Question

Briefly explain why, upon solidification, an alloy of eutectic composition forms a microstructure consisting of alternating layers of the two solid phases. What is this structure called? What kind of effect does this structure have on the melting point of the alloy and why? (5 points)

Answer 1

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proportions at a no Considering a mixture of elements A and B in their eutectic high enough temperature to make the mixture fully liquid- The mixline is slowly cooled undergoing change in state until it reaches T2 , whose it starts to solidify at any favorable nuclear siter. The alloy forms into alternate layers of diß. TPC) dil Lef 14-T2 L Ließ of C B Sites solid alloy where growing ocem This microstructure is known as lathellau microstructure As the alloy continues to cool, the existing nucleation will grow , adding atoa and ß to ß. these nucleating and growing regions of alloy will form grains. Grain boundarios grains which will be of differing orientation and from different nucleation files meet Further nucleation site will continue to form withirs the liquid parts of the mixture The entire mixture rapidly solifies into a eutectic solid From the phase diagram it can be seen that the composition of d, ß change with temperature

be seen that the has a is now solid. By considering tie lines and the phone diagrams, it B decreasing proportional of A in it as the temperature decreases. Similarly, the proportion of B in a decreases This means that even though the alloy the composition of the stripes of a and ß must continue to change it cools Atome diffuse the strepies to produce the equilibriuni at a given temperature f A,B will acros compositions of a , ß at a L Ltd ZIP f Teruperaline K LeB А. 1001. 3 1007. composition of B 2 f يد temperature overall of Eutectic deimperative the lowest possible melting overall of the mixing ratio's for the involved com porett species. Upon heating any other mixtures ration and reaching the Eutectic temperature, one component's lattice will melt first, while the temperature of the mixture has to further increase for the other for the other componente Conversely non entectic mixture cools down, each component ( mixture) will ai melt. lattice to solidify

(form its lattice) at a distinct temperature, until all material es soled.