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Metal Matrix Composites MMC






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Purpose of using MMCs . higher specific modulus and strengthbetter properties at elevated temperaturelower CTEbetter wear resistanceDisadvantages of using MMCs:less toughnessmore expensive. Applications of MMCs. Mid-fuselage structure of Space Shuttle Orbiter showing boron-aluminum tubes. (Photo courtesy of U.S. Air Force/NASA). .
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

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

19. Strength of MMCs

21. Temperature Effect on MMCs

22. Creep Curves of MMCs

23. Fatigue of MMCs

24. Commercial MMCs Multi-filamentary superconductor

26. Aluminum reinforced with silicon carbide particles

27. Tuning of CTE

28. Ageing Hardening of MMCs

29. Improvement in Creep Resistance


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