Martensite formation and magnetic property of AlNiCo compounds

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Martensite formation and magnetic property of
Al-Ni-Co compounds
Student Rongxiang Hu
hurongx_at_iit.edu Hsin-Ning Su
suhsinn_at_iit.edu Advisor Prof. Nash
nash_at_iit.edu This
work was supported by the National Science
Foundation under grant No.DMR0209624
9/10/2004
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Martensite formation in Al-Ni-Co compounds
L10
L12
Al0.4Ni0.5Co0.1
L10
Martensite might be a potential means of
ductilizing polycrystalline NiAl alloys due to
the transformation and reorientation of the
martensite variants under applied stresses.
Al0.4Ni0.4Co0.2
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Factors influencing Martensite ductilization

• B2 to L10 transformation strain anisotropy
• Large strain anisotropy results in stress
  concentration at grain boundaries and leads to
  premature failure
• strain anisotropy is a function of lattice
  parameters of B2 and L10 phases (no idea about
  this relationship)
• Scott et al found in 36 Al Al-Ni-Co alloys,
  with Co increasing, the anisotropy factor (the
  ratio of largest strain to the smallest strain
  along different crystal directions) decreased,
  which is favorable for higher ductility.
• B2 and L10 interface mobility
• B2 and L10 interface mobility can be
  reflected from the transformation temperature
  hysteresis H
• H(Af As)/2 (Ms Mf)/2
• H ?, interface mobility ?

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Lattice parameter of L10 phase
Scott L10 lattice parameters a(A)3.1774
1.6955?10-2Al 6.2398?10-3Co
c(A)3.9368-1.9591?10-2Al - 6.2798?10-3Co
Al----Al atomic fraction
Co----Co atomic fraction
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DSC of Al0.4Ni0.4Co0.2
a2
a1
a3
Three peaks L10? B2 L12? B2 ? Or multiple
stage of M transformation?
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DSC of Al0.4Ni0.5Co0.1
a
a
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Vacuum furnace melting of AlxNiyCoz
Compounds Al0.4Ni0.5Co0.1 and Al0.4Ni0.4Co0.2
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Thermal induced martensite in Al0.4Ni0.5Co0.1
Quenched in Liquid N2
Quenched in Liquid N2
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Different between calorimeter alloys and Vacuum
furnace alloys

• The cooling rate(crystal size? Ms)
• Calorimeter ? 300C/min
  (Al0.4Ni0.5Co0.1 ?100?m)
• Vacuum furnace alloys ? 10 C/min
  (Al0.4Ni0.5Co0.1 ?300?m )
• Al vaporization
• VFM Al0.4Ni0.5Co0.1 35-37at.Al
  Calor. Al0.4Ni0.5Co0.1 26-28Al
• Ms 4433.5-116.47Al-23.194Co
  (Scott M.R. et al)
• Ms -457.24K
  (Al0.4Ni0.5Co0.1 )
• Ms -689.18K
  (Al0.4Ni0.4Co0.2 )

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Magnetic permeability of Al-Ni-Co system
Tc ? RT ?
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Promising ferromagnetic Al-Ni-Co shape memory
alloys
K.Oilkawa et al Composition dependence of the
Curie temperature TC , the martensitic transformat
ion temperature Ms and the austenitic finishing
temperature Af in Ni71-xCoxAl29 alloys. The FSME
can be observed in the hatched region
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Conclusion and possible future work

• Martensite formed in some Al-Ni-Co alloys might
  increase their room temperature ductility.
  Desirable Ms can be obtained by changing Co
  content.
• DSC indicated the As in Al0.4Ni0.4Co0.2 and
  Al0.4Ni0.5Co0.1 is 23 and 18 degree C
  respectively.
• After quenching in liquid N2, SEM showed more
  martensite appeared in Al0.4Ni0.5Co0.1,
• Promising ferromagnetic Al-Ni-Co shape memory
  alloys might be another potential smart material.
• Arc-melting the promising Al-Ni-Co shape memory
  alloys