Faults In Alloys Research Articles

Atomic configuration of microtwins in alloys having Ll2 superstructure

In the approximation of paired interatomic potentials of the Morse type, modeling is done on the atomic configuration and energy of formation of superstructure stacking faults and superstructure twinning stacking faults in the ordered alloys Cu3Au and Ni3Fe, and also in the intermetallide Ni3Al. Features are observed in the local deformation of the crystal lattice defects near equilibrium (in terms of internal energy), and the principle difference in the state of the atomic surroundings of the examined plane defects is shown. In alloys of Cu3Au and Ni3Fe, calculations are done for different values of the long-range order parameter. A difference is detected in the variation of the energy of formation of superstructure twinning stacking faults in alloys of Cu3Au and Ni3Fe with the long-range order parameter. This difference correlates with experimental observation of the properties when varying the temperature in the alloys.

Observation of faint contrast at planar faults in alloys

The contrast in electron microscopic images of planar faults in a crystal is characterized by a phase factor , where is the reciprocal lattice vector of the operating reflection, and the lattice displacement due to the fault under consideration. Within the two-beam theory a planar fault with an integer value of is invisible, but a detectable contrast is expected when the many-beam dynamical effect is not negligibly small. A weak fringe contrast is also expected when differs slightly from an integer owing to an additional small displacement of the lattice across the fault. These faint contrasts are termed as many-beam contrasts in the former case, and as ε fringe contrasts in the latter. In the present work stacking faults in Cu-Al alloys and antiphase boundaries (APB) in CuZn, FeCo and Fe-Al alloys were observed under such conditions as mentioned above, and the results were compared with the image profiles of the faults calculated in the systematic ten-beam approximation.

Thermodynamics of stacking faults

The Gibbs treatment of interfacial free energy is reviewed and applied to the specific case of stacking faults in alloys. The alternative model of viewing the fault region as a second phase is briefly reviewed. Prior treatments of the topic using the later approach are shown to have led to thermodynamic inconsistencies in some cases. The relation between stacking fault energy and equilibrium separation of partial dislocations is established. The stress required to move partial dislocations or perfect dislocations in alloys is developed on the basis of a virtual displacement from equilibrium approach.

X-ray diffraction from hexagonal close-packed crystals with deformation stacking faults. I. Effect of solute segregation at faults in alloys

The Christian–Gevers theory of X-ray diffraction from homogeneous hexagonal close-packed (h.c.p.) crystals with deformation stacking faults is extended to include the effect of segregation of solute atoms at the faults. The results show that the breadths of reflexions remain unaffected by solute segregation. The ratios of integrated intensities of reflexions with H − K ≠ 0 mod 3, L = 1 mod 2 and L = 0 mod 2 respectively are affected, but only to a small extent, that is, within the limits of possible accuracy in experimental measurements of integrated intensity.