For each of the original chemical compositions and temperatures at 1 atmosphere of pressure for the aluminum (Al)-nickel (Ni) alloys (see Figure 5.15) listed below, give the following:

Question

1. The phases present.

2. From the Gibbs phase rule, determine the degrees of freedom in the material. Can the composition of the phases or phases present be adjusted by changing the original chemical composition?

3. The chemical composition of each phase.

4. The atom fraction of each phase.

Answer 1

a.1 The point 95 atomic % Ni and 1200?C is in the single phase region of Ni. Ni in this phase diagram is the FCC Ni crystal structure with substitutional atoms of Al.

a.2 The GPR is P + F = C + 1, 1 + F = 2 + 1, F=2. The temperature and composition can be set for the single phase for F = 2.

a.3 In the single phase region of Ni, CNi = 0.950 atoms of Ni in Ni/total atoms. a.4 fNi = 1, or 100% of the atoms are in Ni.

b.1 80Ni-20Al and 1000?C is in the two phase region of Ni and AlNi3

In this phase diagram only the single phase regions are labeled. Areas between single phase regions will always be two phase regions made up of the two single phases on either side of the two phase region.

b.2 P = 2, therefore the GPR is 2 + F = 2 + 1 and F =1 and that one choice is temperature. There is no possible choice in composition.