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Metal Matrix Composites (MMC)

Metal Matrix Composites (MMC). Purpose of using MMCs. higher specific modulus and strength better properties at elevated temperature lower CTE better wear resistance Disadvantages of using MMCs: less toughness more expensive. Applications of MMCs.

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Metal Matrix Composites (MMC)

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  1. Metal Matrix Composites(MMC)

  2. Purpose of using MMCs • higher specific modulus and strength • better properties at elevated temperature • lower CTE • better wear resistance Disadvantages of using MMCs: • less toughness • more expensive

  3. Applications of MMCs Mid-fuselage structure of Space Shuttle Orbiter showing boron-aluminum tubes. (Photo courtesy of U.S. Air Force/NASA). Cast SiCp/Al attachment fittings: (a-top) multi-inlet fitting for a truss node

  4. MMC processing • solid-state processing: suitable for composite with large surface area of high energy solid-gas interface, e.g. matrix in particle or fail form. • diffusion bonding: using foil matrix Fig 3.1 e.g. Ti, Ni, Cu, Al reinforced with boron • power metallurgy: using particle materials, suitable for particle or whisker reinforced composites, Vf < 25% • co-extrusion, drawing limited to ductile reinforcement and matrix

  5. Diffusion bonding

  6. liquid-state processing • Casting Difficulties:  wetting  chemical reaction  non-uniform mixing (due to density difference) ,  can be improved by • using precoating on reinforcements, e.g. pyrolitic graphite coating • modifying the melt, e.g. add Li in Al melt • compo casting, rheocasting: • infiltration on perform: • squeeze casting: Fig 3.2

  7. Squeeze Casting

  8. Liquid Melt Infiltration on Preform

  9. Deposition processing • spray co-deposition, Fig 3.4 • chemical and physical vapour deposition (e.g. tungsten) • electroplating (e.g. nickel) • sputtering and plasma spraying

  10. Spray Co-deposition

  11. In-situ processing Unidirectional laminar or rod-like eutectic alloys, Fig 3.5 (in-situ composites)

  12. Interface reactions Interdiffusion between matrix and reinforcement: Where x = extent of interdiffusion Dd = diffusion coefficient Interdiffusion  interfacial layer (Fig 3.6)  mechanical properties are degraded (Fig 3.7)

  13. Effect of Interfacial layer

  14. Mechanical properties of MMCs  lower CTE than metals (Fig 3.8)  lower coefficient of thermal and electrical conductivity (Table 3.2)  higher thermal deformation resistance  improvement in stiffness (Fig 3.9, Fig 3.10)  strength and ductility Reinforcement-matrix interface: Strong  high strength Extensive interaction  low strength, low fatigue resistance Fig 3.12～Fig 3.17  creep (Fig 3.18, Fig 3.19)  fatigue (Table 3.4, Fig 3.20)

  15. Thermal Expansions of MMCs

  16. Thermal Conductivity of MMCs

  17. Young’s Modulus of MMCs

  18. Strength of MMCs

  19. Temperature Effect on MMCs

  20. Creep Curves of MMCs

  21. Fatigue of MMCs

  22. Commercial MMCs • Multi-filamentary superconductor

  23. Aluminum reinforced with silicon carbide particles

  24. Tuning of CTE

  25. Ageing Hardening of MMCs

  26. Improvement in Creep Resistance

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