US20240076794A1

US20240076794A1 - Metallic component with a ceramic coating

Info

Publication number: US20240076794A1
Application number: US17/929,960
Authority: US
Inventors: Xueyuan Nie; Jingzeng Zhang
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-09-06
Filing date: 2022-09-06
Publication date: 2024-03-07

Abstract

This invention involves an alumina-based coating deposited on a steel or copper metallic component for enhanced anti-corrosion and electric insulation properties. The coated metallic component can be a bearing, laminate, shaft, gear, bolt, washer, bush or shim made of steels; or wire and hairpin winding made of copper.

Description

TECHNICAL FIELD

This invention involves an alumina-based ceramic coating on an iron-based or copper-based metallic component for enhanced anti-corrosion and electric insulation.

BACKGROUND OF THE INVENTION

Iron-based metallic or copper-based metallic component are widely used for machine, transportation, infrastructure and plant. The metallic component often suffers from general corrosion or galvanic corrosion. When electric or magnetic field is involved, the corrosion damaging would accelerate. Addition of anti-corrosion and electric insulation coating can be beneficial for longevity of the component.
Electric vehicles (EVs) use electric motors as powertrains which also involve the electric power and magnetic field. The bearings, gears and shafts in the drivetrain may need to have electric insulation to avoid electric discharging-induced erosion. Washers and bushes may also need such an electrical insulation to avoid the mentioned electric erosion and to reduce galvanic corrosion. The high-power density electric motor need a better cooling system which may however cause corrosion concerns. Therefore, there is a great demand for motor components to have an improved property in terms of anti-corrosion and electric insulation.
The electric insulation on a bearing can be realized by a ceramic coating deposited on the bearing surface. United States patents U.S. Pat. Nos. 9,646,737 and 9,581,203 B2 disclose an insulating coating which is made up of a ceramic layer with a plurality of particles and a plurality of pores between the particles. The ceramic layer is selected from a group of powders consisting of an oxide, a combination of oxides, a nitride and a spinel. The coating deposition is carried out using a thermal spraying method in dry air atmosphere as shown in patent number WO 2014156206 A1.
A new coating technology, called plasma electrolytic aluminating (PEA), has been developing by inventors of this patent for improving corrosion and wear resistance as well as electric insulation. Unlike conventional plasma electrolytic oxidation (PEO) which can only treat aluminum, titanium and magnesium alloys, the PEA process can apply to iron-based alloys and copper. In brief, the PEA process is a new coating method which combines electrochemical reaction, plasma discharging in a liquid environment, and plasma sintering of in-situ formed ceramic coating materials onto iron-based alloys or copper in the liquid environment. The PEA process is significantly different from known ceramic and coating fabrication methods. When someone speaks about ceramic sintering, the sintering is often operated in a furnace to densify a ceramic bulk material, not in a form of a coating [US patent US 2017/0088471 A1]. The sintering is performed by high temperature heating, not by plasma discharging in liquid. A traditional ceramic coating can be prepared in liquid environment through electrochemical [US patent U.S. Pat. No. 4,882,014] or sol-gel methods where again no plasma discharging is involved but sometime furnace sintering as a post-heat treatment is applied [patent US20060147699A1]. When a plasma discharging is relied on for a ceramic coating deposition, it is often that the coating operation is carried out in a vacuum system, e.g., physical vapour deposition or chemical vapour deposition [Canada patent number CA 2850270], or in air environments, e.g., thermal spraying [Canada patent number CA 2883157]. A plasma discharging in a liquid environment for a ceramic coating preparation can be found in plasma electrolytic oxidation (PEO) processes [Surf Coat Technol, 122 (1999) 73-93]. However, the conventional PEO process can be applied only onto engineering materials made of aluminium, titanium and magnesium and their alloys, because the PEO process is a coating conversion process associated with its substrate. A US patent [patent U.S. Pat. No. 9,701,177-B2] disclosed a coating method, called plasma electrochemical deposition, which is actually similar to the PEO process that can be applied again only to aluminium, titanium and magnesium. The PEA process is developed for components that are not made of aluminum, titanium or magnesium. Therefore, the PEA process is significantly different from the conventional PEO and totally different from vacuum plasma and thermal spraying coating process.
In this invention, a modified PEA process is applied on a metallic component that is a bearing, laminate, shaft, gear, bolt, washer, bush or shim made of an iron-based alloy; or wire, hairpin windings made of copper. The process is to provide metallic surfaces (i.e., steel, Cu and Cu alloy) with an anticorrosion and electric insulation coating.

SUMMARY OF THE INVENTION

The invention hereby involves an alumina-based ceramic coating which is synthesized using a process similar to the PEA (plasma electrolytic aluminating). The PEA process reported in prior work is an immersion treatment process where a small cast iron coupon sample is immersed into an electrolyte. The coating process in this invention is modified to treat a component on its localized surface, wherein the component is located preferentially outside an electrolyte tank and an aqueous electrolyte is applied onto the localized component surface where the coating is needed. The coating has a double layered structure with surface pores. The inner layer is formed through electrochemical reaction between the electrolyte and the metallic surface being treated. The formed inner layer is made of environmental-friendly inorganic compounds (i.e., iron aluminate, copper aluminate, or aluminum hydroxide depended on the electrolyte used), which is totally different from the metal-based supportive layer (e.g., chromium and nickel) involved in the previously-mentioned thermal spraying technology. The outer layer is an alumina-based ceramic comprising alumina (i.e., Al2O3 in chemical formula), aluminium-silicon-oxide, aluminium-titanium-based oxide, or titanium-based oxide, depended on the electrolyte used but independent from the component's material being treated. Thus, the coating contains no heavy metal in this invention. This coating has multifunctionality which includes anti-wear, anti-corrosion and electric insulation. The coating surface has some pores which can be sealed obviously by a commercial coating sealing method, if needed, for even better anti-corrosion and electric insulation properties.
The electrolyte used in this invention contains deionized or distilled water dissolved with 4-40 grams/litre of at least one of sodium aluminate, potassium aluminate, sodium silicate, potassium silicate, sodium phosphate, potassium phosphate, or sodium titanium oxalate.
The involved metallic component surface is made of steel, copper, or copper alloy.
The voltage applied during the coating process is 60-600 Volts of a DC or pulsed DC power with a current density of 0.05-5 A/cm2.
The formed ceramic coating has a double-layer microstructure, wherein the inner layer thickness is 0.5-5 microns, and the outside layer thickness is 5-100 microns.
The said ceramic coating has anti-wear and anti-corrosion resistances 5-10 times higher than the substrate material without the coating. The coating has an electric resistance of 0.1-1 Giga-ohms (G□).
The coated components (or parts) can be used for applications in bearings, laminates, wires, windings, shafts, gears, bolts, washers, bushes and shims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a coating on a metallic substrate.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the schematic illustration in FIG. 1 , a metallic component 1 is connected to a negative electrode (extended from the negative output terminal) of a DC or pulsed DC power supply through providing a liquid electrolyte to complete a closed electric circuit. The provision of the electrolyte can be carried out using a spraying method or using a localized immersion method. A surface of the component 1 firstly reacts with the electrolyte under a positive bias voltage of 60V-600V to form a thin inorganic compound layer 2. The compound layer would dielectrically breakdown when the bias voltage is increased to a certain voltage (preferably beyond 200V up to 600V). Under the increased bias voltage, precursors (ionic compounds) in the electrolyte stick onto the top of the inorganic compound layer surface 2 where a simultaneous process of electrochemical reaction and sintering (by plasma discharging) occurs and forms a hard ceramic outer layer 3. Therefore, the coating has a two-layered microstructure. The plasma electric discharging under the high bias voltages also generates small pores 4. The inner layer thickness can be in a range of 0.5-5 microns and the outer layer thickness can be in a range of 5-100 microns, depended on the treatment time, current density used and the final ending voltage. Longer treatment time, higher current density used and higher ending voltage generate a thicker coating.
In accordance with embodiments of this invention, a metallic component made of iron-based steel, or copper or copper alloy is treated using a coating process stated above in paragraph
. Exampled applications of this coating are for bearings, laminates, wires, shafts, gears, washers and bushes in electric motors. Electric insulating property of the coating is applied onto inner diameter (ID) or outer diameter (OD) surfaces of bearings or onto shafts and gears especially for avoiding electric erosion problems that may otherwise occur on the bearing rollers and raceways or gear teeth during the service involving electric current and voltage.
In accordance with embodiments of this invention, a metallic bearing component made of an iron-based alloy (e.g., steel) has an alumina-based ceramic coating that is deposited on either inner diameter (ID) or outer diameter (OD) or both inner and outer diameter surface(s) of the motor bearing. The alumina-based ceramic coating provides the bearing with anti-corrosion and electric insulation. The corrosion resistance increases 5-10 times compared with an uncoated bearing. The coating has properties of a breakdown voltage in a range of 500 V to 1000 V and an electric resistance in a range of 100 mega-ohms to 300 mega-ohms.
In accordance with embodiments of this invention, a metallic laminate component made of electric steels has an alumina-based ceramic coating that is deposited on one side surface or both side surfaces of the laminate. The alumina-based ceramic coating provides the laminate with anti-corrosion and electric insulation. The corrosion resistance increases 5-10 times compared with an uncoated laminate. The coating has properties of a breakdown voltage in a range of 500 V to 1000 V and an electric resistance in a range of 100 mega-ohms to 300 mega-ohms.
In accordance with embodiments of this invention, a metallic wire or hairpin-shaped component made of copper has an alumina-based ceramic coating that is deposited on outer surface of the wire or hairpin. The alumina-based ceramic coating provides the wire or hairpin with anti-corrosion and electric insulation. The corrosion resistance increases 5-10 times compared with an uncoated wire or hairpin. The coating has properties of a breakdown voltage in a range of 500 V to 1000 V and an electric resistance in a range of 100 mega-ohms to 300 mega-ohms.

Claims

What is claimed is:

1. A method of depositing an alumina coating on a metallic component, the method comprising:

applying a liquid electrolyte onto a metallic component;

applying a high electric voltage of 200-600 volts onto the metallic component;

depositing an aluminium hydroxide substance onto a surface of the metallic component; and

transforming the aluminium hydroxide substance to an alumina coating on the surface of the metallic component through high voltage electrical discharging in the liquid electrolyte.

2. The method as claimed in claim 1, wherein the metallic component is a steel bearing.

3. The method as claimed in claim 1, wherein the metallic component is a steel laminate.

4. The method as claimed in claim 1, wherein the metallic component is a copper hairpin.