GB1569145A

GB1569145A - Process for depositing protective coatings and article produced

Info

Publication number: GB1569145A
Application number: GB4426576A
Authority: GB
Original assignee: WARNER LONDON Inc
Current assignee: WARNER LONDON Inc
Priority date: 1976-10-25
Filing date: 1976-10-25
Publication date: 1980-06-11

Description

(54) PROCESS FOR DEPOSITING PROTECTIVE COATINGS AND ARTICLE PRODUCED (71) We, WARNER-LONDON. INC.. a corporation organised and existing under the laws of the State of So. Carolina. United States of America. and having its primary place of business located in Greensboro. North Carolina. United States of America. do hereby declare the invention for which we pray that a patent may be granted to us. and the method by which it is to be performed. to be particularly described in and by the following statement: This invention relates generally to protective coatings.More particularly. the present invention relates to discontinuous coatings of refractory metal particles such as abrasionresistant, heat-resistant. or chemical resistant. or the like. materials. applied to surfaces that may be composed of metal, metallic allovs. and metal containing bases.

According to the present invention there is provided a process for depositing upon a relatively low wear resistant base metal a refractory metal comprising: providing an electrolyte material capable of dissociation into ions. and having a conductance ratio of between 0.13 and ().93 calculated at a 0.1 normal solution, providing a particulate refractory metal to be deposited within the near-surface region of said base material. said refractory metal having a melting point of at least 1490 C.

admixing 99 to 50% by weight of said refractory metal and 1 to 5()C/e bv weight of said electrolyte for a sufficient time to form a nascent surface on at least a portion of each said refractory metal particles to be deposited and at least partially surrounding said refractory metal particles with said electrolyte.

maintaining a moisture content in said mixture sufficient to maintain a resistivitv of said electrolyte of less than about 10' ohm-centimeters of said admixture, forming a refractory metal ion concentraton of 1-60,000 mg. per liter of solution, contacting and at least partially coating the surface of said base material with said refractory metal in particulate form and said electrolyte admixture, reacting said admixture with said base material at temperatures between ()"C and 200CC, and depositing said refractory metal within the near-surface region of said base material in the form of discrete particles, whereby to provide a protcctive surface for said base material.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made. bv wav of example to the accompanying single Figure drawing which is a schematic representation of various possible structural characteristics of the near-surface of the base metal.

The present invention is based on the discoverv that any metal, metallic alloy or metal-containing base may have deposited thereon a refractory or protective metal having a melting point of at least 14900C when combined with an electrolyte that is at least in part positioned between the refractory metal particle and the surface of the base material.

Among those refractory or protective metals that mav be used are the following in powder or particulate form and all allovs incorporating these rhodium chromium ruthenium cobalt tantalum iridium thorium molybdenum titanium niobium tungsten osmium vanadium palladium yttrium platinum zirconium rhenium The initial shape of these metal particles is any one of the following, idiomorphic or blocky or equiaxial or spheroidal or acicular or dendritic and they are preferably of as small a size as practicable, usually in the range of 0.01 micrometer to about I mm.The base materials upon which the refractory material may be deposited include any of the metals, such as: aluminium, iron, chromium. cobalt, copper. nickel. magnesium. tin. titanium. or any alloy of these, including: steels. cast irons. brasses. bronzes. solders. etc.. or any other suitable base metal.

In order to effect the deposition of particulate refractory metal within the near-surface region of the base. it is also necessarv that there be present a finely dispersed electrolyte material which should be positioned at least partially between the particulate refractorv metal and the base metal.

Among those electrolytes found suitable are the acids including: the mineral acids, hydrochloric, nitric. sulphuric. phosphoric. perchloric. fluorosilicic. etc.. and the acid anhvdrides such as arsenic trioxide and chromium trioxide. etc: the organic acids, tartaric.

malonic, and the like. Useful basic electrolytes include: alkali and alkaline earth hvdroxides such as sodium, potassium. lithium. calcium. magnesium. etc. Also useful as electrolytes are: alkali and alkaline earth salts of the acids set forth above. such as the alkali halide salts, particularly the chlorides. chlorates. fluorides. nitrates. sulfates. phosphates. carbonates, etc. and metal salts, wherein the metal now used as a part of the electrolyte may be any one of the metals mentioned previously as a refractory metal or as a base metal. forming any salt such as the sulfates, phosphates. nitrates. carbonates. chromates. molybdenates. tungstates. etc.

Also found useful as the electrolyte are the chemical compounds such as ammonium thiocyanate, potassium thiocvanate. zinc sulfate. ammonium carbonate. ammonium sulfate, potassium sulfate, sodium sulfite. sodium carbonate. potassium cyanide. calcium nitrate. potassium chloride. and calcium chloride.

While the electrolyte may be generallv any acid. base or salt. it must dissociate in the presence of moisture. i.e.. be capable of conducting electrical current and have an adequate degree or percentage of dissociation or more correctly a sufficiently high equivalent conductance ratio.

For purposes of this invention. the conductance ratio is determined as the ratio between the equivalent conductance at a dilution of I gm-equivalent per 1() liters of water and the equivalent conductance at infinite dilution. the temperature being '5 C (see "The Phvsical Chemistrv of Electrolvtic Solutions". Harned and Oxen. Rheinhold Publishing Corp., 1958). The electrolytes that are used in the present invention are limited to those having conductance ratios in the range of 0.13 to 0.93 approximately. and preferably above 0.60.

The following are some of the acids, bases and salts and the approximate values of their corresponding equivalent conductance ratios that meet the requirements of this invention: ACIDS BASES hydrochloric acid ().9() sodium hvdroxide O.Xt( nitric acid 0.92 potassium hydroxide (1.93 sulfuric acid ().6() calcium hydroxide ().X() strontium hydroxide ().86 barium hydroxide ().86 SALTS silver nitrate 0.86 sodium carbonate 0.61 potassium chloride 0.86 ammonium sulfate 0::59 sodium chloride 0.82 barium nitrate 0.57 potassium bromide 0.92 strontium nitrate 0.62 sodium nitrate 0.82 lead nitrate 0.54 sodium acetate 0.79 cupric acetate 0.33 potassium chlorate 0.83 zinc sulphate ().3to calcium chloride 0.75 copper sulphate 0.38 Because dissociation is a criterion for the selection of an electrolvte in this process. it may be concluded that the greater the capability of the dissociation of the electrolyte, the more effective it would become in causing the reaction of this process to take place. The assumption here is that the more complete the ionization of an electrolyte may be, the more effectively will it serve the purposes of this process.

Insofar as this process is concerned. no electrical current need be applied in depositing the refractory or protective metal within and upon surfaces: however. because this process is believed to be fundamentally electrolytic in nature. the application of an electrical current will influence and may assist this process. An applied current is not a requisite of the process as the internally-generated electrolytic currents are of sufficient magnitude on a microscopic scale to obtain the results of this invention.

In order to achieve the electrochemical reaction for the deposit of the refractory metal upon the base material, it is believed that an intimate association between the particulate refractory metal, the electrolyte. and the base material takes place. In this respect. it has been found for the case of solid electrolytes that the precise combined particle size of the electrolyte and refractory metal is not critical or important as this size depends primarily upon the dimensions of the usuallv harder refractory metal. The electrolyte particle is preferably finely divided and in the range of 10 i micrometer to approximately I mm, preferably 10 to 100 times smaller than the conjugate refractory metal particle at the time of the application to the base metal.

To initiate the reaction in which it is believed that a portion ot the base metal is exchanged for the refractory metal. it is important that the refractory metal become partially ionized to effect the exchange reaction with the base metal. It has been found that the ion concentration should be in the range of I to 60.0()() mg of refractory metal ion per liter of solution. Preferably. the range should be between I 1.000 and 15,000 mg of refractory metal ion per liter of solution.

The refractory metal ion, after it has exchange-reacted with the base metal, is believed to provide a site for the particle of refractory metal to be deposited. These reactions are thought to occur only on a microscopic scale. In order to produce refractory metal ions, at least in sufficient quantity to bring about the desired reactions. it is important that the refractory metal have a nascent surface on at least a portion of the surface of the refractory metal particle to be deposited. This fresh surface, for reasons that cannot be fully explained, enables the refractory metal in combination with the electrolyte and the moisture present to produce in sufficient time the necessarv concentration of refractory metal ions.All of the refractory metals are insoluble. in the usual sense of the term. in the moisture present but sufficient concentrations of ions as required for this invention are nevertheless produced from the nascent surfaces of the refractory particles in the presence of the electrolyte and sufficient moisture. The nascent surface required can be easily produced by a mechanical action such as mulling. milling. or other admixing, abrading, or by chemical action of the electrolyte or other reactive material which forms a nascent surface on the refractory metal particle.

The amount of mechanical or chemical action to produce the nascent surface is not critical since some nascent surface would be produced by any such mixing actions. From the nascent surface the refractory metal ions will be produced in a time span of about 1 minute to 30 days, preferably 1 to 2i) hours, the time depending upon the amount of moisture, the temperature and the solubilitv of the refractory metal. The time is therefore not critical. It is important only that the necessarv concentration of refractory metal ions be present and that some nascent surface be produced whereby the particulate refractory metal may be deposited within the near-surface region of the base metal.

To provide the intimate relationship between the electrolyte and the particulate refractory metal and to position the electrolyte between the surface of the base metal and the refractory metal, as well as cause more nascent surface to be exposed on the particles of refractory metal, several alternate methods are possible. When the refractory metal is in the physical state of a dry powder under ambient conditions. and the electrolvte is also in a sensibly dry granule form, an intimate mixture mav be achieved by thoroughly mixing the two powders together. The range of amounts of the refractory metal is from tj99 to 50%, preferably 96% to 66% by weight, of the dry mixture of refractorv metal and electrolyte.

The electrolyte mav range from 1% to 50C/c. and preferably 4% to 34 bv weight of the dry mixture of the refractory metal and the electrolyte.

It has been found that to enhance the electrochemical action of this invention an element or compound which acts as an agent for preventing electrochemical polarization may be incorporated optionally with the particulate refractory metal and electrolyte in the amount of 1 to 10% by weight of the total refractory metal and electrolyte admixture. Examples of such depolarizing compounds or elements are Mono, platinum metal powder, CuO. HgO, ionizable iron or tin salts such as the halides. sulfates, nitrates, etc. thereof and activated carbon.

The thickness of the electrolyte coating upon the refractory particle should be as continuous and uniform as possible and may be from molecular films to 25 micrometers or thicker up to 1 mm. Preferably. a major portion of the refractory metal surface is to be coated although a minor portion as low as about lOr is acceptable.

It has been found that the mixing or mulling to produce either or both the nascent surfaces on the refractory metal particle and the coating of the refractory particle with electrolyte powder may occur when both the electrolyte and refractory metal powders are sensibly dry having little or no observable moisture. This mixing period will usuallv be about 30 minutes to 30 days. But to produce the refractory metal ions there must be adequate moisture present or the ions will not form.

Whether either or both of the refractory metal and electrolyte is dry under ambient conditions, water should be present in the refractory metal-electrolyte mixture in the amount of about 0.59 to 60 bv weight of the total mixture prior to the treatment of the base metal with the mixture. Preferably the amount of moisture should be 1% to 40% by weight.

It is also feasible to achieve the benefits of the present invention by forming an intimate wet addition of the electrolyte and refractory metal as a paste. slurrv or solution as in a liquid medium such as water.

Sufficient amount of water in the mixture can be determined when the electrolyte exhibits an electrical resistivitv of less than about 10" ohm-centimeters. If the electrolyte is liquid, no added liquid medium may be necessary but is preferable particularly with strong mineral acids.

The presence of some water in the mixture of refractory metal and electrolyte is important to produce the ionic concentration of the protective metal and to permit the reactivity of the electrolyte to presumably engage in an ion exchange with the base metal.

This single mixing or combined mixing and ageing step if carried out for 1O minutes to 30 days can substitute for the time required to achieve the nascent surfaces and the concentration of refractory metal ions. although. if the concentration of refractory metal ions is not found to be adequate. then admixing andior further ageing time usually between 1 and 30 days may be required. The actual concentration of the refractory metal ions will be the test for the need for further mixing or ageing time.

The intimately mixed powders. paste. liquid. etc. of electrolyte with the refractory metal may then be applied by spraying the base metal, submerging. brushing. tumbling, sprinkling. or any suitable means of distribution or coating of the mixed refractory metal and electrolyte to provide a thin coat on the base metal.

A prepared mixture of the refractory mental having nascent surfaces and the electrolyte, having the required moisture content and refractory metal ion concentration. may be tumbled with the parts to be treated in a ball-millin machine without using any balls in order to attain an adequate coating of both the refractory metal and the electrolyte so as to accomplish the next step of this invention. the deposition of the refractory metal. For the wet mixture, the electrolyte is present between the surface of the base metal and the refractory metal, and acts in exactly the same manner as if the particles of the refractory metal had been coated with the electrolvte.

The temperature at which the substitution or replacing of the refractory metal for the base metal takes place has the effect of increasing the rate of reaction with temperature rise.

At ambient temperatures. it has been found that a time between about 1 and 168 hours and preferably 6 and 72 hours will be adequate to effect an impregnation or exchange of the refractory metal for the base material. Longer times are not critical and do not adversely affect the process. Shorter times mav be feasible if an adequate reaction occurs. The temperature range is O"C to 200C, preferably between l0CC and 100CC, and more particularly between 15"C and 4() C.

The densitv of the mixed electrolyte and refractory metal as the protective material that may be applied to the base metal is not critical and may varv from about 0.5 refractorv particles of protective coating/mm' to a complete even coating of the mixture on the surface ithe base metal which would be about 10b particles/mm- for a 1.0 micrometer particle size.

Particles of 1 to 5 micrometers in size may have a concentration of these particles ranging from approximately 4 x lü4 to 10' particles/mm2 for full coverage. With particles of approximately minus 325 mesh size (44 micrometer nominal maximum diameter) such as to include commercially available metal powders and an electrolyte in combination. the concentration of particles to be deposited on the base metal may vary from approximately 10 to 104 particles/mm2. The amount and the size of the refractory metal particles applied does determine the proximity of the particles and the size of the discrete particles thereafter actually deposited onto the base.

The product The accompanying single figure drawing is a composite schematic illustration of the various possible structures that may be found on the base metal 1(1 and within the near-surface region 12 defined by the planes A-A.

The character of the discrete particles 14 of refractory metal deposited within the near-surface region of the base metal is to a degree dependent upon the practice of this invention. For instance. there are refractory metal particles present in the near-surface region of the base of substantially the same shape and nominally of the same or somewhat smaller size compared to the particles in the powder or particulate form of the refractory metal initially entering the process of this invention. This characteristic feature of the present invention has been supported by microscopic observations of both the refractory metal powder or particulate entering the process and the deposited refractory metal particles in the processed metallic bases.A pluralitv of such deposited particles are of such dimension not greater than about 2 micrometers and all such deposited refractory metal particles have been found to be within the size range of ().U1 micrometer to 100 micrometers.

Additionally there may be deposited in the near-surfacc region 12 of the base metal 1() a quantity of refractory metal particles 14 having dimension both greater and lesser than the nominal mean particle dimension of the refractory metal powder or particulate initially entering the process of this invention Thus. for example. if the initial forms of the refractory metal particles entering the process of this invention are idiomorphic or blockv of mean dimension 1 micrometer. then the deposited refractory metal particles may be of this character and additionally exhibit both the form of large spheroidal particles up to 10 micrometers in diameter and small contiguous particles of mean dimension less than O.2 micrometer.Although the deposited refractory metal particles (4 mav take on such additional forms, it has been found that these deposited particles range in size from 0.01 micrometer to 100 micrometers and that a pluralitv of the deposited refractory particles have dimension less than about 2 micrometers.

The locations of the discrete deposited refractory metal particles are preferentially found at the grain boundaries. the pores or vallevs of a microscopic nature in the near-surface region of the base metal. and/or in effect within any irregularity in the near-surface region of the base metal that may have been formed bv previous phvsical or chemical action, as matching grooves 16. etc. The distribution of refractory metal particles upon essentially planar microscopic single-phase areas of the base metal is apparently spatially random.

Similarly, the phenomenon of micro-electrolysis is believed to occur in an essentially spatially random fashion upon such planar portions of the base metal to form the initially discontinuous pattern of the deposited discrete refractory metal particles.

As the operation of this invention progresses. a pluralitv of these discrete refractory metal particles are deposited in a contiguous pattern to form clusters 18 of these particles randomly disposed upon the essentially planar areas 20 of the base metal. These clusters of particles are spaced from each other. and are prefrrentially formed at irregularities in the near-surface region of the base metal such as the machining grooves 16.

As the process reactions of this invention are carried to further stages of advancement as by increasing treatment time. or increasing treatment temperature. or the like. the preferentially and the randomly disposed clusters I 8 of discrete particles 14 become contiguous to other proximal clusters and thus form microscopic (small scale) regions 22 of deposited refractory metal within the near-surface region of the base metal. Such microscopic regions of deposited refractory metal appear to be continuous because within said regions the base metal is obscured from view. These microscopic regions 22 of refractory metal are spaced from each other in random fashion but are preferentially formed at irregularities in the near-surface region of the base metal such as machining grooves 16 and the like.

As the process reactions of this invention are carried to still further stages of advancement and more particularly as the multiplicity of reacting areas is increased by increasing the density of discrete particles upon the substrate, the mutual refractory metal bonding processes become more evident. Both the preferentially and the randomly disposed microscopic refractory metal regions 22 become contiguous to other proximal microscopic regions of refractory metal as at 24 to produce macroscopic (large scale) regions 26 of deposited refractory metal within the near-surface region of the base metal.

Such macroscopic regions 26 of deposited refractory metal appear to the unaided eye to be continuous as within such regions the base metal is obscured from view. These macroscopic regions of deposited refractory metal are spaced from each other and are apparently randomly disposed in the near-surface region of the base metal.

Subsequently, and with continued lateral growth of the refractory metal bv the above-described processes. the entire base metal 10 becomes covered with and obscured by deposited refractory metal as shown at 28. Additionallv. the refractory metal builds itself in a direction normal to the surface of the base, thus thickening the refractory metal laver at 30 and providing a coherent and apparently continuous laver 32 of refractory metal adherently bonded to and as an integral part of the base metal 10.

Such distribution and subsequent association of deposited discrete refractory metal particles as described above provide a pattern of deposition unlike any other metal deposition process, including especially electrochemical processes. For instance. metal sheet stock of mild steel when treated with the present invention appears to the unaided eve to have a continuous coating yet is able to withstand a bend of 140" about a 318 inch radius without visible cracks or rupture even at magnification of 3 diameters. This coating though apparently continuous actuallv has a discontinuous structure.

Thus, the treatment of a tool steel base by the process of this invention provides the deposition of discrete refractory metal particles in the form of randomly-spaced clusters of particles. These particle clusters are deposited within the near-surface region of the base metal and preferentially upon the essentially planar metallic matrix exposed between the carbide particles of this steel. The treatment of tvpe SAE 1018 steel by the process of this invention provides a similar but more complex pattern of refractory metal particle deposition within the near-surface region of the base.In this instance. the refractory metal particles were deposited discretelv in the form of randomlv-spaced clusters of particles upon the essentially planar ferrite microconstitutent of the base and were additionallv distributed preferentially upon the intercarbide ferritic portion of the pearlite microconstituent of the base metal. For both types of steels. the continuous metallic matrix phase was observed to be the preferred site for refractory metal particle deposition and in both cases, randomly-spaced clusters of discrete particles were observed to have been deposited upon the essentially planar portions of the continuous metallic matrix phase of the base.

The thickness of the build-up of the deposited particles that form an adherent coating that may be applied varies in accordance with the time. temperature and ion concentrations. Even an impressed current applied for a period during which the electrolyte or refractory metal is in contact with the base material may also affect the coating characteristics. Thickness beginning with molecular films up to 0.5 mm in thickness may be deposited within the near-surface region of the base material. It should be understood that one of the unique features of this invention is the fact that the refractory metal is applied to and in part substitutes for or replaces a portion of the base material and. as such. there usually is no change in the dimension of the base metal detectable bv ordinary shop practice measuring techniques.Only in the most advanced starve of deposition can a detectable dimensional change be noted.

Finally, and according to the particular practice of this invention. there may be present in the near-surface region of the base metal microscopic quantities of at least one corrosion product 24. These corrosion products are the solid chemical compounds. essentially insoluble in the electrolyte. formed as a result of any corrosion reaction in which the base metal is chemically attacked by the electrolyte and in a pluralitv of instances these compounds are composed essentially of cations from the base metal and anions from the electrolyte. Thus. the corrosion products mav be evidenced in the form of base metal hydroxides. chlorides. nitrates, sulfates. cvanates. carbonates. acetates and the like or may alternatively be more complex base metal compounds as oxvhydrates. oxvchlorides.

thiocyanates and the like.

When present. the corrosion products tend to nucleate and grow in the near-surface region 12 of the base 10 and at those areas accessible to the electrolyte: specifically. at areas other than those where the refractorv metal is in direct phvsical contact with the base. The essentially lateral growth of the corrosion products tends at least partially to surround as at 36, embed as at 38. partially embed as at 39 or entrap as at 40 the deposited refractory metal in the form of particles 14. clusters 1X. the microscopic regions 22 as well as the macroscopic regions 26.As these corrosion products are adherent to the base metal. thev are believed to provide enhanced adherence of the refractory metal particles to the base, surrounding or entrapping the refractory metal particles.

The composite coating structure so produced is composed of refractory metal particles adherently bonded to the base metal, refractory metal particles surrounded or entrapped by corrosion product and, additionally. some refractory metal particulate totallv encapsulated by corrosion product. Such a composite structure increases the likelihood that certain of the refractory metal particles, especially those totally encapsulated by corrosion product. will be mechanically embedded or friction welded or the like to the base metal in its near-surface region as a natural result of forces generated when the coated part is put into service. In this sense, the composite coating acts as a reservoir to assure a continuing supply of refractory metal particulate adherent to the near-surface region of the base metal.

Further, in some instances. the corrosion product itself will act as a lubricant to reduce friction and/or wear either through properties of itself or as a porous reservoir for common lubricants as oils, greases, graphite, molybdenum disulfide. and the like.

The preferred final step in the treatment of base metals in accordance with the present invention is a rapid washing with hot water followed bv rapid air drying. This operation terminates the microelectrolytic action and removes nearlv all ionized products and salts from the vicinity of the base metal substrate. The effluent wash liquid. usually water, contains valuable undeposited refractory metal particles which are desirable to recover and use in subsequent applications of this invention. Up to 99 per cent of the total weight of refractory metal particles may be recovered by standard operations of decanting, sedimentation, centrifuging. and the like when they are applied to the effluent wash water, however, the particles of not all refractory metals are recoverable in this manner.

There are specific refractory metal-electrolyte combinations which unfortunately undergo mutual cementation subsequent to the washing cvcle. This cementation process is undesirable as the product mass so formed is essentially unusable for recvcling purposes and cannot be easily reformed into the particles. In such cases. it has been found that mineral acid treatments of the wash water may be emploved in which the concentration of acid in the wash water is maintained between 1% and l()'s bv volume of the total in order to obviate the cementation process.For example. with the treatment mixture composed of tungsten metal powder as the refractory metal and calcium chloride as the electrolyte. it has been found that cementation may be obviated bv the addition bv hydrochloric acid to the level of approximately 5% bv volume of the total effluent wash water after which time the effluent may be rewashed and decanted or centriftiged to recover the tungsten powder which has not been consumed in the treating reaction. The concentration of the hydrochloric acid used to achieve the proper wash water concentration is not critical.

The following are examples of the process of the present invention: Example 1 To apply tungsten metal as a wear-resistant refractory material to the near-surface region of high-carbon steel textile machine travelers, tungsten powder of a pure form is used although the purity is not particularly critical. This powder is of minus 325 mesh size indicating that the tungsten metal particles are of maximum dimension 45 micrometers and that many of the particles are much smaller than this size. down to approximately 1 micrometer maximum dimension. This dry tungsten powder is mixed with dry anhvdrous calcium chloride powder of commercial particle size in the ratio I weight part of CACTI to 10 weight parts of tungsten powder.These two powders are then mixed or co-milled for a period of approximately 24 hours in a jar-type ball mill. using 114" to 1/2" porcelain balls in a porcelain jar, although the use of a mortar and pestle for the same period of time is also satisfactory. During this co-milling operation it is believed that nascent surfaces are provided on the refractory tungsten particles. the particle size of the CaCI. is reduced and the CaC17 is deposited or smeared upon the surfaces of the tungsten metal powder particles.

The co-milled mixture of dry powders is then allowed to stand for approximately 20 hours in contact with humid air of 60cue relative humiditv and because of the hygroscopic nature of the CaCI2, water is taken on bv this mixture in an amount equal to approximatelv 10% to 20% of the total weight of the wetted mixture. At this point. the bulk of the CaCI2 has dissociated into ions and a small amount of the tungsten metal powder has also entered solution in ionic form producing an equivalent concentration of approximately 3,000 to 10,000 milligrams of refractory metal ion per liter of the liquid phase of the mixture. The wetted and aged mixture is then applied as a slurrv bv co-tumbling the mixture and the travelers, said parts having been previously cleaned in a CCiv bath to remove grease. oil, or other foreign matter, so as to expose the near-surface region of the steel base material of the travelers to the action of and contact with the electrolyte and refractory metal mixture.

Within 24 hours at room temperature. the refractory metal powder particles and the refractory metal ions acting in concert with the clectrolvte and the steel base produce a deposit of metallic tungsten particles in the near-surface region of the steel substrate of the traveler. The final step in processing the steel travelers described above is a rapid washing with hot (80" to 100"C) water followed by a rapid air drving. This operation terminates the micro-electrolytic action and removes ionized products and salts from the vicinity of the steel substrate.

The resultant product is a steel part in whose near-surface region is deposited tungsten metal in the form of randomly-spaced clusters of discrete particles. This spatially discontinuous deposit of tungsten particles is infiltrated by a solid corrosion product believed to be composed essentially of hydrated ferric oxides. deposited as a contiguous mass in the near-surface region of the steel base and adherent to it. This corrosion product surrounds, entraps, and partially overlays the deposited tungsten particles to form an adherent composite corrosion product layer upon the steel base.

The coated steel surfaces appear to the unaided eve to be uniformly coated and darkened, exhibiting a macroscopic grey color and being preferentially adsorbent to visible electromagnetic radiation in the range of wavelengths between 580 and 610 nanometers as compared to an uncoated base. Such quality of treated surfaces provides both enhanced adsorption and enhanced emission of electromagnetic radiation. the latter being of special import with regard to the dissipation of radiant heat.

Example 2 To apply tungsten as a wear-resistant refractory metal to the surfaces of heat-treated low-alloy steel bevel gears. the wetted and aged mixture of tungsten and CaCI. is prepared exactly as outlined in Example 1 above. This mixture is then applied as a slurry by painting upon the wearing surfaces of the gears in such manner to provide an areal densitv of approximately 10' refractory metal particles per mm- on the surface of the cleaned steel gears. Within 24 hours at room temperature. the refractory metal ions acting in concert with the electrolyte and the low-allov steel base material produce a deposit of metallic tungsten particles in the near-surface region of the steel gear. The part is then washed and dried as indicated in Example 1 above.

Laboratory sliding wear tests of similarly treated type SAE 1018 low-carbon steel plates indicated that for a load of 0.5 Kg and a speed of 120 cmxsec the treated material was approximately 250 times more resistant to wear than similar untreated specimens. as measured by weight loss. The treated material used in these l-hour accelerated wear tests had the same macroscopic appearance as the above-described treated low-alloy bevel gears.

Example 3 To apply tungsten as a wear-resistant refractory material to the surfaces of the parts.

tungsten powder of a minus 325 mesh size is used. The dry tungsten powder is mixed with dry anhydrous CaCI2 of a commercial particle size and the powders are mixed and co-milled as described in Example 1 above.

The co-milled mixture of dry powders is then sprinkled bv siftine onto the cleaned wear bearing surfaces in such manner so as to provide a density of approximately 3x10' refractory metal particles per mm2 on the surfaces. Such wear bearing surfaces are then exposed at 40"C to air of 40 to 50% relative humidity for a period of 20 hours. Within this 9()-hour period. the refractory metal powder particles and the refractory metal ions acting in concert with the electrolyte and the wear-bearing surfaces product a deposit of metallic tungsten particles in the near-surface region of these surfaces.

Example 4 To apply tungsten as a wear-resistant refractory metal to the surfaces of such parts. the wetted and aged mixture of tungsten and calcium chloride is prepared exactly as outlined in Example 1 above. A relatively large amount of this mixture is then placed in a stainless steel vessel which is to serve as the positive pole of an electrolytic cell. The wetted mixture in this instance serves as the 'electrolyte" of the electrolytic cell. Given the polarities indicated. a D.C. potential of approximately I volt is applied across the cell (stainless steel "electrolyte"-substrate to be coated). Electric current is thus allowed to flow for a period of approximately 6 hours after which time it is found that the substrate acquires the tvpical blue cast associated with the surface produced in accordance with the Examples 1-3 where no current has been applied.It is seen that the application of current in this instance accelerates the deposition of discrete particles.

Example 5 Differentlv styled and shaped loopers and needles of hardened carbon steel and some of chromium steel and tufting knives of a tungsten steel are exposed to a mixture of 1 li' cubic centimeters of hydrochloric acid combined with '(l grams of powdered minus 325 mesh tungsten. The hydrochloric acid forms the electrolyte and is to be mixed one part acid to five parts water. The hydrochloric acid and tungsten mixture before contact with the parts to be treated is mulled to a uniform mixture for 24 hours finallv taking the form of a dampened powder. The moisture content is adjusted to be 9%, bv weight of the total mixture. Upon a further 24 hours ageing period the tungsten ion concentration should be at least 5,000 mg. per liter of solution.The mixed product is then sifted at 2UO particles per mum , evenly at 250C over the surfaces of the loopers. the tufting knives and needles. and permitted to stand for 12 hours in open trays. At the end of the period. all the pieces will be round to have a somewhat darker cast. At the end of the reaction period. the pieces will be found to have longer wearing abrasion-resistant surfaces than similar untreated pieces.

Special definitions Various terms are used throughout the description and claims of the present invention.

The following are definitions of three terms. Terms not defined herein are to have their ordinary meaning.

Deposit: includes the chemical, mechanical or physical attachment of one material to another and specifically includes coating. bonding. adhering and embedding.

Refractory metal ion concentration: is the concentration of refractory metal ions in aqueous solution, on a weight basis, considered as if the metal itself had ionized to a univalent or multivalent state. It is recognized that this simple concept of ionization mav not represent the actual case. thus. for example. tungsten in solution mav appear as the tungstate ion, where tungsten is intimatelv associated with oxygen.

Near-surface region: let the base metal and its immediate environment be regarded as the system in question. Parallel to the actual boundary between the base metal and the environment, consider two surfaces. one on each side of the actual boundary and situated far enough from that boundary so that all irregularities and inhomogeneities of the base metal surface will be included entirelv between them. The volume included between these two surfaces is the "near-surface region" of the base metal. This definition is patterned after that J. Willard Gibbs (see C.E. Reid. Principles of Chemical Thermodvnamics".

Reinhold Publishing Company. New York. l96()). In structural details. the near-surface region will be dependent upon the practice used to prepare the surface. but in general. all such surfaces would have characteristic openings or crevices or pores of irregular size or shape as follows: a width or lateral dimension between ().()2 micrometer and l mm and a depth of approximately 0.02 micrometer to 2()0 micrometers. irregularly spaced throughout the surface of the article to be treated. Substantially planar surfaces of base material remain between these openings. The openings mav or may not appear to have an undercut and therefore have an overhanging portion of the surface extending into the openings of the base material.All such geometrical structural details are here defined as being within the near-surface region.

Relatively low wear resistant: means that the wear resistance of the base metal is relatively low compared with that of the refractory metal.

WHAT WE CLAIM IS: 1. A process for depositing upon a relatively low wear resistant base metal a refractory metal comprising.

providing an electrolyte material capable of dissociation into ions. and having a conductance ratio of between 0.13 and 0.93 calculated at a 0.1 normal solution.

providing a particulate refractory metal to be deposited within the near-surface region of said base material, said refractory metal having a melting point of at least l49(YC.

admixing 99 to 50cue by weight of said refractory metal and I to 5()'s by weight of said electrolyte for a sufficient time to form a nascent surface on at least a portion of each said refractory metal particles to be deposited and at least partially surrounding said refractory metal particles with said electrolyte.

maintaining a moisture content in said mixture sufficient to maintain a resistivitv of said electrolyte of less than 10" ohm-centimeters of said admixture to form a refractory metal ion concentration of 1-60.000 mg. per liter of solution.

contacting and at least partially coating the surface of said base material with said refractory metal in particulate form and said electrolyte admixture.

reacting said admixture with said base material at temperatures between O"C and 2()() C.

and depositing said refractory metal within the near surface region of said base material in the form of discrete particles. wherebv to provide a protective surface for said base material.

2. A process according to claim I including said reaction being at a temperature between 15 and 40"C 3. A process according to claim 1 or 2 including depositing within said base metal near-surface region said refractory metal with a thickness up to ().5 mm.

4. A process according to any of claims I - 3 including said electrolyte having a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. five parts water. The hydrochloric acid and tungsten mixture before contact with the parts to be treated is mulled to a uniform mixture for 24 hours finallv taking the form of a dampened powder. The moisture content is adjusted to be 9%, bv weight of the total mixture. Upon a further 24 hours ageing period the tungsten ion concentration should be at least 5,000 mg. per liter of solution. The mixed product is then sifted at 2UO particles per mum , evenly at 250C over the surfaces of the loopers. the tufting knives and needles. and permitted to stand for 12 hours in open trays. At the end of the period. all the pieces will be round to have a somewhat darker cast.At the end of the reaction period. the pieces will be found to have longer wearing abrasion-resistant surfaces than similar untreated pieces. Special definitions Various terms are used throughout the description and claims of the present invention. The following are definitions of three terms. Terms not defined herein are to have their ordinary meaning. Deposit: includes the chemical, mechanical or physical attachment of one material to another and specifically includes coating. bonding. adhering and embedding. Refractory metal ion concentration: is the concentration of refractory metal ions in aqueous solution, on a weight basis, considered as if the metal itself had ionized to a univalent or multivalent state. It is recognized that this simple concept of ionization mav not represent the actual case. thus. for example. tungsten in solution mav appear as the tungstate ion, where tungsten is intimatelv associated with oxygen. Near-surface region: let the base metal and its immediate environment be regarded as the system in question. Parallel to the actual boundary between the base metal and the environment, consider two surfaces. one on each side of the actual boundary and situated far enough from that boundary so that all irregularities and inhomogeneities of the base metal surface will be included entirelv between them. The volume included between these two surfaces is the "near-surface region" of the base metal. This definition is patterned after that J. Willard Gibbs (see C.E. Reid. Principles of Chemical Thermodvnamics". Reinhold Publishing Company. New York. l96()). In structural details. the near-surface region will be dependent upon the practice used to prepare the surface. but in general. all such surfaces would have characteristic openings or crevices or pores of irregular size or shape as follows: a width or lateral dimension between ().()2 micrometer and l mm and a depth of approximately 0.02 micrometer to 2()0 micrometers. irregularly spaced throughout the surface of the article to be treated. Substantially planar surfaces of base material remain between these openings. The openings mav or may not appear to have an undercut and therefore have an overhanging portion of the surface extending into the openings of the base material.All such geometrical structural details are here defined as being within the near-surface region. Relatively low wear resistant: means that the wear resistance of the base metal is relatively low compared with that of the refractory metal. WHAT WE CLAIM IS:

1. A process for depositing upon a relatively low wear resistant base metal a refractory metal comprising.

2. A process according to claim I including said reaction being at a temperature between 15 and 40"C

3. A process according to claim 1 or 2 including depositing within said base metal near-surface region said refractory metal with a thickness up to ().5 mm.

conductance ratio of 0.60 to 0.5)3.

5. A process according to any of claims 1 - 4 including said electrolyte being any one of the following: mineral acid. organic acid. base. salts of said acids and bases. and acid anhydrides.

6. A process according to any of claims 1 - 5 including said refractory metal being any one of the following: chromium, cobalt. iridium. molybdenum. niobium. osmium.

paladium, platinum, rhenium. rhodium. ruthenium. tantalum, thorium. titanium, tungsten.

vanadium, yttrium, zirconium. and alloys thereof.

7. A process according to any of claims 1 - 6 wherein said refractory metal has a particle size of 0.01 micrometer to 1.0 mm.

8. A process according to any of claims 1 - 7 wherein said base metal is any one of the following: aluminum, iron, chromium. cobalt. copper, nickel. magnesium. tin. titanium. or any alloy of these, including: steels, cast irons. brasses. bronzes and solders.

9. A process according to any of claims l - 8 including mixing said mixture of refractory metal and electrolyte for 30 minutes to 30 days to produce said nascent surfaces.

10. A process according to any of claims 1 - 9 including forming said refractory metal ion concentration by maintaining said refractory metal particles having nascent surfaces in contact with said electrolyte and said moisture concentration for 10 minutes to 60 days,

11. A process according to any of claims 1 - 10 including said reaction time being between 1 and 168 hours.

12. A process according to any of claims I - 11 including said moisture being 0.5 to 60%.

13. A process according to any of claims I - 17 including the addition of 1 ',/c to 10'it by weight of the admixture of a material which acts as an aeent preventing electrochemical polarization.

14. A process according to any of claims I - 13 wherein the agent for preventing electrochemical polarization is selected from MnO.. CuO. HYPO. platinum metal powder, ionizable iron and tin halides. sulfates. nitrates. and activated carbon.

15. A process according to any of claims I - 14 including the steps of washing the product with water and recovering the refractory metal bv treating the effluent-containing refractory metal with a mineral acid solution in sufficient quantity to produce a resultant composition of 1% to 1OC/e by volume of the mineral acid.

16. A process for depositing upon a relatively low wear resistant base metal a refractory metal, according to claim 1. substantiallv as hereinbefore described with reference to the accompanying Example 1, 2. 3. 4 or 5.