Equiaxed grains

Why is it undesirable to have a columnar grain structure in castings Why is a fine equiaxed grain structure the most desirable option What factors determine the extent to which the grain structure is columnar or equiaxed ... 

It is often convenient to express the growth law given by Eq. 15.39 in terms of a linear grain-size dimension. If f rms is the effective root-mean-square radius of the roughly equiaxed grains,... 

There are relatively few direct transmission, electron microscopy (TEM) studies of domain structures in polyurethanes (3-7,13,14,15). No distinct micelle-lamellae platelets have been observed in the urethane systems thus studied. Instead, the domain structures which have been observed generally appear as isolated equiaxed grains 30-500 A in diameter (4,13,14,15). Randomly oriented fibrils with lateral dimensions of 300-600 A have been observed in a polyether/MDI/BDO system (3,6). It remains to be seen what relation the equiaxed grains (domains) and the fibrils observed by transmission electron microscopy have with the micelle-lamellae structures inferred from WAXS and SAXS (12,16). 

Figure 7.69 Micrograph away from the fracture surface, showing equiaxed grains...

Fig. 26. Microstructure of ALON. (a) Small equiaxed-grain, pore-free structure, (b) Stacking fault type defect found occasionally within grains.

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