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PHASES OF ALLOY

 A Phase is physically and chemically homogenous portion of matter. This is homogenous in the sense that its smallest adjacent parts are indistinguishable from one another. Each phase has its own atomic arrangement physical properties and chemical properties. A phase change accordingly , is accompanied by change in properties. 


                                                image of Ni alloy UNS N07725

It is therefore evident that solid solution, intermetallic compound and mechanical mixture that a solid alloy may contain are considered as different phases. 

All changes which take place in a system consisting of several phases, in accordance with thermal conditions such as temperature and pressure, conform to the so-called phase rule. The phase rule establishes the relationship between the number of degrees of freedom, the number of components and number of phases. It is expressed mathematically as follows :

P = C +2 - F

in which P is the number of phases, C is the number of components, F is the number of degrees of freedom in the system (The temperature, pressure and concentration).

The effects of pressure may be neglected in applying the phase rule. 

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