Metals A and B of melting points 700 and 920oC, respectively, are mutually soluble in the liquid state but only partially soluble in the solid state. At 4000C the solubility of B in A is 14 wt%, and the solubility of A in B is 9 wt%; at room temperature the solubilities are 1 wt% and 0.1 wt%, respectively. Thermal analysis (from cooling curves) yields the following data:
Alloy Composition Liquidus Solidus
wt% B temp in oC temp in oC
10 640 500
20 572 400
40 435 400
50 450 400
70 660 400
90 840 400
95 880 650
a) Using the above data, use graph paper to construct a phase diagram. Label all phase regions, lines, and points. (Hint: remember to use the solubility data, too; Hint: think about how the curves will extrapolate, because your data is incomplete).
b) Estimate the eutectic composition (in wt%B). What are the compositions of the phases in the eutectic, just below the eutectic temperature?
c) Sketch the microstructures which form during slow cooling of an alloy containing 25%B from its liquid state to room temperature.
d) Sketch final microstructures for alloys of composition 5%B, the eutectic composition, and 60%B.