Fiber Based Amalgams for InSpace Flight Repair and Fabrication

1
Fiber Based Amalgams for In-Space Flight Repair
and Fabrication

• NASA Academy
• Brian Dolan
• PI Dr. Richard Grugel

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Objective

• To develop new materials for applications that
  relate to in-space flight application and repair.
  
• Amalgams are utilized primarily for dental
  applications due to their low tensile, but high
  compressive strength.
• The goal is to increase the tensile strength of
  these amalgams by replacing the current powder
  alloys with fiber strands, creating a brand new
  material.

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Background

• What are amalgams?
• They are an alloy of liquid mercury or liquid
  gallium and one or more metals (generally Ag or
  Cu based) that is formed at room temperature.
• Most commonly used for dental fillings.
• Explored as a solder material and for joining
  ceramic to metal components.

Amalgam made from the gallium alloy with copper
wool (1.351) sample. Has .75cm average fiber
length, mixed with mortar and pestle.
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Background

• Current dental amalgams use a powder alloy that
  generally has spherical or lathe cut particles
  that are around 50mm in diameter.
• The particles are the cause for low tensile
  strength.

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Background

• The concept behind composites and metal-matrix
  materials is to embed fibers in the matrix to
  increase tensile strength.
• The same concept can be applied to amalgams.
• By replacing the powders with fibers, the path
  which cracks must propagate in order to fracture
  is more difficult.

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Amalgam Advantages

• Fiber based amalgams can produce near-net shape
  parts with room temperature solidification and
  little supporting equipment.
• The parts created from amalgams will not need to
  be machined after casting.
• Intermetallics also have high temperature
  applications making them an excellent candidate
  for repair applications during long duration
  space missions.

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Experimental Work

• The liquid and solid are mechanically mixed
  together.
• This breaks the oxide film off the metal and
  allows the liquid to wet the solid.
• This causes a peritectic reaction, meaning a
  liquid and a solid react to form a new
  intermetallic solid.

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So What are Intermetallic Compounds?

• Intermetallic compounds form when two unlike
  metals diffuse into one another creating species
  materials which are combinations of the two
  materials.
• Have hardness and/or resistance to high
  temperatures.
• Low ductility at room temperature. (low strength)

Have chemical compositions like Cu2Ga6
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Experimental Work

• Fibers were cut in lengths of up to 1 cm.
• The liquid gallium alloy has properties of Ga
  62.5, In 21.5, Sn 16, m.p. 10.7oC.
• Gallium has a m.p. of 30oC
• The amalgams are classified as short fiber
  composites with random disorder in regards to
  fiber orientation.
• Long fiber composites are generally stronger then
  short fiber composites, but they are much harder
  to process.

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Experimental Work

• Initially, samples were made through trituration,
  a process that rapidly shook capsules filled with
  the liquid gallium alloy and fibers.
• Had a max capacity of about 3000mg of material.

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Experimental Work

• For larger samples a mortar (bowl) and pestle
  (grinder) were used to mash and ground the
  materials together.
• Once the amalgam began to form a cohesive but
  workable material, it was compressed into a
  Plexiglas mold.

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Samples Created

• Over 45 different samples were created using
  parametric changes to the following
• Varying fiber/liquid ratios (from 0.11 to
  1.51).
• Addition of small amounts of powder to the fiber
  samples.
• Lengths of samples under an inch to over three
  inches.
• Different fibers types including copper clad
  steel wires, copper wool, steel wool, and
  stainless steel wool.

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Parametric Samples
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Samples Created

• Samples sat in the molds for at least 12 hours
  before being removed.
• Samples that were marked for future tensile
  testing were micro-milled to ensure that they
  were parallel sides to ensure a plane stress on a
  uniform cross-sectional area.
• Other samples were mounted and polished to be
  examined via microprobe and optical microscopy.

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What Weve Learned

• Characterization of all fibers and powders was
  done using scanning electron microscopy.
• From this analysis it was discovered the
  machining method used created small notches in
  the copper wool.
• These notches may allow for easier crack
  propagation and weaken the overall amalgam.

Scale on all 4 images is 500mm
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What Weve Learned

• Liquid to solid ratios
• Too high a ratio creates high amounts of
  intermetallic compounds which weaken the
  structure.
• Too low and there wont be enough liquid to form
  an intermetallic matrix and cohesively bond the
  material.
• Early tensile testing indicates that the fiber
  amalgams have maximum strengths of around 70MPa
  or 10 Kips compared to powder amalgams that
  break when being removed from their molds
  (gt5MPa).

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What Weve Learned

• Microprobing used to map a image for locations of
  elements and mixtures of elements (i.e.
  intermetallics).
• The main intermetallic compound formed is a GaCu
  phase, implying that the copper fibers have the
  same reaction characteristics as the powder.

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What Weve Learned

• The more liquid in the sample, the longer the
  setup time of the amalgam in the mold.
• Samples with gallium of over 11 were still
  hardening after 4 days , where as samples with
  gt0.751 took less than 2 days.
• When the surfaces are completely coated in
  gallium the reaction switches from a surface
  reaction to a slower diffusion based reaction.
• Further evidence of this is that liquid gallium
  will sweat out of the amalgam at compositions
  over 11, indicating excess gallium in the
  structure.

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Conclusions

• Demonstrated that fiber based amalgams are an
  easily created material that have the advantage
  of increased tensile strength.
• Copper cladded steel are an ideal fiber material
  because the thin layer of copper will react to
  form intermetallics that compose the matrix but
  the steel will remain un-reacted to provide
  tensile strength as fibers.

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Future Work

• Quantitative testing must be done to identify
  specific compositions of fiber, powder and
  gallium that provide the best materials
  characteristics.
• Tests must be conducted at high temperatures to
  determine melting points of the amalgams.
• The dependence of strength as function of time
  during the hardening of the material.
• Finally, work needs to be done to test heat
  treating, electrical conductivity, corrosion and
  oxidation resistance.

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In closing

• Thanks of course to my P.I. Dr. Richard Grugel
  for always being available even with his busy
  schedule.
• And of course Dr. Six and Dr. Karr and everyone
  on the Academy Staff without whom I wouldnt have
  had this incredible 10 week experience.
• Questions?