Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/137—Spraying in vacuum or in an inert atmosphere

Definitions

• the invention relates to a method for applying a layer of ceramic material to a substrate by plasma spraying, in which the material is added to the plasma jet, the material comprising a chemical compound, one component of which is a non-metallic element from the group N , C, B or from the sixth or seventh main group, which decomposes at least partially before reaching the melting point and which is present in the solid phase in the applied state.
• Such a method is known from DE-OS 30 24 611, in which iron spinel and cobalt spinel are applied by plasma spraying at low burner output. Due to the low burner output, it can be assumed that only the iron spinel is melted since it has a low melting point, whereas the cobalt spinel is only embedded in the melted iron spinel. Furthermore, it can be expected that, despite the low burner output, decomposition products of the cobalt spinel are present. In plasma spraying with a low burner output, the bond between the applied layer and the substrate is not optimal and the internal strength of the outer layer is also limited. Furthermore, the coating yield is also very low, since when the spray material is thrown against the substrate by the plasma jet while still solid, an impact reflection occurs on the substrate and thus only a small part of the spray material remains adhering to the substrate.
• the invention is therefore based on the object of improving a method of the generic type in such a way that the chemical compound comprised by the material is stoichiometric, i.e. not decomposed, can be applied to the substrate and forms a dense, firmly adhering and stable layer.
• the length of the laminar jet from the nozzle is at least 60 mm, even better results are achieved with 80 mm and very good results with a length of the laminar jet of 100 mm. Optimal results can be achieved with a length of the laminar beam of 150 mm.
• the plasma jet used is that of a direct current plasma torch with which a plasma jet with a temperature that is as constant as possible and a flow profile that is as constant as possible can be generated.
• the non-metallic element is carried along in the plasma jet in dissociated or atomic form.
• the non-metallic element is guided in the plasma jet.
• the non-metallic element is guided in the core region of the plasma jet close to the axis so that it interacts as intensively as possible with the plasma jet surrounding it, but at the same time also provides good shielding by the plasma jet surrounding it.
• reaction equilibrium can be shifted particularly well in the manner according to the invention in that the non-metallic element is carried in the plasma jet in ionized form.
• the non-metallic element could be supplied to the plasma jet, for example with the plasma gas stream.
• this would require electrode materials which are not attacked by the non-metallic element.
• the non-metallic element is added to a primary plasma jet downstream of the high-current arc.
• the non-metallic element is added to the plasma jet on its side facing the high-current arc and close to it.
• the dissociation or ionization of the non-metallic element in the plasma jet can be achieved and maintained particularly easily if this is brought about by interaction with the primary plasma jet.
• An embodiment of the method according to the invention has proven to be particularly suitable, in which the non-metallic element is added to the plasma jet in a Laval nozzle serving as a laminar jet-generating nozzle.
• a particularly simple embodiment provides that the non-metallic element with the spray material is added to the plasma jet, so that no additional devices are necessary to add the non-metallic element to the plasma jet, but rather the devices that are usually suitable for plasma spraying are used can.
• an embodiment is particularly preferred in which the non-metallic element is introduced into the plasma jet in gaseous form, since this enables good, uniform distribution and easy dissociation or ionization of the non-metallic element.
• the non-metallic element is introduced into the plasma jet by a gas which releases it.
• the material serving as spray material is usually in solid form and must therefore be added to the plasma jet by a conveying medium, it is provided in a preferred solution that the non-metallic element is surrounded by a conveying medium for the spray material.
• the delivery medium for the spray material is gaseous.
• the sprayed material is in powder form.
• the spray material is added to a primary plasma jet downstream of the high-current arc. This is preferably done by adding the spray material to the primary plasma jet on its side facing the high-current arc and close to it.
• a particularly preferred embodiment of the method according to the invention provides that the spray material is added to the plasma jet in the laminar jet-generating nozzle of the burner.
• the plasma jet is essentially free of chemical elements which react with the non-metallic element to form stable chemical compounds. It is particularly expedient here if the plasma jet is essentially free of hydrogen.
• plasma gas it is expediently provided that it comprises a noble gas.
• the primary plasma comprises argon gas, preferably a predominant component of which consists of argon.
• the primary plasma gas comprises, in addition to the argon, enthalpy-increasing and toughness-increasing additional gases, with these being added serve to provide the necessary energy once to heat the sprayed material and, if necessary, to dissociate or ionize the non-metallic element.
• Advantageous parameters for the enthalpy of the primary plasma are enthalpies of> 20 kJ / kg at 10,000 ° C, it is even better if the enthalpy is> 30 kJ / kg at 10,000 ° C and optimal values are achieved when the Enthalpy> 40 kJ / kg at 10,000 ° C.
• Another preferred noble gas is helium.
• helium as the additional gas increasing the free enthalpy is added to the argon as the main plasma gas.
• Another advantageous possibility is to add nitrogen instead of helium as the additional enthalpy-increasing gas to argon as the main plasma gas.
• the gaseous, non-metallic element is carried in it with a proportion of more than 5% of the gases comprised by the plasma jet.
• the plasma jet has an enthalpy and temperature which causes the non-metallic element to dissociate.
• the non-metallic element is also to be ionized, it is even better if the plasma jet has a temperature and free enthalpy which causes the non-metallic element to ionize.
• a heater downstream of the high-current arc is additionally provided for the plasma jet.
• the additional heating takes place via high-frequency coupling into the plasma beam, which can be an inductive or a capacitive coupling.
• a chemical compound which comprises a metal as a further chemical element has proven to be particularly suitable for the use of the method according to the invention.
• Preferred materials here are oxidic materials, such as spinels and perovskites based on nickel or cobalt or nickel-cobalt. However, it is also conceivable to apply all possible types of spinels and perovskites according to the method according to the invention.
• All these compounds can preferably be characterized in that the chemical compound has a free enthalpy of formation in the region of its melting temperature, i.e. that it is a chemical compound which tends to decompose with increasing temperature.
• a sufficient and uniform heating of the chemical compound required for a good layer formation on the substrate can advantageously be achieved in that the chemical compound interacts with the laminar plasma jet within the same over a length of at least 60 mm. Even better values can be achieved if the length of the interaction is at least 80 mm, very good values if the length of the interaction is at least 100 mm and optimal values if the length of the interaction is at least 150 mm.
• the spray material In order to achieve a well-adhering layer on the substrate, it is necessary, as already mentioned at the beginning, to heat the spray material to a temperature which is as high as possible, for example above the melting point, although there is still no noticeable evaporation of the material may. For this reason, it is advantageous if the chemical compound in the plasma jet is heated to at least about 500 ° C, it is even better if the chemical compound is at least 1,000 ° C, or even better at least 1,500 ° C or best is heated to at least 2,000 ° C. The best adhesive properties of the layers are achieved when the chemical compound in the plasma jet is heated to at least a temperature in the region of its melting point.
• the chemical compound is moderately heated in the plasma jet, which means that the chemical compound has a surface temperature between 0 and 1000 ° C., preferably 0 and 500 ° C. is heated above its melting point, i.e. there is no strong heating beyond the melting point.
• the method according to the invention is used in particular when the material serves as a catalytically active coating.
• Another embodiment provides that the material serves as an electrocatalytically active coating.
• the material serves as a superconducting coating.
• the plasma spraying is carried out with a supersonic jet, since very firmly adhering layers can then be achieved on the substrate.
• Fig. 1 is a schematic representation of an apparatus for performing the method
• Fig. 2 is an X-ray diffractogram, wherein
• Fig. 2c the X-ray diffractogram of an applied
• a device for carrying out the method according to the invention comprises - as shown schematically in FIG. 1 - a vacuum chamber 10 which can be evacuated to a preselectable pressure by means of a vacuum pump system 12.
• a plasma torch 14 which generates a plasma jet 16 which strikes a substrate 18 which is likewise arranged in the vacuum chamber 10 and which in turn has a movement device 20 relative to the plasma jet 16 in a direction perpendicular to a longitudinal axis 22 of the Plasma jet 16 extending plane is movable.
• a spray material 24 is carried from particles of a material to be applied, which produces a coating 26 of this material when it hits the substrate 18.
• the plasma torch 14 operates as a direct current burner and in turn comprises a tubular housing 28, in which a sleeve-shaped anode 34 is arranged, which has a gas channel 32 conically narrowing towards an end 30 of the housing 18 facing the substrate 18.
• a pin-shaped cathode 36 protrudes into the gas channel 32 from a rear side opposite the end 30, an annular gap 38 remaining between the anode 34 and the cathode 36, through which a plasma gas stream 40 can enter the gas channel 32.
• the plasma gas stream 40 is fed to this annular gap 38 via an annular space 42 between the cathode 36 and the housing 28.
• the gas supply to this annular space 42 takes place in a manner known per se via a plasma torch supply device, designated as a whole as 44, which also provides the necessary direct voltage between the anode 34 and the cathode 36 and also a cooling channel 46 in the cathode 36 supplied with coolant.
• the gas channel 32 of the anode continues toward the substrate 18 in a nozzle channel 48 of a Laval nozzle 50 directly adjoining the anode 34, from which the essentially parallel laminar plasma jet 16 emerges if the parameters are correctly selected.
• the Laval nozzle 50 and the gas channel 32 are arranged coaxially to the longitudinal axis 22 of the plasma jet 16.
• a first inlet duct 52 opening into the nozzle duct 48 of the Laval nozzle 50 is provided, which is supplied via a first feed device 54.
• Plasma spraying with a plasma torch 14 in the vacuum chamber 10 is described in detail in DE-OS 35 38 390. There is also a detailed description of the function and mode of operation of the plasma torch in the article W. Mayr and R. Henne "Investigation of a VPS burner with laval nozzle by means of an automated laser doppler measuring equipment" Proc. Is. Plasma technology symposium, Lucerne, 1988.
• cobalt spinel (COgO * ).
• This cobalt spinel is applied to a substrate as a coating.
• the cobalt spinel can be added, for example, via the first feed device 54 and the first inlet channel 52, the cobalt spinel being in powder form and by means of a carrier gas from the first feed device 54 to the first inlet channel 52 and from there into the Laval nozzle.
• a gas mixture of 80% O 2 and 20% Ar is preferably used as the carrier gas for the powdered cobalt spinel.
• This oxygen (C * ⁇ ) represents the non-metallic element carried in addition to the spray material in the plasma jet 16 in a free form that is not bound to a foreign element.
• the burner is operated with a primary plasma gas stream, which preferably comprises argon as the main gas.
• a primary plasma gas stream which preferably comprises argon as the main gas.
• Helium can also be added to increase the enthalpy. It would also be possible to add nitrogen to increase the enthalpy.
• the plasma torch 14 is preferably to be operated in such a way that a long, laminar plasma beam running parallel to the longitudinal axis 22 and having a length of at least 150 mm is formed, which in vacuum can have a speed of 2,000 to 3,000 meters per second.
• the injection of the sprayed material, ie the cobalt spinel is to be carried out in such a way that a sprayed material spray 24 close to the longitudinal axis 22 also occurs in the core region of the plasma jet, sprayed material speeds of up to approximately 1,000 m / sec then being obtained and this sprayed material spray 24 then passing through the part of the plasma jet 16 surrounding it is protected.
• the time that the spray material spends between its injection into the Laval nozzle 50 and its impact on the substrate 18 in the plasma jet 16 is then less than 10 seconds, with an interaction with the plasma jet over a length of more than 150 mm.
• the sprayed material is heated to the melting temperature range, preferably the sprayed material is melted, so that it remains in the molten liquid state during the residence time in the plasma jet 16.
• the sprayed material is only heated moderately to a surface temperature in the range from 0 to 1,000 degrees above its melting point.
• the time available for the sprayed material to decompose is kept very short.
• the oxygen carried in the plasma spraying of cobalt spinel according to the invention counteracts the decomposition of the cobalt spinel since it shifts the dissociation or decomposition equilibrium towards the undecomposed cobalt spinel.
• the power of the plasma torch 14 is preferably such that the plasma in the plasma jet is sufficiently hot and enthalpy-rich to dissociate and ionize the oxygen supplied downstream to the plasma jet 16, and thus in particular to shift the reaction equilibrium of the cobalt spinel to the oxide towards, ie towards the undecomposed cobalt spinel, or to carry out a reoxidation of any oxides that have become unstoichiometric.
• An enthalpy of the plasma of more than 40 kJ / kg at 10,000 ° C. is preferably used.
• no hydrogen may be added to the plasma gas stream, since this would react to form water with the oxygen supplied via the carrier gas.
• the layer of cobalt spinel was achieved with the following parameters: power of the plasma torch 14, 30 kW, pressure in the vacuum chamber 10, 50 mbar, plasma gas made of argon and helium and carrier gas for the powdered cobalt spinel from 80% 0 2 and 20% ar.
• the layer thickness was 200 ⁇ .mu.m and showed a very dense structure, wherein it was firmly bonded to nickel as a substrate.
• the preferred size for the layer growth is 10 ⁇ m / sec based on a coating area of 10 cm, so that the desired layer can be applied in a single operation in a controllable thermal application of substrate without, for example, aftertreatment being necessary.
• the non-metallic element being able to be fed either in the carrier gas of one or the other, or in both of them one suitable for the respective material , non-metallic element.
• a further modification of the method according to the invention provides that if the plasma torch 14 does not generate sufficient temperatures and enthalpies, the Plasma stream 16 downstream of the Laval nozzle is still heated by an additional heater 60, this heater being, for example, a device for coupling high frequency into the plasma jet 16 and this can be done capacitively or inductively.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Coating By Spraying Or Casting (AREA)

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• 1989
  • 1989-05-04 DE DE3914722A patent/DE3914722A1/de not_active Ceased
• 1990
  • 1990-04-26 DE DE90906956T patent/DE59005005D1/de not_active Expired - Fee Related
  • 1990-04-26 CA CA002032172A patent/CA2032172C/en not_active Expired - Fee Related
  • 1990-04-26 EP EP90906956A patent/EP0425623B1/de not_active Expired - Lifetime
  • 1990-04-26 WO PCT/EP1990/000674 patent/WO1990013681A1/de active IP Right Grant

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