A novel solidification technique of metals and alloys: Under the influence of applied potential
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Fig. 2 - - A [001] diffraction pattern of an as-quenched Cu85Tij~ alloy. Note that the SRO reflections are present and some oxide reflections. No LRO reflections are observed.
section, the Dla reflections appeared. Thus, the Cu85Ti15 alloy orders before the spinodal decomposition process begins, in a similar way as the Fe-A1 alloy and as the solid solution models predict. In the present case, however, the ordering process that occurs prior to the decomposition is different from the ordering process which occurs concomitant with it. Using the terminology of de Fontaine ~5the later process can be called "spinodal ordering." Accepting Biehl and Wagner's interpretation of the LRO reaction and spinodal decomposition we have the following sequence of reactions in Cu-Ti alloys: a --~ a ' ( S R O )
Reaction [1]
a ' ( S R O ) --~ a + D l a
Reaction [2]
where a ' (SRO) is the short range order state, a is the disordered fcc Cu alloy, and Dla is the LRO ordered Tienriched phase. Reaction [1] is the spinodal ordering reaction; Reaction [2] is the concomitant decomposition and LRO reaction reported and described by Biehl and Wagner. 7,8 In summary, we have demonstrated that a supersaturated Cu-Ti solid solution decomposes after the spinodal ordering reaction. We were able to do this because of the high rate of quenching made possible by the melt spinning technique. The decomposition process in Cu-Ti is thus similar to other binary alloys that both order and decompose. Furthermore, the Cu-Ti alloy is similar to the Ni-Mo alloy in which a {1 89 SRO solid solution is also obtained prior to the formation of the LRO Dla phase. ~6
A Novel Solidification Technique of Metals and Alloys: Under the Influence of Applied Potential ASOKA K. MISRA A technique has been devised by which liquid alloys are cooled under direct electrical potential to bring changes in the normal process of nucleation and growth of equilibrium phases. Earlier Vashchenko et al.l have used electric current (d.c.) through the sand mold (one electrode was the mold frame and the other was the casting itself) to effect changes in the as-cast structures of cast irons. However, the effect of the hydrogen concentration change I in the melt due to the hydrogen evolution by the passage of current in the moist mold could not be ruled out. The present experiments were carried out with low melting Pb-15 pct Sb-7 pct Sn (monotype metal) alloy in glass tubes of 5 mm diameter and 100 mm long with electrodes on both ends of the tube in direct contact with the melt. Thus, the applied potential is entirely responsible for the observed modification of the structure. The glass tube assembly with the alloy in it was melted in a vertical resistance furnace, heated to a temperature about 50 ~ above the melting point, and then furnace cooled (with the natural furnace cooling rate of few degrees a minute) while direct current (30 to 40 mA/cm 2 at about 30 V) was passed through the melt until the completion of solidification. In the same furnace, another sample was also solidified under
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