13. The method according to claim 1, characterized in that M _{1 is selected} from groups IHb, IVb and Vb of the Periodic Table of the Elements. 14. The method according to claim 12, characterized in that that X is nitrogen. 15. The method according to claim 12, characterized in that that X is carbon. 16. A coated metal article, characterized by (a) a metal substrate and (B) a protective coating adhering to at least one surface of the metal substrate, which consists of an outer layer of a compound M ₁ X, where X = nitrogen, carbon, boron or silicon and η denotes the atomic ratio of X to M .., and an inner layer Layer consists of at least one metal M2 connected to the substrate, the metals M- and M2 being selected according to the following criteria: (1) M- is reactive with a reactive gaseous species of an element X (where X is nitrogen, carbon, boron or silicon) to form a stable compound of M ₁ and X at a selected temperature and pressure of this reactive species, (2) M ₂ does not form a stable bond with X under such conditions and bonds the coating to the substrate. 17. Coated metal object according to claim 16, characterized in that that the metal substrate is an iron alloy. 18. Coated metal object according to claim 16, characterized in that that the metal substrate is a non-ferrous alloy. 19. Coated metal object according to claim 16, characterized in that X is nitrogen. 20. Coated metal object according to claim 16, characterized in that that X is carbon. 21. Coated metal article according to claim 16, characterized, ; that X is boron. i 22. Coated metal object according to claim 16, characterized in that that X is silicon. 23. Coated metal object according to claim 16, characterized in that that M. from groups IHb, IVb and Vb of the periodic table the item is selected.