DE102004060538B3 - Firmly adhered hard metal layers on substrates, especially valve seating rings on cylinder heads, produced using adhesion-promoting layer formed by applying plasma jet containing hard metal to substrate - Google Patents

Abstract

Production of a hard metal (HM) layer (I) firmly adhered to a substrate (A) via a chemically bonded adhesion-promoting layer (II) involves: (a) melting (A) using a plasma jet; (b) incorporating HM (or its components) in the plasma jet; (c) depositing HM (or its components) in the molten surface layer of (A) to form (II); and (d) overcoating (II) with HM (or its components) to form (I). An independent claim is included for a cylinder head for a combustion engine. having a material seal bonded valve seating ring of HM based on cobalt, nickel or cobalt/molybdenum alloy formed by the above process, where the material seal is formed via a chemically bonded adhesion promoting layer, between the head and the ring, of an alloy of the materials of the head and ring.

Description

The The invention relates to a method for forming hard metal layers, the above a chemically bonded adhesive layer solid with a metallic Substrate are connected, and a cylinder head for internal combustion engines with cohesively bonded Valve seat ring made of carbide based on Ni, Co and / or Mo alloys.

Cylinder heads are in local areas, in particular. the valve seats, to the Limit their thermal or mechanical strength claimed. This has the consequence that a local failure can occur, which recognizable, for example, by cracks and / or tribological wear becomes.

Conventional Valve seat rings are made of high quality material in the cylinder head shrunk or pressed.

For this Valve seat rings are especially Co, Ni and Co / Mo base alloys of great interest. These alloys are characterized by partially very high Hardness and very high wear resistance out. This is one of the applications of these alloys also in the armor technique. Very disadvantageous in this approach is the need to manufacture the valve seat rings individually and fit. Especially for The very strong Co / Mo base alloys are very complex process steps necessary to get to the required precision components.

When Alternative to the shrunk or pressed valve seat rings The direct structure of the valve seat rings on the ground through Coating process into consideration. Here are different thermal spray processes, such as plasma, flame or arc wire spraying examined more closely.

For example, in the US 4661371 discloses a method in which a protective layer is applied to the specially prepared contact surface between valve and valve seat. This is done by thermal spraying a powder mixture of ceramic and metal particles, wherein the layer formed has a gradient of the composition, whereby a quasi-ceramic cover layer is formed. The layers formed do not yet have optimum material properties.

From the DE 100 41 974 A1 is a method for the deposition of protective layers is known in which a powder mixture of at least three powder components is used as powder particles. A first powder component is made of a Fe, Co, or Ni-based alloy, a second powder component is preferably formed by Mo or refractory metal sulfide, and a third powder component preferably comprises Cu, Al, or Ag. For the process carried out, or the layer formed therewith, it is essential that the individual powder components do not melt together and no alloys of the different powder components are formed. Only in this way can the individual functional properties (hardness, lubrication and heat conduction) of the components used also be retained in the layer. The powders are deposited, for example, by an HVOF process or by gas compaction. In the area of highest stresses, the hardness of the layers proves to be in part insufficient.

The different thermal spray processes, such as plasma, flame or arc wire spraying have inherently a high overspray on, that is a loss of material and contamination of the uncoated Surfaces. This increases the raw material costs and requires covering measures. On top of that, that too Achieving a good coating adhesion a surface conditioning, for example by roughening by means of high-pressure water jet or Sandblasting is required. The layer connection in these blasting processes takes place mainly mechanically, that is in particular by toothing and not over one much more advantageous chemical binding.

In order to the process costs are high and the procedures usually pose not an economically acceptable replacement for the seat rings.

It is therefore an object of the invention, metallic valve seat rings higher Hardness and wear resistance to provide that over a chemically bonded adhesive layer is firmly connected to the substrate, and a simple method for the thermal deposition of hard metal layers show high adhesion to the metallic substrate.

The Task is solved by a method of forming cemented carbide layers containing a chemical bonded adhesive layer firmly bonded to a metallic substrate are, with the characterizing features of claim 1, as well as a Cylinder head for Internal combustion engines with materially bonded valve seat ring made of carbide based on Ni, Co and / or Mo alloys with the characterizing Features of claim 10. Further advantageous embodiments emerge from the dependent claims.

• – Aufschmelzen des Ungrundes mittels eines Plasmastrahls
• – Einbringen des Hartmetallwerkstoffs oder dessen Komponenten in den Plasmastrahl
• – Abscheiden des Hartmetallwerkstoffs oder dessen Komponenten in der aufgeschmolzenen Oberflächenschicht des Untergrundes unter Bildung einer Haftschicht
• – Überschichten der Haftschicht mit Hartmetallwerkstoff oder dessen Komponenten unter Bildung der Hartmetallschicht.

According to the invention, a method is thus provided which comprises the following essential steps:

• - Melting of the Ungrunde by means of a plasma jet
• - Introducing the hard metal material or its components in the plasma jet
• - Depositing the hard metal material or its components in the molten surface layer of the substrate to form an adhesive layer
• - Overcoating the adhesive layer with hard metal material or its components to form the hard metal layer.

The inventive method has opposite the well-known thermal spraying method the great advantage that in a single easy-to-carry process step both the adhesive layer and the hard metal layer are applied can.

in the The first step of the coating process is to be coated Substrate or the surface melted superficially. Of the Plasma jet provides a powerful and at the same time easily available source of energy The melting preferably extends to a depth in the range from 0.1 to 1 mm.

immediate after melting the surface layer is started with the deposition of the hard metal material. For this becomes the hard metal material or its components in the plasma jet brought in. Among the components of the hard metal material are in particular the individual metals or metallic elements understand, which form the hard metal material.

At the Impact on the molten surface of the underground penetrates the hard metal material or its components in the melt one. At least part of this is with the surrounding melt converted into a homogeneous new alloy. The composition This new alloy is made by the components of metallic Underground and carbide alloy formed. In this process step Thus, a layer is formed, which is a nearly optimal chemical and physical connection to the ground.

in the The next step in the process is the deposition of the carbide or its components continued on the surface. The energy of Plasma jet is controlled so that no additional Melt of the underground can be formed more. Thus takes the offer of melt on the surface with the progression of Deposition continuously or abruptly, leaving the deposited Material increasingly higher Has proportions of the components of the hard metal material. Of the now formed in the deposition material corresponds to the in the plasma jet introduced carbide material, or from the the carbide material formed by the components.

Become only the corresponding components of the hard metal material in the Plasma jet introduced so they are in the plasma jet or on the freshly deposited layer for the most part to the corresponding Alloy, or implement a hard metal material. Prefers the deposition is driven so that the components in the Convert hard metal layer to homogeneous alloys. This is possible in particular by the energy of the plasma jet and the amount of dosed carbide components regulate.

It It is obvious that the adhesive layer is also deposited on the surface thereof Hard metal layer has a very high chemical and physical compatibility.

The Process is particularly cost-effective to carry out, if a very high-energy plasma jet, in particular a high-pressure plasma jet is used. Preference is given to a microwave-induced plasma used.

Of the typical pressure range of the high-pressure plasma is above 2 bar, where 5 to 10 bar for plant and process engineering reasons particularly are well suited. Too high a pressure is needed for the melting of the surface of the Metallic substrate unsuitable, because the melt is not allowed be blown away.

The plasma gas used is inert gas, preferably Ar or N ₂ . The content of metal oxides or metal nitrides is comparatively low in this procedure in the deposited material. Preferably, less than 1 metal oxides are deposited.

Of the Hard metal material or its components are in the process of the invention introduced into the already formed plasma jet. This one can if necessary, again focused by suitable devices become.

In principle, the hard metals or their components can be introduced in powder form. However, it has been shown that it is considerably cheaper to spray the hard metal material or its components in the form of a slip of metal powder into the jet. The components can be very well homogenized in a slurry and the Promote slip in a simple manner and reliably from a storage container to the spray into the plasma jet. This applies in particular to the fine powder particles preferably used below an average particle diameter of 50 μm. Since very fine metallic powders are partially pyrophoric due to their high surface area, the particle diameter is preferably limited downwards to 1 μm. Preferably, the mean particle diameter is in the range of 1 to 10 microns.

It is appropriate the concentrate metallic powder in the slurry as high as possible. The slip preferably has a metal powder content of at least 50% by weight on.

Of the Slip may contain different solvents, preferably but become watery Slip used as they are easy to handle and more environmentally friendly as a slip with organic solvents are.

When Stabilizers can added to the slurry polymers and surfactants become. For example, cellulose, polyether, polyglycol or starch solutions good suitable. Other suitable adjuvants are viscosity modifiers multivalent higher Alcohols, ethylene glycol, diethylene glycol or glycerol.

The solvent and organic additives of the slurry are in the plasma jet largely decomposed and evaporated. The one with the organic compounds introduced excess carbon is partly incorporated as carbon in the alloys. hereby can advantageously hard and wear resistance increasing Metal carbides form, for example chromium carbide.

In Another variant is the content of organic components so much in the slip, that carbon is elemental, or graphitic Phase separates. The graphitic precipitates formed in this case improve the friction behavior of the surface.

The Introduction of the slurry in the plasma jet is done by atomization, such as in principle, for example, in the fine jet painting known.

It is appropriate the Deposit carbide layer on the workpiece to be coated in excess or excess, in order to be able to carry out a subsequent machining or finishing.

One Another aspect of the invention relates to a cylinder head for internal combustion engines with cohesive bonded valve seat ring made of carbide.

According to the invention, it is provided the valve seat rings are made of the very hard and wear-resistant Ni, Co- and / or Co / Mo-based alloys to manufacture, the valve seat rings not in a known manner individually and to fit in the cylinder heads are, but rather are deposited directly on the base material of the cylinder head. It is essential that on the ground first a Adhesive layer is arranged, due to their chemical composition a high chemical and physical compatibility with the cylinder head and to the valve seat rings. The adhesive layer is up and below chemically and cohesively bound.

The high compatibility the adhesive layer is inventively achieved in that they made of an alloy of the material of the cylinder head and the material is formed of the valve seat ring. The material of the cylinder head is usually steel or an iron casting alloy. It is preferred the cylinder head formed by gray cast iron. The adhesive layer is included with the substrate and with the valve seat ring arranged above it chemically linked.

Prefers the proportion of the valve seat ring material is in the adhesive layer above 10% by weight, preferably in the range of 15 to 85% by weight. Especially For example, the proportion of Ni, Co and / or Mo in the adhesive layer is preferred above 20 wt.%, Particularly preferably in the range of 30 to 70 Wt.%. The remainder of the adhesive layer is usually made of iron and the usual Steel attendants formed.

It is beneficial to the underside of the adhesive layer of the chemical composition the background and the top of those of the valve seat ring adapt. Preferably changes the composition of the adhesive layer perpendicular to the surface of the Background gradient. The adhesive layer has almost the same composition on its underside the cylinder head and on the top almost the composition of the valve seat ring on. Particularly preferred are the compositions of cylinder head and valve seat ring flowing into each other.

The Valve seat rings preferably have a dense and homogeneous mixed structure, as it is for thermal Spraying processes usual is. Particularly preferably, the adhesive layer and the valve seat rings via a formed thermal deposition process.

The alloys which are particularly suitable as valve seat rings include the Ni, Co or Co / Mo base alloy. The Co / Mo base alloys are to be understood as meaning those compositions which, in addition to the Co, have a Mo content in the range from 20 to 40% by weight and among the Co base alloys those which are adjacent Co may also have a Mo content of less than 10% by weight. The Co and / or (Co + Mo) content is preferably above 65% by weight.

When other typical alloying constituents contain the alloys at least one element from the group Cr, W, Ni, Fe, Si, Mn in one Amount of 0.1 to 20 wt.%. Furthermore, the usual for the corresponding metals Impurities are present in traces.

Of the Content of metal oxides or metal nitrides in the deposited Valve seat rings is comparatively low. Preferably lies the content of oxides or nitrides below 2 wt.%. Especially preferred the oxygen content of the alloys is below 1% by weight.

The nominal composition (% by weight) of particularly preferred Co base alloy is as follows:
C: 0.1 to 3%
Cr: 5 to 30%
W: 0 to 20%
Ni: 1 to 25%
Fe: 0.1 to 5%
Si: 0 to 4%
Mo: 0.5 to 3%
Mn: 0 to 1%
Co: balance, but at least 50% and usual impurities

The nominal composition (% by weight) of particularly preferred Co / Mo base alloy is as follows:
C: 0.05 to 1%
Cr: 5 to 30%
W: 0 to 20%
Ni: 0 to 10%
Fe: 0.1 to 4%
Si: 0 to 4%
Mn: 0 to 1%
Mo: 5 to 35%
Co: remainder, but at least 45%, and common impurities.

Particularly preferred alloy compositions include those known as Tribaloy ^®, Stellite ^{® ®} or Colmonoy alloys.

Further preferred embodiments of the alloy composition comprise, in addition to Co, 7 to 15% by weight of Cr, 20 to 30% by weight of Mo and 1 to 4% by weight of Si,
or 25 to 32% by weight of Cr, 2 to 2.5% by weight of C, 1 to 4% by weight of Ni and 10 to 15% by weight of W.

The nominal composition (% by weight) of particularly preferred Ni base alloy has a Ni content of 14 to 33%, a Cr content of 15 to 29% and a Mo content from 3 to 15% and residual Fe, as well as usual steel companions.

For the wear resistance is in addition to the chemical composition in particular the structure of the surface layer significant. The open porosity also plays an important role here Role. The deposited according to the invention Layers preferably have an open and / or closed porosity below 5% up.

For the geometric Design of the valve seat rings on the cylinder head, the known dimensions are taken in general. by virtue of the good fit and connection of the separated valve seat rings But their thickness can also be compared to the individually manufactured and be fitted rings reduced. The thickness of the valve seat rings together with the adhesive layer is preferably in the range of 0.2 to 5 mm, more preferably 0.5 to 2 mm. Compared to the common cast and fitted valve seat rings are the valve seat rings according to the invention clearly lighter or less thick. This can be in Advantageous savings on the relatively expensive raw materials Realize Co and Mo

Claims (17)

Method for forming hard metal layers, the above a chemically bonded adhesive layer solid with a metallic Underground, characterized by the steps of - melting of the subsurface by means of a plasma jet - bring in of the hard metal material or its components in the plasma jet - Separate of the hard metal material or its components in the molten surface layer of the substrate to form an adhesive layer - Overlay the adhesive layer with hard metal material or its components forming the hard metal layer. Method according to claim 1, characterized in that in that the plasma jet uses a microwave-induced plasma becomes. Method according to claim 1 or 2, characterized that the hard metal material or its components in the form of a Schlickers be introduced from metal powder. A method according to claim 3, characterized in that a slurry having a metal powder content of at least 50 wt.% Is used becomes. Method according to claim 3 or 4, characterized that metal powder with average particle size in the range of 1 to 50 microns used become. Method according to claim 5, characterized in that in that the metal powders consist of Co, Ni or Co / Mo base alloys and / or their components selected become. Method according to one of the preceding claims, characterized characterized in that the melt of the substrate and the hard metal material or its components, an adhesive layer of homogeneous alloy form. Method according to one of the preceding claims, characterized characterized in that the components in the hard metal layer convert to a homogeneous alloy. Method according to one of the preceding claims, characterized in that an iron casting alloy is selected as the substrate. Cylinder head for Internal combustion engines with cohesively bonded valve seat rings tungsten carbide based on Ni, Co and / or Mo alloys, available by a method according to any one of the preceding claims characterized in that the material connection via an intermediate cylinder head and valve seat ring chemically bonded adhesive layer of an alloy formed of the material of the cylinder head and the valve seat ring is. Cylinder head according to claim 10, characterized in that the composition of the adhesive layer perpendicular to the surface of the Substrate changes in a gradient shape. Cylinder head according to claim 11, characterized that the adhesive layer on its bottom almost the composition the cylinder head and on the top almost the composition corresponds to the valve seat ring. Cylinder head according to one of claims 10 to 12, characterized in that the valve seat ring of a Ni, Co or Co / Mo base alloy formed is, wherein the Ni, Co or Mo content at over 50% by weight. Cylinder head according to claim 13, characterized that the Co / Mo base alloy has a Cr content of 5 to 30% by weight Cylinder head according to one of claims 10 to 14, characterized by the nominal chemical composition of the valve seat ring in wt.%, Mo 25 to 35%, Si 1 to 4%, Fe <3%, Cr 5 to 20 %, C 0.05 to 1%, balance Co and trace components below 1%. Cylinder head according to claim 10 to 15, characterized that the proportion of Ni, Co and / or Mo in the adhesive layer above 10% by weight. Cylinder head according to claim 10 to 16, characterized that valve seat ring and adhesive layer together have a thickness in the range from 0.2 to 5 mm.