Experimental Methods of Studying Alloys

These compounds and the pure elements form a series of eutectics for example, the alloy containing 25 weight percent strontium is the eutectic mixture of Ag.-,Sr and Ag.-,Sr..  

Some other binary systems are far more complicated than this one. As many as a dozen different phases may be present, and these phases may involve variation in composition, resulting from the formation of solid solutions. Ternary alloys (formed from three components) and alloys involving four or more components are of course still more complex. 

These techniques for studying phase transitions, although powerful, are time-consuming and difficult. A simple and easily applied technique, called thermal analysis, has been used for more than a century. Phase transitions are characterized by the absorption or emission of a heat of transition. The way in which the heat of transition is involved in the technique of thermal analysis can be illustrated by discussion of a simple experiment. 

Cooling curves for samples of arsenic-lead alloys. 

The next curve, for the alloy with 80 atomic percent lead, shows a lower temperature at which crystallization of arsenic begins (that is, a lower liquidus temperature) and then a longer horizontal section, representing crystallization of a larger amount of the eutectic mixture of the two crystalline phases. 

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