Grain boundaries twins

Fig. 5.19 A helium field ion image of a tungsten tip electroplated with a thick layer of platinum. Many lattice defects such as grain boundaries, twin boundaries, vacancies and vacancy clusters can be seen. From the work of Rendulic ...

Two-dimensional area defects, such as stacking faults, grain boundaries, twin boundaries and contact areas with other phases. 

Stacking faults Grain boundaries Twin planes... 

Etching is performed in order to observe microstructural constituents, including grain boundaries, twin planes, slip lines, and second phase particles. In addition, etching can sometimes, as will be discussed later, reveal a material s propensity towards certain corrosion mechanisms. 

In this chapter the special features of surfaces and internal boundaries in single-phase crystalline systems are described. The orientation dependence of the surface functions will be discussed and the use of Wulff plots and stereographic triangles to present the orientation dependence of surface energy will be demonstrated. The various types of internal boundaries (grain boundaries, twin boundaries, etc.) and their thermodynamic properties will be discussed. 

A series of events can take place in response to the thermal stresses (/) plastic deformation of the ductile metal matrix (sHp, twinning, cavitation, grain boundary sliding, and/or migration) (2) cracking and failure of the brittle fiber (5) an adverse reaction at the interface and (4) failure of the fiber—matrix interface (17—20). 

On cooling to room temperature after annealing, maraging steels transform completely to martensite. The as-annealed structure consists of packets of parallel lath-like martensite platelets arranged within a network of prior-austenite grain boundaries. The platelets have a high dislocation density but are not twinned. 

Other methods for impeding dislocation motion are the introduction of grain boundaries, and/or twin boundaries. While these impediments may increase the hardness, they are also likely to decrease the tensile strength. 

The introduction to this chapter mentions that crystals often contain extended defects as well as point defects. The simplest linear defect is a dislocation where there is a fault in the arrangement of the atoms in a line through the crystal lattice. There are many different types of planar defects, most of which we are not able to discuss here either for reasons of space or of complexity, such as grain boundaries, which are of more relevance to materials scientists, and chemical twinning, which can contain unit cells mirrored about the twin plane through the crystal. However,... 

The lattice defects are classified as (i) point defects, such as vacancies, interstitial atoms, substitutional impurity atoms, and interstitial impurity atoms, (ii) line defects, such as edge, screw, and mixed dislocations, and (iii) planar defects, such as stacking faults, twin planes, and grain boundaries. 

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