CA2032172C - Process for applying ceramic coating using a plasma jet carrying a free form non-metallic element - Google Patents
Process for applying ceramic coating using a plasma jet carrying a free form non-metallic elementInfo
- Publication number
- CA2032172C CA2032172C CA002032172A CA2032172A CA2032172C CA 2032172 C CA2032172 C CA 2032172C CA 002032172 A CA002032172 A CA 002032172A CA 2032172 A CA2032172 A CA 2032172A CA 2032172 C CA2032172 C CA 2032172C
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- Prior art keywords
- plasma jet
- plasma
- sprayed
- metallic element
- jet
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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
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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)
Abstract
Process for applying a coating of ceramic material on a substrate by plasma spraying. The material to be sprayed, which is incorporated in the plasma jet, includes a chemical compound one constituent of which is a nonmetallic element from the group N, C, B or from main groups VI or VII of the periodic classification, which decomposes, at least partially, in an inert environment before reaching the melting point and which is present in the solid phase in the applied state. To improve the process so that the chemical compound contained in the material can be applied to the substrate stiochiometrically, i.e., undecomposed, and form an impermeable, adherent, stable coating, the non-metallic element is incorporated in the plasma jet, in addition to the material to be sprayed, in a free form, not bound to a foreign element.
Description
2~32~
PROCESS FOR APPLYING CERAMIC MATERIAL
The invention relates to a process for applying a coating of ceramic material to a substrate by plasma spraying wherein the material is added to the plasma jet and includes a chemical compound, one constituent of which is a non-metallic element from the group N, C, B
or from the main groups VI or VII of tne Periodic Table which decomposes at least partially before reaching the melting point and is present in the solid phase in the applied state.
Such a process is known from DE-OS 30 24 611. Herein, iron spinel and cobalt spinel are applied by plasma spraying at low torch power. In view of the low torch power, it is to be assumed that only the iron spinel will melt as it has a low melting point, while the co-balt spinel will only be embedded in the molten iron spinel. Furthermore, decomposition products of the co-balt spinel will presumably be present in spite of the low torch power.
With plasma spraying at low torch power, the bonding of the applied coating to the substrate is not optimum and the internal solidity of the outer coating is also li-mited. Furthermore, the coating yield is also very low for when the material to be sprayed is hurled in the still solid state by the plasma jet against the sub-strate, an impact reflection occurs at the substrate and hence only a small part of the material to be sprayed remains adhering to the substrate.
2832~7~
The object underlying the invention is, thereforer to so improve a process of the generic kind that the chemical compound contained in the material can be applied stoi-chiometrically, i.e., undecomposed to the substrate and forms an impermeable, adherent and stable coating.
This object is accomplished in accordance with the in-vention in a process of the kind described at the be-ginning in that in addition to the material to be spray-ed, the non-metallic element is carried along in the plasma jet in a free form not bound to a foreign element.
In this way, by addition of tha element, the reaction balance of the compound tending to decompose is shifted to the undecomposed compound and so this compound can be heated to sufficiently high tempertures in the plasma jet and hence form on contacting the substrate an imper-meable, adherent and stable coating which, in addition, contains the chemical compound essentially in unde-composed form.
It has proven particularly advantageous within the scope of the inventive process for a laminar jet generated by a plasma torch with a noz~le generating a laminar jet to be used as plasma jet as this laminar jet offers the best preconditions for the material to be sprayed to be heated constantly and uniformly and for an ade~uate time in order to achieve as uniform a coating as possibls on the substrate.
;
It is particularly expedient for the length of the la-2 5~ 7 ~
minar jet to be at least 60 mm from the nozzle on. Even better results are obtained with 80 mm and very good re-sults with a laminar jet length of 100 mm. Optimum results are to be achieved with a laminar jet length of 150 mm.
It has, furthermore, proven particularly expedient within the scope of the inventive solution for the latter to be carried out in vacuum as problems other-wise arise from impurities or interactions owing to the atmosphere surrounding the plasma jet.
It is preferable to use as plasma je-t that of a d.c.
plasma torch with which a plasma jet having as constant a temperature as possible and as constant a flow profile as possibla can be generated.
To shift the reaction balance in the direction towards the undecomposed chemical compound, it is particularly advantàgeous for the non-metallic element to be carried along in the plasma jet in dissocia-ted or atomic form.
In the examples of the inventive process described so far, no details were given as to how the non-metallic element is conducted in the plasma jet. It is expedi-ent for the non-metallic element to be conducted, after its introduction, in the core region near the axis of the plasma jet so there is as intensive an interaction as possible with the plasma jet surrounding it but, at th~ same time, also good shielding by the plasma jet surrounding it.
~32~72 The reaction balance can be shifted particularly well in an inven-tive way by the non-me-tallic element being car-ried along in ionized form in the plasma jet.
In principle, within the scope of the inventive process, the non-metallic element could be added to the plasma jet, for example, with the plasma gas flow. However, this would require electrode materials which are not affected by the non-metallic element. For this reason, it is more advantageous for the non-metallic element to be added to a primary plasma jet downstream from the high-current arc.
- ~ -However, in order to heat the non-metallic element as strongly as possible-and hence carry it along at least in dissociated, if not in ionized form in the plasma jet, it has proven expedient for the non-metallic ele-ment to be added to the plasma jet on the side thereof facing the high-current arc and near the latter.
The dissociation or ionization of the non-metallic ele-ment in the~plasma jet is particularly easily achieved and maintained by it being brought about by interaction with the primary plasma jet.
Introduction of the non-metallic element into the plasma jet can be achieved in a structurally simple way by the non-metallic element being added to the plasma jet in the nozzle of the torch generating the laminar jet.
2~32 i ~2 An ernbodiment of the inventive process has proven parti-cularly suitable wherein the non-metallic element is added to the plasma jet in a I,aval nozzle sarving as noz21e for generating the laminar jet.
In a particularly simple embodiment, provision is made for the non-metallic element to be added to the plasma jet together with the material to be sprayed so no ad-ditional apparatus is necessary for adding the non-me-tallic element to the plasma jet and the apparatus nor-mally suitable for the plasma spraying can be used.
Within the scope of the inventive solution, an embodi-ment is particularly preferred wherein the non-metallic element is introduced into the plasma jet in gaseous form as good, uniform distribution and easy dissoci-ation or ionization of the non-metallic element are thereby possible.
~- 'Hence-it isj for example, expedient for the non-metallic element to be introduced into the plasma jet by a gas which liberates it.
Since the material serving as material to be sprayed is usually present in solid form and hence has to be added to the plasma jet by a conveying medium, provision is made in a preferred solution for the non-metallic ele-ment to be included in a conveying medium for the ma-terial to be sprayed.
2~32~
Herein, it has proven expedient for the conveying medium for the material to be sprayed to be gaseous.
Within the scope of the embodiments described hereinabove, provision is expediently also made for the material to be sprayed to be present in powder form.
Within the scope of the embodiments described so far, no details were given as to how the material to be sprayed is conducted in the plasma jet. It is particularly ad-vantageous for the material to be sprayed to be condnc-ted, after its introduction, in the core region near the axis of the plasma jet so it is, on the one hand, heated as-uniformly.as.possible::by.the plasma jet surrounding it and, on the other hand, is also protected.
Similarly,.no.details were given as to how the material to be sprayed is introduced into the plasma jet. It has likewise proven expedient for the material to be sprayed to be added to a primary plasma jet downstream from the high-current arc.
This is preferably carried out by t.he material to be sprayed being added to the primary plasma jet on its side facing the high-current arc and near the latter.
In a particularly preferred embodiment of the inven-tive process, provision is made for the material to be sprayed to be added to the plasma jet in the nozzle of the torch for generating the laminar jet.
2~32~7~
Particularly good results are obtained when the material to be sprayed is addod to the plasma jet in a Laval nozzle serving as nozzle for generating the laminar jet.
Since relatively high temperatures are usually present in the plasma jet, undesired reactions of the non-metallic carried along in it can also occur very easily therein.
For this reason, provision is expediently made fo~ the plasma jet to be essentially free from chemical elements which react with the non-metallic element to form stable chemical compounds. In particular, it is expedient for the plasma jet to be substantially free of hydrogen.
Regarding the type of. the plasma.gas, provision is expe-~ .-.. .:- -diently made for.th.is.to include an inert gas.
In a preferred embodiment, provision is made for the primary plasma gas to include argon, with a major con-stituent thereof preferably consisting of argon.
In addition, provision is expediently made for the primary plasma:gas to include-in-addition to the argon addition-al gases which increase enthalpy and toughness, with these serving to provide the necessary energy, on the one hand, for heating the material to be sprayed and, as the case may be, for the dissociation or ionization of the non-metallic element.
Advantageous values for the enthalpy of the primary plasma are enthalpies of ~ 20 kJ/kg at 10 000 degrees C, 2~32~'2 it is even better for the enthalpy to be > 30 kJ/kg at 10 000 degrees and optimum values are obtained when the enthalpy is ~ 40 kJ/kg at 10 000 degrees C.
A further preferred inert gas is helium.
In a preferred embodiment of the present invention, pro-vision is made for helium as additional gas increasing the free enthalpy to be added to the argon as main plasma gas.
Another advantageous possibility is to add nitrogen in-stead of helium as additional gas increasing the free enthalpy to the argon as main plasma gas.
, - -- -To ensure-tha-t the non-metallic element is present in a sufficiently high concentration to carry out the in-ventive process, provision is preferably made for the - gaseous, non-metallic element to be carried along in the plasma jet in a proportion of more than 5 ~ of the gases included therein~
.
It is even better for this proportion to be more than 15 % of the gases included in the plasma jet~
To ensure that the non-metallic element is present in the pIasma jet in dissociated form, provision is made for the plasma jet to have an enthalpy and temperature bringing about dissociation of the non metallic element.
21 ~ 3 2 .3L 71 f'~
If the non-metallic element is also to be present in i.onized form, it is even better for the plasma jet to have a temperature and free enthalpy bringing about ionization of the non-metallic element.
If a sufficiently high temperature of the plasma jet cannot be achieved with the plasma torch itself, it is advantageous for heating to be provided in addition for the plasma jet following the high-current arc. In par-ticular, it is expedient for the additional heating to be carried out by high-frequency coupling into the plasma jet, with this being inductive or capacitive coupling-in.
So far, no further details were given as to the compo-s.ition of.th~e.chemica~l..compound. A chemical-compound in-cluding a metal as fu.rther chemical'element has proven particular'ly suitable for use of the inventive process.
Preferred materials are oxidized materials, for example, spinels and perovskites-on a-nickel or cobalt or nickel-cobalt basis. It is, however, also conceivable to apply all..-.~possibl~e...kinds..of spine-ls.and perovskites in accor-dance~wi'th:the'inventive process. This aIso applies'to spinel-like and perovskite-like compounds and to non-oxidized compounds, for example, nitrides, halides, carbides, etc., with nitrogen or halogens or also non-metallic compounds, methane or acetylene then being carried along as non-metallic.element by the plasma jet.
All-these-.compounds are preferably characterized by ~3~7~
the chemical compound exhibiting in the region of its melting temperature a free enthalpy of formation lying in the region of zero or above, i.e., it is a chemical compound which has an increasing tendency to deco~pose as the temperature rises.
Sufficient and uniform heating of the chemical compound which is requird for good formation of the coating on the substrate is advantageously achieved by tha chemi-cal.compound interacting with the laminar plasma jet within the latter over a length of at least 60 mm. Even better values are obtained when the length of the in-teraction is at least 80 mm, very good values when the length~of..the interaction is at least 100 mm and opti-mum values when the.length.of the interaction is at least 150 mm.
To obtain a.coating-which adheres well on the substrate, it is necessary, as mentioned at the beginning, to heat the material to be sprayed to as high a temperature as possible, for example, above the melting point, but there must still not:-be.any noticeable vapori~ation of the material. For this-reason, it is adv.antageous for the chemical compound to be heated to at least approxi-mately 500 degrees C in the plasma jet. It is even better for the chemical compound to be heated to at least l,000 degrees C or even better to at least 1,500 degrees C or best''of:all to at least 2,000 degrees C.
., ~ - The be'st adhering properties of the coatings are ach-2~32;~ ~
ieved when -the chemical compound is hea-ted in the plasma jet to at least a temperature in the region of its melting point.
The best results are obtained when the chemical com-pound is heated to at least a temperature corresponding to its melting point.
Particularly good results are obtained with the inven-tive process when the chemical compound is moderately heated in the plasma jet, this meaning that the chemi-cal compound is heated to a surface temperature of be-tween O and 1000 degrees C, preferably O and 500 de--grees C above its melting point, i.e., there is no strong heating-beyond the melting point.
.
The:inventive process is used particularly when the material serves as catalytically active coating.
In a further embodiment, the material serves as elec-trocatalytically active coating.
, - . . : . - :
In other preferred embodiments within the scope of the ' inventive process, the material serves as tribolo~ically effective coating.
In a further embodiment, the material serves as super-conductive coating.
'' . -Particularly good~results are achieved within the scope 2~37,~
of the present invention when the plasma sprayiny is carried out with an ultrasonic jet as coatings which adhere very firmly to the substrate are thereby obtained.
Further features and advantages of the present invention are the subject matter of the following description in conjunction with the drawings. The drawings show:
~igure 1 a schematic illustration of an apparatus for carrying out-the inventive process; and ~igure 2 an X-ray diffractogram wherein ~igure 2a --shows the-X-r-ay diffractogram of cobalt spine'l powder produced at ~00 degrees;
~igure 2b?: the-X-ray-;diffractogram of an applied coat-ing of cobalt spinel with argon as plasma -gas-and argon as-carrier gas for the material to be sprayed;
~Figure._2c_.: the.X-ra-y diffractogram of an applied coat-ing o cobalt spinsl with argon and hydrogen as plasma gas and argon as carrier gas for the material to be sprayed; and ~igure 2d:.the:.X-r.ay.dif.fractogram of an applied coat-. :ing with argon plus-helium as plasma gas and argon..and::-oxygen-as carrier gas for the ma-terial to be sprayed.
~2~i'2 ~n apparatus for performing the inventive process com-prises - as illustrated scheTnatically in Figure 1 - a vacuum chamber 10 which is evacuatable to a preselec-table pressure by a vacuum pumping system 12. There is, furthermore, arranged in this vacuum chamber 10 a plasma torch 14 whicb generates a plasma jet 16 which strikes a substrate 18 likewise arranged in the vacuum chamber 10 and, for its part, moveable by a moving device 20 rela-tive to the plasma jet 16 in a plane extending perpen-dicular to a longitudinal axis 22 of the plasma jet 16.
A jet 24 of material to be sprayed consisting of parti-cles of a material to be applied is carried along in this plasma jet 16 and on striking the substrate 18, produces a coating 26 of this material.
The plasma torch 14 operates as d.c. torch and, f~r its ;'--?-- part, comprises-a tube-like housing 28 in which a sleave~shaped anode-34 comprising a gas channel 32 tapering conically towards an end 30 of the housing 18 facing the substrate 18 is arranged. A pin-shaped cathode 36 protrudes f:rom a rear side opposite the end 30.into-the gas-channel 32, with there remaining between --~ -thè anode 34 and the cathode 36 a ring gap 38 through which a plasrna gas flow 40 can enter the gas channel 32.
The plasma gas flow 40 is supplied to this ring gap 38 via a ring space 42 between the cathode 36 and the~ - housing 28. The gas is supplied to this ring space 42 in a manner known-per se via a plasma torch supplying -device designated in its-entirety 44 which also provides the necessary d.c. voltage between the anode 34 and the ~32~
1.
cathode 36 and, in addition, supplies a cooling channel 46 in the cathode 36 with coolant.
The gas channel 32 of the anode continues towards the substrate 18 in a nozzle channel 48 of a Laval nozzle 50 which immediately adjoins the anode 34 and from which, with the proper choice of parameters, the substantially parallsl, laminar plasma jet 16 exits. The Lavel nozzle 50 and the gas channel 32 are arranged coaxially with the longitudinal.axis 22 of the plasma jet 16.
, There is at least one first inlet channel 52 opening into the nozzle channel 48 of the Laval nozzle 50 for supplying--t~e material--to be--sprayed forming the jet 24 of matarial to be sprayed. The inlet channel 52 is supplied via a-first--f-eed--means 54. It is, however, additi-onally possible to::provide on the~.side of the - - :- -:--first inlet channel 52 facing the substrate 18 a second inlet channel 56 which is supplied via a second feed means 58.
The plasma spraying with-a- p-l-asma torch 14 in the vacuum chamber 10 is descri~ed in detail in DE-OS 35 38 390.
Furthermore, a detailed illustration of the function and mode of operation of the plasma torch is to be found in the article by:W. ~layr and R. ~enne "Investigation of a VPS~iburner-with.laval nozzle.by means of an automated -laser doppler measuring equipment" Proc. 1st Plasma-Technology Symposium, Lucerne, 1988.
.
2~2~7~
The inventive process will be described in detail here-inbelow with reference to cobalt spinel (Co304). This cobalt spinel is applied as coating to a substrate. The cobalt spinel may, for example, be supplied via the first feed means 54 and the first inlet channel 52. The cobalt spinel is present in powder form and is conveyed by a carrier gas from the first feed means 54 to the first inlet channel 52 and from there into the Laval nozzle.
gas mixture consisting of 80 ~ ~2 and 20 % Ar is prefer-ably used as carrier gas for the cobalt spinel in powder form. This oxygen (~2) constitutes the non-metallic ele-ment in free form, not bound to a foreign element, which is carried along in addition to the material to be' sprayed in the plasma ~et 16.
The torch is operated with a primary plasma gas flow which preferably includeszargon-as main gas. To increase~ ~ -the enthaIpy,-helium can be added thereto. It is also possible to add nitrogen to increase the enthalpy.
The plasma torch 14 is preferably operated such that -a-longj--laminar plasma jet-extending parallel to the longitudinal axis 22 is formed with a length of at least 150 mm. In vacuum, its speed may be from 2,000 to 3,000 meters per second. In addition, the material to be sprayed, i.e. the cobalt spinel is to be supplied such that an axially close-jet 24-of material to be sprayed~-- ~-- ~-~extending near the-longitudinal axis 22 is likewise formed-in -the core region of the-plasma jet, with speeds of the material to be sprayed of up to approximately 2~'~2~72 1,000 m/sec then prevailing and this jet 24 of material to be sprayed bei.ng protected by the part of the plasma jet 16 surrounding it. The time spent by the material to be sprayed in the plasma jet 16 between its injection into the Laval no~zle 50 and its striking the substra,e 18 is then less than 10 seconds, with interaction with the plasma jet occurring over a length of more than 150 mm.
During this short.time spent by the material to be sprayed in the plasma jet 16, the material to be sprayed is heated up in accordance with the invention to the region of the melting temperature, with melting of the ~ -- .. .... .material.to.be sprayed preferably taking place so it is - present in the molten state during the time spent in the ~ plasma jet 16. It is.. expedient for the material to be - ~s .~ s~~ sp-rayed-to----be--heated.up.~:onl~,m-oderately to a surface tem- -perature in the range of from O to 1,000 degrees above it melting point.
Owing to the short time spent by the material to be sprayed-in-the-plasma jet, the time available to the material to be sprayed for decomposition is kept very short. In addition, the oxygen carried along by the plasma jet in the inventive manner during the plasma - - spraying of cobalt spinel counteracts the decomposition ::s - . ~ of. the:cobalt.spinel as.it shifts the dissociation or -:-: ..: -..-- -decompasition-balance.toward:s:the undecomposed cobalt ~ spinel.
2~2 The power of the plasma -torch 14 is preferably such that che plasma in the plasma je-t is sufficiently hot arl~
rich in enthalpy to dissociate and ionize the oxygen supplied downstream from the plasma jet 16 and hence especially to shift the reaction balance of the cobalt spinel towards the oxide, i.e., towards the undecomposed cobalt spinel or to carry out a reoxidation of any oxides which may have become unstoichiometric. It is preferable to work with an enthalpy of the plasma of more:than 40 kJ/.kg at 10,000 degrees C..
In the inventive process, in particular to increase the enthalpy of the plasma torch 14, there must be no ad--d:ition of-hydrogen-to the-plasma gas flow as this would rsact~with-~lie ox-yge.n..supplied via the carrier gas to form water.
The advantages of the inventive process become particu-larly clear from a comparison of a coating 26 applied by the inventive process with processes in which no oxygen is carried along in the plasma jet 16. Figure 2d shows an X-ray di-f~r-actogram--of coh.alt spinel applied by the inventive process wherein it is clearly evident that essentially the reflexes of cobalt spinel (characterized by ~ ) prevail, whereas in the processes in which no oxygen was carried along in the plasma jet 16 (Figures 2b and:.2c)-clearLy-:-the reflexes of CoO (characterized by ~ ) and Co (.characterized-by-.V ) predomina-te over the reflexas-of:cobalt:spinel~ ),.-which clearly proves that the inv.ent:ive process~prevents the decomposition of co-2~3~7 ~
balt spinel in the plasma spraying.
The cobalt spinel coating, the X-ray diffractogram of which is shown in Figure 2d, was achieved with the fol-lowing parameters: Power of the plasma torch 14, 30 kW, pressure in the vacuum chamber 10, 50 mbar, plasma gas consisting of argon and helium and carrier gas for the cobalt spinel in powder form of 80 ~ ~2 and 20 % ~r. The thickness of the coating was 200 ~um and exhibited a very dense structure..and.was firmly bonded to nickel as sub-strate. The preferred order of magnitude for the coating growth is 10 ~m/sec in relation to a coating area of 10 cm and so by subjecting the substrate to controllable, ' ''~ ~. '.~th'ermal 'action,'~.t'he des'ired~coating~can be applied in one work cycle without, for example, subsequent treat-ment being necessary.
In a modification o~ the embodiment of the inventive process described hereinabove, it is, however, also possible to add the matarial to be sprayed to the plasma jet.16..via~.the second.feed means 58 and the second in-let channel 56,:with only argon serving as carrier gas and the oxygen being added separately via the first feed means 54 and the first inlet channel 52, i.e. on the "hotter" side of the plasma jet as the oxygen requires very high temperatures for the dissociation and ioni-zation, while the temperatures for the material to be~~ . .. ...:.-. ~-sprayed can be..chosen lower,.particularly when this is not cobalt spinel-but a-material with a lower melting temperature.
2~2~
~s an alternative to this, it is li~ewise possible to supply two dif~erent materials via the first feed means 5~ and via the second feed means 58, with the non-me-tallic element being supplied in the carrier gas of either the one or the other or a non-metallic element suitable for the respective material in both.
In a further modification of the inventive process, provision is made, in the event the plasma torch 14 does not.generate su.fficient-temperatures and enthalpies, for the plasma flow 16 to be heated up by an additional heating 60 downstream from the Laval nozzle, with this heating being, for example, in the form of a device for co.upling..hi.gh..f.requenc.y.into the plasma jet 16 and this bein.g carried-ou~Gap:acitively or inductively.-.
-
PROCESS FOR APPLYING CERAMIC MATERIAL
The invention relates to a process for applying a coating of ceramic material to a substrate by plasma spraying wherein the material is added to the plasma jet and includes a chemical compound, one constituent of which is a non-metallic element from the group N, C, B
or from the main groups VI or VII of tne Periodic Table which decomposes at least partially before reaching the melting point and is present in the solid phase in the applied state.
Such a process is known from DE-OS 30 24 611. Herein, iron spinel and cobalt spinel are applied by plasma spraying at low torch power. In view of the low torch power, it is to be assumed that only the iron spinel will melt as it has a low melting point, while the co-balt spinel will only be embedded in the molten iron spinel. Furthermore, decomposition products of the co-balt spinel will presumably be present in spite of the low torch power.
With plasma spraying at low torch power, the bonding of the applied coating to the substrate is not optimum and the internal solidity of the outer coating is also li-mited. Furthermore, the coating yield is also very low for when the material to be sprayed is hurled in the still solid state by the plasma jet against the sub-strate, an impact reflection occurs at the substrate and hence only a small part of the material to be sprayed remains adhering to the substrate.
2832~7~
The object underlying the invention is, thereforer to so improve a process of the generic kind that the chemical compound contained in the material can be applied stoi-chiometrically, i.e., undecomposed to the substrate and forms an impermeable, adherent and stable coating.
This object is accomplished in accordance with the in-vention in a process of the kind described at the be-ginning in that in addition to the material to be spray-ed, the non-metallic element is carried along in the plasma jet in a free form not bound to a foreign element.
In this way, by addition of tha element, the reaction balance of the compound tending to decompose is shifted to the undecomposed compound and so this compound can be heated to sufficiently high tempertures in the plasma jet and hence form on contacting the substrate an imper-meable, adherent and stable coating which, in addition, contains the chemical compound essentially in unde-composed form.
It has proven particularly advantageous within the scope of the inventive process for a laminar jet generated by a plasma torch with a noz~le generating a laminar jet to be used as plasma jet as this laminar jet offers the best preconditions for the material to be sprayed to be heated constantly and uniformly and for an ade~uate time in order to achieve as uniform a coating as possibls on the substrate.
;
It is particularly expedient for the length of the la-2 5~ 7 ~
minar jet to be at least 60 mm from the nozzle on. Even better results are obtained with 80 mm and very good re-sults with a laminar jet length of 100 mm. Optimum results are to be achieved with a laminar jet length of 150 mm.
It has, furthermore, proven particularly expedient within the scope of the inventive solution for the latter to be carried out in vacuum as problems other-wise arise from impurities or interactions owing to the atmosphere surrounding the plasma jet.
It is preferable to use as plasma je-t that of a d.c.
plasma torch with which a plasma jet having as constant a temperature as possible and as constant a flow profile as possibla can be generated.
To shift the reaction balance in the direction towards the undecomposed chemical compound, it is particularly advantàgeous for the non-metallic element to be carried along in the plasma jet in dissocia-ted or atomic form.
In the examples of the inventive process described so far, no details were given as to how the non-metallic element is conducted in the plasma jet. It is expedi-ent for the non-metallic element to be conducted, after its introduction, in the core region near the axis of the plasma jet so there is as intensive an interaction as possible with the plasma jet surrounding it but, at th~ same time, also good shielding by the plasma jet surrounding it.
~32~72 The reaction balance can be shifted particularly well in an inven-tive way by the non-me-tallic element being car-ried along in ionized form in the plasma jet.
In principle, within the scope of the inventive process, the non-metallic element could be added to the plasma jet, for example, with the plasma gas flow. However, this would require electrode materials which are not affected by the non-metallic element. For this reason, it is more advantageous for the non-metallic element to be added to a primary plasma jet downstream from the high-current arc.
- ~ -However, in order to heat the non-metallic element as strongly as possible-and hence carry it along at least in dissociated, if not in ionized form in the plasma jet, it has proven expedient for the non-metallic ele-ment to be added to the plasma jet on the side thereof facing the high-current arc and near the latter.
The dissociation or ionization of the non-metallic ele-ment in the~plasma jet is particularly easily achieved and maintained by it being brought about by interaction with the primary plasma jet.
Introduction of the non-metallic element into the plasma jet can be achieved in a structurally simple way by the non-metallic element being added to the plasma jet in the nozzle of the torch generating the laminar jet.
2~32 i ~2 An ernbodiment of the inventive process has proven parti-cularly suitable wherein the non-metallic element is added to the plasma jet in a I,aval nozzle sarving as noz21e for generating the laminar jet.
In a particularly simple embodiment, provision is made for the non-metallic element to be added to the plasma jet together with the material to be sprayed so no ad-ditional apparatus is necessary for adding the non-me-tallic element to the plasma jet and the apparatus nor-mally suitable for the plasma spraying can be used.
Within the scope of the inventive solution, an embodi-ment is particularly preferred wherein the non-metallic element is introduced into the plasma jet in gaseous form as good, uniform distribution and easy dissoci-ation or ionization of the non-metallic element are thereby possible.
~- 'Hence-it isj for example, expedient for the non-metallic element to be introduced into the plasma jet by a gas which liberates it.
Since the material serving as material to be sprayed is usually present in solid form and hence has to be added to the plasma jet by a conveying medium, provision is made in a preferred solution for the non-metallic ele-ment to be included in a conveying medium for the ma-terial to be sprayed.
2~32~
Herein, it has proven expedient for the conveying medium for the material to be sprayed to be gaseous.
Within the scope of the embodiments described hereinabove, provision is expediently also made for the material to be sprayed to be present in powder form.
Within the scope of the embodiments described so far, no details were given as to how the material to be sprayed is conducted in the plasma jet. It is particularly ad-vantageous for the material to be sprayed to be condnc-ted, after its introduction, in the core region near the axis of the plasma jet so it is, on the one hand, heated as-uniformly.as.possible::by.the plasma jet surrounding it and, on the other hand, is also protected.
Similarly,.no.details were given as to how the material to be sprayed is introduced into the plasma jet. It has likewise proven expedient for the material to be sprayed to be added to a primary plasma jet downstream from the high-current arc.
This is preferably carried out by t.he material to be sprayed being added to the primary plasma jet on its side facing the high-current arc and near the latter.
In a particularly preferred embodiment of the inven-tive process, provision is made for the material to be sprayed to be added to the plasma jet in the nozzle of the torch for generating the laminar jet.
2~32~7~
Particularly good results are obtained when the material to be sprayed is addod to the plasma jet in a Laval nozzle serving as nozzle for generating the laminar jet.
Since relatively high temperatures are usually present in the plasma jet, undesired reactions of the non-metallic carried along in it can also occur very easily therein.
For this reason, provision is expediently made fo~ the plasma jet to be essentially free from chemical elements which react with the non-metallic element to form stable chemical compounds. In particular, it is expedient for the plasma jet to be substantially free of hydrogen.
Regarding the type of. the plasma.gas, provision is expe-~ .-.. .:- -diently made for.th.is.to include an inert gas.
In a preferred embodiment, provision is made for the primary plasma gas to include argon, with a major con-stituent thereof preferably consisting of argon.
In addition, provision is expediently made for the primary plasma:gas to include-in-addition to the argon addition-al gases which increase enthalpy and toughness, with these serving to provide the necessary energy, on the one hand, for heating the material to be sprayed and, as the case may be, for the dissociation or ionization of the non-metallic element.
Advantageous values for the enthalpy of the primary plasma are enthalpies of ~ 20 kJ/kg at 10 000 degrees C, 2~32~'2 it is even better for the enthalpy to be > 30 kJ/kg at 10 000 degrees and optimum values are obtained when the enthalpy is ~ 40 kJ/kg at 10 000 degrees C.
A further preferred inert gas is helium.
In a preferred embodiment of the present invention, pro-vision is made for helium as additional gas increasing the free enthalpy to be added to the argon as main plasma gas.
Another advantageous possibility is to add nitrogen in-stead of helium as additional gas increasing the free enthalpy to the argon as main plasma gas.
, - -- -To ensure-tha-t the non-metallic element is present in a sufficiently high concentration to carry out the in-ventive process, provision is preferably made for the - gaseous, non-metallic element to be carried along in the plasma jet in a proportion of more than 5 ~ of the gases included therein~
.
It is even better for this proportion to be more than 15 % of the gases included in the plasma jet~
To ensure that the non-metallic element is present in the pIasma jet in dissociated form, provision is made for the plasma jet to have an enthalpy and temperature bringing about dissociation of the non metallic element.
21 ~ 3 2 .3L 71 f'~
If the non-metallic element is also to be present in i.onized form, it is even better for the plasma jet to have a temperature and free enthalpy bringing about ionization of the non-metallic element.
If a sufficiently high temperature of the plasma jet cannot be achieved with the plasma torch itself, it is advantageous for heating to be provided in addition for the plasma jet following the high-current arc. In par-ticular, it is expedient for the additional heating to be carried out by high-frequency coupling into the plasma jet, with this being inductive or capacitive coupling-in.
So far, no further details were given as to the compo-s.ition of.th~e.chemica~l..compound. A chemical-compound in-cluding a metal as fu.rther chemical'element has proven particular'ly suitable for use of the inventive process.
Preferred materials are oxidized materials, for example, spinels and perovskites-on a-nickel or cobalt or nickel-cobalt basis. It is, however, also conceivable to apply all..-.~possibl~e...kinds..of spine-ls.and perovskites in accor-dance~wi'th:the'inventive process. This aIso applies'to spinel-like and perovskite-like compounds and to non-oxidized compounds, for example, nitrides, halides, carbides, etc., with nitrogen or halogens or also non-metallic compounds, methane or acetylene then being carried along as non-metallic.element by the plasma jet.
All-these-.compounds are preferably characterized by ~3~7~
the chemical compound exhibiting in the region of its melting temperature a free enthalpy of formation lying in the region of zero or above, i.e., it is a chemical compound which has an increasing tendency to deco~pose as the temperature rises.
Sufficient and uniform heating of the chemical compound which is requird for good formation of the coating on the substrate is advantageously achieved by tha chemi-cal.compound interacting with the laminar plasma jet within the latter over a length of at least 60 mm. Even better values are obtained when the length of the in-teraction is at least 80 mm, very good values when the length~of..the interaction is at least 100 mm and opti-mum values when the.length.of the interaction is at least 150 mm.
To obtain a.coating-which adheres well on the substrate, it is necessary, as mentioned at the beginning, to heat the material to be sprayed to as high a temperature as possible, for example, above the melting point, but there must still not:-be.any noticeable vapori~ation of the material. For this-reason, it is adv.antageous for the chemical compound to be heated to at least approxi-mately 500 degrees C in the plasma jet. It is even better for the chemical compound to be heated to at least l,000 degrees C or even better to at least 1,500 degrees C or best''of:all to at least 2,000 degrees C.
., ~ - The be'st adhering properties of the coatings are ach-2~32;~ ~
ieved when -the chemical compound is hea-ted in the plasma jet to at least a temperature in the region of its melting point.
The best results are obtained when the chemical com-pound is heated to at least a temperature corresponding to its melting point.
Particularly good results are obtained with the inven-tive process when the chemical compound is moderately heated in the plasma jet, this meaning that the chemi-cal compound is heated to a surface temperature of be-tween O and 1000 degrees C, preferably O and 500 de--grees C above its melting point, i.e., there is no strong heating-beyond the melting point.
.
The:inventive process is used particularly when the material serves as catalytically active coating.
In a further embodiment, the material serves as elec-trocatalytically active coating.
, - . . : . - :
In other preferred embodiments within the scope of the ' inventive process, the material serves as tribolo~ically effective coating.
In a further embodiment, the material serves as super-conductive coating.
'' . -Particularly good~results are achieved within the scope 2~37,~
of the present invention when the plasma sprayiny is carried out with an ultrasonic jet as coatings which adhere very firmly to the substrate are thereby obtained.
Further features and advantages of the present invention are the subject matter of the following description in conjunction with the drawings. The drawings show:
~igure 1 a schematic illustration of an apparatus for carrying out-the inventive process; and ~igure 2 an X-ray diffractogram wherein ~igure 2a --shows the-X-r-ay diffractogram of cobalt spine'l powder produced at ~00 degrees;
~igure 2b?: the-X-ray-;diffractogram of an applied coat-ing of cobalt spinel with argon as plasma -gas-and argon as-carrier gas for the material to be sprayed;
~Figure._2c_.: the.X-ra-y diffractogram of an applied coat-ing o cobalt spinsl with argon and hydrogen as plasma gas and argon as carrier gas for the material to be sprayed; and ~igure 2d:.the:.X-r.ay.dif.fractogram of an applied coat-. :ing with argon plus-helium as plasma gas and argon..and::-oxygen-as carrier gas for the ma-terial to be sprayed.
~2~i'2 ~n apparatus for performing the inventive process com-prises - as illustrated scheTnatically in Figure 1 - a vacuum chamber 10 which is evacuatable to a preselec-table pressure by a vacuum pumping system 12. There is, furthermore, arranged in this vacuum chamber 10 a plasma torch 14 whicb generates a plasma jet 16 which strikes a substrate 18 likewise arranged in the vacuum chamber 10 and, for its part, moveable by a moving device 20 rela-tive to the plasma jet 16 in a plane extending perpen-dicular to a longitudinal axis 22 of the plasma jet 16.
A jet 24 of material to be sprayed consisting of parti-cles of a material to be applied is carried along in this plasma jet 16 and on striking the substrate 18, produces a coating 26 of this material.
The plasma torch 14 operates as d.c. torch and, f~r its ;'--?-- part, comprises-a tube-like housing 28 in which a sleave~shaped anode-34 comprising a gas channel 32 tapering conically towards an end 30 of the housing 18 facing the substrate 18 is arranged. A pin-shaped cathode 36 protrudes f:rom a rear side opposite the end 30.into-the gas-channel 32, with there remaining between --~ -thè anode 34 and the cathode 36 a ring gap 38 through which a plasrna gas flow 40 can enter the gas channel 32.
The plasma gas flow 40 is supplied to this ring gap 38 via a ring space 42 between the cathode 36 and the~ - housing 28. The gas is supplied to this ring space 42 in a manner known-per se via a plasma torch supplying -device designated in its-entirety 44 which also provides the necessary d.c. voltage between the anode 34 and the ~32~
1.
cathode 36 and, in addition, supplies a cooling channel 46 in the cathode 36 with coolant.
The gas channel 32 of the anode continues towards the substrate 18 in a nozzle channel 48 of a Laval nozzle 50 which immediately adjoins the anode 34 and from which, with the proper choice of parameters, the substantially parallsl, laminar plasma jet 16 exits. The Lavel nozzle 50 and the gas channel 32 are arranged coaxially with the longitudinal.axis 22 of the plasma jet 16.
, There is at least one first inlet channel 52 opening into the nozzle channel 48 of the Laval nozzle 50 for supplying--t~e material--to be--sprayed forming the jet 24 of matarial to be sprayed. The inlet channel 52 is supplied via a-first--f-eed--means 54. It is, however, additi-onally possible to::provide on the~.side of the - - :- -:--first inlet channel 52 facing the substrate 18 a second inlet channel 56 which is supplied via a second feed means 58.
The plasma spraying with-a- p-l-asma torch 14 in the vacuum chamber 10 is descri~ed in detail in DE-OS 35 38 390.
Furthermore, a detailed illustration of the function and mode of operation of the plasma torch is to be found in the article by:W. ~layr and R. ~enne "Investigation of a VPS~iburner-with.laval nozzle.by means of an automated -laser doppler measuring equipment" Proc. 1st Plasma-Technology Symposium, Lucerne, 1988.
.
2~2~7~
The inventive process will be described in detail here-inbelow with reference to cobalt spinel (Co304). This cobalt spinel is applied as coating to a substrate. The cobalt spinel may, for example, be supplied via the first feed means 54 and the first inlet channel 52. The cobalt spinel is present in powder form and is conveyed by a carrier gas from the first feed means 54 to the first inlet channel 52 and from there into the Laval nozzle.
gas mixture consisting of 80 ~ ~2 and 20 % Ar is prefer-ably used as carrier gas for the cobalt spinel in powder form. This oxygen (~2) constitutes the non-metallic ele-ment in free form, not bound to a foreign element, which is carried along in addition to the material to be' sprayed in the plasma ~et 16.
The torch is operated with a primary plasma gas flow which preferably includeszargon-as main gas. To increase~ ~ -the enthaIpy,-helium can be added thereto. It is also possible to add nitrogen to increase the enthalpy.
The plasma torch 14 is preferably operated such that -a-longj--laminar plasma jet-extending parallel to the longitudinal axis 22 is formed with a length of at least 150 mm. In vacuum, its speed may be from 2,000 to 3,000 meters per second. In addition, the material to be sprayed, i.e. the cobalt spinel is to be supplied such that an axially close-jet 24-of material to be sprayed~-- ~-- ~-~extending near the-longitudinal axis 22 is likewise formed-in -the core region of the-plasma jet, with speeds of the material to be sprayed of up to approximately 2~'~2~72 1,000 m/sec then prevailing and this jet 24 of material to be sprayed bei.ng protected by the part of the plasma jet 16 surrounding it. The time spent by the material to be sprayed in the plasma jet 16 between its injection into the Laval no~zle 50 and its striking the substra,e 18 is then less than 10 seconds, with interaction with the plasma jet occurring over a length of more than 150 mm.
During this short.time spent by the material to be sprayed in the plasma jet 16, the material to be sprayed is heated up in accordance with the invention to the region of the melting temperature, with melting of the ~ -- .. .... .material.to.be sprayed preferably taking place so it is - present in the molten state during the time spent in the ~ plasma jet 16. It is.. expedient for the material to be - ~s .~ s~~ sp-rayed-to----be--heated.up.~:onl~,m-oderately to a surface tem- -perature in the range of from O to 1,000 degrees above it melting point.
Owing to the short time spent by the material to be sprayed-in-the-plasma jet, the time available to the material to be sprayed for decomposition is kept very short. In addition, the oxygen carried along by the plasma jet in the inventive manner during the plasma - - spraying of cobalt spinel counteracts the decomposition ::s - . ~ of. the:cobalt.spinel as.it shifts the dissociation or -:-: ..: -..-- -decompasition-balance.toward:s:the undecomposed cobalt ~ spinel.
2~2 The power of the plasma -torch 14 is preferably such that che plasma in the plasma je-t is sufficiently hot arl~
rich in enthalpy to dissociate and ionize the oxygen supplied downstream from the plasma jet 16 and hence especially to shift the reaction balance of the cobalt spinel towards the oxide, i.e., towards the undecomposed cobalt spinel or to carry out a reoxidation of any oxides which may have become unstoichiometric. It is preferable to work with an enthalpy of the plasma of more:than 40 kJ/.kg at 10,000 degrees C..
In the inventive process, in particular to increase the enthalpy of the plasma torch 14, there must be no ad--d:ition of-hydrogen-to the-plasma gas flow as this would rsact~with-~lie ox-yge.n..supplied via the carrier gas to form water.
The advantages of the inventive process become particu-larly clear from a comparison of a coating 26 applied by the inventive process with processes in which no oxygen is carried along in the plasma jet 16. Figure 2d shows an X-ray di-f~r-actogram--of coh.alt spinel applied by the inventive process wherein it is clearly evident that essentially the reflexes of cobalt spinel (characterized by ~ ) prevail, whereas in the processes in which no oxygen was carried along in the plasma jet 16 (Figures 2b and:.2c)-clearLy-:-the reflexes of CoO (characterized by ~ ) and Co (.characterized-by-.V ) predomina-te over the reflexas-of:cobalt:spinel~ ),.-which clearly proves that the inv.ent:ive process~prevents the decomposition of co-2~3~7 ~
balt spinel in the plasma spraying.
The cobalt spinel coating, the X-ray diffractogram of which is shown in Figure 2d, was achieved with the fol-lowing parameters: Power of the plasma torch 14, 30 kW, pressure in the vacuum chamber 10, 50 mbar, plasma gas consisting of argon and helium and carrier gas for the cobalt spinel in powder form of 80 ~ ~2 and 20 % ~r. The thickness of the coating was 200 ~um and exhibited a very dense structure..and.was firmly bonded to nickel as sub-strate. The preferred order of magnitude for the coating growth is 10 ~m/sec in relation to a coating area of 10 cm and so by subjecting the substrate to controllable, ' ''~ ~. '.~th'ermal 'action,'~.t'he des'ired~coating~can be applied in one work cycle without, for example, subsequent treat-ment being necessary.
In a modification o~ the embodiment of the inventive process described hereinabove, it is, however, also possible to add the matarial to be sprayed to the plasma jet.16..via~.the second.feed means 58 and the second in-let channel 56,:with only argon serving as carrier gas and the oxygen being added separately via the first feed means 54 and the first inlet channel 52, i.e. on the "hotter" side of the plasma jet as the oxygen requires very high temperatures for the dissociation and ioni-zation, while the temperatures for the material to be~~ . .. ...:.-. ~-sprayed can be..chosen lower,.particularly when this is not cobalt spinel-but a-material with a lower melting temperature.
2~2~
~s an alternative to this, it is li~ewise possible to supply two dif~erent materials via the first feed means 5~ and via the second feed means 58, with the non-me-tallic element being supplied in the carrier gas of either the one or the other or a non-metallic element suitable for the respective material in both.
In a further modification of the inventive process, provision is made, in the event the plasma torch 14 does not.generate su.fficient-temperatures and enthalpies, for the plasma flow 16 to be heated up by an additional heating 60 downstream from the Laval nozzle, with this heating being, for example, in the form of a device for co.upling..hi.gh..f.requenc.y.into the plasma jet 16 and this bein.g carried-ou~Gap:acitively or inductively.-.
-
Claims (45)
1. A process for applying a coating of ceramic material to a substrate by plasma spraying, wherein a material forming the coating of ceramic material is added to a plasma jet as a material to be sprayed, comprising the steps of:
providing a plasma torch;
introducing a primary plasma gas comprising argon and additional gas other than argon and hydrogen for increasing enthalpy to said plasma torch to produce a plasma jet having an enthalpy of more than 20 MJ/kg at 10,000°C.;
providing a material to be sprayed, said material including a chemical compound having the property of decomposing at least partially when heated in an inert environment before reaching its melting point, providing a non-metallic element from the group N, C, B or from the main groups VIa or VIIa of the Periodic Table, introducing said material to be sprayed and said non-metallic element into said plasma jet downstream of a high-current arc of said plasma torch, wherein said plasma jet heats said nonmetallic element to a free dissociated or ionized form not bound to a foreign element;
heating said material to be sprayed in said plasma jet to a temperature of at most 1000 degrees C. above the melting point of said chemical compound and;
spraying said material to be sprayed, with said plasma jet, onto said substrate.
providing a plasma torch;
introducing a primary plasma gas comprising argon and additional gas other than argon and hydrogen for increasing enthalpy to said plasma torch to produce a plasma jet having an enthalpy of more than 20 MJ/kg at 10,000°C.;
providing a material to be sprayed, said material including a chemical compound having the property of decomposing at least partially when heated in an inert environment before reaching its melting point, providing a non-metallic element from the group N, C, B or from the main groups VIa or VIIa of the Periodic Table, introducing said material to be sprayed and said non-metallic element into said plasma jet downstream of a high-current arc of said plasma torch, wherein said plasma jet heats said nonmetallic element to a free dissociated or ionized form not bound to a foreign element;
heating said material to be sprayed in said plasma jet to a temperature of at most 1000 degrees C. above the melting point of said chemical compound and;
spraying said material to be sprayed, with said plasma jet, onto said substrate.
2. A process as defined in claim 1, characterized in that a nozzle for generating a laminar jet as said plasma jet is provided downstream of said high current arc.
3. A process as defined in claim 2, characterized in that said plasma jet is generated by a d.c. torch.
4. A process as defined in claim 3, characterized in that said non-metallic element is added to said plasma jet downstream from said high-current arc.
5. A process as defined in claim 4, characterized in that said non-metallic element is added to said plasma jet downstream of said high-current arc, and closer to said arc than to said substrate.
6. A process as defined in claim 2, characterized in that said non-metallic element is conducted, after its introduction, in the core region ofsaid plasma jet.
7. A process as defined in claim 2, characterized in that said non-metallic element is added to said plasma jet in the nozzle of said torch generating said laminar jet.
8. A process as defined in claim 7, characterized in that said non-metallic element is added to said plasma jet in a Laval nozzle serving as the nozzle generating said laminar jet.
9. A process as defined in claim 2, characterized in that said chemical compound interacts with said laminar plasma jet over a length of at least 60 mm.
10. A process as defined in claim 1, characterized in that said plasma spraying is carried out in a vacuum.
11. A process as defined in claim 1, characterized in that said non-metallic element is carried along in dissociated form in said plasma jet.
12. A process as defined in claim 1, characterized in that said non-metallic element is carried along in ionized form in said plasma jet.
13. A process as defined in claim 1, characterized in that said non-metallic element is added to said plasma jet together with said material to be sprayed.
14. A process as defined in claim 1, characterized in that said non-metallic element is introduced into said plasma jet in gaseous form.
15. A process as defined in claim 1, characterized in that said non-metallic element is liberated from a gas introduced into said plasma jet.
16. A process as defined in claim 1, characterized in that said non-metallic element is included in a conveying medium for said material to be sprayed.
17. A process as defined in claim 16, characterized in that said conveying medium for said material to be sprayed is gaseous.
18. A process as defined in claim 1, characterized in that said material to be sprayed which is added to said plasma jet is in powder form.
19. A process as defined in claim 1, characterized in that said material to be sprayed is conducted, after its introduction, in the core region of said plasma jet.
20. A process as defined in claim 1, wherein a nozzle is provided downstream of said high current arc, and said material to be sprayed is added to said plasma jet in said nozzle.
21. A process as defined in claim 20, wherein said nozzle is a Laval nozzle which forms said plasma jet into a laminar jet.
22. A process as defined in claim 1, characterized in that said plasma jet is essentially free of chemical elements which could react with said non-metallic element to form stable chemical compounds.
23. A process as defined in claim 22, characterized in that said plasma jet is essentially free of hydrogen.
24. A process as defined in claim 1, characterized in that said primary plasma gas exhibits an enthalpy of >30 MJ/Kg at 10,000 degrees C.
25. A process as defined in claim 24, characterized in that said primary plasma gas exhibits an enthalpy of >40 MJ/Kg at 10,000 degrees C.
26. A process as defined in claim 1, characterized in that said plasma gas includes helium.
27. A process as defined in claim 1, characterized in that helium or nitrogen is added as additional gas increasing the free enthalpy and the viscosity of the primary plasma gas.
28. A process as defined in claim 1, characterized in that said plasma jet exhibits an enthalpy and temperature bringing about dissociation of said non-metallic element.
29. A process as defined in claim 1, characterized in that said plasma jet exhibits an enthalpy and temperature bringing about ionization of said non-metallic element.
30. A process as defined in claim 1, characterized in that an additional heating step is provided for said plasma jet following said high-current arc generating said plasma jet.
31. A process as defined in claim 30, characterized in that said additional heating is carried out by a high-frequency coupling into said plasma jet.
32. A process as defined in claim 1, characterized in that said chemical compound includes a metal.
33. A process as defined in claim 1, characterized in that said chemical compound exhibits in the region of its melting temperature a free enthalpy of formation lying in the region of zero and above.
34. A process as defined in claim 1, characterized in that said chemical compound is heated in said plasma jet to at least approximately 500 degrees C.
35. A process as defined in claim 1, characterized in that said coating of ceramic material comprises a catalytically active coating.
36. A process as defined in claim 1, characterized in that said coating of ceramic material comprises an electro-catalytically active coating.
37. A process as defined in claim 1, characterized in that said coating of ceramic material comprises a tribologically active coating.
38. A process as defined in claim 1, characterized in that said coating of ceramic material comprises a superconductive coating.
39. A process as defined in claim 1, characterized in that said plasma spraying is carried out with an ultrasonic jet.
40. A process as defined in claim 1, characterized in that said primary plasma gas comprises additional gases for increasing the viscosity of said primary plasma gas.
41. A process for applying a coating of ceramic material to a substrate by plasma spraying, wherein a material forming the coating of ceramic material is added to a plasma jet as a material to be sprayed, comprising the steps of:
providing a plasma torch;
introducing a primary plasma gas, comprising argon and additional gas other than argon and hydrogen for increasing enthalpy and the viscosity of said plasma gas, to said plasma torch to produce a laminar plasma jet;
providing a material to be sprayed, said material including a chemcial compound having the property of decomposing at least partially when heated in an inert environment before reaching its melting point, providing a non-metallic element from the group N, C, B or from the main groups VIa or VIIa of the Periodic Table, introducing said material to be sprayed and said non-metallic element into said plasma jet downstream of a high-current arc of said plasma torch, wherein said plasma jet interacts with said non-metallic element for obtaining said non-metallic element in dissociated or ionized form in addition to said material to be sprayed;
heating said material to be sprayed in said plasma jet to a temperature of at most 1000 degrees C. above the melting point of said chemical compound and;
spraying said material to be sprayed, with said plasma jet, onto said substrate.
providing a plasma torch;
introducing a primary plasma gas, comprising argon and additional gas other than argon and hydrogen for increasing enthalpy and the viscosity of said plasma gas, to said plasma torch to produce a laminar plasma jet;
providing a material to be sprayed, said material including a chemcial compound having the property of decomposing at least partially when heated in an inert environment before reaching its melting point, providing a non-metallic element from the group N, C, B or from the main groups VIa or VIIa of the Periodic Table, introducing said material to be sprayed and said non-metallic element into said plasma jet downstream of a high-current arc of said plasma torch, wherein said plasma jet interacts with said non-metallic element for obtaining said non-metallic element in dissociated or ionized form in addition to said material to be sprayed;
heating said material to be sprayed in said plasma jet to a temperature of at most 1000 degrees C. above the melting point of said chemical compound and;
spraying said material to be sprayed, with said plasma jet, onto said substrate.
42. A process in accordance with claim 41, wherein a nozzle adapted to generate said laminar plasma jet is provided downstream of said high-current arc, comprising the further step of:
providing a vacuum for plasma spraying therein, wherein said laminar plasma jet is produced in said vacuum, minimizing decomposition of said material to be sprayed by:
(i) heating said non-metallic element to a dissociated or ionized form in said laminar plasma jet having said enthalpy, (ii) heating said chemical compound in said plasma jet to a temperature of no greater than 1000 degrees C. above its melting point, and (iii) said spraying step carries said material to be sprayed with said laminar plasma jet under said vacuum, said heating step (i) heats said non-metallic element to a dissociated or ionized form in said laminar plasma jet and said additional gas in said primary plasma gas increases enthalpy to said plasma torch to provide said laminar plasma jet with an enthalpy of more than 20 MJ/kg at 10,000°C.
providing a vacuum for plasma spraying therein, wherein said laminar plasma jet is produced in said vacuum, minimizing decomposition of said material to be sprayed by:
(i) heating said non-metallic element to a dissociated or ionized form in said laminar plasma jet having said enthalpy, (ii) heating said chemical compound in said plasma jet to a temperature of no greater than 1000 degrees C. above its melting point, and (iii) said spraying step carries said material to be sprayed with said laminar plasma jet under said vacuum, said heating step (i) heats said non-metallic element to a dissociated or ionized form in said laminar plasma jet and said additional gas in said primary plasma gas increases enthalpy to said plasma torch to provide said laminar plasma jet with an enthalpy of more than 20 MJ/kg at 10,000°C.
43. A process as defined in claim 41, wherein said additional gas for increasing enthalpy comprises helium.
44. A process for applying a coating of ceramic material to a substrate by plasma spraying, wherein a material forming the coating of ceramic material is added to a plasma jet as a material to be sprayed, comprising the steps of:
providing a vacuum for plasma spraying therein;
providing a plasma torch with a nozzle adapted to generate a laminar plasma jet;
introducing a primary plasma gas comprising argon and additional gas other than argon and hydrogen for increasing enthalpy to said plasma torch to produce said laminar plasma jet;
providing a material to be sprayed, said material including a chemical compound having the property of decomposing at least partially when heated in an inert environment before reaching its melting point;
providing a non-metallic element from the group N, C, B or from the main groups Vla or Vlla of the Periodic Table;
introducing said material to be sprayed and said non-metallic element into said plasma jet downstream of a high-current arc of said plasma torch, wherein said plasma jet carries said non-metallic element in a free form not bound to a foreign element in addition to said material to be sprayed; and uniformly heating said material to be sprayed and said chemical compound in said laminar plasma jet to at most 1000 degrees C.
above the melting point of said chemical compound, and spraying said material to be sprayed onto said substrate with said laminar plasma jet in said vacuum.
providing a vacuum for plasma spraying therein;
providing a plasma torch with a nozzle adapted to generate a laminar plasma jet;
introducing a primary plasma gas comprising argon and additional gas other than argon and hydrogen for increasing enthalpy to said plasma torch to produce said laminar plasma jet;
providing a material to be sprayed, said material including a chemical compound having the property of decomposing at least partially when heated in an inert environment before reaching its melting point;
providing a non-metallic element from the group N, C, B or from the main groups Vla or Vlla of the Periodic Table;
introducing said material to be sprayed and said non-metallic element into said plasma jet downstream of a high-current arc of said plasma torch, wherein said plasma jet carries said non-metallic element in a free form not bound to a foreign element in addition to said material to be sprayed; and uniformly heating said material to be sprayed and said chemical compound in said laminar plasma jet to at most 1000 degrees C.
above the melting point of said chemical compound, and spraying said material to be sprayed onto said substrate with said laminar plasma jet in said vacuum.
45. A process as defined in claim 44, wherein said additional gas for increasing enthalpy comprises helium.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3914722A DE3914722A1 (en) | 1989-05-04 | 1989-05-04 | METHOD FOR APPLYING CERAMIC MATERIAL |
| DEP3914722.3 | 1989-05-04 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2032172A1 CA2032172A1 (en) | 1990-11-05 |
| CA2032172C true CA2032172C (en) | 1997-12-16 |
Family
ID=6380075
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002032172A Expired - Fee Related CA2032172C (en) | 1989-05-04 | 1990-04-26 | Process for applying ceramic coating using a plasma jet carrying a free form non-metallic element |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0425623B1 (en) |
| CA (1) | CA2032172C (en) |
| DE (2) | DE3914722A1 (en) |
| WO (1) | WO1990013681A1 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4237980A1 (en) * | 1992-11-11 | 1994-05-19 | Krupp Ag Hoesch Krupp | Prodn. of multilayered nitrated or nitride coating by reactive plasma spraying - in which successive layers are sprayed onto base layer with step increases of partial pressure of nitrogen in the plasma jet |
| DE4406940A1 (en) * | 1994-03-03 | 1995-09-07 | Cerasiv Gmbh | Process for the production of coated materials |
| US5573682A (en) * | 1995-04-20 | 1996-11-12 | Plasma Processes | Plasma spray nozzle with low overspray and collimated flow |
| GB9712801D0 (en) * | 1997-06-19 | 1997-08-20 | Boc Group Plc | Improved plasma spraying |
| DE10001620A1 (en) * | 2000-01-17 | 2001-07-19 | Abb Alstom Power Ch Ag | Process used for coating a blade of a gas turbine comprises exciting the base material during coating in an ultrasound frequency range using a transmitting head connected to a vibrator |
| EP1495151B1 (en) * | 2002-04-12 | 2008-11-26 | Sulzer Metco AG | Plasma injection method |
| DE102009037846A1 (en) * | 2009-08-18 | 2011-02-24 | Siemens Aktiengesellschaft | Particle filled coatings, methods of manufacture and uses therefor |
| RU2735385C1 (en) * | 2019-12-10 | 2020-10-30 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Сибирский государственный университет науки и технологий имени академика М.Ф. Решетнева" (СибГУ им. М.Ф. Решетнева) | Plasmatron for application of coatings on inner surfaces of articles |
| CN116121691A (en) * | 2023-03-23 | 2023-05-16 | 西安稀有金属材料研究院有限公司 | Laminar plasma spraying wear-resistant coating and preparation method thereof |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1429278A (en) * | 1964-08-06 | 1966-02-25 | Air Liquide | Improvement in metal carbide spraying processes |
| GB1182242A (en) * | 1966-02-11 | 1970-02-25 | United States Borax Chem | Improvements in or relating to Nitrides. |
| US3640757A (en) * | 1968-08-09 | 1972-02-08 | Avco Corp | Flame deposited oxide coating and method of making same |
| DE2038894C3 (en) * | 1970-08-05 | 1974-08-29 | Bosch Gmbh Robert | Process for the production of coated electrodes for spark gaps and electrodes produced according to this process |
| LU71343A1 (en) * | 1974-11-22 | 1976-03-17 | ||
| DD144426A1 (en) * | 1979-06-21 | 1980-10-15 | Norbert Dittmann | PROCESS FOR COATING METAL SURFACES |
| JPS61259777A (en) * | 1985-05-13 | 1986-11-18 | Onoda Cement Co Ltd | Single-torch type plasma spraying method and apparatus |
-
1989
- 1989-05-04 DE DE3914722A patent/DE3914722A1/en not_active Ceased
-
1990
- 1990-04-26 WO PCT/EP1990/000674 patent/WO1990013681A1/en active IP Right Grant
- 1990-04-26 DE DE90906956T patent/DE59005005D1/en not_active Expired - Fee Related
- 1990-04-26 EP EP90906956A patent/EP0425623B1/en not_active Expired - Lifetime
- 1990-04-26 CA CA002032172A patent/CA2032172C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2032172A1 (en) | 1990-11-05 |
| DE3914722A1 (en) | 1990-11-08 |
| DE59005005D1 (en) | 1994-04-21 |
| EP0425623A1 (en) | 1991-05-08 |
| EP0425623B1 (en) | 1994-03-16 |
| WO1990013681A1 (en) | 1990-11-15 |
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| MKLA | Lapsed |