The constitution point for a Sn60 at Pb alloy at 250 degree

The constitution point for a Sn-60 at% Pb alloy at 250 degree C lies in a two-phase field. Construct a tie line on the Figure and read off the two phases and their compositions. The phases are The composition of phase 1 is The composition of phase 2 is The alloy is slowly cooled to 200 degree C. At 200 degree C: The phases are The composition of phase 1 is The composition of phase 2 is The alloy is cooled further to 150 degree C. At this temperature: The phases are The composition of phase 1 is The composition of phase 2 is Indicate with arrows on the figure the lines along which: The composition of phase 1 moves The composition of phase 2 moves The overall composition of the alloy stays the same, of course. How can the compositions of the phases change?

Solution

Since the diagram couldnot be copied and pasted in the answer I shall tell how to do the problem

a) Draw a line parallel to x axis through 250 degree C it cuts the raph at two places, they are 53% and 79%

b) repeat the same at 200 degreeC and read the graph.34 % and 73%

c) at 150 degree C (Sn + Pb) is at 1% and 84%

d) for 150 degree C the movement of phase 1 is it starts at zero traces the curve upto 150 degree and moves parallel to x axis.

the phase 2 starts at the intersection of 150 degree line and traces down the curve line given.

the composition remains the same but the states aare different.

The Sn solidifies first and later only the Pb solidifies marked by the solidifying line.