DE1521187B2 - Process for coating a metallic object by diffusion and diffusion coating packing for carrying out the process - Google Patents

Description

The invention relates to a method for coating a metallic object by diffusion, in which the article in a non-oxidizing atmosphere in a powdery package is heated, which contains the metallic material to be diffused and a carrier to the To effect transfer of the metallic material from the package to the surface of the article.

The invention also relates to a diffusion packing for carrying out this method, which is to be diffused Metal and a heat-volatile carrier to remove the metal from the pack to promote the subject.

The invention is based on the object of a too rapid transition of the metal to be diffused from the pack into the surface of the item to be coated. The solution this object arises from the above claims, which are not derived from the prior art can be.

The chromizing process known from German patent specification 976 039 is based on an insert pack made of ferrochrome, kaolin and aluminum iodide. Because ferrochrome is an alloy component serves, it cannot serve as a metallic control component.

From Minkewitsch, Chemisch-Thermal 5 surface treatment of steel, 1953, p. 337 bis 34Ü, it is known that only alloys such as iron-aluminum alloys are used for aluminumizing or iron-aluminum-copper alloys, which also contain a few tenths of a percent of magnesium

ίο use. It is expressly emphasized that the Additions of copper and magnesium have no significant influence on the depth of the aluminized layer. the Components such as iron, copper and magnesium contained in the aforementioned alloys can are not regarded as control components that act in the sense of the method according to the invention. According to US Pat. No. 30 61 463, according to Example 4, iron is applied using silicon powder + Chromium powder + aluminum oxide + ammonium fluoride a silicon layer with only a low chromium content manufactured. However, layers are also produced that are free from the second metal, such as example 5 teaches according to which on zirconium with chromium powder + beryllium powder + zirconium oxide + iodine a Chromium layer is produced without beryllium. It emerges from the USA patent specification 30 61 463, that as additional metals to that to be applied to a metallic object by diffusion Metal, those metals should be used which themselves diffuse, i. E. H. into the surface of the too the covering metallic object. These metals are listed in column 5, line 6 of the patent expressly referred to as "solute or diffusing metals". Opposite is for the procedure Characteristic of the present invention that practically no "solute or diffusing metals" as so-called Control components should be used.

In British Patent 911414 and the this corresponding French patent specification 12 73 888 is the production of metallic diffusion coatings on Co or Ni alloys using a powder pack made of Al2O3, Cr, Al and J2. The coatings contain Cr and Al.

The method of the present invention is the combination of chromium as a control component and Except for aluminum as a diffusing metal.

According to British patent specification 915 090

metallic objects made of steel, Ni, etc. with metallic Provided diffusion coatings in that the objects in powder packs from an inert Filler, the element to be diffused, a halide as a means of transport and an auxiliary material (Mg, Al, Ca or Ni) are heated to the diffusion temperature. Since the auxiliary material is not diffused, it does not play the role as a metallic control component, apart from that magnesium as well as the diffusion of aluminum in the presence of chromium for the purpose of Invention is not provided.

The French patent specification 12 21 455 also describes the production of Cr diffusion coatings by diffusion of aluminum in the presence of chromium. According to Examples 2 to 4 of these Patent two metals including silicon are diffused, and Example 5 is used as an additional Metal beryllium used, which is not covered by the present invention.

With regard to the state of the art, it should also be pointed out that there is no publication on it It is pointed out that slowing down and regulating the diffusion of coating material into the Surface of the object to be treated is possible through certain additives incorporated in the packs is. With regard to the prior art, it should also be taken into account that the production of coatings not always satisfactory results on metallic objects for the following reasons led.

The chemical properties of the coating package can for example be for a certain temperature determine the speed with which the coating material approaches the surface of a the object being coated; however, this speed does not necessarily need to be with the Rate of diffusion of the coating material into the article after this has penetrated the surface. So it can be a certain high temperature appropriately be so that a certain coating material begins to diffuse into the surface of the object, but so high in terms of the rate of diffusion of the material within the article be that it gets further from the surface into the center of the object than is desired. The received The surface coating is then not dense enough.

On the other hand, the diffusion that takes place initially can occur a portion of the coating material in the surface of the article to further penetrate Prevent the formation of the desired thickness of the required coating material as far as possible, that there is no longer any agreement with a treatment temperature that is required, thus bringing the reversible reactions in the coating pack to the required equilibrium will. It is also possible that the composition of the article to be coated at different Temperature undergoes crystallographic or metallographic changes under conditions, which have no relation to the reaction rates of the various conversions taking place in the pack itself, so that for initiation Treatment temperatures sufficient for diffusion are too low to achieve the desired temperature or to achieve the metallographic thermal state of the object so that it does Absorbs coating material in the desired manner. With some metallic objects with low melting points and when using a closed retort, and / or when a certain Temperature is required to break the coating package, for example that to be coated The object almost melts before the thermal conditions exist, in which the desired diffusion of the coating materials out of the pack takes place.

To illustrate the difficulties encountered when coating a metallic object can occur through diffusion, it is assumed that aluminum in the surface of a metallic, for An example of an object comprising a considerable amount of copper is to diffuse around a protective layer from a certain copper-aluminum alloy, the formation of which is obtained from a certain Temperature depends. As is known, aluminum diffuses as a function of temperature objects that are easily and quickly contained in copper even at relatively low temperatures. If you now set the treatment temperature so that only aluminum is sufficient for one diffuses at a moderate speed so that a deep diffusion of the aluminum is avoided, it can be determined that the copper-aluminum alloy formed in the coating is not the desired one is. On the other hand, if the treatment temperature is increased so that the desired specific one Copper-aluminum alloy is formed in the surface of the object, can reduce the diffusion rate of the aluminum must be so large that it penetrates too deeply into the object. These Difficulties can be overcome by using a control component according to the method of the invention overcome.

The problem of too fast a transfer rate of the coating material from the components the packing on the surface of the item to be coated also occurs when High-temperature or complex alloys or metallic objects are present in which the coating material and the object can form low-melting complexes or systems, and especially if so desired, a more or less standardized technical working method to apply various coating materials to a wide variety of metallic objects to apply fundamentally different chemical and metallurgical properties. In such Cases can e.g. B. to initiate and maintain the initial reactions between the temperatures required by the specific substrate and the source of the coating material in the pack and / or the thermal conditions and temperatures that must be maintained, in order to complete such reactions within technically useful periods of time, not immediately Causal relationship with the chemical properties and / or diffusion rates of the coating material.

Furthermore, the complex composition of the alloy or the intermetallic surface determines of the object to be coated, be it from the start or after a part of the coating material diffused into the object, another difficulty, at least as far as the possibility is concerned, To establish working conditions which in all cases lead to a satisfactory diffusion coating, and / or to enable working conditions in which one of several possible but desirable Implementations is running. It should be noted here that there are a large number of different can form intermetallic compounds, namely from a certain coating material and a certain component of the object to be coated, again depending on of the temperatures and working conditions used, which have rarely been so coordinated with one another up to now could be to achieve the desired Coating obtained by diffusion. The invention also solves this problem by applying a Control component.

The selection of the control component used to carry out the method of the invention is taken into account in each case

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applied carrier material preferably on the me- ζ. Β. 69% inert filler, such as aluminum oxide,

metallic or chemical properties of 22% of a control component, 8% aluminum and

coating article and the diffusion or 1% vaporizable halide carrier, wherein

Reaction rates of the coating material in the production of a diffusion coating at a

the metallic object to be coated, so 5 temperature of about 760 to 1200 ° C for 15

as is done on the various possible intermetal minutes to 40 hours,

ical compounds matched that come from the over- More examples of alloys that have worked with success

Zugsmaterial and the constituents of the coated according to the method of the invention by diffusion

Object can be formed. can be coated are:

Satisfactory results can be achieved after ver io. ... _XT . ,,,,

drive the invention with nickel as a control component alloy with a high nickel content:

component for the production of aluminum coatings on a percentage by weight

nickel- or cobalt-rich superalloys, also on carbon. 0.12

refractory metals such as molybdenum with pak chromium 19 '

be achieved in mixtures containing 40% metallic 15 cobalt 19

Nickel, 20% metallic aluminum, 40% inert iron . '.'.: .. .............. 1

Filler (aluminum oxide) and a vaporizable molybdenum ............. 4

Halogen carriers such as ammonium fluoride contain. In aluminum ............... 3

in a corresponding way, .z. B. Cobalt, Vana titanium 3

dium, carbon, silicon and even in some cases nickel residue

len iron can be used as a control component,

where aluminum and / or various other Me alloys with a high cobalt content:

talle into the surface of a variety of materials weight percent

are diffused. ^p _

Nickel, cobalt, silicon and silicon carbide are 25 carbon 0.50

as a control component in the production of dif- ^ " ^ΓΟ1 " ² ^

fusion coatings of chrome on a variety of wif 74

Super alloys, especially on nickel-rich alloy tungsten 7.4

wrestled, suitable containing about 13% chromium and 44% vv ^ i r>

Contain nickel. Metals like nickel and chromium are cobalt 30 remainder

suitable among other things, the transition speed carbon 0.4

ability of lower melting coating metals, chromium 20

z. B. of copper or iron, with the diffusion of nickel 2

a coating pack into the surface of a tungsten 11

to inhibit the object being coated, especially 35 niobium 15

when the composition of the article is cobalt 63

or the thermal properties of the coating material. rest
terials too rapid a transition or diffusion

at the desired treatment temperatures. Good results are also achieved with the »SAE 1045« -

change. In a corresponding manner, for. B. with SiIi-40 and "SAE 52100" steels as well as with such ma-

adornment of steel or other iron alloys achieved with materials that are made of relatively pure egg

temperatures so high that the inner diffusion sen (Armco iron) or commercially pure nickel

silicon speed greater than desired ("A" nickel).

is a control of the transition of silicon from the manufactured by the method of the invention

the pack on the metallic object according to 45 th coatings in the order of z. B. 0.0254

the method of the invention can be controlled to 0.0508 mm at high operating temperatures

that a treatment temperature is possible which is very malleable, so that it is opposite to thermal

Formation of a particular silicide leads. Shocks can be very resistant. The inventive

z. B. Metals, such as nickel, iron or cobalt, are also used as control aluminum coatings

er component for diffusion coatings of aluminum 50 resistant to oxidation and erosion at high temperatures

to be used or silicon; Silicon, iron solid. All coatings have a good permanent adhesion

or carbon are useful control components even in spite of rapid and strong temperature changes.

ten for chromium, silicon for aluminum and iron.

for silicon and aluminum. If thinner coating layers are required

The use of the aforementioned EIe- 55 the, z. B. when the objects strict elements and metals as control components excludes thermal impacts and deformations, that they diffuse themselves to a limited extent, the diffusion coating will preferably be given; this must not include the addition of z. B. Koh- ner low temperature and / or during a fuel to a pack for carburizing or for a shorter period of time at a higher temperature control of the decarburization of an iron alloy, 60 formed; if, on the other hand, thicker coatings are required and that are borrowed within the metallic object in order to e.g. B. a greater oxidation and Eroselelf be confused. The same is true e.g. B. to achieve tensile strength, the diffusion overview of the addition of iron halide is formed in order to pull this into the diffusion coating of iron materials at a higher temperature and / or during a longer period of time,
bring to. 65 The amount of inert filler is not critical;

When coating superalloys with high aluminum is preferred as a filler. As a carrier

Nickel and high cobalt content through diffusion with can also contain elemental iodine and, in addition, ammo

A coating packing is advantageous for aluminum, which contains nium iodide and ammonium fluoride as particularly

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can be used in part. As indicated, can be irreversibly at temperatures lower than that depending on the desired thickness of the coating time control component melts and diffuses, is one and working conditions of producing excess amount of inert filler or stretching tensile means by diffusion to some extent, such as alumina, then generally increases will be changed. 5 prefer if the aluminum portion of the pack

The aluminum diffusion into the surface of one of the proportions of the control component equals predominantly nickel-containing article may or exceeds this. In any case, this applies to gezur Formation of a large number of different nickel-aluminum temperature ranges. For a given Temminium alloy lead, whereby the temperature formed can reduce the thickness of the coating achieved in the Yield may be a function of the general increase as the surface area increases the object brought or increased in this with ge metallic component of the pack; everyone given working temperature diffused people, but it is generally recommended, from economic Can be aluminum. If the desired aluminum considerations in each case a considerable one Alloy containing minerals use less than the maximum amount of filler.

If this alloy should contain aluminum, the formation cannot take place if the aluminum is allowed to diffuse if the aluminum treatment temperatures require many, if not minium, from the pack too quickly or all, amounts in which the control component is supplied the surface of the article is available, no inert filler is operable. If the treatment - at a sufficient speed, since satisfactory results even without an inert high temperature for such a long time - is achieved 20 filler, if the proportion of the control room is carried out to a desired strength component prevails; What alloys can achieve with the coating layer, however, can lead to too rapid a high nickel and high cobalt content transfer of the aluminum from the packing, are the proportions of control components the surface of the object or the diffusion te and aluminum in the packing over 90% control of the Surface into the article below 25 component not preferred, although they can also be effective in the formation of an alloy other than the desired one, mainly because of the success, namely a lower-melting, modynamically-related difficulty, the aluminum alloy having a high Al content. in order to be appropriate and controllable from such mixtures. Such technical difficulties are mainly concerned with the sintering of the packs, so their diffusion can only occur with the desired components in the vicinity of the working temperature to be covered with a slowed surface or purely mechanical side effects or perhaps not at all which may go through other methods so that the availability or the excess can be regulated. Excessively large amounts of the aluminum component in the aluminum pack can therefore impair the effect of the control on diffusion into the surface of the object, excessively high levels can be easily inhibited or controlled, the control component can achieve the desired level of temperature or other thermo-miniumdiffusion destroy
dynamic conditions that are necessary to achieve the 40 If the weight ratio of preliminary aluminum-containing alloy in the packing for a control component to aluminum is substantially less than 0.5, the diffusion of aluminum is sufficient, then the desired effect of the dimensions is to destroy the desired Conditions for speed control either neglect the formation of the respectively desired nickel-aluminum packing or less than normal aluminum packing compared to a nium alloy in the surface of the object. If on the other hand that give. Weight ratio of control component to aluminum

If an aluminum-containing alloy is in the range well above 4.6, then a final-build package can has formed, it may be necessary to additionally be formed that is less than the optional to control the temperature has an extremely high resistance to oxidation, perhaps because one is too aggressive carrier material, e.g. B. a fluoride, too much inhibition of the diffusion coating for turn to destroy such an aluminide. An available aluminum takes place or However, aluminide can also be a pak from the outset because it is also partly a diffusion coating from the can be added, since it arises anyway in the control component instead of aluminum. Do not investigate these quantitative ratios until the pack is being heated forms, and in general, before any 55 point out that relationships are tax compoliche Diffusion of the aluminum occurs. Too great for aluminum within the wide range With an amount of inert filler, about 0.1 to 8 formation can be considered effective a diffusion coating can already be alkynes through a; Ratios of the control component to aluminum excessive Dilution of the metallic or dif- minium in the packing, which is initially outside the Interfere with the fusible component of the pack. 60 range from about 0.5 to 4.6 are, however, im

If, on the other hand, the method of the present general for customary technical working methods is used Finding even without an inert filler with most types of superalloys and additives Can be carried out successfully, will be provided with an aluminum cover ' In general, the results improved when the items are not preferred. For different effective, d. H. diffusible, metallic 65 applications, and especially around objects geComponents of the packing in an amount greater than that of any attack other than oxidation about 5 percent by weight of the package. If to protect, e.g. B. for the production of diffusion plants Diffusing aluminum component is what pulls nickel objects through from attack

9 10

Protecting sulfur will result in satisfactory aluminum in the surface of the object, though Nisse also achieved outside of these ranges, with the diffusion also being achieved by a conversion or also The benefits of speed control can only be harnessed by the dilution at such high chrome levels and can be unusually inhibited according to the method of the present Ergel. Discovery the improved results in the manufacture of 5 extended and carefully carried out analyzes (mediation of diffusion coatings with one or another »micro-prob« method) of with a coating ren of the components of the coating packing achieved provided superalloys as well as overzowerden, and benefit from speed control of pure nickel and pure cobalt items tion or the diffusion inhibition. It indicates that there is primarily a diffusion of aluminum furthermore, that various metals took place as a tax io minium. Even if some aluminum components Deviations from these specific minium alloys of the control component and / or Quantities may or must require. other forms of control component occasionally

In the method of the invention, e.g. B. the analog in the coated surface of the object

For the production of coatings, certain coating can be determined lytically, but these are

Packing initially a metallic control component apparently to the presence of considerable quantities

component roughly two to four times the amount of the control component in the base alloy itself

Aluminum, the aluminum being about 3 to 20 attributable as they are not of the same extent

Percent by weight of the cover pack, and occur in items that do not contain tax components

a substantial amount of the pack, e.g. B. have 60 to nents in the base alloy, and they over-

70%, of powdered alumina and about 20 rarely pace a fraction of a percent even if

1% ammonium fluoride as a carrier component be the method of the invention on pure nickel or

stands. A satisfactory mixture points for the pure cobalt objects is applied and in spite of it

technical treatment of the various specified- a predominant part of the tax component

NEN metals z. B. 69% aluminum oxide, 22% metal in the coating pack.

control component, 8% aluminum and 1% ² 5 These observations also justify the fixed

Ammonium fluoride. position that a control component that deals with

When the treatment retort first connects the aluminum in the pack during experiments opened and emptied, the powder cans separated, primarily inhibiting the passage or the shaped components of the pack are easily controlled by the speed, but not diffusion-coated Object that is the desired smooth 3 ° component of the packing, at least not in the case of the Ar surface and had a certain color, with working temperatures at which the desired Audie Coating layer or thickness of the casing in minium diffusion coating for the specified meder Size range from 0.048 to 0.056 mm for metallic objects in the also specified nickel and cobalt objects and larger areas should be achieved. If excessively Iron objects was. Sharp Oxidation Attempts 35 a lot of control component is present in the pack, can at 1093 ° C in an oxidizing atmosphere in a but also a small amount of the control components conventional test ovens showed no failure of any diffuse; however, these effects are one of the coated parts during a test and, as should be pointed out, the function duration of over 85 hours. The packings can contain a particular metallic component completely can be reused in a known manner. 40 subordinate to the speed of transition of the

The type of the respective in the surface of the counter-coating material from the pack to the coating actually diffused to the supernatant changes to control the pulling object,
practically a little over a very large area. Even though, as should be pointed out, the explanations given above in a package, serving as an example, relate in the component compared to the amount of aluminum, 45 essentially to a superalloy with a howenn within such If the depth of the nickel content as the object to be coated relate to coating and other working conditions in advance, these explanations also apply with regard to correct and for technical production reasons, the superalloys already mentioned above can also be changed. If z. B. in the coating nem high cobalt content and with regard to the formation pack an amount as high as 92 percent by weight 5 ° of a suitable cobalt aluminide present in the Dif control component, first diffuses the fusion formed coating layer.

Claims (2)

Patent claims: 1. A method of coating a metallic object by diffusion, in which the article is heated in a non-oxidizing atmosphere in a powdery package which contains the metallic material to be diffused and a support to make the transition to effect the metallic material from the pack onto the surface of the object, characterized in that the packing additionally serves as a control component aluminum, boron, carbon, cobalt, iron, Nickel, a refractory metal or silicon that contains chemically with the metallic Material connects in order to regulate and inhibit the transition from the pack, and the Control component is present in sufficient quantity to effect such a controlling inhibition, without this component itself being passed over to a notable extent. 2. Diffusion coating packing, which includes a metal to be diffused and one volatile in heat Having carriers to convey the metal from the package onto the article, thereby characterized in that the packing is additionally used as a control component aluminum, boron, carbon, Contains cobalt, iron, nickel, a refractory metal or silicon that is chemically connects with the metal to be diffused to form an intermetallic complex, which is less accessible for reaction with the carrier than the metal to be diffused is, and this control component is present in a sufficient amount to this complex without being transferred to any appreciable extent.