Methods for investigating thermal changes occuring during transformations in a solid solution

Abstract

When an alloy or metal undergoes a change in structure or allotropic modification during cooling, heat is evolved and by this means the temperature at which the change takes place can be obtained by well-known experimental methods. These methods are based on the fact that, when an alloy is cooled through a transition point, there is a change in the rate of cooling at that temperature. There are certain distinct types of transformations occurring in solid alloys and they may be classed in the following way: ( a ) transformations occurring at a definite temperature, such as, for example, a phase-change; ( b ) transformations occurring over a range in temperature, such as those due to the deposition of an additional phase from those already existing. During recent years another type of transformation has been shown to exist in pure binary alloys which at all temperatures below their melting points consist of a single homogeneous phase. This type of transformation consists merely of rearrangement of the atoms inside the solid solution. A considerable amount of evidence exists to show that such rearrangement of atoms takes place over a considerable range of temperature irrespective of the cooling rate.