Crystal equiaxed

Equiaxed crystals growing from solution in mould centre... 

Solidification. When the ingot or casting solidifies, there are three main possible microstructures that form (see Figure 7.5). We will describe here only the final structures the thermodynamics of the liquid-solid phase transformation have been described previously in Chapter 2. The outside layer of the ingot is called the chill zone and consists of a thin layer of equiaxed crystals with random orientation. 

SEM micrographs of the surfaces of all the specimens (Zl, Z2, and Z3) exposed in SCW at 400 C under a pressure of 30 MPa for 100 h are shown in Figure 4.18. The microstructures of Zl and Z2 before corrosion are similar to Z3 therefore, we only show Z3 here. The microstructure of the specimen before corrosion showed dense surface with uniform equiaxed crystals. After corrosion, we can see that the surfaces of the specimens were oxidized considerably, and Zl looked more accidental than Z2 and Z3. The local magnification of the microstructure on the surfaces was very different from each other. After corrosion, on the surface of Zl, there were large numbers of white needle-like oxides of less than 1 pm in length. For Z2, except for many needle-like oxides, some rod-like crystals could also be seen. But belt-like crystals of less than 0.5 pm in width and several micrometers in length were observed for Z3. Although, the microstructure of the oxides was... 

Group Equant or equiaxed crystal habits (i.e., form similarly developed in all three directions) Crystal habit Equiaxed Fluorite Granular Olivine ... 

Due to the small width of chilled crystals zone, the usable properties of casting dejjend mainly on the width and length of the columnar crystals, the size of equiaxed crystals and content of theirs zone on section of ingot, as well as on interdendritic or interphase distance in grains such as eutectic or monotectic. For example, you can refer here to a well-known the Hall-Peth law describing the influence of grain size on yield strength (Fig.3) (Adamczyk, 2004) ... 

Fig. 20. The influence of current frequency (f) supplied to the induction coil on equiaxed crystals zone content (SKR) on transverse section of pure A1 ingot...

Based on conducted calculations of number of macro-grains in equiaxed crystals zone following formula was formulated ... 

Dendrite segregation 3. The dendrite segregation derives from the component difference of inside, the interdendrite and the dendrite bole of the usual equiaxed crystals or columnar crystals. 

It has been observed " that two structures of equiaxed and columnar (monoclinic) crystals exist in the oxide films of zircaloy-4. The columnar crystal was found to be composed of m-Zr02, while the equiaxed crystal was found to be... 

These characteristics of the dendritic structure in rare-earth-added steel will have an indirect effect on the pattern of occurrence of the inverted V segregate (Nuri et al. 1976, Suzuki and Miyamoto 1977, Iwata et al. 1976), the formation of a loose structure in the ingot, the macrosolidification structure, including the ratio of equiaxed crystals, and the central segregation in the continuously cast slab. They will also greatly affect the heat-treatment conditions and mechanical properties of the rolled products. 

Studies of metal analogue systems show quite clearly that the nuclei of the equiaxed crystals arise from a number of sources ... 

The evidence is that the columnar crystals will persist provided conditions are not favourable for the formation of equiaxed crystals. Because of this, control over the columnar growth is normally exerted by inducing the formation of equiaxed crystals. It is this control which is foremost in the control of the overall cast structure. 

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