Structure Control Engineering

7/21/2019 Structure Control Engineering

http://slidepdf.com/reader/full/structure-control-engineering 1/15

Application of Diffraction to Texture Analysis









Application of Diffraction to Texture AnalysisPole figure measurements









i is the imaginary constant, i.e. i = ( −1) 0.5

The intensity of the reflected radiation is proportional to F 2 and, hence,reflection only occurs if the reflected waves are all in phase, that is, if F ≠ 0.

Diffraction of radiation at the various atoms in a crystalline structure is governed bythe structure factor F ,

The differences between the various radiations used for texture analysis , that is,x-rays, neutrons, and electrons, are represented by the atomic scatteringamplitude f , but the geometrical considerations associated with structure factorF hold for all kinds of radiation.




It is seen that if ( h + k + l ) is odd, the exponentialterm in the equation becomes -1, so that F = 0.However, if ( h + k + l ) is even, then F = 2 f , whichmeans reflection.

(100), (200), (110), (220)

To derive the rules of extinction, the followingrelations with complex numbers are helpful;

BCC materials




FCC materials

(112), (200), (222), (111)




Ni3Al

(111), (211)




Application of Diffraction to Texture AnalysisStructure factors

Inverse pole figure map of pearlitic steelCementite (iron Carbide)

Orthorhombic structure



Cementite (iron Carbide)

Orthorhombic structure

In literature it has been commonly reported that it is rather difficult to index cementite

lamellae due to their low structure factors of its lattice???? .








For PFs measurement, asymmetric scanning should be used. In this scanning acertain set of hkl-planes is selected, and the sample has to be tilted and rotated inspace.

If the goniometer is set for {100} reflections, thenall directions in the sample that are parallel to

<100> directions will exhibit diffraction.




Documents

Structure Control Engineering