FIELD OF DISCLOSURE
[0001] The present disclosure relates to metallic coatings. In particular, it relates to a method of coating steel with a dissimilar metal.
BACKGROUND OF THE DISCLOSURE
[0002] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Bronze Coating can be applied to almost any surface, causing the substrate material to take on the appearance of real bronze. Bronze plating is durable, it is extremely wear resistant and it is ideal for high friction environment such as bearings. It can be deposited on steels and cast iron and can withstand severe grind and shear adhesion testing. Rather than using only bronze for a component, using steel as a substrate and a coating/plating of bronze leads to properties proven many times to be superior to solid bronze, while at the same time has substantial cost savings. Such plating can be selectively provided on machined components thereby making for still further reduction in costs and desired properties such as hardness only where required.
[0004] Many coating techniques for achieving a bronze coating/plating on steel substrate exist. A Low pressure-Plasma spray technique is described at http://dx.doi.org/10.1016/S0043-1648(00)00520-2 (“Friction and wear characteristics of aluminum bronze coatings on steel substrates sprayed by a low pressure plasma technique”) for Aluminum-Bronze coating on Steel (SS400) as wear resistance coating. It is found that operating conditions such as spraying distance, current, particles temperature and velocity, vacuum and pressure of gases have a significant influence on the morphology of the coating’s microstructure and also considerably influence their tribological performance. The coating can sustain from 25 N to 100 N load in wear.
[0005] Article “The slurry erosion behaviour of high velocity oxy-fuel (HVOF) sprayed aluminium bronze coatings” (http://dx.doi.org/10.1016/S0043-1648(03)00088-7) describes a 2
method of coating Aluminium-Bronze on 1020 carbon steel to provide an erosion wear resistance surface for the marine industry, employing High velocity-Oxy-fuel spray. Article “Solid particle erosion–corrosion behaviour of a novel HVOF nickel aluminium bronze coating for marine applications—correlation between mass loss and electrochemical measurements” (http://dx.doi.org/10.1016/j.wear.2004.02.019) describes a method of coating Nickel-Aluminium-Bronze on BS 4360 steel, using High velocity-Oxy-fuel spray to provide erosion-corrosion resistance surface for marine applications.
[0006] Similarly, “High temperature performance of arc-sprayed aluminum bronze coatings for steel” (http://dx.doi.org/10.1016/S1003-6326(06)60342-7 ) describes using Arc spray to provide Aluminium-bronze on mild steel as anti-oxidation coatings. Article “Effect of the spraying process on the microstructure and tribological properties of bronze–alumina composite coatings” (http://dx.doi.org/10.1016/j.surfcoat.2010.08.150) describes using Conventional plasma spray and cold spray techniques to form Aluminum bronze-alumina composite coatings on mild steel and to understand the effect of the spraying process and alumina particle on the structure and tribological properties.
[0007] Article “Investigation of the microstructure and tribological behavior of cold-sprayed tin-bronze-based composite coatings” (http://dx.doi.org/10.1016/j.apsusc.2008.10.041) describes a cold spray technique to coat Tin-bronze, tin-bronze/TiN and Tin-bronze/ AlCuFeB on mild steel in order to improve tribological performance. Article “Electrodeposition of bronze–PTFE composite coatings and study on their tribological characteristics” (http://dx.doi.org/10.1016/j.surfcoat.2006.06.039) describes using Electrodeposition to deposit Tin-bronze with polytetrafluoroethylene (PTFE) on mild steel in order to obtain lubricant composite coatings. Article “Electrodeposition of graphite-bronze composite coatings and study of electroplating characteristics” (http://dx.doi.org/10.1016/j.surfcoat.2004.04.096) describes using Electrodeposition to deposit Tin-Bronze and Tin-Bronze with graphite particles on steel to have elctrodeposition of graphite. Article “Wear and friction characteristics of electrodeposited graphite–bronze composite coatings” (http://dx.doi.org/10.1016/j.surfcoat.2004.04.092) describes using Electrodeposition to deposit Tin-Bronze with graphite particles on steel, to understand the effect of graphite and tin content on frictional behaviour of coating..
[0008] Article “Corrosion protection properties of electroless Nickel/PTFE, Phosphate/MoS2 and Bronze/PTFE coatings applied to improve the wear resistance of carbon 3
steel” (http://dx.doi.org/10.1016/S0257-8972(03)00662-5) describes using Electroless Coating to provide Nickel-Phosphorus and Bronze particles in polytetrafluoroethylene matrix coating on carbon steel, to evaluate corrosion behaviour of coatings. Article “ Structural, microstructural and corrosion properties of brush plated copper–tin alloy coatings”(http://dx.doi.org/10.1016/j.surfcoat.2006.01.042 ) describes a Brush plating technique to provide Cu-tin alloy coating on mild steel in order to evaluate performance in corrosive environment.
[0009] As can be readily appreciated from above, several techniques like electrodeposition, electroless deposition or spray techniques like high velocity oxy-fuel spray, arc spray, cold spray etc. are being used to coat bronze on steel substrate. Majority of studies elaborated above are performed to understand the tribological or corrosion characteristics of the coatings. Studies are also done to understand the effect of parameters of the coating process.
[00010] However, techniques currently used for metallic coating such as bronze on steel are inferior with respect to complexity and quality along with their high processing cost. They also give inhomogeneous surface finish and poor mechanical properties of product, and also adversely alter properties of substrate. The time required for the coating is also too long; for example, an electrodeposition of bronze on steel requires few hours. Therefore, a quick, easy and environment friendly production process for improved quality of metallic coating on steel is highly necessary.
[00011] Similarly, several patents and their applications as under describe various techniques elaborated as under for coating different metals.
[00012] Patent US2849337 A (Metal coating baths) elaborates upon a method of Bronze coating on Uranium describing a process of uranium dipping into the melt without a flux coating wherein it is found that baths of 67% copper and 33% tin content tend to coat uniformly. Patent US4927798 A ( Diffusion-coated metals) elaborates upon a method of coating of iron and nickel activated by diffusing aluminum describing a method in which the metal treated is freshly activated by caustic leach and a method of treating a pyrophorically-activated iron surface
[00013] Patent application EP2071057 A2 (Electroplating Bronze) elaborates a method of coating of White bronze on steel, describing coating material composition, comprising sources of tin ions, copper ions and mercaptans selected from the group consisting of mercaptotriazoles and mercaptotetrazoles, and a method of coating comprising generating an electrical current through 4
the composition to deposit an alloy comprising copper and tin on the substrate. Patent US6607653 B1 (Plating bath and process for depositing alloy containing tin and copper) describes a Bronze alloy coating, claiming about a bath of lead-free tin-copper alloy plating, tin-copper-bismuth alloy and tin-copper-silver alloy
[00014] Patent US5589220 A ( Method of depositing chromium and silicon on a metal to form a diffusion coating) describes using Chromium and silicon to form a diffusion coating in steel and a method for forming a diffusion coating by depositing chromium and silicon on an iron-based substrate wherein the rate of heating is sufficient to cause deposition of silicon on the substrate to initiate the formation of ferrite layer at the substrate surface prior to the subsequent deposition of a substantial amount of chromium on the substrate. Patent US5972192 A (Pulse electroplating copper or copper alloys) describes a method of Copper or copper base alloy coating, describing a method of filling high aspect ratio opening in excess of three, such as trenches, via holes or contact holes, in a dielectric layer are filled employing a pulse or forward-reverse pulse electroplating technique to deposit copper or a copper-base alloy.
[00015] Patent application US20060137991A1 ( Method for bronze galvanic coating) describes a method of electrodeposition of bronzes in which the substrate to be coated is plated in an acid electrolyte that contains at least tin and copper ions, an alkylsulfonic acid and a wetting agent, and a method of preparation of such an electrolyte. Patent application US20050263403A1 (Method for electrodeposition of bronzes) describes a method for electrolytic deposition of bronze onto a substrate.
[00016] Patent US5080056A (Thermally sprayed aluminum-bronze coatings on aluminum engine bores) describes a method of making a cast hypoeutectic aluminum-silicon alloy engine block with a wear-resistant Aluminum-bronze alloy coating. Patent EP1001054 A2 ( Tin-copper alloy electroplating bath and plating process therewith) describes a tin-copper alloy electroplating bath comprising a water-soluble tin salt, a water-soluble copper salt, an inorganic or organic acid or a water-soluble salt thereof.
[00017] Patent application WO2015091201 A1 (Deposition of copper-tin and copper-tin-zinc alloys from an electrolyte) describes an aqueous, cyanide-free electrolyte for the electrolytic deposition of an alloy of copper, tin and optionally zinc, which comprises at least one salt from the group consisting of phosphates, phosphonates, polyphosphates, diphosphates and mixtures. Patent application EP 3002350 A1 (Cyanide-free electroplating baths for white bronze based on
5
copper (i) ions) describes copper/tin alloy coating using an electroplating bath comprising one or more sources of copper (i) ions, one or more sources of alloying tin ions, optionally one or more sources of alloying silver ions.
[00018] Patent US1970549 A (Process of electroplating bronze) describes a process for electrodepositing a coating composition at a rapid rate and at low cost while still obtaining desirable properties of an undercoating, and a process of electrodepositing a copper tin coating comprising electrolyzing a solution containing a soluble tin compound and a soluble copper compound and maintaining free cyanide in an amount not to exceed 60 grams per liter.
[00019] However, general techniques such as electrodeposition, electroless deposition or spray techniques described above of coating different metals carry their inherited demerits of relatively high processing cost, long processing time and inhomogeneous surface finish and poor mechanical properties, whether used for steel or other substrates. They often adversely affect the properties of the substrate. Moreover, majority of these techniques necessarily depend on chemical reactions and the storage or disposal of harmful reaction products is of environmental concern.
[00020] Hence there is a need in the art for a method to coat a metal with a dissimilar metal that leads to high quality, homogenous surface finish and excellent mechanical properties of the finished (coated) product. The process should be quick and easy with little/no potential for environmental damage.
[00021] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[00022] In some embodiments, the numbers expressing quantities or dimensions of items, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding
6
techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[00023] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00024] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[00025] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
OBJECTS OF THE INVENTION
[00026] Some of the objects of the present disclosure, which at least one embodiment herein satisfies are as listed herein below. 7
[00027] It is an object of the present disclosure to provide a method of coating a metal with a dissimilar metal that leads to effective coating of the metal within a short processing time.
[00028] It is another object of the present disclosure to provide a method as above that yields significant improvement in product quality with reference to desired surface characterization lading to a homogenous surface finish with excellent mechanical properties such as hardness; and does not adversely affect the properties of the substrate.
[00029] It is yet another object of the present disclosure to provide a method as above that is environment friendly.
[00030] It is another object of the present disclosure to provide a method as above that is easy to implement and monitor and has low processing cost.
SUMMARY
[00031] This summary is provided to introduce a selection of concepts in a simplified form to be further described below in the Detailed Description. This summary is not intended to identity key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[00032] The present disclosure mainly relates to a method of coating a metal substrate with a dissimilar metal. In particular, it relates to a method using activated sintering and diffusion under optimum parameters leading to coating of bronze on steel via diffusion of bronze particles in steel substrate.
[00033] In an aspect, a method of coating a metal substrate with another dissimilar metal using a field assisted activated sintering and diffusion process is disclosed wherein the method can include: covering the metal substrate with powder of the dissimilar metal; applying, through graphite punches, a pre-determined pressure on the metal substrate covered with the powder; activating and heating the powder and the metal substrate to a pre-determined temperature at a pre-determined heating rate using DC pulsed current; and holding the metal substrate covered with the powder for a pre-determined holding time at the pre-determined temperature, to coat the metal substrate with the dissimilar metal.
[00034] In another aspect, the holding can include holding the metal substrate, the powder and the graphite punches in an inert gas. 8
[00035] In yet another aspect, the metal substrate can be steel, the dissimilar metal can be bronze, and the inert gas can be argon.
[00036] In an aspect, when the metal substrate is steel, the dissimilar metal bronze and the inert gas argon; the pre-determined pressure can be 30 MPa to 50 MPa, the pre-determined temperature can be 600-750 Degrees Centigrade, the pre-determined heating rate can be 50 Degrees Centigrade/minute, and the pre-determined holding time can be 30 minutes.
[00037] In another aspect, when the metal substrate is steel, the dissimilar metal bronze and the inert gas argon; the pre-determined pressure can be 40 MPa and the pre-determined temperature can be 700 Degrees Centigrade.
[00038] In yet another aspect, when the metal substrate is steel, the dissimilar metal bronze and the inert gas argon; the DC pulsed current can be of 2V-4V and 200 Amps to 300 Amps range.
[00039] In another aspect, the pre-determined pressure can be 30 MPa to 50 MPa, the pre-determined temperature can be 600-750 Degrees Centigrade, the metal substrate can be austenitic steel and the dissimilar metal can be bronze, and the coating achieved can be 1 mm thick.
[00040] In an aspect, an activated sintering furnace is disclosed, wherein the furnace can include : a chamber infused with an inert gas, the chamber comprising: graphite dies and graphite punches configured to hold a metal substrate covered with powder of a dissimilar metal; and loading mechanism to put pressure on the metal substrate covered with the powder via the graphite punches; and an on-off pulsed DC generator to provide pulses of electric power across the metal substrate and the powder combination, to coat the metal substrate with the dissimilar metal.
[00041] In another aspect of the activated sintering furnace, the metal substrate can be steel, the dissimilar metal can be bronze, and the inert gas can be argon.
[00042] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.
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BRIEF DESCRIPTION OF DRAWINGS
[00043] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure, and wherein:
[00044] FIG. 1 illustrates the process of activated sintering and diffusion employed in accordance with an exemplary embodiment of the present disclosure.
[00045] FIG. 2 illustrates optical microstructure showing bronze (Cu-15 wt% Sn) coating on steel processed by optimized conditions of activated sintering and diffusion in accordance with an exemplary embodiment of the present disclosure.
[00046] FIG. 3 illustrates nanohardness measurements on cross sectioned parts of coated samples in accordance with an exemplary embodiment of the present disclosure.
[00047] FIG. 4 illustrates the disclosed method, in accordance with an exemplary embodiment of the present disclosure.
DETAILED DESCRIPTION
[00048] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[00049] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details.
[00050] Embodiments of the present invention include various steps, which will be described below. The steps may be performed by hardware components or may be embodied in machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor programmed with the instructions to perform the steps. Alternatively, steps 10
may be performed by a combination of hardware, software, and firmware and/or by human operators.
[00051] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[00052] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00053] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. These exemplary embodiments are provided only for illustrative purposes and so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skill in the art. The invention disclosed may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention.
[00054] Thus, for example, it will be appreciated by those of ordinary skill in the art that the diagrams, schematics, illustrations, and the like represent conceptual views or processes illustrating systems and methods embodying this invention. The functions of the various 11
elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing associated software. Similarly, any switches shown in the figures are conceptual only. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the entity implementing this invention. Those of ordinary skill in the art further understand that the exemplary hardware, software, processes, methods, and/or operating systems described herein are for illustrative purposes and, thus, are not intended to be limited to any particular named element.
[00055] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[00056] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[00057] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[00058] In an aspect, a method of coating a metal substrate with another dissimilar metal using a field assisted activated sintering and diffusion process is disclosed wherein the method can include: covering the metal substrate with powder of the dissimilar metal; applying, through graphite punches, a pre-determined pressure on the metal substrate covered with the powder; activating and heating the powder and the metal substrate to a pre-determined temperature at a pre-determined heating rate using DC pulsed current; and holding the metal substrate covered with the powder for a pre-determined holding time at the pre-determined temperature, to coat the metal substrate with the dissimilar metal. 12
[00059] In another aspect, the holding can include holding the metal substrate, the powder and the graphite punches in an inert gas.
[00060] In yet another aspect, the metal substrate can be steel, the dissimilar metal can be bronze, and the inert gas can be argon.
[00061] In an aspect, when the metal substrate is steel, the dissimilar metal bronze and the inert gas argon; the pre-determined pressure can be 30 MPa to 50 MPa, the pre-determined temperature can be 600-750 Degrees Centigrade, the pre-determined heating rate can be 50 Degrees Centigrade/minute, and the pre-determined holding time can be 30 minutes.
[00062] In another aspect, when the metal substrate is steel, the dissimilar metal bronze and the inert gas argon; the pre-determined pressure can be 40 MPa and the pre-determined temperature can be 700 Degrees Centigrade.
[00063] In yet another aspect, when the metal substrate is steel, the dissimilar metal bronze and the inert gas argon; the DC pulsed current can be of 2V-4V and 200 Amps to 300 Amps range.
[00064] In another aspect, the pre-determined pressure can be 30 MPa to 50 MPa, the pre-determined temperature can be 600-750 Degrees Centigrade, the metal substrate can be austenitic steel and the dissimilar metal can be bronze, and the coating achieved can be 1 mm thick.
[00065] In an aspect, an activated sintering furnace is disclosed, wherein the furnace can include : a chamber infused with an inert gas, the chamber comprising: graphite dies and graphite punches configured to hold a metal substrate covered with powder of a dissimilar metal; and loading mechanism to put pressure on the metal substrate covered with the powder via the graphite punches; and an on-off pulsed DC generator to provide pulses of electric power across the metal substrate and the powder combination, to coat the metal substrate with the dissimilar metal.
[00066] In another aspect of the activated sintering furnace, the metal substrate can be steel, the dissimilar metal can be bronze, and the inert gas can be argon.
[00067] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features. 13
[00068] The present disclosure mainly relates to a method of coating a metal with a dissimilar metal. In particular, it relates to a method using activated sintering and diffusion under optimum parameters leading to coating of bronze on steel via diffusion of bronze particles in steel substrate.
[00069] FIG. 1 illustrates the process of activated sintering and diffusion employed in accordance with an exemplary embodiment of the present disclosure.
[00070] Activated sintering is a method used to create objects from metal powders. It is performed in the gaseous atmosphere which enhances aggregation of metal particles. Activated sintering allows sintering diffusion to occur at lower temperature and shorter time with better properties. Under high amount of pressure and pulsed electric current, localized necking can occur due to Joule heating leading to fast heating.
[00071] In an aspect, process disclosed comprises diffusion of bronze powder particles on to a bulk steel surface while deploying activated sintering technique using different combinations of temperature, pressure and/or heating rates to develop a coating of desired thickness. In this process, temperature rises very fast and the densification of bronze particles can be completed within few minutes. Besides, copper and tin (that constitute the bronze particles) can be diffused onto the steel surface making a strong bond. The process disclosed uses an activated sintering furnace and parameters elaborated herein.
[00072] In an exemplary embodiment, an activated sintering furnace 100 can include graphite dies 104, graphite punches 108, and loading mechanisms that can include plates 112, ram 114 and load 116. These components can be configured in a chamber 110 that can be filled with appropriate inert gases (for instance, argon) to facilitate the activated sintering process. Instead of load 116, rams 114 can be hydraulically loaded to exert appropriate pressure as required onto a substrate and powder to be sintered, as elaborated hereunder
[00073] In an exemplary embodiment, a polished steel substrate sample 102 (that can be a suitable shape, for instance cylindrical) can be held between graphite dies 104 of suitable dimensions. The other sides of the steel substrate 102 (for instance, its top and bottom sides as illustrated) can be covered with appropriate amount of loose bronze powder illustrated as 106.
[00074] In an aspect, bronze powder 106 can further be pressed on both sides of substrate102 using graphite punches 108. As can be appreciated, pressure using graphite punches 14
108 transfers to bronze powder 106 as well as to steel substrate 102 held tight between graphite punches 108 and graphite dies 104.
[00075] All above components can be kept in chamber 110 of the activated sintering furnace 100.The chamber 110 can be infused with argon gas. Further, load plates 112, ram 114 (that can be a hydraulic ram, for instance) and load 116 can be used to put appropriate uniaxial pressure onto bronze powder 106 as well as to steel substrate 102. Instead of load 116, a hydraulic pressure of pre-configured range may be put on to the bronze powder 106 as well as to steel substrate 102.
[00076] In another aspect, an on-off pulsed DC generator 118 can be used to provide pulses of electric power across the substrate 102 and bronze powder 106 combination. In an exemplary embodiment, DC generator 118 can provide an on/off low voltage of 2 to 4 volts, with a high current of 200-300 Amperes. The assisting electric field and consequent current passing through sample 102 and bronze powder106 can induce a Joule heating effect on the sample 102 and bronze powder 106. An optimized pressure across the substrate 102 and powder 106 can be kept at 30-50MPa (Megapascals), while an optimized temperature of 600-750 Degrees Centigrade can be achieved ( due to Joule heating ) across the substrate 102 and powder 106. These conditions can lead to field assisted diffusion of bronze powder in steel substrate. Joule heating (also termed as ohmic heating and resistive heating) is the process by which the passage of an electric current through a conductor produces heat.
[00077] In yet another aspect, process disclosed can include maintaining a heating rate of 50 Degrees Centigrade /minute range of the substrate 102 and powder 106.
[00078] In aspect, process disclosed can include holding the substrate 102 and powder 106 for a holding time of sintering/diffusion of 30 minutes, once the optimized temperature of 600-750 Degrees Centigrade is reached.
[00079] In an exemplary embodiment, most optimum results can be achieved when the pre-determined pressure is 40 MPa and the pre-determined temperature 700 Degrees Centigrade.
[00080] In this manner, in exemplary embodiment elaborated above, surface of the bronze powder can be activated by pulse electric current, while temperature and pressure can be optimized in a field assisted activated sintering furnace. 15
[00081] In this manner, proposed method includes achieving activated sintering and diffusion by field assisted Joule heating and pressure in controlled atmosphere to produce quality coat in less processing time without altering properties of steel substrate.
[00082] Using above procedure/method, it is found that the resultant well diffused coating is hard and strongly adherent with less decrease in hardness of the substrate steel material, while time required for coating is less and no special preparation of the surface (substrate) is required for coating nor any special finishing is required after coating.
[00083] In this manner, proposed inventive process can improve the ease of effective coating of bronze on steel in shortest possible time with significantly improved product quality in reference to desired surface characterization.
[00084] In an aspect, based on coating materials on steel substrate, the working parameters can be varied in a wide range to obtain uniform and sound quality coating.
[00085] In another exemplary embodiment, the workable range of parameters for producing 1 mm thick coating of Cu-15%Sn (bronze) on austenitic steel substrate can be temperature 600-750 Degrees Centigrade and pressure 30-50 MPa; with appropriate direct pulse current and voltage requirements.
[00086] FIG. 2 illustrates optical microstructure showing bronze (Cu-15 wt% Sn) coating on steel processed by optimized conditions of activated sintering and diffusion in accordance with an exemplary embodiment of the present disclosure.
[00087] Illustrated in FIG. 2 is a steel substrate 202 with a bronze coating 204, the two having an intervening diffusion layer 206 of about 10 μm thickness.
[00088] As illustrated a diffusion layer 206 of uniform thickness of about 10 μm, the layer being a mixture rich in Iron(Fe), Tin (Sn), Copper (Cu), Chromium (Cr) and Carbon (C) is observed between coating 204 and substrate 202.
[00089] FIG. 3 illustrates nanohardness measurements on cross sectioned parts of coated samples in accordance with an exemplary embodiment of the present disclosure.
[00090] Illustrated in FIG. 3 is a graph with contact depth (mm) along X axis and Hardness (Giga Pascal -GPa) along Y axis.
[00091] In an aspect, zone 302 is the steel substrate, zone 304 the diffusion layer formed by process as elaborated above and zone 306 bronze layer formed. 16
[00092] As can be seen, optimized conditions of diffusion as achieved using activated sintering and diffusion process as elaborated above provide less decrease in hardness of steel substrate since, as can be seen, hardness found is about 7 GPa at point 308 and 4.5 GPa at point 310 (where the diffusion layer begins). Besides, a uniform hardness of 2 GPa to 4 GPa is achieved in the diffusion layer as can be seen at points 312 and 310 of graphs as illustrated.
[00093] FIG. 4 illustrates the disclosed method, in accordance with an exemplary embodiment of the present disclosure.
[00094] In an aspect, the method includes, at step 402 covering a metal substrate with powder of a dissimilar metal and holding the metal substrate covered with the powder within graphite punches in an environment of an inert gas.
[00095] In another aspect, the method includes, at step 404, applying, through the graphite punches, a pre-determined pressure on the metal substrate covered with the powder.
[00096] In yet another aspect, the method includes, at step 406, activating and heating the powder and the metal substrate to a pre-determined temperature at a pre-determined heating rate using DC pulsed current.
[00097] In an aspect, the method includes, at step 408, holding the metal substrate covered with the powder for a pre-determined holding time at the pre-determined temperature.
[00098] While the invention has been elaborated above using an example of coating a steel substrate with bronze, it can readily be appreciated that the method can be applied to coating of any suitable metal with another dissimilar metal. All such modifications and embodiments are fully within the scope of the present disclosure.
[00099] As used herein, and unless the context dictates otherwise, the term “coupled to” is intended to include both direct coupling (in which two elements that are coupled to each other or in contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms “coupled to” and “coupled with” are used synonymously. Within the context of this document terms “coupled to” and “coupled with” are also used euphemistically to mean “communicatively coupled with” over a network, where two or more devices are able to exchange data with each other over the network, possibly via one or more intermediary device.
[000100] Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the 17
terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
[000101] While some embodiments of the present disclosure have been illustrated and described, those are completely exemplary in nature. The disclosure is not limited to the embodiments as elaborated herein only and it would be apparent to those skilled in the art that numerous modifications besides those already described are possible without departing from the inventive concepts herein. All such modifications, changes, variations, substitutions, and equivalents are completely within the scope of the present disclosure. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims.
ADVANTAGES OF THE INVENTION
[000102] The present disclosure provides a method of providing a dissimilar metal coating on a metal that leads to effective coating of the metal within a short processing time.
[000103] The present disclosure provides a method as above that yields significant improvement in product quality with reference to desired surface characterization, leading to a homogenous surface finish with excellent mechanical properties such as hardness; and does not adversely affect the properties of the substrate.
[000104] The present disclosure provides a method as above that is environment friendly.
[000105] The present disclosure provides a method as above that is easy to implement and monitor and has low processing cost.

We Claim:
1) A method of coating a metal substrate with another dissimilar metal using a field assisted activated sintering and diffusion process, the method comprising:
covering the metal substrate with powder of the dissimilar metal;
applying, through graphite punches, a pre-determined pressure on the metal substrate covered with the powder;
activating and heating the powder and the metal substrate to a pre-determined temperature at a pre-determined heating rate using DC pulsed current; and
holding the metal substrate covered with the powder for a pre-determined holding time at the pre-determined temperature, to coat the metal substrate with the dissimilar metal.
2) The method of claim 1, wherein the holding comprises holding the metal substrate, the powder and the graphite punches in an inert gas.
3) The method of claim 2, wherein the metal substrate is steel, the dissimilar metal is bronze, and the inert gas is argon.
4) The method of claim 3, wherein the pre-determined pressure is 30 MPa to 50 MPa, the pre-determined temperature is 600-750 Degrees Centigrade, the pre-determined heating rate is 50 Degrees Centigrade/minute, and the pre-determined holding time is 30 minutes.
5) The method of claim 3, wherein the pre-determined pressure is 40 MPa and the pre-determined temperature is 700 Degrees Centigrade.
6) The method of claim 3, wherein the DC pulsed current is of 2V-4 V and 200 Amperes to 300 Amperes range.
7) The method of claim 2, wherein the pre-determined pressure is 30 MPa to 50 MPa, the pre-determined temperature is 600-750 Degrees Centigrade, the metal substrate is austenitic steel and the dissimilar metal is bronze, and wherein the coating achieved is 1 mm thick.
8) An activated sintering furnace comprising:
a chamber infused with an inert gas, the chamber comprising :
graphite dies and graphite punches configured to hold a metal substrate covered with powder of a dissimilar metal; and 19
loading mechanism to put pressure on the metal substrate covered with the powder via the graphite punches; and
an on-off pulsed DC generator to provide pulses of electric power across the metal substrate and the powder combination, to coat the metal substrate with the dissimilar metal.
9) The activated sintering furnace of claim 8, wherein the metal substrate is steel, the dissimilar metal is bronze, and the inert gas is argon.