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Assignment deadline Monday . Explain in a one page essay, how an iron alloy can be designed to emulate the nickel based superalloy , containing ordered precipitates which are coherent with the matrix. For information on nickel based alloy see: - PowerPoint PPT Presentation

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Interstices in Cubic-I, Cubic-F and HCP Structures

Assignment deadline Monday Explain in a one page essay, how an iron alloy can be designed to emulate the nickel based superalloy, containing ordered precipitates which are coherent with the matrix.For information on nickel based alloy see:http://www.msm.cam.ac.uk/phase-trans/2003/Superalloys/superalloys.html

Interstices in Cubic-I, Cubic-F and HCP StructuresCrystallography

H. K. D. H. Bhadeshia

C 62 pm Ni 126 pm Fe 124 pm Cr 130 pm (Andrew Fairbank)

silicon in ironcarbon in iron

Insterstitial solid solution strengthening(Ghosh & Olson)Cubic-I

Close-packed direction?

(Andrew Fairbank)Ferrite

radius of iron atom in ferrite

octahedral interstice in ferritepoint group symmetry?

Carbon does not fit. Therefore, placing in octahedral site reduces the tetragonality of the site.

Largest atom that can fit in octahedral site

tertrahedral interstice in ferriteVector joining centres of iron and carbon?Structure projection of 4 unit cells of ferrite

What it the vector joining iron and carbon atom neighbours?xy

structure projection

3 octahedral sites per Fe6 tetrahedral sites per Fe

austenitecubic-F

17octahedral interstice in austenitepoint group symmetry?

Carbon does not fit. It causes uniform expansion.

Largest atom that can fit in octahedral site

tertrahedral interstice in austeniteVector joining centres of iron and carbon?

Insterstitial solid solution strengthening(Ghosh & Olson)

ferriteausteniteFerriteCarbon in smaller anisotropic octahedral intersticesResulting strain is anisotropicStrong interaction with deviatoric and dilatational strain fields of dislocationsIntense strengthening3 octahedral and 6 tetrahedral holes per ironAustenitecarbon in larger isotropic octahedral intersticestherefore, behaves like substitutional solute with weak interactions with dislocationsmild strengthening1 octahedral and 2 tetrahedral holes per iron(a)

BAIN STRAIN(c) Body-centered tetragonal austenite(d) Body-centered cubic martensiteaaa123

b3

b1

b2(b)26

tetragonal martensite?