Structure columnar zone

Figure 22.5 Classic grain structure of casting (or ingot) containing chill zone, columnar zone, and equiaxed zone. From Bower and Flemings [5].

FIGURE 6.31 Typical micro structure obtained during ingot casting (1) chiU zone, (2) columnar zone, (3) equaixed grain zone. Adapted from Bower and Flemings 1967 [12]. 

The structure of a CVD material can be classified into three major types which are shown schematically in Fig. 2.13. In Zone (A), the structure consists of columnar grains which are capped by a domelike top. In Zone (B), the structure is also columnar but more faceted and angular. In Zone (C), it consists of fine accost grains. Examples of these structures are shown in Fig. 2.14. " This is the CVD equivalent of the structural model for vacuum-evaporated films first introduced by Movchan and Demshishin.P l... 

As the substrate temperature increases, the surface mobility increases and the structural morphology first transforms to that of Zone T, ie, tighdy packed fibrous grains having weak grain boundaries, and then to a hill density columnar morphology corresponding to Zone 2 (see Fig. 7). 

Fig. 17. Structural diagram (51) for sputtered layers. Zone 1 is a porous structure consisting of tapered crystallites separated by voids. Zone 2 shows columnar grains, and Zone 3 has a recrystallized grain structure. Zone T is a transition structure consisting of densely packed fibrous grains.

This zone is characterised by high substrate temperatures at which both surface and grain boundary diffusion occur at significant levels. A homogeneous structure is obtained through the film thickness and is composed of columnar grains from the bottom to the top of the film. The grain boundaries are nearly perpendicular to the surface of the substrate. 

Summarize, was affirmed that application of common exogenous (electromagnetic field) and endogenous (Ti + B) inoculation strengthens effect of structure refinement in comparison with application of one type of inoculation, only if is used skinning of ingot surface i.e. machining in aim of columnar crystals zone elimination. 

The position of the transition was located by visual observation and optical microscopy. The distance from the chill zone of the sample was measured with a ruler. It is noted in Figure 1 that the CET is not sharp, showing an area where some equiaxed grains co-exist with columnar grains. As was reported before, the size of the transition area is in the order of up to 10 mm (Ares et al., 2007, 2010). The grain structure was inspected by visual observation under Arcano optical microscopy. 

Figure 3.23. Schematic representation of zone-casting process and AFM images of the resulting films of HBC-C12, showing details of the long-ranged order columnar structures with some defects (in circle). Reproduced by permission ofThe Royal...

Fig, 6.2 Possible casting structures (a) wholly columnar except for chill zone (b) partially columnar, partially equiaxed (c) wholly equiaxed Heine et al. ). 

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