Dislocation facilitated formation and evolution of basal-prismatic/prismatic-basal interfaces in a Mg alloy

A three-dimensional compression analysis is performed by finite element method using a dislocation-based crystal plasticity model to clarify the formation mechanism of kink band in a polycrystalline Mg alloy with a long-period stacking ordered structure (LPSO) phase. The crystalline structure of LPSO phase is regarded as a HCP for simplicity, however, any deformation twinning is not taken into account. In addition, the activities of non-basal systems are considerably limited in the LPSO phase setting the values of their critical resolved shear stresses to large ones. We analyze a simple polycrystalline specimen composed of two α-Mg matrix phases and a LPSO phase both having a rectangular shape and twist grain boundaries are introduced into the interface. The obtained result shows that the kink band formation in the alloy is accomplished by the basal slips with different variants and the non-basal slips are activated on the grain boundary to maintain the continuity of deformation.

Download Full-text

AFM study of the dynamics of α-alumina surface faceting during high-temperature processing

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010013804x ◽

1995 ◽

Vol 53 ◽

pp. 334-335 ◽

Cited By ~ 1

Author(s):

Michael W. Bench ◽

Jason R. Heffelfinger ◽

C. Barry Carter

Keyword(s):

High Temperature ◽

Thin Foil ◽

Sem Analysis ◽

Conductive Coatings ◽

Force Microscopy ◽

Minimal Sample ◽

Atomic Force ◽

Formation And Evolution ◽

High Temperature Processing ◽

Nominal Surface

To gain a better understanding of the surface faceting that occurs in α-alumina during high temperature processing, atomic force microscopy (AFM) studies have been performed to follow the formation and evolution of the facets. AFM was chosen because it allows for analysis of topographical details down to the atomic level with minimal sample preparation. This is in contrast to SEM analysis, which typically requires the application of conductive coatings that can alter the surface between subsequent heat treatments. Similar experiments have been performed in the TEM; however, due to thin foil and hole edge effects the results may not be representative of the behavior of bulk surfaces.The AFM studies were performed on a Digital Instruments Nanoscope III using microfabricated Si3N4 cantilevers. All images were recorded in air with a nominal applied force of 10-15 nN. The alumina samples were prepared from pre-polished single crystals with (0001), , and nominal surface orientations.

Download Full-text

Lattice imaging of precipitates in Al-Zn-Mg alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100143651 ◽

1986 ◽

Vol 44 ◽

pp. 412-413

Author(s):

C. K. Wu

Keyword(s):

Grain Boundaries ◽

Homogeneous Nucleation ◽

Alloy System ◽

Mg Alloy ◽

List Type ◽

Lattice Structures ◽

Type Number ◽

Orientation Relationships ◽

Lattice Imaging ◽

The Matrix

The precipitation phenomenon in Al-Zn-Mg alloy is quite interesting and complicated and can be described in the following categories:(i) heterogeneous nucleation at grain boundaries;(ii) precipitate-free-zones (PFZ) adjacent to the grain boundaries;(iii) homogeneous nucleation of snherical G.P. zones, n' and n phases inside the grains. The spherical G.P. zones are coherent with the matrix, whereas the n' and n phases are incoherent. It is noticed that n' and n phases exhibit plate-like morpholoay with several orientation relationship with the matrix. The high resolution lattice imaging techninue of TEM is then applied to study precipitates in this alloy system. It reveals the characteristics of lattice structures of each phase and the orientation relationships with the matrix.

Download Full-text