Development of New Generation Of Coatings with Strength

							Development of New Generation Of
  Coatings with Strength-Ductility
Relationship, Wear, Corrosion and
Hydrogen Embrittlement Resistance
   Beyond the Current Materials
    Accomplishments till date


n   As the structural scale reduces to the nanometer range,
    one accomplishes
     n High strength

     n High interface–to-volume ratio

     n Enhancement of the interface-driven processes which

        will extend the strain to failure and plasticity
n   Mechanical strength is controlled by the Hall-Pitcher
    relationship σ =kd-1/2 + σo. A limitation of current in
    engineering materials is that gain in strength results in a
    loss of ductility
    Accomplishments till date

n   Reducing the
    structural scale to
    the nanometer
    range one can
    extend the
    strength-ductility
    relationship
    beyond the
    current materials
    limit
    Accomplishments till date

n   Nanostructured powders with increased strength and
    ductility have been produced by plasma processing where
    the reactor vaporizes coarse meat particles; by
    combustion synthesis where redox reaction takes place at
    elevated temperature, followed by quenching; and by
    mechanical alloying with gas atomization
n   Cu/Nb composites (Han at al 1998) showed a complete
    suppression of the wire brittle fracture.
n   Au-single crystals surfaces have dramatic effects on the
    yield strength
Accomplishments till date
n   Erb et al. found that the passive current density of
    nano crystalline Ni is higher than conventional Ni
    which showed higher susceptibility to localized
    corrosion
n   Erb et al., synthesized nanocrystalline Ni-Fe with
    increased hardness, wear resistance and improved
    corrosion performance in terms of localized corrosion
       Objectives for the Next decade

n   Development of the next generation of protective coatings
    with high corrosion, wear and erosion resistance, integrity
    under thermal stress and complete inhibition of hydrogen
    permeation and embrittlement
n   Development of theoretical models which will explain how
    the shape and the size of the nanostructure affect its
    properties and optimize the materials surface and bulk
    properties
n   Development of novel treatment for synthesis of
    nanostructured materials.
    Objectives for the Next decade


n   Development of monolayers and the nanometer range
    coatings in order extend the strength-ductility relationship
    beyond the current materials limits
n   Development of procedures capable by using oxide
    nanoparticles to convert metals into material with wear
    resistance equal of that of the bets bearing steel.
n   Development of advanced scratch free resistant films, with
    high strength, wear resistance and ductility (Cu coatings
    for printing industry).
       Why electrodeposition ?

n   Multilayer structures with nanometer-scale thickness have
    been produced by various deposition processes, such as
    sputtering, molecular beam epitaxy, and chemical vapor
    deposition.

n   While, versatile, the vacuum deposition techniques require
    expensive equipment; they cannot be used for fabrication
    of large structures with complex shapes and in most of the
    cases are difficult to control.

n   Molecular beam epitaxy is well controlled deposition
    technique; however, this is not a volume production
    method.
     Why electrodeposition ?

n   Multilayer structures with specific textures can also be easily
    synthesized      using    the    chemical     reduction    and
    electrodeposition processes

n   For example, 3D nanostructured, crystallites can be
    prepared using this method by utilizing the interface of one
    ion with the deposition of the other.

n   Also, the size of the particles can be controlled precisely by
    the use of various micellar structures and lyotrophic phases
    in the solution phase during deposition.
    Why electrodeposition ?
n   Pulse and pulse reversal deposition of multilayer
    structures with nanometer scale requires minimal capital
    investment and can be applied to fabrication of parts of
    any shape or size.

n   The deposition rates at 10 nm layer level are about 0.05
    nm/h, however, the process is non-labor intensive and can
    run automatically for long periods of time.

n   Multi layer structures with specific textures can also be
    easily synthesized using the electrodeposition process
A Novel Autocatalytic Reduction Process
(ARP) for deposition of nanostructured
composites

n   One step process

n   No external current for deposition.

n   Nanosized amorphous layers of Co-P, Ni-P, Co-Ni-P ,
    deposition of amorphous nanostructured multilayers of
    Ni-Mo-P, Ni-W-P, Ni-Ce-P, Ni-Mo-B can be deposited by
    controlling the concentration of the electroactive species
    in the electrolyte and by controlling the factors which
    control the deposition rate
    Factors controlling the deposition rates


n    Substrate pretreatment
n    pH and temperature
n    Concentration of the reducing agent
n    Presence of leveling agents
n    Presence of dendrimers
n    Presence of any of the three liquid crystalline
     phases    exhibited    by   nonionic  surfactant
     octaethylene glycol monohexadecyl ether (OGME)
A Novel Pulse and Pulse Reversal Plating of Nickel-Iron,
     Co-Ni, Zn-Ni, Zn-Ni-P alloys and Zn-Ni-SiO2
  Composites Procedures are Under Development at
                         USC

Why Pulse or Pulse Reversal Technique?
  n The deposit particle size is proportional to the crystal

     growth rate while inversely proportional to the nucleation
     rate. decreases with increasing the nucleation rate.
  n The crystal growth is proportional to the surface adatom

     concentrations surrounding the site.
  n The nucleation rate is enhanced by increasing the

     overpotentials.
  n Using Pulse technique, leveling agents, dendrimers and

     nonionic surfactant the nucleation rate dramatically
     increases due to increased overpotential
      Why Pulse or Pulse Reversal Technique?

n   Since the surface adatom concentration is proportional to the
    solution concentration in the vicinity of the surface one can expect
    a controlled pulse of less than milliseconds or micro seconds to
    deposit in the presence of additives in the electrolyte layers of
    metals, alloys and composites which have lower growth rate that
    DC technique.
n   Nanosized layers of Zn and Zn-Ni alloys are deposited by
    controlling, the average current , the pulse duration, the
    concentration of Zn and Ni ions in the electrolyte and by controlling
    the factors which control the deposition rate such as:
     n substrate pretreatment

     n  pH and temperature
     n the presence of leveling agents

     n the presence dendrimers, and nonionic surfactant octaethylene
       glycol monohexadecyl ether (OGME).
      Why Pulse or Pulse Reversal Technique?


n    Pulse and pulse reversal technique can be used do deposit
    multilayer structures composed of hundreds (up to one
    thousand) layers (5-10 nm) of Ni//Ni-Zn-P//Ni//Ni-Zn-P; Ni-
    Mo//Ni-Cu-Mo; Ni-Mo-Si//Ni-Cu-Mo-Si; and Ni-Mo-Ti//Ni-Mo-Cu-
    Ti nanostructured composites
n   The specific objectives should be:
     n to develop coatings with very large interfacial surface area
        and with superior ductility, strength and hardness,
     n microstructural and mechanical characterizaton and

     n fundamental modeling of crack initiation and propagation.
        Also, theoretical studies should be carried out which will
        correlate and tailor both strength (Koehler effect) and elastic
        modulus by varying the number of layers the layer thickness
        of nanostructured coatings
     Under Potential Deposition of Metals (UPD)

n   UPD occurs with a formation of monatomic layers at
    potentials more noble the an the reversible Nernst potential
n   UPD has been engineered at USC for Zn, Pb and Bi by using
    the work functions of these metals and the work functions of
    the substrates
n   The underpotential shift (∆E) in volts when the monatomic
    layers are formed is determined by the work functions in
    electron volts of both metals.
n   In situ polarization experiments showed that UPD formed
    monoatomic layers of Pb, Zn, and Bi on steel surfaces inhibit
    corrosion, hydrogen penetration and embrittlememnt due to
    lowering of the binding energy of the hydrogen adatoms on
    Zn, Pb and Bi adsorbates
   Under Potential Deposition of Metals (UPD)


 Future work is necessary which will
n Characterize the nature of the deposits plated when pulse

   and DC technique at overvoltages between UPD potential
   and Nernst potentials in the presence of leveling agents,
   dendrimers and nonionic surfactant octaethylene glycol
   monohexadecyl ether (OGME). With an objective to
    n deposit monolayers of metals or alloys on large

      surfaces, carbons or carbon nanotubes.
    n to increase the adhesion and the strength of the

      deposits
      Structural Studies

n   In     the    layered    and
    filamentary nanostructures,
    the nature of the interfaces
    has not been studied in
    details and there is not
    much information in the
    literature.
n   The microstructure should
    be investigated by high
    resolution TEM, scanning
    tunneling microscopy (STM)
                                    The Jeol 100 CX II is a transmission electron
    and       neutron diffraction   microscope capable of accelerating voltages
    techniques                      from 20-100kv. It can provide magnification from
                                    100x to 600000x and a resolution of 0.2nm
      Structural Studies
n The microstructural features should include
   n the nature and morphology of grain boundaries and

     interfaces
   n grain size and morphology

   n the nature of intergrain defects,

   n composition profiles across grains and interfaces and
     identification of residual trapped species from processing
n The electrodeposited multi layered nanostructures should be
  studied in order to evaluate
   n composition profiles across interfaces

   n nature of defects and

   n coherency and thickness of interfaces
     Mechanical Characterization Studies

n   Hardness of the deposit defines the abrasion resistance
    and general wear and tear qualities of the coating. Vickers
    and Knoop hardness tests are generally used to determine
    the hardness. Knoop hardness should be used since this is
    ideally suited for thin electrodeposits.
n   The ductility, the resistance to fatigue damage, abrasion
    (wear) resistance, porosity, bending and cup impact test
    will be done using standard methods.
n   Coefficient of Sliding Friction will be determined by
    measuring the coefficient of sliding friction according to the
    Coulomb’s Law              R = µN
n   The adhesion test should be based on ASTM B571-97
    Standard Practice for Qualitative Adhesion Testing of
    Metallic Coatings.
     Mechanical Characterization Studies

n   The ductility, the resistance to fatigue damage, abrasion
    (wear) resistance, porosity, bending and cup impact test
    should be done using standard methods.
n   The strength        properties of multilayered deposits
    suggested in this proposal should            be evaluated
    theoretically and experimentally.
n   A mathematical model should be developed which will
    predict
     n the dislocations as a function of the elastic constants
       and the thickness of the multi layered nanostructures
       and
     n the susceptibility to plastic deformation and brittle
       fracture as a function of the deposit layer thickness