US20100282613A1 - Methods for tailoring the surface topography of a nanocrystalline or amorphous metal or alloy and articles formed by such methods - Google Patents

Methods for tailoring the surface topography of a nanocrystalline or amorphous metal or alloy and articles formed by such methods Download PDF

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US20100282613A1
US20100282613A1 US11/985,569 US98556907A US2010282613A1 US 20100282613 A1 US20100282613 A1 US 20100282613A1 US 98556907 A US98556907 A US 98556907A US 2010282613 A1 US2010282613 A1 US 2010282613A1
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etching
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Christopher A. Schuh
Shiyun Ruan
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Massachusetts Institute of Technology
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
    • B23H9/00—Machining specially adapted for treating particular metal objects or for obtaining special effects or results on metal objects
    • B23H9/008—Surface roughening or texturing
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/18—Electroplating using modulated, pulsed or reversing current
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
    • C25D5/611—Smooth layers
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/615—Microstructure of the layers, e.g. mixed structure
    • C25D5/617—Crystalline layers
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/615—Microstructure of the layers, e.g. mixed structure
    • C25D5/619—Amorphous layers
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/627—Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/02—Etching
    • C25F3/08—Etching of refractory metals
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/02—Etching
    • C25F3/14—Etching locally

Definitions

  • Metals and alloys with nanocrystalline or amorphous structures often exhibit superior physical and/or functional properties, such as high strength, high corrosion-resistance and low coefficient of friction. They may also have desirable magnetic, electronic, optical, or biological properties in specific applications. For these reasons, nanocrystalline or amorphous metals and alloys are gaining wide usage throughout many industries.
  • Nanocrystalline metal refers to a metallic body in which the number-average size of the crystalline grains is less than one micrometer.
  • the number-average size of the crystalline grains provides equal statistical weight to each grain.
  • the number-average size of the crystalline grains is calculated as the sum of all spherical equivalent grain diameters divided by the total number of grains in a representative volume of the body.
  • Amorphous metal refers to a metallic body without long-range crystalline order, i.e., a metallic body which is solid but not crystalline.
  • Nanocrystalline or amorphous metals and alloys can be produced by many existing techniques, including severe deformation processing methods, mechanical milling, novel recrystallization or crystallization pathways, vapor phase deposition, and electrochemical deposition (called electrodeposition throughout this disclosure). Electrodeposition is particularly important as a technology for creating nanocrystalline or amorphous metals and alloys, because it can be used to plate out metal on a conductive material of virtually any shape, to yield exceptional surface properties, such as enhanced corrosion and wear resistance and increased yield strength. Such coatings are particularly useful for machine parts, which are subject to high frictional forces, and plastic extrusion molds.
  • the phrase, at most nanocrystalline, is used to mean a metal or alloy having a structure which is either amorphous, or which has the number-average size of any crystalline grains being less than one micrometer or a composite of both.
  • Nanocrystalline alloys may be constituted, prepared, and deposited according to various methods, such as those described by Detor and Schuh in U.S. Ser. No. 11/147,146, filed on Jun. 7, 2005, entitled METHOD FOR PRODUCING ALLOY DEPOSITS AND CONTROLLING THE NANOSTRUCTURE THEREOF USING NEGATIVE CURRENT PULSING ELECTRO-DEPOSITION, AND ARTICLES INCORPORATING SUCH DEPOSITS, the full disclosure of which is fully incorporated herein by reference.
  • a rough surface may be desirable to control the frictional contact with a mating component, (i.e., to improve traction, or reduce contact area, etc.).
  • a controlled surface structure allows a range of optical luster and/or colors.
  • the surface topography may require control as part of a micro-manufacturing application, as for example in electroformed stamps or embossing equipment.
  • surface crevices or pits may be desirable to contain a fluid or particulate medium, as for lubricated surfaces for sliding.
  • the terms pits, pores and voids are all used herein interchangeably to mean a region of a surface that is open, devoid of the substance that makes up the body of the material, and having an opening shape that has a length and width that are of the same order in size. In general, the term pit will be used.
  • An extension on this last concept is for the creation of self-lubricating surfaces, in which surface pits or crevices are filled with a lubricant, and then covered over, as for example by electroplating.
  • Other functional secondary components can be incorporated into a nanocrystalline or amorphous metal in this way.
  • Similar control over surfaces may be useful to improve joining operations such as brazing.
  • increasing the surface area through roughening or through the controlled introduction of surface topography may be desirable for catalytic properties or for increasing the amount of active surface area.
  • porous surfaces are desirable for the in-growth of biological cells and tissues into the implants. Many other possible applications exist or will come to be, in which control over the surface topography of a nanocrystalline or amorphous metal or alloy would be required or desirable.
  • a particularly pertinent example of the use for a surface structuring method for nanocrystalline or amorphous metal or alloy is in the area of tribological coatings.
  • nanocrystalline or amorphous metal or alloy coatings are being considered for applications where, formerly, chromium coatings were used.
  • electrochemically deposited nanocrystalline nickel-tungsten (Ni—W) alloys exhibit many superior properties, such as higher hardness, higher corrosion-resistance and lower coefficient of friction; thus making them better coating materials.
  • chromium would be selected in these applications for its high corrosion resistance and low coefficient of friction.
  • a reverse current etch process is commonly employed to create pits that can trap lubricants on the surfaces of chromium coatings, thus further reducing frictional effects in service of the coating.
  • the chromium film is sometimes covered with a perforated insulating sleeve during reverse current etching.
  • the regions of the chromium film that are not covered by the sleeve are etched, leading to the formation of pits on the chromium film.
  • the size and density of the pits are directly controlled by varying the corresponding parameters of the perforations.
  • Another common existing method of imparting a desired surface topography to a component is to apply a texture prior to coating the component with chromium.
  • techniques like mechanical abrasion, electro-discharge surface texturing, shot peening, sand blasting, etc. are used to create a desirable surface texture or article surface topography. These treatments may (or may not) be followed by the application of a coating which, to at least some extent, replicates the topography of the material beneath, leading to a coated component with a desired surface topography or texture.
  • nanocyrstalline coatings or deposits in many of these cases, such as nickel-tungsten.
  • a nanocrystalline or amorphous metal or alloy coating is used in a similar application to a chromium coating made with such a sleeve, there is need for a complementary process to tailor the surface topography. It would be even further desirable if the size, shape, and number density of pits could be controlled in the nanocrystalline or amorphous metal or alloy surface without requiring the use of a perforated sleeve in the etching process.
  • FIG. 1 is a schematic representation of components of processes to tailor surface morphology of nanocrystalline or amorphous metal or alloy
  • FIG. 2A is a digital image of a Scanning Electron Micrograph (SEM) of Ni—W film electrochemically deposited using a 100% duty cycle and with a current density of 0.2 A/cm 2 ;
  • FIG. 2B is a digital image of an SEM of Ni—W film electrochemically deposited using a 25% duty cycle and with a current density of 0.2 A/cm 2 ;
  • FIG. 3A is a digital image of an SEM of Ni—W film after reverse current etching, the deposit having been made using a high (100%) deposition phase duty cycle, a current density of 0.2 A/cm 2 , and etching having been done with a 30% duty cycle and with a current density of 0.1 A/cm 2 ;
  • FIG. 3B is a digital image of an SEM of Ni—W film after reverse current etching, the deposit having been made using a low (25%) deposition phase duty cycle a current density of 0.2 A/cm 2 and the other parameters the same as was for FIG. 3A ;
  • FIG. 4 is a digital image of an SEM of Ni—W film formed using a 0.2 A/cm 2 electrochemical deposition current at 12.5% duty cycle for 400 minutes after reverse current etching under the same conditions as for FIGS. 3A and 3B ;
  • FIG. 5A is a digital image of an SEM of Ni—W film deposited with a 0.2 A/cm 2 at 25% duty cycle for 200 minutes after reverse current etching with a 50% etching duty cycle and a current density of 0.1 A/cm 2 ;
  • FIG. 5B is a digital image of an SEM of Ni—W film deposited with a current duty of 0.2 A/cm 2 at 25% duty cycle after reverse current etching with a 30% etching duty cycle and current density of 0.1 A/cm 2 (which is the same as FIG. 3B , shown here for purposes of a different comparison);
  • FIG. 6A is a digital image of an SEM of Ni—W film deposited at 0.2 A/cm 2 current density at 100% duty cycle after reverse current etching with a current density of 0.2 A/cm 2 with a duty cycle of 30%;
  • FIG. 6B is a digital image of an SEM of Ni—W film after reverse current etching, the deposit having been made using a high (100%) deposition phase duty cycle at 0.2 A/cm 2 , and etching having been done with a 30% duty cycle and with a current density of 0.1 A/cm 2 (which is the same as FIG. 3A , shown here for purposes of a different comparison); and
  • FIG. 7 is a digital image of an SEM of Ni—W film along a fracture.
  • Novel technology disclosed here uses etching methods to tailor the surface of a nanocrystalline or amorphous metal or alloy.
  • the nanocrystalline or amorphous metal or alloy may be produced by many existing techniques, including but not limited to severe deformation processing methods, mechanical milling, novel recrystallization or crystallization pathways, vapor phase deposition, and electrodeposition.
  • Common etching methods include but are not limited to dry etching, wet etching, potentiostatic etching, galvanostatic etching and ion beam etching.
  • the surface morphology, or topography which is used herein synonomously with surface morphology of the nanocrystalline or amorphous metal or alloy, can be controlled by varying the processing parameters or the etching parameters or both.
  • the schematic chart in FIG. 1 summarizes inventions disclosed herein. It illustrates a process of tailoring the surface topography of a nanocrystalline or amorphous metal or alloy article.
  • nanocrystalline and amorphous metals or alloys (labeled as blocks ‘M 1 ’, ‘M 2 ’, ‘M 3 ’ . . . ) can be made via different routes (represented by arrows ‘A’, ‘B’, ‘C’ . . . ).
  • Blocks ‘M 1 ’, ‘M 2 ’ and ‘M 3 ’ represent nanocrystalline or amorphous metals or alloys of different composition, microstructures and surface morphologies; arrows ‘A’, ‘B’ and ‘C’ represent different processing methods and/or parameters.
  • Each nanocrystalline or amorphous metal or alloy take for example block ‘M 1 ’, can in turn be tailored to form nanocrystalline or amorphous metals or alloys of different surface morphologies, as represented in this example by blocks ‘S 1 ’, ‘S 2 ’ and ‘S 3 ’.
  • Arrows ‘ 1 ’, ‘ 2 ’ and ‘ 3 ’ represent different etching methods and/or parameters.
  • blocks ‘M 1 ’ and ‘M 2 ’ which have different surface morphologies and microstructures, may be tailored to form the same structure ‘S 3 ’ via different etching processes and/or parameters.
  • nanocrystalline or amorphous metals or alloys with different surface morphologies and microstructures may be tailored to form the same end product structure via different etching processes and/or parameters.
  • a more specific embodiment of an invention disclosed herein is to couple electrochemical deposition of a nanocrystalline or amorphous structure with electrochemical etching, to introduce a tailored surface.
  • electrochemical deposition is a particular technique (corresponding to an arrow such as ‘A’) to form a nanocrystalline or amorphous metal or alloy (corresponding to a block such as ‘M 1 ’) from precursor chemicals (corresponding to a block such as ‘E 1 ’).
  • the process of electrochemical etching (corresponding to an arrow such as ‘ 1 ’) is a particular technique to introduce a desirable surface morphology (e.g., ‘S 1 ’) into the nanocrystalline or amorphous metal or alloy (e.g., ‘M 1 ’).
  • Etching is a controlled corrosion process and is a consequence of electrolytic action between surfaces of different potential.
  • electrochemical etching is used to mean galvanostatic etching, potentiometric etching, electro etching and any other electrochemical etching process.
  • a potential difference exists between grain interiors and grain boundaries, between grains with different orientations, or at concentration gradients in single phase alloys.
  • alloys there is generally a potential difference between the elements in the alloy.
  • a potential also exists between the different phases present. In many cases, the more electrochemically positive phase is attacked to a greater extent than the more electrochemically negative phase during etching.
  • the electrochemically more positive phase is referred to herein as the more electrochemically active phase.
  • the more electrochemically active phase in many cases is more electrochemically active by virtue of containing a higher proportion of the more electrochemically active element in an alloy. Thus, upon etching the more electrochemically active element is preferentially removed from the surface. It is also helpful to note that the electrochemical activity of the phases or elements depend on the specific chemistry of the medium in which the activities are carried out. Other terms in the art that have also been used to mean the same thing, and are intended to be included within the meaning of electrochemically active phase are electroactive, electropositive, and electromotive. Furthermore, in some alloys, a specific element may be selectively removed during etching in a process called dealloying.
  • a nanocrystalline or amorphous metal or alloy is etched depends on its microstructure (i.e. the arrangement and distribution of the various phases, the orientation of surface areas of different chemical potential, the grain size and shape etc.).
  • processing parameters of an earlier stage such as alloy deposition, which affect the microstructure of the nanocrystalline or amorphous metal or alloy, also affect the surface morphology of the subsequently etched nanocrystalline or amorphous metal or alloy.
  • the surface morphology of a nanocrystalline or amorphous metal or alloy that has high residual stress due to processing is likely to differ appreciably from one that has lower residual stress.
  • electrochemical deposition is used to mean electrodeposit and electrochemical deposition, as those terms are understood in the art.
  • the surface morphology of the etched nanocrystalline or amorphous metal or alloy can also be established by controlling the etching parameters, such as the concentration and type of the etching reagent as in the case of wet or dry etching; the magnitude of the applied potential or current as in the case of potentiostatic or galvanostatic methods, respectively; the temperature and duration of the reaction etc.
  • the etching parameters such as the concentration and type of the etching reagent as in the case of wet or dry etching; the magnitude of the applied potential or current as in the case of potentiostatic or galvanostatic methods, respectively; the temperature and duration of the reaction etc.
  • the processing parameters affect the microstructure of a nanocrystalline or amorphous metal or alloy, (which in turn influences the extent to which it is etched).
  • the etching parameters also affect the extent of etching.
  • the surface morphology of an alloy can be controlled by controlling the deposition and etching parameters, either individually, or both, together.
  • the nanocrystalline or amorphous metal or alloy may be produced by many existing techniques and then etched by a number of different methods; it is by varying the processing and etching parameters that surface morphology may be controlled.
  • etching methods to establish the surface morphology of nanocrystalline or amorphous metals or alloys has been reduced to practice for a particular case of a binary alloy of nickel-tungsten.
  • electrochemical deposition has been used successfully.
  • the electrochemically deposited nanocrystalline nickel-tungsten alloy is etched by a galvanostatic electrochemical etching method.
  • the composition of the electrolytic bath which is maintained at approximately 76° C., is shown in Table 1.
  • the cathode and anode used for electrochemical deposition are a copper substrate and platinum electrode respectively.
  • the surface morphology of electrochemically deposited nanocrystalline Ni—W alloys consists of nodular-like structures, which are called colonies. It has been found by the present inventors that the shape of the waveform of the electrochemical deposition current affects the average colony size. (By shape of the waveform, it is meant the shape of a repeating portion of a wave, and also relationships among positive polarity and negative polarity parts of wave forms, the relative duty cycles for each, and the Polarity Ratio, as that term is used in the Detor application, which is fully incorporated by reference herein, above.)
  • FIGS. 2A and 2B show the surface morphologies of the Ni—W films, which are both electrochemically deposited using an applied current density of 0.2 A/cm 2 .
  • the duty cycle of the applied current is 100% and the total duration of the electrochemical deposition process is 30 minutes; for the film shown in FIG. 2B , the duty cycle of the applied current is 25% and the total duration of the electrochemical deposition process is 200 minutes.
  • the surface of the film in FIG. 2B has a more shiny silver appearance than that in FIG. 2A .
  • the resulting colony structures are on the order of from about 3 ⁇ m to 10 ⁇ m.
  • the resulting colony structures are on the order of from about 1 ⁇ m and smaller to about 3 ⁇ m.
  • Other parameters, such as the current density, polarity ratio, and total duration of the electrochemical deposition process can also influence the surface morphology of the electrochemically deposited nanocrystalline alloy.
  • FIGS. 3A and B show the etched surface morphology of Ni—W alloy, whose surface morphologies before reverse etching correspond to FIGS. 2A and 2B respectively.
  • the current density, duty cycle and total duration of the current are 0.1 A/cm 2 , 30% and 20 minutes respectively for both films.
  • the etched surface appears as a network of channels, which surround fully, or partially, nodular structures which are between about 1 ⁇ m and 10 ⁇ m in width. Each nodular structure is in turn traversed by what appear to be a network of much narrower channels than those which surround the nodular structures at the magnification shown.
  • nodular structures For films formed using low duty cycles of direct current, generally circular pits appear on the etched surface, having a diameter of about 1 ⁇ m to 5 ⁇ m, and even larger, where multiple pits have coalesced. Solid ligaments surround and the pits, and run from individual pits to adjacent pits.
  • FIG. 4 shows the etched surface morphology of a Ni—W film that is formed using a 0.2 A/cm 2 electrochemical deposition current at 12.5% duty cycle for 400 minutes.
  • the conditions of the electrochemical etching process are the same as the films shown in FIGS. 3A and 3B .
  • the surface of the film shown in FIG. 4 has a more shiny silver appearance than that shown in FIG. 3B when viewed optically.
  • the lower the duty cycle of the electrochemical deposition current the lower is the density and the smaller is the size of the pits formed after electrochemical etching, and the shinier is the etched surface.
  • the scanning electron micrograph of this specimen also reveals clear micro-scale differences in the surface morphology as compared with the samples from FIGS. 3A , 3 B.
  • the surface is characterized by a relatively lower number density of shallow and broad pits; it appears that the width of the pits is between about one and five micrometers, and the spacing between the pits is relatively large, being between one and 20 micrometers.
  • the spacing between pits is much smaller, being between one and about five micrometers in general.
  • the deposition current density may range from about 0.01 A/cm 2 to about 1 A/cm 2 , depending upon the chemistry, temperature, and other conditions used.
  • the shape of the waveform of the applied current during electrochemical deposition affects the surface morphology of both the un-etched and etched nanocrystalline alloy.
  • the parameters of the various processing methods that are used to make nanocrystalline or amorphous metals and alloys affect the surface morphology of the etched nanocrystalline or amorphous metal or alloy. All of these tailored surfaces are potentially useful, and these experiments show how the etched surface morphology can be controlled by changing the initial electrochemical deposition process parameters.
  • the nanocrystalline or amorphous alloy is an anode of an electrochemical cell.
  • the applied current flows such that metal atoms in the nanocrystalline or amorphous alloy oxidize into ions and dissolve back into the electrolytic solution.
  • the more reactive metal atoms i.e. those with higher oxidation potential
  • regions with higher concentrations of the more reactive metal will be etched to a greater extent.
  • the electrochemical etching process can be carried out in a different electrolyte from that used for electrochemical deposition.
  • the same electrolytic bath can be used, and a graphite electrode is used as the cathode.
  • unipolar pulsed current is used during etching in this example.
  • the periodic “off-time,” when no current flows, allows the atoms on the nanocrystalline or amorphous alloy surface to diffuse and rearrange.
  • the duty cycle of the applied current affects the surface morphology of the etched film.
  • FIGS. 5A and 5B show the effects of the duty cycle of the etching current on nanocrystalline Ni—W electrochemically deposited with a current density of 0.2 A/cm 2 at 25% duty cycle for 200 minutes.
  • FIG. 5B is the same as FIG. 3B and thus, the conditions of the sample's creation are the same, and is presented here again adjacent FIG. 5A to facilitate comparison.
  • the alloy in FIG. 5A is subject to a reverse current with a duty cycle of 50%
  • that in FIG. 5B is subject to a reverse current with a duty cycle of 30%.
  • the reverse current density in both cases is 0.1 A/cm 2 and the total duration is 20 minutes. It is observed optically that the surface of the film in FIG.
  • a higher etching duty cycle in this system results in larger pits, as measured by a representative diameter, and relatively thicker solid regions between pits.
  • the number density of the pits is also relatively lower and the spacing between the pits is generally relatively higher.
  • a lower etching duty cycle in this system results in smaller pits, as measured by a representative diameter, and relatively thinner solid regions between pits. The number density of the pits is also relatively higher.
  • FIGS. 6A and 6B show the etched surface morphologies of two Ni—W films that are electrochemically deposited under the same conditions: 0.2 A/cm 2 current at 100% duty cycle for 30 minutes.
  • FIG. 6B is the same as FIG. 3A and thus, the conditions of the sample's creation are the same, and is presented here again adjacent FIG. 6A to facilitate comparison.
  • the reverse current density applied with a duty cycle of 30% to the alloy in FIG. 6A is 0.2 A/cm 2 while that applied to the alloy in FIG. 6B is 0.1 A/cm 2 . While the surface of the film shown in FIG.
  • etching current density produces a duller, less reflective surface
  • a generally lower etching current density produces a shinier, more reflective surface, both of which are black.
  • the reverse current density affects the width of the etched channels and the general pattern of the network formed by the channels on the selectively-etched nanocrystalline alloy. In general, a generally higher etching current density results in wider, more dispersed channels with some relatively large open pits, while a generally lower etching current density produces a relatively finer grain network of relatively narrower width channels, with relatively far fewer pits.
  • pits may be formed as part of the surface morphology.
  • the examples shown above reveal conditions under which more complex channel structures may be formed, and these channels may coexist with pits.
  • Channels may be regarded as a specific form of pits with a high degree of spatial correlation (i.e., a row of very closely spaced pits). Therefore, in general, the relations and trends presented in this specification focus on the formation of pits, but can be read more generally to apply to channels, channels in combination with pits, or other surface features. For example, it may in some cases be possible to conduct an etching process composed of two separate sub-processes.
  • etching current densities may be used, or different etching duty cycles, or different etching current waveforms.
  • the shape of the waveform of the reverse current affects the surface morphology of the etched nanocrystalline alloy.
  • the parameters of the various etching processes such as wet and dry etching, as well as electrochemical and potentiostatic etching, affect the surface morphology of the etched nanocrystalline or amorphous metal or alloy.
  • the current density employed in electrochemical etching may vary quite broadly, for example over the range 0.001-10 A/cm 2 . It may also vary as etching continues, as for example if the voltage of the process were regulated rather than the current.
  • the as-deposited film which is electrochemically deposited using a 100% duty cycle forward current is fractured immediately after electrochemical deposition. As shown in FIG. 7 , the Ni—W film fractures along the colony boundaries. Energy-dispersive analysis (EDS) and X-ray photoelectron spectroscopy (XPS) analysis are then carried out on the as-deposited surface and the fracture surface. The chemical compositions of these two surfaces correspond to those of the colony interiors and colony boundaries respectively.
  • EDS Energy-dispersive analysis
  • XPS X-ray photoelectron spectroscopy
  • EDS analysis which has a depth resolution of ⁇ 10 microns, shows uniform composition between the as-deposited surface (23.1 at % W) and the fracture surface (23.2 at % W).
  • XPS analysis which has a depth resolution of ⁇ 10 nm, reveals that the W composition along the fracture surface (31.3 at % W) is significantly higher than that of the as-deposited surface (21.5 at % W). This suggests that W segregates to a high degree along the colony boundary; and that the segregation occurs to a small spatial extent of ⁇ 10 microns.
  • the designer has an engineering purpose to achieve, such as a desired friction condition, or reflectivity condition, or surface area requirement. He identifies a topography, such as a distribution of pits of a given size range, depth range and number density per unit area, to achieve the engineering purpose. The designer then determines a spatial distribution for the most electrochemically active phase, or perhaps phases, prior to etching, which bears a definite, known spatial and predecessor relationship to the specified topography, such that, from experience and considerations such as are disclosed herein, the designer understands that the spatial distribution of the most electrochemically active element, in combination with properly chosen etching processing steps and parameters, would cause or enable the desired topography to arise, either directly or indirectly.
  • a desired friction condition such as a desired friction condition, or reflectivity condition, or surface area requirement.
  • a topography such as a distribution of pits of a given size range, depth range and number density per unit area
  • the designer chooses parameters for the processing stage of providing an at most nanocrystalline surface, either by: electrochemically depositing, or another suitable method, that will cause the desired spatial distribution to arise before etching.
  • electrochemical deposition the engineer might also apply thermal treatments or other surface treatments to change the distribution of electrochemically active elements and/or phases.
  • the designer now has a set of parameters for providing an at most nanocrystalline surface, which, upon etching, using proper parameters, will cause a topography that will have features that will achieve the engineering purpose.
  • the designer also has in mind parameters for either an electrochemical deposition step, or another processing step, that will provide the at most nanocrystalline surface to use for the etching step.
  • etched nanocrystalline or amorphous metal or alloy surfaces there are many potential applications of etched nanocrystalline or amorphous metal or alloy surfaces. By tailoring the surface morphology of the etched nanocrystalline or amorphous metal or alloy, its roughness can be controlled. Thus, a desired amount of frictional contact between the nanocrystalline or amorphous metal or alloy and a mating component can be achieved.
  • Etched nanocrystalline or amorphous metal or alloy can be used to coat industrial equipment and landing gears of aircraft, where frictional forces between moving parts are of concern.
  • Etched nanocrystalline or amorphous metal or alloy are also ideal for coating dies that are used for plastic extrusion molding. The microscopic surface roughness of the etched film helps to release hot plastic material from a die.
  • the roughness of the surface could be measured and quantified using, for example, a profilometer or other roughness measurement system.
  • the roughness could be quantified using the standard R a measurement, or the root-mean-square or RMS roughness, the density of peaks in the topography, their average height, etc. This roughness could then be correlated to processing parameters, both for a provided workpiece, deposition parameters and etching parameters, to establish a relationship between these properties and finished article roughness.
  • the etched surface of the nanocrystalline or amorphous metal or alloy contains surface crevices or pits that can be used to trap a lubricant fluid, such as oil, or particulate medium, such as molybdenum disulphide or carbon. Such lubricated surfaces are ideal for applications where there is a need to reduce friction.
  • An extension of this concept is for the creation of self-lubricating surfaces, in which surface pits or crevices are filled with a lubricant, and then covered over, as for example by electroplating.
  • Other functional secondary components can be incorporated into a nanocrystalline or amorphous metal or alloy in this way.
  • the depth of the crevices or pits of the etched nanocrystalline or amorphous metal or alloy can be controlled by controlling the etching parameters.
  • corrosion failure can be avoided by making sure that the depth of the pits or crevices is less than the thickness of the nanocrystalline or amorphous metal or alloy
  • the size and density of pits on traditional chromium films are controlled primarily, if not exclusively, by controlling the corresponding parameters of the perforations on the insulating sleeve during reverse current etching. This is rather cumbersome and limited in flexibility.
  • the size, shape, and number density of pits can be controlled according to inventions disclosed herein in the nanocrystalline or amorphous metal or alloy surface without requiring the use of a perforated sleeve in the etching process.
  • examples are related where the size of pits, characterized primarily in the discussion by a width, or diameter, for roughly circular pits, is controlled by changing a parameter, for instance the duty cycle used in the deposition step. As shown with reference to FIGS. 3B and 4 , the lower the duty cycle of the deposition current, the smaller is the size of the pits formed after etching.
  • channels and their widths and depths.
  • a generally higher etching current density results in wider, more dispersed channels
  • a generally lower etching current density produces a relatively finer grain network of relatively narrower width channels.
  • the observed trends are also that the wider channels are also relatively deeper, than the narrower channels, which are relatively shallower.
  • a relatively higher etching current density leads to relatively deeper channels.
  • the surfaces of the etched nanocrystalline or amorphous metal or alloy can range in appearance from a shiny silver to a uniformly black appearance in the embodiments described above. Additional colors and lusters can also be achievable through variations upon this invention.
  • a controlled surface structure of the nanocrystalline or amorphous metal or alloy allows a range of optical luster and/or colors.
  • Nanocrystalline or amorphous metals or alloys also have applications in micro-manufacturing, as for example in electroformed stamps or embossing equipment.
  • Etched nanocrystalline or amorphous metal or alloy may also be useful in joining operations such as brazing.
  • etched nanocrystalline or amorphous metal or alloy may have desirable catalytic properties because of their high surface area per volume.
  • porous surfaces are desirable for the in-growth of biological cells and tissues into the implants.
  • the control of surface roughness and texture is important.
  • Specific root-mean-square roughness values may be desired, a specific density of peaks in the surface topography, controlled numerical roughness parameters, like R a , etc., may all be desired.
  • these parameters might be relevant to tribological performance, or may be important in impressing a desired texture or surface pattern into another material that comes in contact with the nanocrystalline material.
  • polymer sheets, metal sheets, etc. may be printed with surface textures through a contact with a properly structured nanocrystalline or amorphous alloy.
  • the present invention by allowing the surface texture of amorphous or nanocrystalline alloys to be tuned, in turn allows different impressions on other products.
  • the surface topography will depend on parameters during the initial surface creation, for instance by deposition, but also by other means, and also parameters of the etching process. It has been shown, herein, how the values for parameters in electrochemical deposition and electrochemical etching in a Ni—W system, affect end properties.
  • deposition duty cycle deposition current density; relative electrochemical activity of the elements, or higher complexity phases of the deposited surface
  • etching duty cycle etching current density
  • deposition environment fluid
  • etching environment fluid
  • colony formation properties affect the surface topography and properties of the etched product, including: roughness; pit size (diameter), pit number density, pit depth, intervening solid network element width; shininess, dullness, blackness, silveryness, reflectivity channel network density (for example, expressed as a linear density of channel length, i.e., length of channel per unit area, or perhaps as an area density, i.e., projected area density of channels per unit area of surface.); channel width; channel depths; and size of solid ligaments between channels.
  • the Detor application discusses the effects that varying polarity ratio has on some surface properties, such as nanocrystalline grain size and composition.
  • varying polarity ratio during an electrochemical depositions phase will also affect the intermediate, un-etched workpiece, and thus, the final article surface topography.
  • Etching can also be done with a non-zero polarity ratio, and it is expected that variations of etching polarity ratio will affect the article surface topography.
  • both deposition and etching can be conducted using a polarity ratio of between 0 and 1, or could be conducted using D.C. (direct current) or with an on-time and off-time duty cycle, and the on times can be D.C. or can exhibit a variation, which variation can include both positive and negative polarity current, further characterized by a polarity ratio.
  • the relationships between each of the parameters' value, and one or more pertinent resultant properties can be noted and recorded and collated, as has been done with the Ni—W system herein.
  • the collated relationships among the parameters' values, the resultant topographies, and the physical properties that the topographies enable (such as roughness or blackness, just to name two) together establish a constitutive relationship among all of these factors.
  • the relation between the parameters for both the stages of providing, (which may be by electrochemical depositing) an initial at most nanocrystalline surface, and then etching away portions of the surface to achieve a desired end product surface topography can be exploited, based on the noted and collated trends, or relationships.
  • larger pits may be achieved by adjusting one or more of two or more different parameters.
  • the workpiece can be provided either by electrochemical deposition, or some other way, such as by severe mechanical deformation. Once provided, it can be etched.
  • Target article topography properties can be achieved primarily by altering deposition parameters, or, if possible, etching parameters, or both. For instance, shininess is affected by both the deposition duty cycle and the etching duty cycle. A desired degree of shine can be established by adjusting either, or both.
  • One invention disclosed herein is a method of making an article having an at most nanocrystalline surface with a specified topography.
  • the method comprises the steps of: providing a workpiece having a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the others, and which more electrochemically active element has a definite spatial distribution in the workpiece, which definite distribution bears a predecessor spatial relationship to the specified topography.
  • the method includes etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, to achieve the specified topography
  • the step of providing a workpiece may comprise electrochemically depositing the at most nanocrystalline material on a substrate to achieve the definite spatial distribution of the more electrochemically active element. If so, the step of electrochemically depositing may comprise electrochemically depositing by using pulsed current, and that may comprise using pulsed current, having a polarity ratio, or, alternatively, direct current, or pulsed current of the same polarity. In such a case, the step of etching may comprise electrochemically etching the surface.
  • the step of etching may comprise electrochemically etching the surface.
  • the steps of electrochemically depositing and electrochemically etching both are conducted in an electrolytic liquid.
  • the liquid may be the same liquid, even either by formula, or the same physical volume of liquid, or the liquids may differ.
  • the step of electrochemically depositing may be conducted by choosing deposition parameters that promote segregation of the most electrochemically active element to colony boundaries.
  • the step of choosing parameters may comprise using a relatively larger deposition duty cycle sufficient to promote segregation of the most electrochemically active element to colony boundaries.
  • a useful system is where the two elements comprise nickel (Ni) and tungsten (W).
  • a particularly advantageous embodiment comprises electrochemically depositing an at most nanocrystalline Ni—W surface.
  • the step of etching comprises using a pulse current having a current density of between 0.001 A/cm 2 and 10 A/cm 2 .
  • Still another important embodiment of an invention hereof is a method for making an article having an at most nanocrystalline surface with a specified topography, comprising the steps of: providing a workpiece having a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is a metal, and one of which is more electrochemically active than the others; and etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, to achieve the specified topography.
  • at least one of the following steps is conducted during the providing and etching a workpiece steps.
  • the step of providing a workpiece may be conducted with a value for a parameter for providing, selected with reference to a constitutive relation that relates the providing parameter to the specified surface topography property.
  • the step of etching may be conducted with a value for a parameter for etching, selected with reference to a constitutive relation that relates the etching parameter to the specified surface topography property.
  • the step of conducting at least one of the steps of: providing a workpiece with a selected parameter value for providing; and etching with a selected etching parameter value comprises at least one of the steps selected from the group consisting of the following steps.
  • Electrochemically depositing by using a relatively lower depositing duty cycle to achieve an article topography exhibiting a relatively shinier surface.
  • Electrochemically etching using a relatively higher etching current density to achieve an article topography exhibiting primarily a relatively blacker surface is
  • Yet another important invention disclosed herein is a method for making an article having an at most nanocrystalline surface with a topography having a plurality of spaced apart pits, comprising the steps of: providing a workpiece having a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is a metal, and one of which is more electrochemically active than the others, the more electrochemically active element having a definite surface spatial distribution that bears a predecessor relationship to a topography having a plurality of spaced apart pits; and sleevelessly electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, exploiting the spatial distribution of the more electrochemically active element to achieve the topography having a plurality of spaced apart pits
  • a closely related invention is a method for making an article having an at most nanocrystalline surface with a topography having a network of channels.
  • This related method comprises similar steps with the more electrochemically active element having a definite surface spatial distribution that bears a predecessor relationship to a topography having a network of channels; and sleevelessly electrochemically etching the workpiece exploiting the spatial distribution of the more electrochemically active element to achieve the topography exhibiting a network of channels.
  • Another closely related invention hereof is a method for making an article having an at most nanocrystalline surface. It comprises the steps of: providing a workpiece having a surface comprising an at most nanocrystalline material, the material having a thickness, and comprising at least two elements, at least one of which is a metal, and one of which is more electrochemically active than the others. It also comprises sleevelessly, electrochemically, etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the surface, to achieve a surface over which is distributed at least one surface feature of the group consisting of: a network of channels; and a plurality of pits; which surface feature has a depth of less than the thickness of the at most nanocrystalline material. The method also includes the step of providing a lubricating material within the at least one surface feature.
  • the workpiece can be etched to achieve a surface over which are distributed pits or channels of controlled size, shape or number density, or all of these.
  • the lubricating material may comprise a fluid or a particulate or both.
  • a closely related invention hereof is an article having an at most nanocrystalline surface.
  • the article comprises a body portion and at a surface of the body portion, a surface coating comprising an at most nanocrystalline material, the material having a thickness, and comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the others.
  • Distributed over the surface is at least one surface feature, selected from the group consisting of: a network of channels; and a plurality of pits; which surface feature has a depth of less than the thickness of the at most nanocrystalline material; and within the at least one surface feature, a lubricating material.
  • the surface feature may comprise channels or a plurality of pits, or a combination thereof.
  • an invention disclosed herein is a method of making an article having an at most nanocrystalline surface with a specified roughness.
  • the method comprising the steps of: providing a workpiece having a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the others, and which more electrochemically active element has a definite spatial distribution in the workpiece, which distribution bears a predecessor spatial relationship to a topography, which topography functionally establishes the specified roughness.
  • the method also comprises the step of electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, values for parameters of etching having been selected with regard to the predecessor relationship to achieve the topography and thus, the specified roughness.
  • An invention closely related to this, has the step of providing a workpiece comprising electrochemically depositing an at most nanocrystalline material using parameters of deposition selected to achieve the definite spatial distribution of the more electrochemically active element.
  • a general invention hereof is a method of making an article having an at most nanocrystalline surface with a topography property selected from the group consisting of: roughness, blackness, shininess, number density of pits, size of pits, size of channels and spatial distribution of channels, the property having a specified degree.
  • the method comprises the steps of: providing a workpiece having a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which comprises metal, and one of which is more electrochemically active than the others, and which more electrochemically active element has a definite spatial distribution in the workpiece, which distribution bears a predecessor spatial relationship to a topography, which topography functionally establishes the specified selected property to the specified degree.
  • the method also includes the step of electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, parameters of etching having been selected with regard to the predecessor relationship to achieve the topography and thus, the specified selected property to the specified degree.
  • One is a method of making an article having an at most nanocrystalline surface with a specified degree of blackness within a range from black to silver.
  • the method comprises the steps of: providing a workpiece, and electrochemically depositing on the workpiece, a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the others, by using current, defined by a deposition duty cycle of between about 12.5% and about 100% and a deposition current density of between about 0.01 A/cm 2 and about 1.0 A/cm 2 .
  • a relatively higher deposition duty cycle is used to achieve a relatively blacker surface
  • a relatively lower deposition duty cycle is used to achieve a relatively more silver surface
  • a duty cycle intermediate a high duty cycle and a low duty cycle is used to achieve a surface intermediate of black and silver.
  • the deposition stage is followed by electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, by using pulsed current, defined by an etching duty cycle of between about 30% and about 50% and an etching current density, of between about 0.001 A/cm 2 and about 10.0 A/cm 2 to achieve the specified blackness.
  • a closely related embodiment of an invention hereof further comprises using a high deposition duty cycle to obtain relatively wider channels.
  • a similar related embodiment of an invention hereof further comprises using a high deposition duty cycle to obtain relatively deeper channels.
  • Another closely related embodiment of an invention hereof uses a high deposition current density to achieve similar results as a high deposition duty cycle.
  • a related embodiment of an invention hereof uses a high deposition duty cycle and a low etching current density to achieve a black surface with relatively narrower and shallower channels. Rather than a low etching current density, a low etching duty cycle has a similar effect of reducing the width or depth of channels.
  • a very closely related invention is a method of making an article having an at most nanocrystalline surface defined at least in part by at least one of a network of channels and a spatial distribution of pits.
  • the method comprises the steps of: providing a workpiece, and electrochemically depositing on the workpiece, a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the others, by using current, defined by a deposition duty cycle of between about 12.5% and about 100% and a deposition current density of between about 0.01 A/cm 2 and about 1.0 A/cm 2 .
  • a relatively higher deposition duty cycle is used to achieve a surface exhibiting primarily channels
  • a relatively lower deposition duty cycle is used to achieve a surface exhibiting primarily a plurality of pits
  • a duty cycle intermediate a high duty cycle and a low duty cycle is used to achieve a surface exhibiting both a network of channels and a plurality of pits.
  • the deposition stage is followed by electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, by using pulsed current, defined by an etching duty cycle of between about 30% and about 50% and an etching current density, of between about 0.001 A/cm 2 and about 10.0 A/cm 2 to achieve the specified degree of pits and channels.
  • pulsed current defined by an etching duty cycle of between about 30% and about 50% and an etching current density, of between about 0.001 A/cm 2 and about 10.0 A/cm 2 to achieve the specified degree of pits and channels.
  • a closely related embodiment of an invention hereof further comprises using a low deposition duty cycle to obtain a surface exhibiting a plurality of spaced apart pits.
  • a low deposition duty cycle with a high etching duty cycle achieves a plurality of pits that are wide, or deep, or in a lower number density, or any of these three properties in combination.
  • Using a low deposition duty cycle with a high etching current density achieves similar results to that just mentioned with high etching duty cycle. Further, such methods produce thicker ligaments between pits.
  • Yet another related invention is a method using a low deposition duty cycle with a low etching duty cycle, which achieves a plurality of pits that are relatively narrower, or shallower, or having a higher number density, or any of these three properties. Rather than using a low etching duty cycle, a low etching current density may be used to similar effect.
  • Yet another related invention finds the step of electrochemically depositing comprising using such pulsed current to deposit a surface comprising nodular colonies, using a relatively higher deposition duty cycle to achieve nodular colonies having relatively smaller average size and relatively lower deposition duty cycle to achieve nodular colonies having relatively larger average size, and a duty cycle intermediate a high duty cycle and a low duty cycle to achieve nodular colonies having an average size between relatively smaller and relatively larger average sizes.
  • Another invention is a method of making an article having an at most nanocrystalline surface with a specified degree of shininess within a range from shiny to dull.
  • This method comprises the steps of: providing a workpiece and electrochemically depositing at the workpiece, a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the other, by using current, defined by a deposition duty cycle of between about 12.5% and about 100% and a deposition current density, of between about 0.01 A/cm 2 and about 1.0 A/cm 2 , using a relatively lower deposition duty cycle to achieve a relatively shinier surface, a relatively higher deposition duty cycle to achieve a relatively duller surface, and a duty cycle intermediate a low duty cycle and a high duty cycle to achieve a surface that is intermediate shiny and dull.
  • the method further comprises the step of electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, by using pulsed current, defined by an etching duty cycle of between about 10% and about 90% and an etching current density, of between about 0.01 A/cm 2 and about 10.0 A/cm 2 to achieve a surface having the specified shininess.
  • pulsed current defined by an etching duty cycle of between about 10% and about 90% and an etching current density, of between about 0.01 A/cm 2 and about 10.0 A/cm 2 to achieve a surface having the specified shininess.
  • Another invention is a method of making an article having an at most nanocrystalline surface with a specified shininess within a range from shiny to dull.
  • the method comprises the steps of: providing a workpiece, and electrochemically depositing at the workpiece, a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the others, by using current, defined by a deposition duty cycle of between about 10% and about 100% and a deposition current density of between about 0.01 A/cm 2 and about 1.0 A/cm 2 , using a relatively lower deposition current density to achieve a relatively shinier surface, a relatively higher deposition current density to achieve a relatively duller surface, and a deposition current density intermediate a low current density and a high current density to achieve a surface intermediate shiny and dull.
  • the deposition step is followed by electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, by using pulsed reverse current, defined by an etching duty cycle of between about 10% and about 90% and an etching current density of between about 0.001 A/cm 2 and about 10.0 A/cm 2 to achieve the article surface with the specified shininess.
  • pulsed reverse current defined by an etching duty cycle of between about 10% and about 90% and an etching current density of between about 0.001 A/cm 2 and about 10.0 A/cm 2 to achieve the article surface with the specified shininess.
  • Even another invention is a method of making an article having an at most nanocrystalline surface with a specified topography ranging from relatively larger pits bounded by relatively thicker solid ligaments to relatively smaller pits bounded by relatively thinner solid ligaments.
  • the method comprises the steps of: providing a workpiece; and electrochemically depositing at the workpiece, a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the others, by using pulsed current, defined by a deposition duty cycle of between about 12.5% and about 100% and a deposition current density of between about 0.01 A/cm 2 and about 1.0 A/cm 2 .
  • the deposition step is followed by electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, by using pulsed reverse current, defined by an etching duty cycle of between about 10% and about 90% and an etching current density of between about 0.001 A/cm 2 and about 10.0 A/cm 2 to achieve the specified topography, using a relatively higher etching duty cycle to achieve a topography exhibiting primarily relatively larger pits bounded by relatively thicker solid ligaments and by using relatively lower etching duty cycle to achieve a topography exhibiting primarily relatively smaller pits bounded by relatively thinner solid ligaments.
  • pulsed reverse current defined by an etching duty cycle of between about 10% and about 90% and an etching current density of between about 0.001 A/cm 2 and about 10.0 A/cm 2
  • Last but also important is a method of making an article having an at most nanocrystalline surface with a specified topography ranging from a network of relatively wider, irregular channels connecting pits to a network of relatively narrower channels.
  • the method comprising the steps of: providing a workpiece; and electrochemically depositing at the workpiece, a surface comprising an at most nanocrystalline material comprising at least two elements, at least one of which is metal, and one of which is more electrochemically active than the others, by using current, defined by a deposition duty cycle of between about 12.5% and about 100% and a deposition current density of between about 0.01 A/cm 2 and about 1.0 A/cm 2 .
  • the deposition step is followed by electrochemically etching the workpiece to remove a portion of the more electrochemically active element preferentially, as compared to any other components of the workpiece, by using pulsed current, defined by an etching duty cycle of between about 10% and about 90% and an etching current density of between about 0.001 A/cm 2 and about 10.0 A/cm 2 to achieve the specified topography, using a relatively higher etching current density to achieve a topography exhibiting a network of relatively wider, irregular channels connecting pits and a relatively lower etching current density to achieve a network of relatively narrower channels.
  • pulsed current defined by an etching duty cycle of between about 10% and about 90% and an etching current density of between about 0.001 A/cm 2 and about 10.0 A/cm 2 to achieve the specified topography, using a relatively higher etching current density to achieve a topography exhibiting a network of relatively wider, irregular channels connecting pits and a relatively lower etching current density to achieve a network of relatively narrower

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