Casting conditions

Although the pure metal has a silvery-white color, in the cast condition it may have a yellowish tinge caused by a thin film of protective oxide on the surface. When highly poHshed, it has high light reflectivity. It retains its brightness well during exposure, both outdoors and indoors. 

Heat resistance and gas corrosion resistance depends on chemical, phase compositions and stmcture of an alloy. The local corrosion destmction (LCD) of heat resisting alloys (HRS), especially a cast condition, probably, is determined by sweat of alloying elements. 

Gunmetals are alloys of copper, tin and zinc, with or without lead, used in the cast condition. Commonly used alloys are (a) 10Sn-2Zn, and b) 5Sn-5Zn-5Pb. 

Figure II. Effect of film casting conditions on the performance of resulting (a) cellulose acetate (12) and (h) aromatic polyamide-hydrazide membranes. The latter data are tho.se of O. Kutowy and S. Sourirafan (not yet published).

The crysts of TNT in cast expls may vary from microscopic size to a substantial fraction of the size of the charge, depending upon casting conditions and procedure. The approach known as cream casting results in very fine crysts. In mixed expls, which usually are cast in the form of slurries, the solid particles tend to inhibit cryst growth, although TNT crysts sometimes apparently grow around the particles of the slurry. The effects of particle size on initiation sensitivity, failure diameter, and performance characteristics also have been observed to apply to crystal size in cast TNT... 

As a reasonable approximation, the dendritic structure may be represented by the diagram in Fig. 22.4. The solidification in the interdendritic space can be described by constructing the cell (shown dashed) and assuming that solidification proceeds in a manner similar to the plane-front solidification of a bar (as discussed in Section 22.1). Under typical casting conditions, kf k. Therefore, the segregation... 

This so-called "active" layer has characteristics similar to those of cellulose acetate films but with a thickness of the order of 0.1 micrometer (jjm) or less, whereas the total membrane thickness may range from approximately 75 to 125 ym (see Figure 1). The major portion of the membrane is an open-pore sponge-like support structure through which the gases flow without restriction. The permeability and selectivity characteristics of these asymmetric membranes are functions of casting solution composition, film casting conditions and post-treatment, and are relatively independent of total membrane thickness. 

Table III. Properties of Selected Room Temperature Hydrides (2 ) (Based on 10 Atm-1 Atm Desorption at 25°C, As-Cast Condition)...

Copper alloys such as the brasses and bronzes can be cast by either the sand-casting or permanent mould cast methods. The alloys casts in permanent mould condition have greater corrosion resistance than the sand-cast alloys.52 This difference has been attributed to the greater porosity of the alloys in sand-cast conditions. 

The alloy Mar-M-509 has complicated microstructure and contains both M23C6 and MC carbides in the as-cast condition due to the addition of tantalum to the alloy. These carbides provide additional strength. 

Under conventional casting conditions (without ultrasonic cavitation), the supercooling of a melt arising at the solidification front can spread into the liquid metal with a simultaneously decrease of the degree of supercooling. This process is due to convective streams and, particularly, due to forced movement of the melt with electromagnetic or mechanical stirring. 

A second effect of the wet zone in the support is that the drying rate of a supported lyogel film is considerably smaller than that of a unsupported film of comparable thickness. Because the depth of the wetted zone varies, depending on slip cast conditions, the drying rates exhibit some uncertainty even when all external drying conditions are controlled. 

Barrier layers have been applied by all of the above methods on microporous support film with a fibrous backing (as illustrated in Figure 1), or on microporous hollow fibers. Normally, except for Method C in Table I (gas-phase deposition), the support film is used in the wet "as cast" condition for applying the reagents to form the barrier layer. The final step of preparation, drying of the membrane, frequently aids in bonding the barrier layer to the support film. 

The typical dependence of mechanical properties of Ti-Si binary alloys in as-cast and as-deformed states is shown in Fig. 3. It is seen that in as-cast state room temperature plasticity decreases with increase of silicon content, reducing practically to zero at silicon content of 2-3 wt. % then it raises a little at eutectic formation. Unfortunately, our attempts to increase room temperature plasticity in as-cast condition more or less substantially via employing various kinds of heat treatment procedures were not successful. At the same time, using thermo-mechanical treatment (forging at temperature 1050 °C), it was possible to increase plasticity of deformed alloys essentially. 

Positive influence of scandium has a complex character. Thus, the additions of Sc not only increase the yield stress and the ultimate tensile strength, but improve also the workability of alloy and its production ductility, decrease the grain size in as-cast condition, eliminate the dendrite structure and lead to the formation of a fine-grained equiaxial structure, sharply increase the recrystallization temperature (Tab.2), improve metal weldability and raise its corrosion resistance. 

---