US20140287261A1 - Process for producing a protective chromium layer - Google Patents
Process for producing a protective chromium layer Download PDFInfo
- Publication number
- US20140287261A1 US20140287261A1 US14/352,491 US201214352491A US2014287261A1 US 20140287261 A1 US20140287261 A1 US 20140287261A1 US 201214352491 A US201214352491 A US 201214352491A US 2014287261 A1 US2014287261 A1 US 2014287261A1
- Authority
- US
- United States
- Prior art keywords
- chromium
- powder
- layer
- nickel
- protective layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C23C4/127—
-
- 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
- C23C4/134—Plasma spraying
-
- 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
- C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
-
- 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
- C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
- C23C4/06—Metallic material
-
- 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
- C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
- C23C4/06—Metallic material
- C23C4/08—Metallic material containing only metal elements
-
- 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
-
- 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
- C23C4/18—After-treatment
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T50/00—Aeronautics or air transport
- Y02T50/60—Efficient propulsion technologies, e.g. for aircraft
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/1266—O, S, or organic compound in metal component
Definitions
- the invention relates to a process for producing a protective chromium layer according to the preamble of claim 1 as well as to the use of a plasma-sprayed protective layer.
- Chromium is one of the most important metals for coatings. Its very high corrosion resistance to many aggressive media in a broad temperature range is comparable with that of noble metals. Depending on how they are produced, chromium coatings have very different properties.
- Galvanic chromium layers are the oldest and most widely distributed layers based on chromium.
- the first description of electrolytic deposition of chromium goes back to A. C. Becquerel in 1843.
- R. W. Bunsen described the deposition of chromium from hot chromium(III) chloride solution with carbon anodes and platinum cathodes.
- Erik Liebreichs invented chromium deposition in the chromium bath (DE 398054 and DE 448526). Therein the galvanic bath consisted of CrO 3 and H 2 SO 4 .
- almost all chromium layers have been produced according to this method.
- layers of pure chromium with a thickness of ⁇ 1 ⁇ m to approximately 300 ⁇ m are applied on completely different substrates (metals, glasses, ceramics, plastics and even wood).
- the coating is known as decorative chrome plating (layers ⁇ 5 ⁇ m) or as hard chrome plating (layer thicknesses: 10-200 ⁇ m).
- the properties of galvanically deposited chromium layers consist in very high hardness and brittleness, relatively weak adherence to the substrate and a fine network of cracks at layer thicknesses>5 ⁇ m. These properties, together with the fact that chromium has a low coefficient of thermal expansion—well under that of the most important metallic substrates—limit the use of galvanic chromium layers considerably.
- these chromium layers are basically permeable for gaseous and liquid media, their mechanical durability is relatively low due to weak adherence and high brittleness, and the maximum permissible operating temperature is lower than 500° C., even though chromium as a compact metal can withstand temperatures higher than 1100° C. in air.
- PVD and CVD chromium layers are obtained by deposition from the gas phase in the vacuum furnace.
- PVD physical vapor deposition
- CVD chemical vapor deposition
- the CVD chromium layers basically have higher adherence than PVD chromium layers.
- the CVD process requires considerably higher temperatures of 800-1000° C., compared with 200-500° C. for the PVD process. Both processes permit the application of dense thin layers from pure chromium or from chromium nitride (CrN).
- the PVD and especially the CVD chromium layers have very good adherence to the substrate, but on the other hand are much more expensive than galvanic layers and therefore are of only limited use for parts with large surface areas. Moreover, the maximum layer thickness is only approximately 10 ⁇ m.
- thermochemical diffusion of chromium at temperatures of 1000-1200° C. known by the term “thermal chrome plating”
- thermal chrome plating comprises two different process variants, although they lead largely to the same results: the known (DE 1905717) diffusion of chromium from a solid phase, e.g. chromium powder, and the known gas chromizing (EP 0043742 A1) from a gas phase, e.g. CrCl 3 .
- chromium diffuses into a steel surface as far as a depth of approximately 50 ⁇ m, thus forming a protective layer.
- This diffusion layer has a maximum chromium concentration of 50%, together with high corrosion resistance and high hardness of the steel surface.
- the diffusion chromium layers are actually not pure chromium layers such as galvanic or PVD chromium layers, they also have entirely different properties, such as good adherence, good mechanical strength and a coefficient of thermal expansion close to that of steel. These properties permit use of parts coated with diffusion chromium at temperatures higher than 800° C. Compared with layers of pure chromium, however, the high-temperature corrosion resistance of the diffusion chromium layers is much poorer than that for compact metallic chromium. The layers of pure chromium are also superior in terms of wet chemical corrosion resistance. Despite comparatively favorable properties of diffusion chromium layers, their use is only very limited, because of their high complexity.
- thermoly sprayed protective layer for metallic substrates wherein the spray powder comprises at least two components, of which the first is a silicatic mineral or rock and the second is a metal powder and/or a further silicatic mineral or rock.
- DE 69313456 T2 describes a coating material of ceramic composition, wherein the applied metal layer may contain quartz glass among other components.
- WO 2003/031672 A1 discloses a spray powder composed of ceramic particles, including quartz, and a metal powder consisting of Ni, Cr, Fe and Si.
- the objective of the present invention is to exploit the advantages of metallic chromium as a material for protective layers against high-temperature corrosion without having to accept its disadvantages.
- the desired improvement is intended to relate to the following properties of chromium layers:
- the object according to the present invention is to find a solution to the effect that fine-grained chromium powder can be used without disadvantages, i.e. adequate adherence can be achieved despite extensive oxidation of the fine chromium particles; high kinetic energy and thus pore-free and sound microstructure can be obtained and good free-flowing ability of the powder can be achieved despite fine chromium particles; a further object is to find additives for the chromium powder that reduce the brittleness of the layer and increase its coefficient of thermal expansion; finally, another object is to develop a method for heat treatment of the coated substrates that leads to a strong metallurgical bond between layer and substrate.
- the application of the chromium layers by thermal spraying according to claim 1 permits low costs even for large parts. Moreover, it permits the application of quite thick layers, which would not be conceivable with known techniques such as galvanization, PVD, CVD, gas chromizing and inchromizing.
- plasma spraying is optimally selected. Under the process conditions according to claim 1 , it permits melting of the chromium powder but prevents scorching (oxidation) thereof in the flame.
- the inventive process provides for melting the chromium particles and accelerating them against a substrate. Furthermore, it relates to creating oxidation protection both for the free-flowing powder and for the surface of the substrate under the flame. Since the temperature of the particles in the plasma is determined mainly by their size during plasma spraying, the chromium particles should be sufficiently fine-grained to ensure that they will melt. On the other hand, the use of fine-grained chromium powder means that it will be very susceptible to oxidation, because of its large surface area. The particles of chromium oxide Cr 2 O 3 formed in the process cannot be reduced in the plasma but instead are melted and accelerated together with chromium particles against the substrate. A consequent disadvantage is that the chromium oxide hinders the adherence between metallic substrate and chromium, since a metallurgical bond cannot be formed.
- a further disadvantage of fine-grained chromium powder consists in a low kinetic energy of the small particles in the flame, with the consequence that the layer microstructure formed has inadequate adherence and is neither pore-free nor sufficiently sound.
- the powder for plasma spraying is preferably generated by simple dry mixing of three components:
- powder of a nickel-base alloy e.g. 80Ni20Cr
- 80Ni20Cr nickel-base alloy
- lightweight (2.3 g/cm 3 ) coarse-grained cristobalite powder functions as carrier for the heavy fine-grained chromium and nickel-chromium powders: large cristobalite particles, with a volume amounting to more than 70% of the mixture ( ⁇ 30 vol % Cr+NiCr), are covered on the surface with fine chromium-base and nickel-base particles. These fairly large, round agglomerates make the powder efficiently free-flowing. In the plasma, the agglomerates are heated sufficiently at the surface that all metallic particles melt. Under these conditions the large refractory (1720° C.) cristobalite core basically remains solid.
- an agglomerate particle consisting of a cristobalite core ensheathed with a molten metallic “crust” acquires high kinetic energy in the plasma flame.
- the following events take place:
- the solid cristobalite core bursts into small fragments, which rebound from the substrate and are carried away by the gas stream. Only a fraction of the original amount of cristobalite, namely approximately 1-5% of the layer mass, is “also pulled in”. These cristobalite residues then form small uniformly distributed inclusions ( ⁇ 20 ⁇ m) in the finished metallic layer. In contrast, almost the entire metallic fraction of the spray powder remains “sticking” on the substrate, thus forming a fine-structured dense layer.
- the large cristobalite particles fulfill yet another advantageous function: upon colliding with the substrate or with inner strata, the hard and brittle grains act as a kind of sandblasting material, which “strips” oxide layers (Cr 2 O 3 ) immediately during coating. Thereby the adherence to the substrate and between individual strata and the layer microstructure becomes stronger, and only minimum contents of Cr 2 O 3 remain. Since the nickel-base alloy has a much lower melting temperature than chromium, it solidifies later than the chromium. Thus fine nickel-base lamellas are formed on the surface of the chromium particles, meaning that hard chromium particles in the finished layer are ensheathed by a fine “network” of soft nickel-base alloy.
- the “network” of soft nickel-base alloy significantly increases the ductility of the layer. Stresses developing during solidification of molten chromium no longer lead to crack formation, but are dissipated by the plastic deformation of the nickel-base lamellas.
- the resulting layer has the following composition:
- the finished layer contains only cristobalite, because quartz is transformed to cristobalite in the plasma.
- cristobalite Since cristobalite has a very high coefficient of thermal expansion, approximately 50 ⁇ 10 ⁇ 6 K ⁇ 1 , the coefficient of thermal expansion of the layer reaches approximately 9-10 ⁇ 10 ⁇ 6 K ⁇ 1 for the layer as a whole (compared with approximately 6.2 ⁇ 10 ⁇ 6 K ⁇ 1 for pure chromium). This value is already close to values for some steels, nickel-base alloys and titanium alloys, with the result that no harmful stresses can develop in the layer during cooling.
- the adherence of the layer on iron-base and nickel-base alloys can be improved even more by heat treatment of the coated parts. This is carried out in the furnace at temperatures of 900° C. and higher in air. This heat treatment for up to approximately 5 hours leads to diffusion of the chromium from the layer into the substrate to approximately 5 ⁇ m. By virtue of this diffusion, the layer and the substrate are “welded together”, as it were. At the same time, the heat treatment anneals out the residual stresses present in the layer after plasma spraying.
- Plasma gas Argon—200 L/min, nitrogen—55 L/min, hydrogen—12 L/min
- Powder gas Nitrogen—10 L/min
- the coated valve was heat-treated at 1020° C. for one hour in air.
- the layer formed on the surface of the valve disk was 800 ⁇ m thick, free of pores and cracks, and had the following composition:
- Plasma gas Argon—200 L/min, nitrogen—55 L/min, hydrogen—12 L/min
- Powder gas Nitrogen—10 L/min
- the coated pipe was heat-treated at 900° C. for five hours in air.
- the layer formed on the pipe surface was 100 ⁇ m thick, free of pores and cracks, and had the following composition:
- Plasma gas Argon—200 L/min, nitrogen—55 L/min, hydrogen—12 L/min
- Powder gas Nitrogen—10 L/min
- the layer formed on the complete valve surface was 100 ⁇ m thick, free of pores and cracks, and had the following composition:
- This layer on the valve stem also functions as a wear-resistant running layer.
Landscapes
- 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)
- Other Surface Treatments For Metallic Materials (AREA)
Abstract
Process for producing a gastight and crack-free protective chromium layer for substrates composed of iron- and nickel- and titanium-based alloys by means of plasma spraying, where the chromium content in the finished layer is at least 70% by weight and a spray powder composed of three components, namely a first component composed of finely particulate chromium powder, a second composed of finely particulate powder of a nickel-based alloy and a third composed of coarsely particulate cristobalite or quartz powder as support for the first and second component, is selected.
Description
- The invention relates to a process for producing a protective chromium layer according to the preamble of claim 1 as well as to the use of a plasma-sprayed protective layer.
- Chromium is one of the most important metals for coatings. Its very high corrosion resistance to many aggressive media in a broad temperature range is comparable with that of noble metals. Depending on how they are produced, chromium coatings have very different properties.
- Three types of coatings based on chromium are known:
-
- 1. galvanic chromium layers
- 2. PVD and CVD chromium layers
- 3. chromium layers formed by high-temperature diffusion
- Galvanic chromium layers are the oldest and most widely distributed layers based on chromium. The first description of electrolytic deposition of chromium goes back to A. C. Becquerel in 1843. In 1854, R. W. Bunsen described the deposition of chromium from hot chromium(III) chloride solution with carbon anodes and platinum cathodes. Erik Liebreichs invented chromium deposition in the chromium bath (DE 398054 and DE 448526). Therein the galvanic bath consisted of CrO3 and H2SO4. Heretofore almost all chromium layers have been produced according to this method. In the process, layers of pure chromium with a thickness of <1 μm to approximately 300 μm are applied on completely different substrates (metals, glasses, ceramics, plastics and even wood). Depending on layer thickness, the coating is known as decorative chrome plating (layers<5 μm) or as hard chrome plating (layer thicknesses: 10-200 μm). The properties of galvanically deposited chromium layers consist in very high hardness and brittleness, relatively weak adherence to the substrate and a fine network of cracks at layer thicknesses>5 μm. These properties, together with the fact that chromium has a low coefficient of thermal expansion—well under that of the most important metallic substrates—limit the use of galvanic chromium layers considerably. Because of fine cracks, these chromium layers are basically permeable for gaseous and liquid media, their mechanical durability is relatively low due to weak adherence and high brittleness, and the maximum permissible operating temperature is lower than 500° C., even though chromium as a compact metal can withstand temperatures higher than 1100° C. in air.
- PVD and CVD chromium layers are obtained by deposition from the gas phase in the vacuum furnace. A distinction is made between purely physical deposition from chromium vapor (physical vapor deposition, abbreviated PVD) and deposition by means of a chemical reaction between chromium-containing gas and substrate (chemical vapor deposition, abbreviated CVD). Because of this chemical reaction, the CVD chromium layers basically have higher adherence than PVD chromium layers. However, the CVD process requires considerably higher temperatures of 800-1000° C., compared with 200-500° C. for the PVD process. Both processes permit the application of dense thin layers from pure chromium or from chromium nitride (CrN). Compared with galvanic chromium layers, the PVD and especially the CVD chromium layers have very good adherence to the substrate, but on the other hand are much more expensive than galvanic layers and therefore are of only limited use for parts with large surface areas. Moreover, the maximum layer thickness is only approximately 10 μm.
- The coating of steels by means of thermochemical diffusion of chromium at temperatures of 1000-1200° C., known by the term “thermal chrome plating”, comprises two different process variants, although they lead largely to the same results: the known (DE 1905717) diffusion of chromium from a solid phase, e.g. chromium powder, and the known gas chromizing (EP 0043742 A1) from a gas phase, e.g. CrCl3. In both processes, chromium diffuses into a steel surface as far as a depth of approximately 50 μm, thus forming a protective layer. This diffusion layer has a maximum chromium concentration of 50%, together with high corrosion resistance and high hardness of the steel surface. Since the diffusion chromium layers are actually not pure chromium layers such as galvanic or PVD chromium layers, they also have entirely different properties, such as good adherence, good mechanical strength and a coefficient of thermal expansion close to that of steel. These properties permit use of parts coated with diffusion chromium at temperatures higher than 800° C. Compared with layers of pure chromium, however, the high-temperature corrosion resistance of the diffusion chromium layers is much poorer than that for compact metallic chromium. The layers of pure chromium are also superior in terms of wet chemical corrosion resistance. Despite comparatively favorable properties of diffusion chromium layers, their use is only very limited, because of their high complexity.
- Of the known chromium layers described in the foregoing, only diffusion chromium layers are suitable for use at high temperatures above 800° C. Because of their relatively low chromium content of at most 50%, however, they do not attain the desired resistance of pure chromium layers. Relative to the layer thickness, all known chromium layers are inadequate, since the maximum layer thickness of dense crack-free chromium layers is limited to approximately 10 μm.
- From EP 2006410 A2 there is further known a thermally sprayed protective layer for metallic substrates, wherein the spray powder comprises at least two components, of which the first is a silicatic mineral or rock and the second is a metal powder and/or a further silicatic mineral or rock.
- Furthermore, DE 69313456 T2 describes a coating material of ceramic composition, wherein the applied metal layer may contain quartz glass among other components.
- Finally, WO 2003/031672 A1 discloses a spray powder composed of ceramic particles, including quartz, and a metal powder consisting of Ni, Cr, Fe and Si.
- The objective of the present invention is to exploit the advantages of metallic chromium as a material for protective layers against high-temperature corrosion without having to accept its disadvantages. The desired improvement is intended to relate to the following properties of chromium layers:
-
- continuous use in air should be possible up to 1000° C.
- the layer should be resistant to thermal shock
- the chromium content of the layer should be at least 70%
- good adherence to the substrate should be assured
- high gas-tightness of the layer should be achieved by appropriate freedom from cracks
- layer thicknesses up to approximately 1 mm should be possible.
- In particular, the object according to the present invention is to find a solution to the effect that fine-grained chromium powder can be used without disadvantages, i.e. adequate adherence can be achieved despite extensive oxidation of the fine chromium particles; high kinetic energy and thus pore-free and sound microstructure can be obtained and good free-flowing ability of the powder can be achieved despite fine chromium particles; a further object is to find additives for the chromium powder that reduce the brittleness of the layer and increase its coefficient of thermal expansion; finally, another object is to develop a method for heat treatment of the coated substrates that leads to a strong metallurgical bond between layer and substrate.
- This object is achieved according to the body of claim 1 by the combined use of the plasma-spray process with the inventive powder mixture and if necessary a subsequent diffusion heat treatment.
- The application of the chromium layers by thermal spraying according to claim 1 permits low costs even for large parts. Moreover, it permits the application of quite thick layers, which would not be conceivable with known techniques such as galvanization, PVD, CVD, gas chromizing and inchromizing.
- Because of the high melting point of chromium, approximately 1900° C., plasma spraying is optimally selected. Under the process conditions according to claim 1, it permits melting of the chromium powder but prevents scorching (oxidation) thereof in the flame.
- Accordingly, the inventive process provides for melting the chromium particles and accelerating them against a substrate. Furthermore, it relates to creating oxidation protection both for the free-flowing powder and for the surface of the substrate under the flame. Since the temperature of the particles in the plasma is determined mainly by their size during plasma spraying, the chromium particles should be sufficiently fine-grained to ensure that they will melt. On the other hand, the use of fine-grained chromium powder means that it will be very susceptible to oxidation, because of its large surface area. The particles of chromium oxide Cr2O3 formed in the process cannot be reduced in the plasma but instead are melted and accelerated together with chromium particles against the substrate. A consequent disadvantage is that the chromium oxide hinders the adherence between metallic substrate and chromium, since a metallurgical bond cannot be formed.
- A further disadvantage of fine-grained chromium powder consists in a low kinetic energy of the small particles in the flame, with the consequence that the layer microstructure formed has inadequate adherence and is neither pore-free nor sufficiently sound.
- This and further disadvantages due to plasma spraying of pure fine-grained chromium powder are overcome by the inventive process by virtue of the composition of the spray powder according to claim 1.
- In this connection, the powder for plasma spraying is preferably generated by simple dry mixing of three components:
-
chromium powder<20 μm (d50<10 μm): 30-50 wt % -
powder of a nickel-base alloy (e.g. 80Ni20Cr)<20 μm (d50<10 μm): 5-10 wt % -
cristobalite or quartz powder 50-100 μm (d50=70-90 μm): the rest - In this mixture, lightweight (2.3 g/cm3) coarse-grained cristobalite powder functions as carrier for the heavy fine-grained chromium and nickel-chromium powders: large cristobalite particles, with a volume amounting to more than 70% of the mixture (<30 vol % Cr+NiCr), are covered on the surface with fine chromium-base and nickel-base particles. These fairly large, round agglomerates make the powder efficiently free-flowing. In the plasma, the agglomerates are heated sufficiently at the surface that all metallic particles melt. Under these conditions the large refractory (1720° C.) cristobalite core basically remains solid. By virtue of its size and its weight, an agglomerate particle consisting of a cristobalite core ensheathed with a molten metallic “crust” acquires high kinetic energy in the plasma flame. When it collides with the substrate, the following events take place:
- The solid cristobalite core bursts into small fragments, which rebound from the substrate and are carried away by the gas stream. Only a fraction of the original amount of cristobalite, namely approximately 1-5% of the layer mass, is “also pulled in”. These cristobalite residues then form small uniformly distributed inclusions (<20 μm) in the finished metallic layer. In contrast, almost the entire metallic fraction of the spray powder remains “sticking” on the substrate, thus forming a fine-structured dense layer. The large cristobalite particles fulfill yet another advantageous function: upon colliding with the substrate or with inner strata, the hard and brittle grains act as a kind of sandblasting material, which “strips” oxide layers (Cr2O3) immediately during coating. Thereby the adherence to the substrate and between individual strata and the layer microstructure becomes stronger, and only minimum contents of Cr2O3 remain. Since the nickel-base alloy has a much lower melting temperature than chromium, it solidifies later than the chromium. Thus fine nickel-base lamellas are formed on the surface of the chromium particles, meaning that hard chromium particles in the finished layer are ensheathed by a fine “network” of soft nickel-base alloy. The “network” of soft nickel-base alloy significantly increases the ductility of the layer. Stresses developing during solidification of molten chromium no longer lead to crack formation, but are dissipated by the plastic deformation of the nickel-base lamellas.
- The resulting layer has the following composition:
-
- chromium: 70-90 wt %
- nickel-base alloy: 7-25 wt %
- cristobalite: 1-5 wt % (3-15 vol %)
- Even with an admixture of quartz powder, the finished layer contains only cristobalite, because quartz is transformed to cristobalite in the plasma.
- Since cristobalite has a very high coefficient of thermal expansion, approximately 50×10−6 K−1, the coefficient of thermal expansion of the layer reaches approximately 9-10×10−6 K−1 for the layer as a whole (compared with approximately 6.2×10−6 K−1 for pure chromium). This value is already close to values for some steels, nickel-base alloys and titanium alloys, with the result that no harmful stresses can develop in the layer during cooling.
- The adherence of the layer on iron-base and nickel-base alloys can be improved even more by heat treatment of the coated parts. This is carried out in the furnace at temperatures of 900° C. and higher in air. This heat treatment for up to approximately 5 hours leads to diffusion of the chromium from the layer into the substrate to approximately 5 μm. By virtue of this diffusion, the layer and the substrate are “welded together”, as it were. At the same time, the heat treatment anneals out the residual stresses present in the layer after plasma spraying.
- Use in highly-stressed valves of large diesels running on heavy fuel oil: corrosion protection for nickel-base alloys against aggressive fused ashes (sodium vanadate) in combination with SO2-containing exhaust gases and temperatures up to approximately 900° C.
- A powder, mixed together from 40 wt % chromium<20 μm, 10 wt % 80Ni20Cr<20 μm and 50 wt % cristobalite 50-100 μm, was sprayed by means of the Axial-3 plasma spraying system of Thermico GmbH with the following parameters onto a valve disk of Nimonic 80A:
- Nozzle: ⅜″
- Current: 200 A (burner power: 95 kW)
- Plasma gas: Argon—200 L/min, nitrogen—55 L/min, hydrogen—12 L/min
- Powder gas: Nitrogen—10 L/min
- Powder flow: 20 g/min
- The coated valve was heat-treated at 1020° C. for one hour in air.
- After the coating process and the heat treatment, the layer formed on the surface of the valve disk was 800 μm thick, free of pores and cracks, and had the following composition:
- chromium: approximately 82 vol %
- 80Ni20Cr: approximately 12 vol %
- Cr2O3: approximately 3 vol %
- cristobalite: approximately 3 vol %
- Use in highly-stressed pipes of garbage incineration systems: corrosion protection for steels against chloride and sulfate ashes in combination with exhaust gases containing SO2 and HCl and temperatures up to approximately 600° C.
- A powder, mixed together from 40 wt % chromium<20 μm, 10 wt % 80Ni20Cr<20 μm and 50 wt % cristobalite 50-100 μm, was sprayed by means of the Axial-3 plasma spraying system of Thermico GmbH with the following parameters onto a boiler pipe of steel 37:
- Nozzle: ⅜″
- Current: 200 A (burner power: 95 kW)
- Plasma gas: Argon—200 L/min, nitrogen—55 L/min, hydrogen—12 L/min
- Powder gas: Nitrogen—10 L/min
- Powder flow: 20 g/min
- The coated pipe was heat-treated at 900° C. for five hours in air.
- After the coating process and the heat treatment, the layer formed on the pipe surface was 100 μm thick, free of pores and cracks, and had the following composition:
- chromium: approximately 82 vol %
- 80Ni20Cr: approximately 12 vol %
- Cr2O3: approximately 3 vol %
- cristobalite: approximately 3 vol %
- Use in highly-stressed titanium valves of racing engines: oxidation protection for all titanium alloys and titanium aluminides at temperatures up to approximately 800° C.
- A powder, mixed together from 40 wt % chromium<20 μm, 10 wt% 80Ni20Cr<20 μm and 50 wt % cristobalite 50-100 μm, was sprayed by means of the Axial-3 plasma spraying system of Thermico GmbH with the following parameters onto a valve disk and stem of Ti6Al2Sn4Zr2Mo:
- Nozzle: ⅜″
- Current: 200 A (burner power: 95 kW)
- Plasma gas: Argon—200 L/min, nitrogen—55 L/min, hydrogen—12 L/min
- Powder gas: Nitrogen—10 L/min
- Powder flow: 20 g/min
- After the coating process, the layer formed on the complete valve surface was 100 μm thick, free of pores and cracks, and had the following composition:
- chromium: approximately 84 vol %
- 80Ni20Cr: approximately 12 vol %
- Cr2O3: approximately 1 vol %
- cristobalite: approximately 3 vol %
- This layer on the valve stem also functions as a wear-resistant running layer.
Claims (6)
1. A process for producing a gas-tight and crack-free protective chromium layer for substrates of alloys based on iron and nickel and titanium by plasma spraying, wherein a spray powder is selected from three components, a first component of fine-grained chromium powder, a second component for improvement of the mechanical characteristics of the protective layer of fine-grained powder of a nickel-base alloy and a third component for improvement of the coefficients of thermal expansion of the protective layer of coarse-grained cristobalite or quartz powder as carrier for the first and second components, and wherein the chromium content in the formed protective layer is at least 70 wt %, the content of the nickel-base alloy is 7-25 wt % and the cristobalite content is 1-5 wt %.
2. (canceled)
3. (canceled)
4. A process according to claim 1 , characterized by a subsequent heat treatment of the protective layer in air at temperatures higher than 900° C.
5. A process according to claim 1 , wherein the thickness of the protective layer is selected up to 1 mm.
6. The use of a plasma-sprayed protective layer according to claim 1 on substrates threatened by corrosion from components of internal combustion engines, gas turbines, steam turbines, propulsion-unit compressors or heat exchangers.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE102011119087A DE102011119087B3 (en) | 2011-11-22 | 2011-11-22 | Method for producing a chromium protective layer and its use |
DE102011119087.6 | 2011-11-22 | ||
PCT/EP2012/004197 WO2013075769A1 (en) | 2011-11-22 | 2012-10-06 | Process for producing a protective chromium layer |
Publications (1)
Publication Number | Publication Date |
---|---|
US20140287261A1 true US20140287261A1 (en) | 2014-09-25 |
Family
ID=47073404
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US14/352,491 Abandoned US20140287261A1 (en) | 2011-11-22 | 2012-10-06 | Process for producing a protective chromium layer |
Country Status (7)
Country | Link |
---|---|
US (1) | US20140287261A1 (en) |
EP (1) | EP2783021A1 (en) |
JP (1) | JP2014533777A (en) |
KR (1) | KR20140106501A (en) |
CN (1) | CN104053809A (en) |
DE (1) | DE102011119087B3 (en) |
WO (1) | WO2013075769A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2016540123A (en) * | 2013-11-20 | 2016-12-22 | カーエス フアユ アルテヒ ゲゼルシャフト ミット ベシュレンクテル ハフツングKS HUAYU AluTech GmbH | Method for forming a sprayed cylinder sliding surface of a crankcase of an internal combustion engine and such a crankcase |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3696502A (en) * | 1968-07-12 | 1972-10-10 | Johnson Matthey Co Ltd | Method of making a dispersion strengthened metal |
US6746782B2 (en) * | 2001-06-11 | 2004-06-08 | General Electric Company | Diffusion barrier coatings, and related articles and processes |
US20080317966A1 (en) * | 2007-06-19 | 2008-12-25 | Markisches Werk Gmbh | Thermally sprayed gastight protective layer for metal substrates |
US7601431B2 (en) * | 2005-11-21 | 2009-10-13 | General Electric Company | Process for coating articles and articles made therefrom |
Family Cites Families (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE398054C (en) | 1920-03-09 | 1924-07-01 | Erik Liebreich Dr | Process for the electrolytic deposition of metallic chromium |
DE448526C (en) | 1924-07-22 | 1927-07-28 | Elektro-Chrom-Gesellschaft | Process for the preparation of a solution suitable for the electrolytic deposition of metallic chromium |
GB1246851A (en) | 1968-02-09 | 1971-09-22 | Albright & Wilson | Chromising ferrous metal substrates |
FR2483468A2 (en) | 1980-05-29 | 1981-12-04 | Creusot Loire | IMPROVEMENT IN THE CHROMIZATION OF STEELS BY GAS |
US5305726A (en) * | 1992-09-30 | 1994-04-26 | United Technologies Corporation | Ceramic composite coating material |
CA2358624C (en) * | 2001-10-10 | 2009-12-22 | The Westaim Corporation | Sprayable composition |
US6887530B2 (en) * | 2002-06-07 | 2005-05-03 | Sulzer Metco (Canada) Inc. | Thermal spray compositions for abradable seals |
US20110114908A1 (en) * | 2008-07-03 | 2011-05-19 | Fargo Richard N | Wear and corrosion resistant coating having a roughened surface |
CA2639732A1 (en) * | 2008-09-19 | 2010-03-19 | Karel Hajmrle | Sprayable compositions |
-
2011
- 2011-11-22 DE DE102011119087A patent/DE102011119087B3/en active Active
-
2012
- 2012-10-06 EP EP12777862.9A patent/EP2783021A1/en not_active Withdrawn
- 2012-10-06 JP JP2014542723A patent/JP2014533777A/en active Pending
- 2012-10-06 KR KR1020147009153A patent/KR20140106501A/en not_active Application Discontinuation
- 2012-10-06 US US14/352,491 patent/US20140287261A1/en not_active Abandoned
- 2012-10-06 WO PCT/EP2012/004197 patent/WO2013075769A1/en active Application Filing
- 2012-10-06 CN CN201280057442.9A patent/CN104053809A/en active Pending
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3696502A (en) * | 1968-07-12 | 1972-10-10 | Johnson Matthey Co Ltd | Method of making a dispersion strengthened metal |
US6746782B2 (en) * | 2001-06-11 | 2004-06-08 | General Electric Company | Diffusion barrier coatings, and related articles and processes |
US7601431B2 (en) * | 2005-11-21 | 2009-10-13 | General Electric Company | Process for coating articles and articles made therefrom |
US20080317966A1 (en) * | 2007-06-19 | 2008-12-25 | Markisches Werk Gmbh | Thermally sprayed gastight protective layer for metal substrates |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2016540123A (en) * | 2013-11-20 | 2016-12-22 | カーエス フアユ アルテヒ ゲゼルシャフト ミット ベシュレンクテル ハフツングKS HUAYU AluTech GmbH | Method for forming a sprayed cylinder sliding surface of a crankcase of an internal combustion engine and such a crankcase |
Also Published As
Publication number | Publication date |
---|---|
EP2783021A1 (en) | 2014-10-01 |
JP2014533777A (en) | 2014-12-15 |
CN104053809A (en) | 2014-09-17 |
WO2013075769A1 (en) | 2013-05-30 |
KR20140106501A (en) | 2014-09-03 |
DE102011119087B3 (en) | 2013-03-14 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
Chatha et al. | Characterisation and corrosion-erosion behaviour of carbide based thermal spray coatings | |
TWI694156B (en) | Aluminum-cobalt-chromium-iron-nickel-silicon alloy, powder and coating thereof | |
EP1829984B1 (en) | Process for making a high density thermal barrier coating | |
US20160138516A1 (en) | Method for producing an oxidation protection layer for a piston for use in internal combustion engines and piston having an oxidation protection layer | |
JP5755819B2 (en) | Ni-Cr-Co alloy with high-temperature corrosion resistance and surface-modified poppet valve using the same | |
TW201446969A (en) | Thermal spraying powder for highly stressed sliding systems | |
US7445434B2 (en) | Coating material for thermal barrier coating having excellent corrosion resistance and heat resistance and method of producing the same | |
EP1390549B1 (en) | Metal-zirconia composite coating | |
Sidhu et al. | Characterizations and hot corrosion resistance of Cr 3 C 2-NiCr coating on Ni-base superalloys in an aggressive environment | |
US20110165334A1 (en) | Coating material for metallic base material surface | |
Prashar et al. | A Comprehensive Review on Combating The Elevated-Temperature Surface Degradation by M CrAl X Coatings | |
JP2005213605A (en) | Composite material, thermally sprayed film coated member and method for manufacturing the member | |
Prakash et al. | Hot corrosion behaviour of plasma sprayed coatings on a Ni-based superalloy in Na2SO4-60% V2O5 environment | |
Mayoral et al. | Aluminium depletion in NiCrAlY bond coatings by hot corrosion as a function of projection system | |
US20140287261A1 (en) | Process for producing a protective chromium layer | |
JP3522590B2 (en) | High hardness carbide cermet thermal spray coating member and method of manufacturing the same | |
AYER | 12, Patent Application Publication o Pub. No.: US 2014/0287261 A1 | |
Milan Shahana et al. | High-Temperature Oxidation and Hot Corrosion of Thermal Spray Coatings | |
JP3522588B2 (en) | Chromium carbide cermet sprayed coating member excellent in high-temperature hardness and method for producing the same | |
Shahana et al. | High-temperature oxidation and hot corrosion of thermal spray coatings | |
JPH0261051A (en) | Method for coating surface of material and thermal spraying material used in the same method | |
JP5171176B2 (en) | Thermal spraying material coated on metal substrate surface and high temperature corrosion resistant member coated with the material | |
Li et al. | A Novel Bond Coat with Excellent Adhesive Strength Deposited by Plasma-Spraying of Mo-Clad Core-Shell-Structured Metal Powders | |
Prashar et al. | A review on the processing of various coating materials using surface modification techniques for high-temperature solid particle erosion applications | |
JPH0711416A (en) | Surface coated structure excellent in high temperature erosion resistance |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: MARKISCHES WERK GMBH, GERMANY Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:VERLOTSKI, VADIM;REEL/FRAME:032700/0307 Effective date: 20140312 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |