CA2847014A1 - Lubricious composite oxide coating and process for making the same - Google Patents
Lubricious composite oxide coating and process for making the same Download PDFInfo
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- CA2847014A1 CA2847014A1 CA2847014A CA2847014A CA2847014A1 CA 2847014 A1 CA2847014 A1 CA 2847014A1 CA 2847014 A CA2847014 A CA 2847014A CA 2847014 A CA2847014 A CA 2847014A CA 2847014 A1 CA2847014 A1 CA 2847014A1
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- oxide coating
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/30—Anodisation of magnesium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/026—Anodisation with spark discharge
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/04—Anodisation of aluminium or alloys based thereon
- C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/26—Anodisation of refractory metals or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D9/00—Electrolytic coating other than with metals
- C25D9/04—Electrolytic coating other than with metals with inorganic materials
- C25D9/06—Electrolytic coating other than with metals with inorganic materials by anodic processes
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- Electrochemistry (AREA)
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- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Coating By Spraying Or Casting (AREA)
- Other Surface Treatments For Metallic Materials (AREA)
- Sliding-Contact Bearings (AREA)
Abstract
This invention concerns a process of making a lubricious composite oxide coating by plasma oxidation on a metallic surface, wherein said metallic surface is connected to a power supply and in contact with an aqueous electrolyte containing a preliminary substance for forming an oxygen-deficient substoichiometric oxide, a preliminary substance for promoting the formation and stabilization of said substoichiometric oxide, and a substance for adjusting the pH value of said electrolyte. The lubricious composite oxide can be also deposited on the top of a stoichiometric oxide to form a double-layered coating. The lubricious composite oxide coating reduces the wear and friction of a metal or alloy substrate.
Description
Lubricious Composite Oxide Coating and Process for Making the Same Field of the Invention This invention concerns a process of making a lubricious composite oxide ceramic coating on a metallic surface to reduce wear and friction of a component with such a metallic surface. The component can be any manufactured part that undergoes a sliding motion in practical applications, such as a cylinder, piston, shaft, bearing, sealing plate, spacer, sleeve, brushing, swashplate, slipper, chain wheel, pump part, camshaft phaser part, or turbo part.
Background of the Invention Aluminum, titanium, zirconium, magnesium and their alloys have relatively soft surfaces and poor wear resistance. An oxide ceramic coating with high surface hardness can be deposited on the surface of the metals and alloys to improve wear resistance. Coating deposition methods include chemical oxidation at high temperatures, thermal spraying, physical vapor deposition, chemical vapor deposition, anodizing, and plasma electrolytic oxidation. Plasma electrolytic oxidation is a process based on the dielectric discharging of oxide in a solution (Nie, et al., Journal Surface &
Coatings Technology, 122 (1999) 73-93) and is traditionally used to produce stoichiometric oxides, which have stable phase structures and can thus protect aluminum, titanium, magnesium and zirconium alloys against corrosion and wear (patents: US 6896785, US 8608869, CA 2556869). For example, Henkel Corporation (patent applications: W02012/174386 Al, US2012/042681 A) has developed a titanium dioxide coating with a Ti:0 = 1:2 stoichiometric composition for better corrosion resistance and catalyst applications. However, stoichiometric oxides almost always show a high coefficient of friction, which is undesirable for a component that undergoes sliding wear in tribological applications. To reduce friction, solid lubricants such as graphite, MoS2, and WS2 may be incorporated into oxides (patent CA 2479032), or a DLC (diamond-like carbon) layer may be deposited on the top of an oxide coating which also improves its load-bearing capacity (Nie, et al., Journal Surface & Coatings Technology, 121 (2000) 506-513).
Alternatively, the oxide coating can itself be fabricated with a low coefficient of friction if it is substoichiometric, i.e. oxygen-deficient. Substoichiometric oxides have possible crystalline shear planes and can thus be lubricious. However, they are difficult to synthesize and metastable. The present invention introduces a method of producing a stable substoichiometric oxide coating by incorporating silica (silicon oxide) and alumina (aluminum oxide) into the substoichiometric oxide ceramic phase structure. The substoichiometric oxide and at least one of silica and alumina are simultaneously fabricated using the electrolytic plasma oxidation process in an electrolyte solution containing a preliminary substance (i.e. a precursor) that promotes the formation and stabilization of substoichiometric oxide. The silica or alumina stabilizes the crystalline shear planes which provide lubricious characteristics to the substoichiometric oxide.
Summary of the Invention The invention is related to a process of making a composite oxide coating which contains at least one lubricious oxide. The process of making a lubricious composite oxide coating comprises:
(i) preparing an aqueous electrolyte containing a preliminary substance A for forming an oxygen-deficient substoichiometric oxide, a preliminary substance B for promoting the formation and stabilization of said substoichiometric oxide, and a substance C for adjusting pH value of said electrolyte;
(ii) applying electrical power and said electrolyte onto a metallic surface;
(iii) generating plasma discharging on said metallic surface, which is made of aluminum (Al), titanium (Ti), zirconium (Zr) or magnesium (Mg) metal; and (iv) forming a lubricious composite oxide coating on said metallic surface, said coating containing at least one of said substoichiometric oxides, which is stabilized by silica (Si02) or alumina (A1203).
In this invention, said preliminary substance A is a titanium (Ti) complex compound, tungsten (W) compound, or molybdenum (Mo) compound.
Said titanium complex compound for said preliminary substance A is preferably potassium titanium oxalate, sodium titanium oxalate, ammonium titanium oxalate, titanium citrate, ammonium titanium citrate, or ammonium titanium fluoride.
Said tungsten compound for said preliminary substance A is preferably sodium tungstate, potassium tungstate, ammonium tungstate, or a combination of these tungstates.
Said molybdenum compound for said preliminary substance A is preferably sodium molybdate, potassium molybdate, ammonium molybdate, or a combination of these molybdates.
Background of the Invention Aluminum, titanium, zirconium, magnesium and their alloys have relatively soft surfaces and poor wear resistance. An oxide ceramic coating with high surface hardness can be deposited on the surface of the metals and alloys to improve wear resistance. Coating deposition methods include chemical oxidation at high temperatures, thermal spraying, physical vapor deposition, chemical vapor deposition, anodizing, and plasma electrolytic oxidation. Plasma electrolytic oxidation is a process based on the dielectric discharging of oxide in a solution (Nie, et al., Journal Surface &
Coatings Technology, 122 (1999) 73-93) and is traditionally used to produce stoichiometric oxides, which have stable phase structures and can thus protect aluminum, titanium, magnesium and zirconium alloys against corrosion and wear (patents: US 6896785, US 8608869, CA 2556869). For example, Henkel Corporation (patent applications: W02012/174386 Al, US2012/042681 A) has developed a titanium dioxide coating with a Ti:0 = 1:2 stoichiometric composition for better corrosion resistance and catalyst applications. However, stoichiometric oxides almost always show a high coefficient of friction, which is undesirable for a component that undergoes sliding wear in tribological applications. To reduce friction, solid lubricants such as graphite, MoS2, and WS2 may be incorporated into oxides (patent CA 2479032), or a DLC (diamond-like carbon) layer may be deposited on the top of an oxide coating which also improves its load-bearing capacity (Nie, et al., Journal Surface & Coatings Technology, 121 (2000) 506-513).
Alternatively, the oxide coating can itself be fabricated with a low coefficient of friction if it is substoichiometric, i.e. oxygen-deficient. Substoichiometric oxides have possible crystalline shear planes and can thus be lubricious. However, they are difficult to synthesize and metastable. The present invention introduces a method of producing a stable substoichiometric oxide coating by incorporating silica (silicon oxide) and alumina (aluminum oxide) into the substoichiometric oxide ceramic phase structure. The substoichiometric oxide and at least one of silica and alumina are simultaneously fabricated using the electrolytic plasma oxidation process in an electrolyte solution containing a preliminary substance (i.e. a precursor) that promotes the formation and stabilization of substoichiometric oxide. The silica or alumina stabilizes the crystalline shear planes which provide lubricious characteristics to the substoichiometric oxide.
Summary of the Invention The invention is related to a process of making a composite oxide coating which contains at least one lubricious oxide. The process of making a lubricious composite oxide coating comprises:
(i) preparing an aqueous electrolyte containing a preliminary substance A for forming an oxygen-deficient substoichiometric oxide, a preliminary substance B for promoting the formation and stabilization of said substoichiometric oxide, and a substance C for adjusting pH value of said electrolyte;
(ii) applying electrical power and said electrolyte onto a metallic surface;
(iii) generating plasma discharging on said metallic surface, which is made of aluminum (Al), titanium (Ti), zirconium (Zr) or magnesium (Mg) metal; and (iv) forming a lubricious composite oxide coating on said metallic surface, said coating containing at least one of said substoichiometric oxides, which is stabilized by silica (Si02) or alumina (A1203).
In this invention, said preliminary substance A is a titanium (Ti) complex compound, tungsten (W) compound, or molybdenum (Mo) compound.
Said titanium complex compound for said preliminary substance A is preferably potassium titanium oxalate, sodium titanium oxalate, ammonium titanium oxalate, titanium citrate, ammonium titanium citrate, or ammonium titanium fluoride.
Said tungsten compound for said preliminary substance A is preferably sodium tungstate, potassium tungstate, ammonium tungstate, or a combination of these tungstates.
Said molybdenum compound for said preliminary substance A is preferably sodium molybdate, potassium molybdate, ammonium molybdate, or a combination of these molybdates.
2 Said preliminary substance B is a silicon compound, phosphorous compound, or aluminum compound.
The silicon compound for said preliminary substance B is preferably sodium silicate, potassium silicate, or a combination of sodium silicate and potassium silicate.
Said phosphorous compound for said preliminary substance B is preferably sodium phosphate, potassium phosphate, or a combination of these phosphates.
Said aluminum compound for said precursor substance B is preferably sodium aluminate, potassium aluminate, or a combination of these aluminates.
Said substance C is citric acid, potassium hydroxide, or sodium hydroxide.
In accordance with an embodiment of this invented process, the electrolyte disclosed in the present invention preferably contains: 5-50 grams/Litre of potassium titanium oxalate or sodium titanium and 1-20 grams/Litre of sodium molybdate or potassium tungstate oxalate as preliminary substances A for forming a lubricous oxide, 1-20 grams/Litre of sodium silicate or potassium silicate as preliminary substance B for promoting and stabilizing the lubricous oxide, and 1-20 grams/Litre of citric acid and 1-10 grams/Litre of potassium hydroxide or sodium hydroxide as substances C for adjusting the pH of the electrolyte.
The lubricious oxide is oxygen-deficient and has a microstructure with crystalline shear planes and comprised of at least one oxide of silica-stabilized substoichiometric oxide, alumina-stabilized Ti-0 substoichiometric oxide, alumina-stabilized Mo-O substoichiometric oxide, alumina-stabilized W-0 substoichiometric oxide, and silica-stabilized Zr-O substoichiometric oxide.
Said substoichiometric oxide in this invention is preferably TinO2n-1, ZrnO2n-1, W,037-1, Wn03n-29 MOnO3n-19 or Mon03n-2, where n is a natural number.
When the substrate to be coated is made of aluminum alloy, the composite oxide coating disclosed in this invention contains a silica-stabilized substoichiometric lubricious Tin021 oxide and an aluminum oxide A1203.
In accordance with an advantageous embodiment of this invention, the substrate to be coated can be pre-treated using a traditional plasma electrolytic oxidation process to form a stoichiometric oxide coating before a lubricious substoichiometric composite oxide is deposited on the stoichiometric
The silicon compound for said preliminary substance B is preferably sodium silicate, potassium silicate, or a combination of sodium silicate and potassium silicate.
Said phosphorous compound for said preliminary substance B is preferably sodium phosphate, potassium phosphate, or a combination of these phosphates.
Said aluminum compound for said precursor substance B is preferably sodium aluminate, potassium aluminate, or a combination of these aluminates.
Said substance C is citric acid, potassium hydroxide, or sodium hydroxide.
In accordance with an embodiment of this invented process, the electrolyte disclosed in the present invention preferably contains: 5-50 grams/Litre of potassium titanium oxalate or sodium titanium and 1-20 grams/Litre of sodium molybdate or potassium tungstate oxalate as preliminary substances A for forming a lubricous oxide, 1-20 grams/Litre of sodium silicate or potassium silicate as preliminary substance B for promoting and stabilizing the lubricous oxide, and 1-20 grams/Litre of citric acid and 1-10 grams/Litre of potassium hydroxide or sodium hydroxide as substances C for adjusting the pH of the electrolyte.
The lubricious oxide is oxygen-deficient and has a microstructure with crystalline shear planes and comprised of at least one oxide of silica-stabilized substoichiometric oxide, alumina-stabilized Ti-0 substoichiometric oxide, alumina-stabilized Mo-O substoichiometric oxide, alumina-stabilized W-0 substoichiometric oxide, and silica-stabilized Zr-O substoichiometric oxide.
Said substoichiometric oxide in this invention is preferably TinO2n-1, ZrnO2n-1, W,037-1, Wn03n-29 MOnO3n-19 or Mon03n-2, where n is a natural number.
When the substrate to be coated is made of aluminum alloy, the composite oxide coating disclosed in this invention contains a silica-stabilized substoichiometric lubricious Tin021 oxide and an aluminum oxide A1203.
In accordance with an advantageous embodiment of this invention, the substrate to be coated can be pre-treated using a traditional plasma electrolytic oxidation process to form a stoichiometric oxide coating before a lubricious substoichiometric composite oxide is deposited on the stoichiometric
3 oxide as a top layer. The stoichiometric oxide bottom layer can be as thick as 200 microns to provide a strong load-bearing capability against sliding and abrasive wear at high contact stresses.
The top substoichiometric oxide layer reduces friction.
Brief Description of the Drawings Figure 1 is a schematic drawing of the coating deposition process: (a) an immersion process or (b) a spraying process.
Figure 2 is a scanning electron microscopy image of a composite oxide coating, comprising a lubricious oxide 5 and an aluminum oxide 6 when the substrate to be coated is an aluminum alloy in accordance with an embodiment of this invention. The coating in this figure contains more lubricious oxide 5 than aluminum oxide 6.
Figure 3 is a scanning electron microscopy image of a composite oxide coating, comprising a lubricious oxide 5 and an aluminum oxide 6 when the substrate to be coated is an aluminum alloy in accordance with an embodiment of this invention for an embodiment. The coating in this figure contains more lubricious oxide 5 than aluminum oxide 6.
Figure 4 is a scanning electron microscopy image of a composite oxide coating, comprising a lubricious oxide 5 and an aluminum oxide 6 when the substrate to be coated is an aluminum alloy in accordance with an embodiment of this invention. The coating in this figure is polished to an average surface roughness of Ra = 0.2 microns.
Figure 5 is a plot of the coefficient of friction vs. sliding velocity of a lubricious composite oxide coating tested in an oil lubricating condition.
Figure 6 is a plot of the coefficient of friction vs. sliding revolutions of a lubricious composite oxide coating tested in an ambient dry condition.
Detailed Description of the Drawings In Figure 1, an electrolyte 1 is prepared by dissolution of three kinds of substances in distilled water:
a preliminary substance A for forming substoichiometric oxides, a preliminary substance B for stabilizing said substoichiometric oxides, and a substance C for adjusting the pH value of said electrolyte. The electrolyte 1 is applied to a metallic surface 2 either by immersing the metallic substrate 2 into the electrolyte 1 (Fig. 1(a)) or by spraying the electrolyte 1 onto the metallic surface
The top substoichiometric oxide layer reduces friction.
Brief Description of the Drawings Figure 1 is a schematic drawing of the coating deposition process: (a) an immersion process or (b) a spraying process.
Figure 2 is a scanning electron microscopy image of a composite oxide coating, comprising a lubricious oxide 5 and an aluminum oxide 6 when the substrate to be coated is an aluminum alloy in accordance with an embodiment of this invention. The coating in this figure contains more lubricious oxide 5 than aluminum oxide 6.
Figure 3 is a scanning electron microscopy image of a composite oxide coating, comprising a lubricious oxide 5 and an aluminum oxide 6 when the substrate to be coated is an aluminum alloy in accordance with an embodiment of this invention for an embodiment. The coating in this figure contains more lubricious oxide 5 than aluminum oxide 6.
Figure 4 is a scanning electron microscopy image of a composite oxide coating, comprising a lubricious oxide 5 and an aluminum oxide 6 when the substrate to be coated is an aluminum alloy in accordance with an embodiment of this invention. The coating in this figure is polished to an average surface roughness of Ra = 0.2 microns.
Figure 5 is a plot of the coefficient of friction vs. sliding velocity of a lubricious composite oxide coating tested in an oil lubricating condition.
Figure 6 is a plot of the coefficient of friction vs. sliding revolutions of a lubricious composite oxide coating tested in an ambient dry condition.
Detailed Description of the Drawings In Figure 1, an electrolyte 1 is prepared by dissolution of three kinds of substances in distilled water:
a preliminary substance A for forming substoichiometric oxides, a preliminary substance B for stabilizing said substoichiometric oxides, and a substance C for adjusting the pH value of said electrolyte. The electrolyte 1 is applied to a metallic surface 2 either by immersing the metallic substrate 2 into the electrolyte 1 (Fig. 1(a)) or by spraying the electrolyte 1 onto the metallic surface
4 2 (Fig. 1(b)). The metallic item 2 is connected to a positive electrode of a power supply 4, preferably a pulsed DC power supply. In Fig. 1(a), a stainless steel plate 3 is the cathode used to connect to the power supply 4. In Fig. 1(b), the power supply anode is connected to one or multiple spraying nozzles 3 that are preferably made of a stainless steel. At 100-600 volts, the metallic surface 2 generates dielectric discharges and forms a substoichiometric oxide and silica or alumina. Therefore, the coating is a composite oxide coating containing at least one lubricious substoichiometric oxide and at least one of silica or alumina.
The metallic substrate 2 in Figure 1 is made of Al, Ti, Mg, or Zr or their alloys. The lubricious composite coatings prepared on Al, Ti, Mg and Zr metals and alloys have low friction, high wear resistance, and high corrosion resistance.
In accordance with an embodiment of the present invention, the coating shown in Figure 2 is mostly composed of a lubricious substoichiometric oxide 5. However, substoichiometric oxides usually have greater electrical conductivity than their stoichiometric counterparts.
The relatively high electrical conductivity of substoichiometric oxide allows the dielectric discharging to occur at a low voltage during the plasma electrolytic oxidation (PEO) process, resulting in very thin coatings: less than 15 microns.
The coating in Figure 3 has a smaller proportion of lubricious substoichiometric oxide 5. The coating is mostly composed of a stoichiometric oxide 6, which is A1203 if the substrate material is an Al alloy. Stoichiometric oxides usually have high dielectric constants, allowing the PEO process to operate at a high voltage and produce coatings as thick as 200 microns. The presence of the lubricious oxide in the composite oxide coating is still able to reduce friction and wear.
Figure 4 is an image of a polished coating with similar proportions of lubricious oxide 5 and aluminum oxide 6 to Figure 2. The average surface roughness after polishing is preferably in the range of 0.10-0.75 microns. The remaining dimples in the composite coating provide oil-retaining sites for additional friction reduction in engine, pump and bearing applications. Detailed descriptions of dimples in an oxide coating have been given in the inventors' previous patent CA
2556869.
Figure 5 is a plot of the coefficient of friction (COF) vs. sliding velocity of a lubricious composite oxide coating on an Al alloy tested in an oil-lubricating condition. The COF
can range from 0.01-0.1, depending on a sliding velocity of 0.1 rids -7 m/s. At a low sliding velocity, i.e. boundary lubricating condition, a typical COF of the lubricious composite oxide coating is 0.06-0.08. High sliding velocity involves mixed and elastohydrodynamic lubricating conditions, giving COFs as low as 0.01.
As shown in the COF vs. sliding revolutions plot in Figure 6, even in ambient dry testing conditions, a typical composite coating COF is still low, between 0.10-0.15.
The present invention is further described with reference to the following examples.
Examples Example 1 Ti metals and Ti alloys are used as substrate material. To reduce sliding and fretting wear of the substrate, a substoichiometric lubricious coating is prepared on the surface of the substrate using the process disclosed in this invention. The substoichiometric Ti-0 oxide coating is stabilized by silicon and phosphorous.
Example 2 Zr metals and Zr alloys are used as substrate material. To reduce sliding and fretting wear of the substrate, a substoichiometric lubricious coating is prepared on the surface of the substrate using the process disclosed in this invention. The substoichiometric Zr-O oxide coating is stabilized by silicon and phosphorous.
Example 3 Al metals and Al alloys are used as substrate material. To reduce sliding and fretting wear of the substrate, a substoichiometric lubricious coating is prepared on the surface of the substrate using the process disclosed in this invention. The substoichiometric Ti-0, Mo-O, or W-0 oxide coating is stabilized by silicon and phosphorous, which are sourced from silicate and phosphate in the electrolyte, allowing a relatively thick (25-50 microns) lubricious coating to be deposited.
Example 4 Al metals and Al alloys are used as substrate material. To reduce sliding and fretting wear of the substrate, a substoichiometric lubricious coating is prepared on the surface of the substrate using the process disclosed in this invention. The oxide coating contains at least one lubricious oxide and an aluminum oxide. The substoichiometric lubricious oxide reduces friction, and the aluminum oxide improves wear resistance. Coating thickness can be as thick as 200 microns. A
coating thickness of 20-30 microns is preferred with respect to low fabrication cost.
Example 5 The lubricious oxide coating can be applied to a substrate with a flat surface (e.g., spacer, swashplate, slipper, and sealing plate), inner surface (e.g., cylinder barrel, sleeve, brushing, journal bearing and piston pin bearing bore), or outer surface (e.g., piston, ball-joint, shaft and chain wheel).
Example 6 The lubricious oxide coating contains silicon and aluminum to stabilize the substoichiometric Ti-0 oxide formed on cast aluminum-silicon alloys A319, A356, A380, and A390. The composite oxide comprises Si-contained A1203 and Tin021, where n is a natural number. For example, the lubricious composite oxide ceramic coating can be deposited on linerless aluminum engine cylinder bores to reduce wear and friction. The coating also has an excellent corrosion resistance against biofuels.
Example 7 The lubricious composite coating on an Al, Ti, Mg, or Zr alloy substrate exhibits a low coefficient of friction (COF) in both dry and oil lubricating conditions. In a dry ambient temperature testing condition, a typical composite coating COF is 0.1-0.15. In an oil lubricating condition, the COF can range from 0.01-0.1, depending on a sliding speed of 0.1 m/s-7 m/s. In a boundary lubricating condition, a typical COF of the lubricious composite oxide coating is 0.06-0.08. High sliding velocity involves mixed and elastohydrodynamic lubricating conditions, giving COFs as low as 0.01.
Example 8 An Al, Ti, Mg, or Zr alloy substrate is pre-treated using a traditional plasma electrolytic oxidation process to form a stoichiometric oxide coating up to 200 microns thick to provide a strong load-bearing capability against sliding and abrasive wear at high contact stresses.
A lubricious substoichiometric composite oxide is deposited on top of the stoichiometric oxide to reduce friction.
The metallic substrate 2 in Figure 1 is made of Al, Ti, Mg, or Zr or their alloys. The lubricious composite coatings prepared on Al, Ti, Mg and Zr metals and alloys have low friction, high wear resistance, and high corrosion resistance.
In accordance with an embodiment of the present invention, the coating shown in Figure 2 is mostly composed of a lubricious substoichiometric oxide 5. However, substoichiometric oxides usually have greater electrical conductivity than their stoichiometric counterparts.
The relatively high electrical conductivity of substoichiometric oxide allows the dielectric discharging to occur at a low voltage during the plasma electrolytic oxidation (PEO) process, resulting in very thin coatings: less than 15 microns.
The coating in Figure 3 has a smaller proportion of lubricious substoichiometric oxide 5. The coating is mostly composed of a stoichiometric oxide 6, which is A1203 if the substrate material is an Al alloy. Stoichiometric oxides usually have high dielectric constants, allowing the PEO process to operate at a high voltage and produce coatings as thick as 200 microns. The presence of the lubricious oxide in the composite oxide coating is still able to reduce friction and wear.
Figure 4 is an image of a polished coating with similar proportions of lubricious oxide 5 and aluminum oxide 6 to Figure 2. The average surface roughness after polishing is preferably in the range of 0.10-0.75 microns. The remaining dimples in the composite coating provide oil-retaining sites for additional friction reduction in engine, pump and bearing applications. Detailed descriptions of dimples in an oxide coating have been given in the inventors' previous patent CA
2556869.
Figure 5 is a plot of the coefficient of friction (COF) vs. sliding velocity of a lubricious composite oxide coating on an Al alloy tested in an oil-lubricating condition. The COF
can range from 0.01-0.1, depending on a sliding velocity of 0.1 rids -7 m/s. At a low sliding velocity, i.e. boundary lubricating condition, a typical COF of the lubricious composite oxide coating is 0.06-0.08. High sliding velocity involves mixed and elastohydrodynamic lubricating conditions, giving COFs as low as 0.01.
As shown in the COF vs. sliding revolutions plot in Figure 6, even in ambient dry testing conditions, a typical composite coating COF is still low, between 0.10-0.15.
The present invention is further described with reference to the following examples.
Examples Example 1 Ti metals and Ti alloys are used as substrate material. To reduce sliding and fretting wear of the substrate, a substoichiometric lubricious coating is prepared on the surface of the substrate using the process disclosed in this invention. The substoichiometric Ti-0 oxide coating is stabilized by silicon and phosphorous.
Example 2 Zr metals and Zr alloys are used as substrate material. To reduce sliding and fretting wear of the substrate, a substoichiometric lubricious coating is prepared on the surface of the substrate using the process disclosed in this invention. The substoichiometric Zr-O oxide coating is stabilized by silicon and phosphorous.
Example 3 Al metals and Al alloys are used as substrate material. To reduce sliding and fretting wear of the substrate, a substoichiometric lubricious coating is prepared on the surface of the substrate using the process disclosed in this invention. The substoichiometric Ti-0, Mo-O, or W-0 oxide coating is stabilized by silicon and phosphorous, which are sourced from silicate and phosphate in the electrolyte, allowing a relatively thick (25-50 microns) lubricious coating to be deposited.
Example 4 Al metals and Al alloys are used as substrate material. To reduce sliding and fretting wear of the substrate, a substoichiometric lubricious coating is prepared on the surface of the substrate using the process disclosed in this invention. The oxide coating contains at least one lubricious oxide and an aluminum oxide. The substoichiometric lubricious oxide reduces friction, and the aluminum oxide improves wear resistance. Coating thickness can be as thick as 200 microns. A
coating thickness of 20-30 microns is preferred with respect to low fabrication cost.
Example 5 The lubricious oxide coating can be applied to a substrate with a flat surface (e.g., spacer, swashplate, slipper, and sealing plate), inner surface (e.g., cylinder barrel, sleeve, brushing, journal bearing and piston pin bearing bore), or outer surface (e.g., piston, ball-joint, shaft and chain wheel).
Example 6 The lubricious oxide coating contains silicon and aluminum to stabilize the substoichiometric Ti-0 oxide formed on cast aluminum-silicon alloys A319, A356, A380, and A390. The composite oxide comprises Si-contained A1203 and Tin021, where n is a natural number. For example, the lubricious composite oxide ceramic coating can be deposited on linerless aluminum engine cylinder bores to reduce wear and friction. The coating also has an excellent corrosion resistance against biofuels.
Example 7 The lubricious composite coating on an Al, Ti, Mg, or Zr alloy substrate exhibits a low coefficient of friction (COF) in both dry and oil lubricating conditions. In a dry ambient temperature testing condition, a typical composite coating COF is 0.1-0.15. In an oil lubricating condition, the COF can range from 0.01-0.1, depending on a sliding speed of 0.1 m/s-7 m/s. In a boundary lubricating condition, a typical COF of the lubricious composite oxide coating is 0.06-0.08. High sliding velocity involves mixed and elastohydrodynamic lubricating conditions, giving COFs as low as 0.01.
Example 8 An Al, Ti, Mg, or Zr alloy substrate is pre-treated using a traditional plasma electrolytic oxidation process to form a stoichiometric oxide coating up to 200 microns thick to provide a strong load-bearing capability against sliding and abrasive wear at high contact stresses.
A lubricious substoichiometric composite oxide is deposited on top of the stoichiometric oxide to reduce friction.
Claims (21)
1. A process of making a lubricious composite oxide coating, comprising (i) preparing an aqueous electrolyte containing a preliminary substance A for formation of oxygen-deficient substoichiometric oxide, a preliminary substance B for promoting formation and stabilization of said substoichiometric oxide, and a substance C
for adjusting pH value of said electrolyte;
(ii) applying said electrolyte and an electrical power onto a metallic surface;
(iii) generating plasma discharging on said metallic surface, which is made of aluminum (Al), titanium (Ti), zirconium (Zr) or magnesium (Mg) metal; and (iv) forming a lubricious composite oxide coating on said metallic surface, said coating containing at least one of said substoichiometric oxides, which is stabilized by silica (Si02) or alumina (A1203).
for adjusting pH value of said electrolyte;
(ii) applying said electrolyte and an electrical power onto a metallic surface;
(iii) generating plasma discharging on said metallic surface, which is made of aluminum (Al), titanium (Ti), zirconium (Zr) or magnesium (Mg) metal; and (iv) forming a lubricious composite oxide coating on said metallic surface, said coating containing at least one of said substoichiometric oxides, which is stabilized by silica (Si02) or alumina (A1203).
2. A composite oxide coating process as claimed in claim 1, wherein said preliminary substance A is a titanium complex compound, preferably potassium titanium oxalate, sodium titanium oxalate, ammonium titanium oxalate, titanium citrate, ammonium titanium citrate, or ammonium titanium fluoride.
3. A composite oxide coating process as claimed in claim 1, wherein said preliminary substance A is a tungsten (W) compound, preferably sodium tungstate, potassium tungstate, or ammonium tungstate.
4. A composite oxide coating process as claimed in claim 1, wherein said preliminary substance A is a molybdenum (Mo) compound, preferably sodium molybdate, potassium molybdate, or ammonium molybdate.
5. A composite oxide coating process as claimed in claim 1, wherein said preliminary substance B is a silicon compound, preferably sodium silicate or potassium silicate.
6. A composite oxide coating process as claimed in claim 1, wherein said preliminary substance B is a phosphorous compound, preferably sodium phosphate or potassium phosphate.
7. A composite oxide coating process as claimed in claim 1, wherein said preliminary substance B is an aluminum compound, preferably sodium aluminate or potassium aluminate.
8. A composite oxide coating process as claimed in claim 1, wherein said substance C is preferably citric acid, potassium hydroxide, or sodium hydroxide.
9. A composite oxide coating process as claimed in claim 1, wherein said electrolyte preferably contains 5-50 grams/Litre of potassium titanium oxalate or sodium titanium oxalate, 1-20 grams/Litre of sodium molybdate or potassium tungstate, 1-20 grams/Litre of sodium silicate or potassium silicate, 1-20 grams/Litre of citric acid, and 1-10 grams/Litre of potassium hydroxide or sodium hydroxide.
10. A composite oxide coating process as claimed in claim 1, wherein said lubricious oxide coating has a microstructure containing crystalline shear planes.
11. A composite oxide coating process as claimed in claim 1, wherein said lubricious oxide coating is comprised of at least one oxide of silica-stabilized Ti-O
substoichiometric oxide, alumina-stabilized Ti-O substoichiometric oxide, silica-stabilized Mo-O
substoichiometric oxide, alumina-stabilized Mo-O substoichiometric oxide, silica-stabilized W-O
substoichiometric oxide, alumina-stabilized W-O substoichiometric oxide, or silica-stabilized Zr-O substoichiometric oxide.
substoichiometric oxide, alumina-stabilized Ti-O substoichiometric oxide, silica-stabilized Mo-O
substoichiometric oxide, alumina-stabilized Mo-O substoichiometric oxide, silica-stabilized W-O
substoichiometric oxide, alumina-stabilized W-O substoichiometric oxide, or silica-stabilized Zr-O substoichiometric oxide.
12. A composite oxide coating process as claimed in claim 1, wherein said lubricious oxide coating contains silicon or phosphorous to stabilize said substoichiometric Ti-O oxide, which is formed on a surface of Ti metal or Ti alloys.
13. A composite oxide coating process as claimed in claim 1, wherein said lubricious oxide coating contains silicon or phosphorous to stabilize said substoichiometric Zr-O oxide, which is formed on a surface of Zr metal or Zr alloys.
14. A composite oxide coating process as claimed in claim 1, wherein said lubricious oxide coating contains silicon or aluminum to stabilize said substoichiometric Ti-O
oxide, which is formed on a surface of wrought Al metal or Al alloys.
oxide, which is formed on a surface of wrought Al metal or Al alloys.
15. A composite oxide coating process as claimed in claim 1, wherein said lubricious oxide coating contains silicon and aluminum to stabilize said substoichiometric Ti-O
oxide, which is formed on a surface of cast aluminum alloys of preferably A319, A356, A380, or A390.
oxide, which is formed on a surface of cast aluminum alloys of preferably A319, A356, A380, or A390.
16. A composite oxide coating process as claimed in claim 1, wherein said lubricious oxide, which is coating contains silicon or aluminum to stabilize said substoichiometric Mo-O and W-0 oxides, which are formed on wrought Al metal and Al alloys.
17. A composite oxide coating process as claimed in claim 1, wherein said lubricious oxide, which is coating contains silicon and aluminum to stabilize said substoichiometric Mo-O and W-O oxides, which are formed on cast aluminium alloys of preferably A319, A356, A380, or A390.
18. A composite oxide coating process as claimed in claim 1, wherein said lubricous composite oxide coating is deposited on an engine cylinder bore surface to reduce wear and friction.
19. A composite oxide coating process as claimed in claim 1, wherein said lubricous composite oxide coating is deposited on cylinder barrel, sleeve, bushing, journal bearing, piston pin bearing and camshaft bearing to reduce wear and friction.
20. A composite oxide coating process as claimed in claim 1, wherein said lubricious composite oxide coating is deposited on piston, pump, turbocharge part, swashplate, ball-joint, spacer, slipper and slipper plate to reduce wear and friction.
21. A composite oxide coating process as claimed in claim 1, wherein said lubricious composite oxide containing at least one of said substoichiometric oxides can be deposited on the top of a stoichiometric oxide to form a double-layered coating.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2847014A CA2847014A1 (en) | 2014-03-20 | 2014-03-20 | Lubricious composite oxide coating and process for making the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2847014A CA2847014A1 (en) | 2014-03-20 | 2014-03-20 | Lubricious composite oxide coating and process for making the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2847014A1 true CA2847014A1 (en) | 2015-09-20 |
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ID=54250530
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2847014A Abandoned CA2847014A1 (en) | 2014-03-20 | 2014-03-20 | Lubricious composite oxide coating and process for making the same |
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| Country | Link |
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| CA (1) | CA2847014A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR3045736A1 (en) * | 2015-12-18 | 2017-06-23 | Turbomeca | HYDRAULIC DEVICE COMPRISING A CERAMIC COATING |
| CN108018592A (en) * | 2017-10-10 | 2018-05-11 | 上海核工程研究设计院有限公司 | A kind of zircaloy differential arc oxidization surface method of modifying |
| CN109183112A (en) * | 2018-09-26 | 2019-01-11 | 沈阳大学 | A kind of aluminum alloy surface low pressure ceramic coating formed by micro-arc oxidation preparation method |
| EP4198327A1 (en) * | 2021-12-20 | 2023-06-21 | Aktiebolaget SKF | Plain bearing with improved wear resistance |
-
2014
- 2014-03-20 CA CA2847014A patent/CA2847014A1/en not_active Abandoned
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR3045736A1 (en) * | 2015-12-18 | 2017-06-23 | Turbomeca | HYDRAULIC DEVICE COMPRISING A CERAMIC COATING |
| CN108018592A (en) * | 2017-10-10 | 2018-05-11 | 上海核工程研究设计院有限公司 | A kind of zircaloy differential arc oxidization surface method of modifying |
| CN108018592B (en) * | 2017-10-10 | 2022-05-10 | 上海核工程研究设计院有限公司 | Zirconium alloy micro-arc oxidation surface modification method |
| CN109183112A (en) * | 2018-09-26 | 2019-01-11 | 沈阳大学 | A kind of aluminum alloy surface low pressure ceramic coating formed by micro-arc oxidation preparation method |
| EP4198327A1 (en) * | 2021-12-20 | 2023-06-21 | Aktiebolaget SKF | Plain bearing with improved wear resistance |
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