An object comprising a chromium-based coating having a high Vickers hardness, a method for producing the same, and an aqueous electroplating bath

Abstract

An object is disclosed that includes a chromium-based coating on a substrate, where the chromium is electroplated from an aqueous electroplating bath containing trivalent chromium cations, where the chromium-based coating contains 87–98 wt% chromium, 0.3–5 wt% carbon, and 0.1–11 wt% nickel and / or iron, and where the Vickers microhardness value of the chromium-based coating is 1000–2000 HV, and where the chromium-based coating is free of chromium carbide. Also disclosed is a method for its production and an aqueous electroplating bath.

Description

Technical Field

[0001] The present disclosure relates to an object comprising a chromium-based coating on a substrate. The present disclosure also relates to a method for producing an object comprising a chromium-based coating on a substrate. The present disclosure also relates to an aqueous electroplating bath. Background Art

[0002] Objects utilized in demanding environmental conditions often require, for example, mechanical or chemical protection to prevent the environmental conditions from affecting the object. The protection of the object can be achieved by applying a coating thereon (i.e., on the substrate). Protective coatings for various purposes are disclosed; hard coatings that protect the substrate from mechanical effects and diffusion barriers for protection against chemical effects. However, other ways of producing hard coatings in an environmentally friendly manner are needed. Summary of the Invention

[0003] An object comprising a chromium-based coating on a substrate is disclosed. The chromium can be electroplated from an aqueous electroplating bath comprising trivalent chromium cations. The chromium-based coating can comprise 87–98 wt% chromium, 0.3–5 wt% carbon, and 0.1–11 wt% nickel and / or iron. The Vickers microhardness value of the chromium-based coating can be 900–2000 HV. The chromium-based coating is free of chromium carbides.

[0004] An object comprising a chromium-based coating on a substrate is disclosed. The chromium can be electroplated from an aqueous electroplating bath comprising trivalent chromium cations. The chromium-based coating can comprise 87–98 wt% chromium, 0.3–5 wt% carbon, and 0.1–11 wt% nickel and / or iron. The Vickers microhardness value of the chromium-based coating can be 1000–2000 HV. The chromium-based coating is free of chromium carbides.

[0005] A method for producing an object comprising a chromium-based coating on a substrate is also disclosed. The method can comprise:

[0006] - Depositing a chromium-containing layer on the substrate by subjecting the substrate to at least one electroplating cycle from an aqueous electroplating bath, wherein the electroplating cycle is carried out at a current density of 50–300 A / dm 2 and at a deposition rate of 1.5–10 µm / min, and wherein the aqueous electroplating bath comprises:

[0007] - Trivalent chromium cations in an amount of 0.12–0.3 mol / l,

[0008] - Iron cations and / or nickel cations in an amount of 0.18–6.16 mmol / l, and

[0009] - A carboxylate ion in an amount of from 1.22 to 7.4 mol / l, and

[0010] wherein the molar ratio of the trivalent chromium cation to the carboxylate ion is from 0.015 to 0.099, and wherein the pH value of the aqueous trivalent chromium bath is from 2 to 6,

[0011] thereby producing a hard chromium-based coating having a Vickers microhardness value of 900 - 2000 HV without subjecting the deposited chromium-containing layer to heat treatment.

[0012] An aqueous electroplating bath is also disclosed. The aqueous electroplating bath may comprise:

[0013] - A trivalent chromium cation in an amount of from 0.12 to 0.3 mol / l,

[0014] - An iron cation and / or a nickel cation in an amount of from 0.18 to 6.16 mmol / l, and

[0015] - A carboxylate ion in an amount of from 1.22 to 7.4 mol / l, and

[0016] wherein the molar ratio of the trivalent chromium cation to the carboxylate ion is from 0.015 to 0.099, and wherein the pH of the aqueous trivalent chromium bath is from 2 to 6.

[0017] An aqueous electroplating bath is also disclosed. The aqueous trivalent chromium bath may comprise:

[0018] - A trivalent chromium cation in an amount of from 0.12 to 0.3 mol / l,

[0019] - An iron cation and / or a nickel cation in an amount of from 0.18 to 6.16 mmol / l, and

[0020] - A carboxylate ion in an amount of from 1.2 to 7.4 mol / l, and

[0021] wherein the molar ratio of the trivalent chromium cation to the carboxylate ion is from 0.015 to 0.099, wherein the pH of the aqueous trivalent chromium bath is from 2 to 6; and wherein the conductivity of the aqueous electroplating bath is from 160 to 400 mS / cm. Detailed Description

[0022] The present disclosure relates to an object including a chromium-based coating on a substrate. The chromium may be electroplated from an aqueous electroplating bath containing trivalent chromium cations. The chromium-based coating may comprise 87 - 98 wt% chromium, 0.3 - 5 wt% carbon, and 0.1 - 11 wt% nickel and / or iron. The chromium-based coating may have a Vickers microhardness value of 900 - 2000 HV. The chromium-based coating may be free of chromium carbides.

[0023] The present disclosure relates to an object comprising a chromium-based coating on a substrate. The chromium can be electroplated from an aqueous electroplating bath containing trivalent chromium cations. The chromium-based coating can comprise 87–98 wt% chromium, 0.3–5 wt% carbon, and 0.1–11 wt% nickel and / or iron. The chromium-based coating can have a Vickers microhardness value of 1000–2000 HV. The chromium-based coating is free of chromium carbides.

[0024] As will be apparent to those skilled in the art, the total amount of the different elements in the chromium-based coating can not exceed 100 wt%. The amounts of the weight % of the different elements in the chromium-based coating can vary within a given range.

[0025] The present disclosure also relates to a method for producing an object comprising a chromium-based coating on a substrate. The method can comprise:

[0026] - Depositing a chromium-containing layer on the substrate by subjecting the substrate to at least one electroplating cycle from the aqueous electroplating bath, wherein each of the at least one electroplating cycles is carried out at a current density of 50–300 A / dm 2 and at a deposition rate of 1.5–10 µm / min, and wherein the aqueous electroplating bath comprises:

[0027] - Trivalent chromium cations in an amount of 0.12–0.3 mol / l,

[0028] - Iron cations and / or nickel cations in an amount of 0.18–6.16 mmol / l, and

[0029] - Carboxylate ions in an amount of 1.22–7.4 mol / l, and

[0030] wherein the molar ratio of trivalent chromium cations to carboxylate ions is 0.015–0.099, and wherein the pH value of the aqueous trivalent chromium bath is 2–6,

[0031] thereby producing a hard chromium-based coating having a Vickers microhardness value of 900–2000 HV without subjecting the deposited chromium-containing layer to heat treatment.

[0032] In one embodiment, the method for producing an object comprising a chromium-based coating on a substrate comprises producing an object comprising a chromium-based coating on a substrate as defined in this specification.

[0033] The present disclosure relates to an aqueous electroplating bath. The aqueous electroplating bath can comprise:

[0034] - Trivalent chromium cations in an amount of 0.12–0.3 mol / l,

[0035] - Iron cations and / or nickel cations in an amount of 0.18–6.16 mmol / l, and

[0036] - Carboxylate ions in an amount of from -1.22 to 7.4 mol / l, and

[0037] wherein the molar ratio of trivalent chromium cations to carboxylate ions is from 0.015 to 0.099, and wherein the pH value of the aqueous trivalent chromium bath is from 2 to 6.

[0038] The present disclosure relates to an aqueous electroplating bath. The aqueous trivalent chromium bath may comprise:

[0039] - Trivalent chromium cations in an amount of from -0.12 to 0.3 mol / l,

[0040] - Iron cations and / or nickel cations in an amount of from -0.18 to 6.16 mmol / l, and

[0041] - Carboxylate ions in an amount of from -1.2 to 7.4 mol / l, and

[0042] wherein the molar ratio of trivalent chromium cations to carboxylate ions is from 0.015 to 0.099, wherein the pH value of the aqueous trivalent chromium bath is from 2 to 6; and wherein the conductivity of the aqueous electroplating bath is from 160 to 400 mS / cm.

[0043] The inventors have surprisingly found that by using the aqueous electroplating bath as disclosed in the present specification, a hard chromium-based coating with a Vickers microhardness value of 900 - 2000 HV can be produced without using heat treatment on the chromium-containing layer deposited from the electroplating bath. Unless otherwise specified, the expression "heat treatment" in the present specification should be understood to mean subjecting the deposited chromium-containing layer to heat treatment at a temperature of 300 - 1200 °C for a period of time, which will result in the formation of chromium carbides in the chromium-based coating. Such heat treatment can further change the crystal structure of chromium. That is, the method for producing a chromium-based coating may include the provision that the deposited chromium-containing layer is not subjected to heat treatment to form a chromium-based coating with a Vickers microhardness value of 900 - 2000 HV. However, this provision may not exclude, for example, dehydrogenation annealing.

[0044] In one embodiment, the Vickers microhardness value of the chromium-based coating is 1000 - 1900 HV, or 1100 - 1800 HV, or 1200 - 1700 HV, or 1300 - 1600 HV, or 1400 - 1500 HV. The Vickers microhardness can be measured according to standard ISO14577-1:2015.

[0045] In one embodiment, the chromium-based coating may have a Taber index of less than 1.5 mg / 1000 RPM, or less than 1.3 mg / 1000 RPM, or less than 1.2 mg / 1000 RPM, or less than 1.1 mg / 1000 RPM as determined according to ASTM G195-18 (wheel CS10, 1000 g). The Taber index represents the abrasion resistance of the chromium-based coating. The smaller the value of the Taber index, the better the abrasion resistance of the chromium-based coating.

[0046] In one embodiment, the crystal size of chromium may be 7–40 nm, or 9–20 nm, or 11–16 nm. The crystal size of chromium can be determined in the following manner:

[0047] The sample is measured by X-ray diffraction (XRD) in grazing incidence (GID) geometry. In GID geometry, the X-rays are aligned with the sample at a small angle of incidence and remain constant during the measurement. In this way, the X-rays can be focused on the surface layer of the sample, with the aim of minimizing the signal from the substrate. The measurement is carried out in the 2θ angular range from 30° to 120° in increments of 0.075°. The total measurement time for each sample is 1 h. The angle of incidence of the X-rays is 4°. In addition to the sample, a corundum sample was measured with exactly the same settings to measure the instrumental broadening of the diffraction peak. The measurement was carried out on a Bruker D8 DISCOVER diffractometer equipped with a Cu Kα X-ray source. The X-rays are incident on The mirrors are parallel and restricted by a 1-mm slit on the primary side. An equatorial Soller slit of 0.2° is used on the secondary side. The phases from the sample are identified from the measured diffraction patterns using DIFFRAC.EVA 3.1 software with the PDF-2 2015 database. The microcrystalline size and lattice parameters are determined from the sample by performing whole-profile fitting on TOPAS 4.2 software. The instrumental broadening is determined from the measurement results of a corundum sample. The Scherrer equation is used to calculate the microcrystalline size [see Patterson, A. (1939). "The Scherrer Formula for X-Ray Particle Size Determination". Phys. Rev. 56(10):978–982.], where the peak width is determined by the integral breadth method [see Scardi, P., Leoni, M., Delhez, R. (2004). "Linebroadening analysis using integral breadth methods: A critical review". J. Appl. Crystallogr. 37:381-390]. The obtained lattice parameter values are compared with the literature values from the PDF-2 2015 database. The difference between the measured and literature values indicates the presence of residual stress in the coating.

[0048] In one embodiment, the chromium-based coating comprises 87-98 wt% or 92–97 wt% of chromium. In one embodiment, the chromium-based coating comprises 0.3–5 wt% or 1.0–3.0 wt% of carbon. In one embodiment, the chromium-based coating comprises 0.1–11 wt% of nickel and / or iron, or 1.1–8.2 wt% of nickel and / or iron, or 1.5–6.2 wt% of nickel and / or iron. That is, the total amount of nickel and / or iron in the chromium-based coating can be 0.1–11 wt%, or 1.1–8.2 wt%, or 1.5–6.2 wt%. In one embodiment, the chromium-based coating comprises 0–6 wt%, or 0.1–5 wt%, or 0.5–3.0 wt% of nickel. In one embodiment, the chromium-based coating comprises 0.1–5 wt% or 1.0–3.2 wt% of iron.

[0049] The amounts of different elements such as chromium, iron, and nickel in the chromium-based coating can be measured and determined using an XRF analyzer. The amount of carbon in the chromium-based coating can be measured and determined using an infrared (IR) detector. An example of such a detector is the Leco C230 carbon detector.

[0050] The chromium-based coating can also comprise other elements. The chromium-based coating can additionally comprise oxygen and / or nitrogen.

[0051] Typically, in order to obtain a hard chromium-based coating with a Vickers microhardness value of at least 900 HV, when using an aqueous electroplating bath in which chromium is present substantially only in the trivalent form, it may be necessary to subject the deposited chromium-containing layer to at least one heat treatment at a temperature of 300–1200 °C. The inventors have surprisingly found that when using an aqueous electroplating bath as defined in this specification, such heat treatment can be omitted from the process. By omitting such heat treatment, one can be able to form a chromium-based coating substantially free of chromium carbides. The term "chromium carbide" should be understood herein to include all chemical compositions of chromium carbides. Examples of chromium carbides that may be present in the first layer are Cr3C2, Cr7C3, Cr 23 C6 or any combination thereof. When a chromium-containing layer deposited on a substrate by electroplating from a trivalent chromium bath is subjected to at least one heat treatment at a temperature of 300–1200 °C, such chromium carbides typically form in the chromium-based coating.

[0052] In this specification, unless otherwise specified, the terms "electroplating", "electrolytic plating" and "electrodeposition" should be understood as synonyms. Depositing a chromium-containing layer on a substrate herein means depositing a layer directly on the substrate to be coated. In the present disclosure, the chromium-containing layer can be deposited by electroplating from an aqueous electroplating bath containing trivalent chromium cations. In this regard, the term "electroplating from an aqueous electroplating bath containing trivalent chromium cations" is used to define such a process step in which the deposition occurs from an electrolytic bath in which chromium is present substantially only in the trivalent form.

[0053] As presented in this specification, the aqueous electroplating bath can contain:

[0054] - trivalent chromium cations in an amount of 0.12–0.3 mol / l,

[0055] - iron cations and / or nickel cations in an amount of 0.18–6.16 mmol / l, and

[0056] - carboxylate ions in an amount of 1.22–7.4 mol / l.

[0057] In the aqueous electroplating bath, the molar ratio of trivalent chromium cations to carboxylate ions is 0.015–0.099. In one embodiment, the molar ratio of trivalent chromium cations to carboxylate ions is 0.015–0.09, 0.03–0.08 or 0.065–0.075. The inventors have surprisingly found that the specified molar ratio of trivalent chromium cations to carboxylate ions has the additional utility of being able to omit the heat treatment that is typically required for the deposited chromium-containing layer to obtain a hard chromium-based coating.

[0058] Any (one or more) soluble trivalent chromium salts can be used as a source of trivalent chromium cations. Examples of such trivalent chromium salts are potassium chromium sulfate, chromium(III) acetate, and chromium(III) chloride.

[0059] In one embodiment, the source of the carboxylate ions is a carboxylic acid. In one embodiment, the source of the carboxylate ions is formic acid, acetic acid, or citric acid. In one embodiment, the source of the carboxylate ions is formic acid. In one embodiment, the source of the carboxylate ions is formic acid and acetic acid and / or citric acid.

[0060] In one embodiment, the aqueous electroplating bath contains trivalent chromium cations in an amount of 0.13–0.24 mol / l or 0.17–0.21 mol / l.

[0061] The aqueous electroplating bath contains iron cations and / or nickel cations. The inventors have surprisingly found that said cations may be required for depositing a chromium-containing layer. Nickel ions can have the additional effect of reducing the potential required in voltammetry. In one embodiment, the aqueous electroplating bath contains iron cations in an amount of 0.18–3.6 mmol / l or 0.23–0.4 mmol / l. In one embodiment, the aqueous electroplating bath contains nickel cations in an amount of 0.0–2.56 mmol / l or 0.53–1.2 mmol / l. In one embodiment, the aqueous electroplating bath contains iron cations and nickel cations in an amount of 0.18–6.16 mmol / l or 0.76–1.6 mmol / l. In one embodiment, the aqueous electroplating bath contains iron cations but no nickel cations. In one embodiment, the aqueous electroplating bath contains nickel cations but no iron cations. In one embodiment, the aqueous electroplating bath contains both iron cations and nickel cations.

[0062] In one embodiment, the aqueous electroplating bath contains carboxylate ions in an amount of 2.0–6.0 mol / l or 2.3–3.2 mol / l.

[0063] In one embodiment, the aqueous electroplating bath contains bromide ions in an amount of 0.15 - 0.3 mol / l, 0.21–0.25 mol / l. In one embodiment, the source of the bromide ions is selected from the group consisting of potassium bromide, sodium bromide, ammonium bromide, and any combination or mixture thereof. In one embodiment, the source of the bromide ions is potassium bromide, sodium bromide, or ammonium bromide. The use of a bromide such as potassium bromide can have the additional effect of effectively preventing the formation of hexavalent chromium at the anode of the electroplating system.

[0064] In one embodiment, the aqueous electroplating bath contains ammonium ions in an amount of 2–10 mol / l or 2.5–6 mol / l or 3–3.4 mol / l. In one embodiment, the aqueous electroplating bath contains ammonium ions in an amount of 0.18–1.5 mol / l or 0.45–1.12 mol / l. The use of ammonium ions has the additional effect of providing conductivity to the aqueous electroplating bath. The use of ammonium ions has the additional effect of forming a complex with chromium. In one embodiment, the source of ammonium ions is selected from the group consisting of ammonium chloride, ammonium sulfate, ammonium formate, ammonium acetate, and any combination or mixture thereof.

[0065] In one embodiment, the pH of the aqueous electroplating bath can be 2–6, or 3–5.5, or 4.5–5 or 4.1–5. When needed, the pH can be adjusted by including a base in the aqueous electroplating bath. Ammonium hydroxide, sodium hydroxide, and potassium hydroxide can be mentioned as examples of bases that can be used to adjust the pH of the aqueous electroplating bath. In one embodiment, the aqueous electroplating bath contains ammonium hydroxide, sodium hydroxide, and / or potassium hydroxide. In one embodiment, the aqueous electroplating bath contains a base in an amount of 0.5–3.1 mol / l or 1.4–1.8 mol / l.

[0066] In one embodiment, the conductivity of the aqueous electroplating bath is 160–400 mS / cm, 200–350 mS / cm, or 250–300 mS / cm. The conductivity of the aqueous electroplating bath can be adjusted by using salts with different conductivities, for example. Ammonium chloride, potassium chloride, and sodium chloride can be mentioned as examples of salts that can be used to adjust the conductivity. The conductivity can be measured, for example, according to standard EN 27888 (Water quality; Determination of conductivity (ISO 7888:1985)).

[0067] As will be clear to the person skilled in the art, in addition to the above materials, the chromium-based coating may also contain small amounts of residual elements and / or compounds originating from the manufacturing process, such as the electroplating process. Examples of such other elements are copper (Cu), zinc (Zn), and any compounds including them.

[0068] The methods and chromium-based coatings disclosed in this specification are very suitable for protecting metal substrates against corrosion. In one embodiment, the corrosion resistance of the object is at least 24 h, or at least 48 h, or at least 96 h, or at least 168 h, or at least 240 h, or at least 480 h. The corrosion resistance can be determined according to standard EN ISO 9227 NSS (Neutral salt spray) grade 9 or 10 (2017).

[0069] The thickness of the chromium-based coating can vary according to the application of the object in which it is to be used. The thickness of the chromium-based coating can depend on the number and thickness of the layers it contains. In one embodiment, the thickness of the chromium-based coating is 0.05 - 200 μm or 0.5 - 100 μm or 0.3 - 5 μm.

[0070] "Substrate" as used herein means any component or body onto which a chromium-based coating according to the present disclosure is applied. Generally, a chromium-based coating according to the present disclosure can be used on variable substrates. In one embodiment, the substrate comprises, consists of, or is made of a metal, a combination of metals, or a metal alloy. In one embodiment, the substrate is made of steel, copper, nickel, iron, or any combination thereof. The substrate can be made of a ceramic material. The substrate does not need to be a homogeneous material. In other words, the substrate can be a heterogeneous material. The substrate can be layered. For example, the substrate can be a steel object coated with a layer of nickel or nickel-phosphorus alloy (Ni-P). In one embodiment, the substrate is a cutting tool, such as a cutting blade. In one embodiment, the substrate is a cutting tool comprising a metal.

[0071] In one embodiment, an object comprising a chromium-based coating on a substrate does not include a nickel layer. In one embodiment, the chromium-based coating does not include a nickel layer. In one embodiment, the substrate does not include a nickel layer.

[0072] In one embodiment, the object is a gas turbine, a shock absorber, a hydraulic cylinder, a linked pin, a joint pin, a bushing ring, a round bar, a valve, a ball valve, or an engine valve.

[0073] In one embodiment, depositing a chromium-containing layer by subjecting the substrate to at least one electroplating cycle includes subjecting the substrate to one, two, three, four, five, six, seven, eight, nine, or ten electroplating cycles. Each of the at least one electroplating cycles can last 1 minute - 4 hours, or 10 - 60 minutes, or 20 - 40 minutes, or about 30 minutes. Each of the at least one electroplating cycles can be carried out at a current density of 50 - 300 A / dm 2 or 80 - 250 A / dm 2 or 110 - 200 A / dm 2 or 120 - 180 A / dm 2 or 130 - 170 A / dm 2 or 140 - 150 A / dm 2 During the (one or more) electroplating cycles, the temperature of the aqueous electroplating bath can be maintained at 25 - 70 °C or 40 - 50 °C. In one embodiment, each of the at least one electroplating cycles is carried out at a deposition rate of 1.8 - 5 μm / minute, or 2.0 - 4 μm / minute, or 2.5 - 3.5 μm / minute.

[0074] Each of at least one electroplating cycle can be temporally spaced apart from another electroplating cycle to form at least two sub-layers arranged one on top of the other. In one embodiment, each electroplating cycle is temporally spaced apart from each other by stopping the electroplating process for a predetermined period of time. Each of at least two electroplating cycles is spaced from another electroplating cycle by at least 1 second, or at least 10 seconds, or at least 30 seconds, or at least 1 minute, or at least 5 minutes, or at least 10 minutes. In one embodiment, each of at least two electroplating cycles is spaced from another electroplating cycle by 0.1 milliseconds – 3 minutes, or 1 second – 60 seconds or 10 – 30 seconds. In one embodiment, each of at least two electroplating cycles is spaced from another electroplating cycle by 0.5 – 10 minutes, or 2 – 8 minutes or 3 – 7 minutes.

[0075] By stopping the current passing through the aqueous electroplating bath, different electroplating cycles can be spaced apart from each other. The substrate to be electroplated can be removed from the aqueous electroplating bath for a certain period of time and then put back into the electroplating bath to continue electroplating. The substrate to be electroplated can be removed from one trivalent chromium bath for a certain period of time and then placed into another trivalent chromium bath for successive electroplating cycles.

[0076] The method can further include polishing the surface of the chromium-based coating. Polishing or grinding the surface of the chromium-based coating enables the formation of a smooth top surface. The method can include polishing the surface of the chromium-based coating to an Ra value of less than 0.6 or less than 0.2. The roughness value (Ra value) can be determined according to EN ISO 4288:1998. The surface of the chromium-based coating can be polished to the roughness value required for the final application of the object.

[0077] The objects disclosed in this specification have additional utilities that are well-suited for applications related to the hardness of the object. The material of the chromium-based coating has the additional utility of providing a hardness to the substrate suitable for specific applications that require high durability of the object. The chromium-based coating has the additional utility of protecting the underlying substrate from the effects caused by interaction with the environment during use. The chromium-based coating has the additional utility of providing good corrosion resistance. The chromium-based coating also has the additional utility of being formed from trivalent chromium, thereby having less impact on the environment than when using hexavalent chromium. In addition, compared with using hexavalent chromium, the method disclosed in this specification has the additional utility of being a safer production method for chromium-based coatings. In addition, the heat treatment of the chromium-containing layer can be omitted while still providing a chromium-based coating with a high Vickers microhardness value, which has the additional utility of simplifying the production method and thus beneficially affecting the production cost.

[0078] Examples

[0079] Reference will now be made in detail to several embodiments, the examples of which are illustrated in the accompanying drawings.

[0080] The following description discloses some embodiments in as much detail as will enable those skilled in the art to utilize embodiments based on the present disclosure. Not all steps or features of the embodiments are discussed in detail because, based on this specification, many steps or features will be apparent to those skilled in the art.

[0081] Example 1 - Preparation of a chromium-based coating on a substrate

[0082] In this example, different objects were prepared, each object comprising a chromium-based coating on a substrate.

[0083] First, the metal substrate (i.e., a CK45 steel substrate) was cleaned and pretreated by electroplating a nickel layer having a thickness of about 3–4 μm thereon as part of the substrate. The substrate was then rinsed with water and a chromium-based coating was formed on the substrate.

[0084] The aqueous electroplating bath comprised the following:

[0085]

[0086] The aqueous electroplating bath was subjected to normal initial plating and was then ready for use.

[0087] By subjecting the substrates to an electroplating cycle, a chromium-containing coating was deposited on each of these substrates. The electroplating cycle was carried out for 10 minutes. The substrates having the chromium-containing layer were then rinsed and polished to a Ra value of about 0.2.

[0088] The following properties and parameters of the chromium-based coatings of the prepared objects were determined. The results are presented in the table below.

[0089]

[0090] * Measured using an XRF analyzer that does not show the presence of carbon and scales the results to 100%

[0091] Example 2 - Influence of current density on the hardness of a chromium-based coating

[0092] In this example, the effect of the current density during electroplating was tested. The aqueous electroplating bath was a bath similar to bath 3 in Example 1 above. The results are presented in the table below.

[0093] <![CDATA[Current density (A / dm 2 )]]> Crystal size (nm) Hardness (HV) Amount of Ni (wt%) * Amount of Fe (wt%) * 50 4 900 1.9 2.7 70 8 890 1.6 2.0 120 12.4 1418 1.5 1.6 155 11.9 1394 1.2 1.5

[0094] * Measured using an XRF analyzer

[0095] It will be apparent to those skilled in the art that, as technology progresses, the basic concept can be implemented in various ways. Accordingly, the embodiments are not limited to the above examples; rather, they may vary within the scope of the claims.

[0096] The embodiments described above can be used in any combination with one another. Several of the embodiments can be combined together to form another embodiment. The objects, methods, or aqueous electroplating baths disclosed herein can include at least one of the embodiments described above. It will be understood that the benefits and advantages described above can relate to one embodiment or can relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or have any or all of the stated benefits and advantages. It will be further understood that reference to "an" item means one or more of those items. The term "comprising" is used in this specification to mean including the feature or act(s) that follow(s), without excluding the presence of one or more additional features or acts.

Claims

1. An object comprising a chromium-based coating on a substrate, wherein the chromium is electroplated from an aqueous electroplating bath containing trivalent chromium cations, wherein the chromium-based coating comprises 87–98 wt% chromium, 0.3–5 wt% carbon, and 0.1–11 wt% nickel and / or iron, and wherein the Vickers microhardness value of the chromium-based coating is 1000–2000 HV, and wherein the chromium-based coating is free of chromium carbides.

2. The object according to claim 1, wherein the Taber abrasion index of the chromium-based coating is less than 1.5 mg / 1000 RPM as determined according to ASTM G195-18.

3. The object according to claim 1, wherein the Taber abrasion index of the chromium-based coating is less than 1.3 mg / 1000 RPM as determined according to ASTM G195-18.

4. The object according to claim 1, wherein the Taber abrasion index of the chromium-based coating is less than 1.2 mg / 1000 RPM as determined according to ASTM G195-18.

5. The object according to claim 1, wherein the Taber abrasion index of the chromium-based coating is less than 1.1 mg / 1000 RPM as determined according to ASTM G195-18.

6. The object according to claim 1, wherein the crystal size of the chromium is 7–40 nm.

7. The object according to claim 1, wherein the crystal size of the chromium is 9–20 nm.

8. The object according to claim 1, wherein the crystal size of the chromium is 11–16 nm.

9. The object according to claim 1, wherein the Vickers microhardness value of the chromium-based coating is 1000–1900 HV.

10. The object according to claim 1, wherein the Vickers microhardness value of the chromium-based coating is 1100–1800 HV.

11. The object according to claim 1, wherein the Vickers microhardness value of the chromium-based coating is 1200–1700 HV.

12. The object according to claim 1, wherein the Vickers microhardness value of the chromium-based coating is 1300–1600 HV.

13. The object according to claim 1, wherein the Vickers microhardness value of the chromium-based coating is 1400–1500 HV.

14. The object according to any one of the preceding claims, wherein the object is a gas turbine, a shock absorber, a hydraulic cylinder, a connecting pin, a joint pin, a lining ring, a round bar, a valve, a ball valve, or an engine valve.

15. A method for producing an object comprising a chromium-based coating on a substrate, wherein the method comprises: Depositing a chromium-containing layer on the substrate by subjecting the substrate to at least one electroplating cycle from an aqueous electroplating bath, wherein each of said at least one electroplating cycle is carried out at a current density of 50–300 A / dm 2 and at a deposition rate of 1.5–10 µm / min, and wherein said aqueous electroplating bath comprises: In an amount of 0.12–0.3 mol / l of trivalent chromium cations, In an amount of 0.18–6.16 mmol / l of iron cations and / or nickel cations, and In an amount of 1.22–7.4 mol / l of carboxylate ions, and Wherein the molar ratio of the trivalent chromium cations to the carboxylate ions is 0.015–0.099, and wherein the pH of the aqueous electroplating bath is 2–6. Thus, a hard chromium-based coating with a Vickers microhardness value of 900–2000 HV is produced without subjecting the deposited chromium-containing layer to heat treatment.

16. The method according to claim 15, wherein the temperature of the aqueous electroplating bath is maintained at 25–70 °C during the electroplating cycle.

17. The method according to claim 15, wherein the temperature of the aqueous electroplating bath is maintained at 40–50 °C during the electroplating cycle.

18. The method according to claim 15, wherein each of the at least one electroplating cycle lasts from 1 minute to 4 hours.

19. The method according to claim 15, wherein each of the at least one electroplating cycle lasts from 10 to 60 minutes.

20. The method according to claim 15, wherein each of the at least one electroplating cycle lasts from 20 to 40 minutes.

21. The method according to claim 15, wherein each of the at least one electroplating cycle lasts 30 minutes.

22. The method according to any one of claims 15–21, wherein the electroplating cycle is carried out at a current density of 80–250 A / dm 2 .

23. The method according to any one of claims 15–21, wherein the electroplating cycle is carried out at a current density of 110–200 A / dm 2 .

24. The method according to any one of claims 15–21, wherein the electroplating cycle is carried out at a current density of 120–180 A / dm 2 .

25. The method according to any one of claims 15 - 21, wherein the electroplating cycle is carried out at a current density of 130 - 170 A / dm 2 2.

26. The method according to any one of claims 15–21, wherein the electroplating cycle is carried out at a current density of 140–150 A / dm 2 .

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