# Presentation: 887680

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

- NASA Academy
- Brian Dolan
- PI: Dr. Richard Grugel

- Marshall Space Flight Center

- Summer 2005

## 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 (1.35:1) 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 50m 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 Cu****2****Ga****6**

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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 0.1:1 to 1.5:1).
- 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 We’ve 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 500********m**

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## What We’ve Learned

-  Liquid to solid ratios:
- Too high a ratio creates high amounts of intermetallic compounds which weaken the structure.
- Too low and there won’t 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 (>5MPa).

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## What We’ve 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 We’ve Learned

- The more liquid in the sample, the longer the setup time of the amalgam in the mold.
- Samples with gallium of over 1:1 were still hardening after 4 days , where as samples with >0.75:1 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 1:1, 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 wouldn’t have had this incredible 10 week experience.
- Questions?

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