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April 13, 2004 Edward Barnard Elizabeth Hager Kevin McComber Jenny Lichter
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Outline Goal Aluminum and Silicone Molds Ceramic Preform and Binders Pressure Vessel and Infiltration Time Calculations Characterization Initial Part Production Challenges and Solutions INITIAL PROTOTYPE ! Future Work Schedule
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Goal The goal of our project is to design a manufacturing process to create a selectively reinforced metal matrix composite. This project will take the theory developed in Jess Wannasin’s thesis work and scale up to part production.
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Our Process
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Aluminum Mold
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Centrifuge Setup
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Silicone Mold Polytek PLATSIL RTV Silicone Rubber 71-10
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Ceramic Preform SiC 120 Grit (100 µm particles)
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Wannasin Binder REMET R-25 binder (Prehydrolyzed Ethyl Silicate) Sintered a SiC preform at 1500°C for 1hr Cut sintered alumina into preform shape Silica
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http://cyberbuzz.gatech.edu/asm_tms/phase_diagrams/pd/sn_pb.gif Pressure Vessel Calculations 1.5 2.0 0.125 0.50 But…. there’s a catch: as the processing temperature increases, σ UTS decreases
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Swagelok Catalog New Safety Factors High Temp = 250 - 300°C σ UTS, High Temp = [0.2 – 0.3] * σ UTS, Room Temp σ UTS safety factor Safety factors sufficient r inner S. F. 0.755 0.062515 P max = 730 psi = 50 atm S. F. : safety factor = 2
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Infiltration Time Calculations Values: = 2* water, L = 4 inches, D P = 100 m P >> P threshold and infiltration times << 5 mins V P = 0.5V P = 0.7 Threshold pressures1.5 atm3.5 atm Infiltration times<<1 sec Darcy’s Law: pressure driven flowBlake-Kozeny equation
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Hardness Tests Preparation Cut samples with low-speed saw to obtain smooth surface blade is material specific part is a combination of materials of very different materials Polished with 5-micron polishing paper Results: used Rockwell B and H (low hardness) Pure tin-lead: off-the-scale on the low end hardness MMC: on-scale but low MMC is harder than plain tin-lead
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SEM (Scanning Electron Microscopy) Images SiC particles: 500-600 microns Fracture behavior Etchers may be necessary 2mm 1mm 100 m
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Initial Spin tests Small amount of Tin-Lead Completed cleared out of runner
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First Try: Incomplete Infiltration SiC, 120 grit non-sintered preforms 500 rpm Preform floated Not enough metal or pressure
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Challenges and Solutions Insufficient seal and metal leakage But still safe! Solution: graphite o-ring Before…After…
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Challenges and Solutions, ct’d Imbalanced centrifuge Prevents centrifuge from reaching high rpm, reducing volume fraction of ceramic – high V ceramic is the goal Solution: add weights to either side However…. still imbalanced
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Challenges and Solutions, ct’d Removing part from mold Graphite o-ring stuck to mold interface Long-term Solution: on future production runs, spray interface with Boron Nitride Short-term Solution: hit part out with hammer
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INITIAL PROTOTYPE !!!! Tin Lead, R-25 Binder, 700 RPM = 6 atm Preforms: sintered SiC, 120 grit sintered alumina One on left: not full shape because of imbalanced metal distribution (metal left in runner)
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Future Work Make more parts! Try different ceramics Try different binder concentrations Alter shape of part SEM Volume fraction of particles Fracture characteristics Hardness tests
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Projected Work Schedule
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