A study of the structure of Lomer and 60° dislocations in aluminium using high-resolution transmission electron microscopy

Abstract The structure of asymmetric [110] tilt boundaries developed during creep of pure aluminium single crystals is studied using high-resolution electron microscopy. The small- and moderate-misorientation boundaries are composed of Lomer and 60° dislocations. Extensive image simulation is used to deduce the detailed core structures of these two dislocations. Comparisons with calculated elastic displacements indicate that the Lomer dislocation is not detectably dissociated in its (001) glide plane, or into the sessile Lomer-Cottrell configuration. The agreement between the observed atomic column positions and continuum elasticity is excellent, except for the innermost positions near the core of the Lomer dislocation. The core structure of these discrete Lomer dislocations also correlates well with previous atomistic calculations for a larger-misorientation Σ = 19 boundary. A similar analysis of the displacements around 60° dislocations using isotropic elasticity indicates a slight dissociation of about...

[1]  Pierre Stadelmann,et al.  EMS-A software package for electron diffraction analysis and HREM image simulation in materials science , 1987 .

[2]  H. Karnthaler,et al.  Finite Dislocation Elements in Finite Media. II. Trapezoidal Splitting of Partial Dislocations in Thin Foils , 1977 .

[3]  A. Argon,et al.  Climb of extended edge dislocations , 1981 .

[4]  M. Martínez-Hernández,et al.  Deformation mechanisms of Σ = 9 bicrystals of silicon , 1987 .

[5]  A. Korner,et al.  Asymmetrical equilibrium postions and line tensions of composite dislocations , 1979 .

[6]  J. Bonneville,et al.  Cross-slipping process and the stress-orientation dependence in pure copper , 1979 .

[7]  O. Krivanek.  A method for determining the coefficient of spherical aberration from a single electron micrograph , 1976 .

[8]  W. Hutchinson,et al.  On the Formation of Microbands During Plastic Straining of Metals , 1985 .

[9]  K. Urban.  Radiation‐induced processes in experiments carried out in‐situ in the high‐voltage electron microscope , 1979 .

[10]  A. N. Stroh.  LI. The strength of homer-cottrell sessile dislocations , 1956 .

[11]  A. Renault,et al.  Core structure of the Lomer dislocation in germanium and silicon , 1982 .

[12]  A. Bourret,et al.  The low-angle [011] tilt boundary in germanium II. Theoretical analysis of observed configurations and stability , 1979 .

[13]  E. Wintner,et al.  Non-parallel dissociation of dislocations in thin foils , 1975 .

[14]  S. Naka,et al.  High resolution determination of the core structure of 1/3⟨1120⟩ {1010} edge dislocation in titanium , 1983 .

[15]  M. Mills,et al.  THE STRUCTURE OF ASYMMETRICAL TILT BOUNDARIES FORMED DURING CREEP OF [112] ORIENTED ALUMINUM SINGLE CRYSTALS , 1988 .

[16]  A. Renault,et al.  Multi-beam lattice images from germanium oriented in (011) , 1977 .

[17]  E. Wintner,et al.  Weak beam Tem studies of composite dislocations in f.c.c. alloys , 1975 .

[18]  V. Vítek,et al.  Effect of Core Structure on the Determination of the Stacking-Fault Energy in Close-Packed Metals , 1974, October 1.

[19]  J. D. Eshelby,et al.  CXL. Dislocations in thin plates , 1951 .

[20]  H. Kirchner,et al.  Non-dissociation of Lomer-Cottrell dislocations and {001} slip in silicon , 1987 .

[21]  W. Lomer.  A dislocation reaction in the face-centred cubic lattice , 1951 .

[22]  C. Colliex,et al.  Combined HREM and STEM microanalysis on decorated dislocation cores , 1982 .

[23]  A. Cottrell.  LX. The formation of immobile dislocations during slip , 1952 .

[24]  J. Pénisson,et al.  High-resolution study of [011] low-angle tilt boundaries in aluminium , 1979 .

[25]  G. Chin,et al.  On the variation of wire texture with stacking fault energy in f.c.c. metals and alloys , 1965 .

[26]  Jens Lothe John Price Hirth,et al.  Theory of Dislocations , 1968 .

[27]  W. O. Saxton,et al.  The importance of beam alignment and crystal tilt in high resolution electron microscopy , 1983 .

[28]  J. M. Cowley,et al.  THE SCATTERING OF ELECTRONS BY ATOMS AND CRYSTALS. II. THE EFFECTS OF FINITE SOURCE SIZE , 1959 .

[29]  S. K. Maksimov,et al.  Comparison of split dislocation images obtained by the weak-beam method and lattice-resolution techniques , 1987 .

[30]  J. Martín,et al.  A study of (001) glide in [112] aluminium single crystals. II: Microscopic mechanism , 1987 .

[31]  J. Spence,et al.  Distinguishing dissociated glide and shuffle set dislocations by high resolution electron microscopy , 1981 .

[32]  J. Poirier,et al.  Glissement {110} 〈110〉 dans les metaux de structure cubique a faces centrees , 1973 .

[33]  Kazuo Ishizuka,et al.  Contrast transfer of crystal images in TEM , 1980 .

[34]  C. Davies,et al.  The effect of stacking fault energy on the plastic deformation of polycrystalline Ni-Co alloys , 1973 .