Prsentation PowerPoint

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Nanomaterials Mechanical Properties

• Observations/predictions
• lower elastic moduli than for conventional grain
  size materials (30 - 50)
• very high hardness and strength values for
  nanocrystalline pure metals ( 10 nm grain size)
  are 2 to 7 times higher than those of larger
  grained (gt1 m m) metals
• a negative Hall-Petch slope, i.e., decreasing
  hardness with decreasing grain size in the
  nanoscale grain size regime
• ductility-perhaps superplastic behavior-at low
  homologous temperatures in brittle ceramics or
  intermetallics with nanoscale grain sizes,
  believed due to diffusional deformation
  mechanisms

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Nanomaterials Metals
Hall-Petch relation
Diameter of Dislocation loop
Arzt, MPI Stuttgart
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d(t) D
t Gb/D
E. Arzt, Acta mater. Vol. 46, No. 16, pp.
56115626, 1998
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HalL- Petch Hardness of Cu
Arzt, MPI Stuttgart
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Simulation
van Swygenhoven, PSI
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Ni, d 12 nm
van Swygenhoven, PSI
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Ni, d 12 nm
van Swygenhoven, PSI
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Ni, d 12 nm
van Swygenhoven, PSI
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Metals as Nanocomposite Bulk/Grain boundary
10
Metals as NanocompositeBulk/Grain boundary
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Ceramics Nanocomposites
Strength and toughness of Al2O3/SiC and
SiAlON/SiC nanocomposites as a function of SiC
content
C.E. Borsa, S. Jiao, R.I. Todd and R.J. Brook, J.
Microscopy 177 (1994) 305 ii R. W. Davidge,
R.J. Brooks, F. Cambier, M. Poorteman, A.
Leriche, D. OSullivan, S. Hampshire and T.
Kennedy, J. Eur. Ceram. Soc. 16 (1996) 799
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Critical flaw size reduction (c-mechanism)
Zener grain size boundary pinning
Reduction in processing flaw size Hot
pressing,HIP
Crack healing (annealing treatment) compressive
stress around the nanoparticles in the matrix
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Thermal expansion mismatch
Crack deflection
 
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Average internal stresses
Thermoelastical data for matrix and
nanophase   Al2O3 400 0.23 8.3 Si3N4 300
0.27 3.2 MgO 300 0.18 14 TiN 470
0.25 9.4 SiC 480 0.17 4.4
EMpa ? ?10-6 K-1
SiC particles in Alumina
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Local stress distribution