Question 10.10: Design of a Melting Procedure for a Casting You need to prod......

From Figure 10-13, we determine the required composition of the alloy. To meet the required yield strength, the alloy must contain between 40 and 90% Ni; for the tensile strength, 40 to 88% Ni is required. The required % elongation can be obtained for alloys containing less than 60% Ni or more than 90% Ni. To satisfy all of these conditions, we could use Cu-40% to 60% Ni.
We prefer to select a low nickel content, since nickel is more expensive than copper. In addition, the lower nickel alloys have a lower liquidus, permitting castings to be made with less energy. Therefore, a reasonable alloy is Cu-40% Ni.
To produce this composition from the available melting stock, we must blend some of the pure nickel with the Cu-20% Ni ingot. Assume we wish to produce 10 kg of the alloy. Let x be the mass of Cu-20% Ni alloy we will need. The mass of pure nickel needed will be 10 – x. Since the final alloy consists of 40% Ni, the total mass of nickel needed will be

Now let’s write a mass balance for nickel. The sum of the nickel from the Cu-20% Ni alloy and the pure nickel must be equal to the total nickel in the Cu-40% Ni alloy being produced:

0.2x + 10 – x = 4
6 = 0.8x
x = 7.5 kg
Therefore, we need to melt 7.5 kg of Cu-20% Ni with 2.5 kg of pure nickel to produce the required alloy. We would then heat the alloy above the liquidus temperature, which is 1280 °C for the Cu-40% Ni alloy, before pouring the liquid metal into the appropriate mold.
We need to conduct such calculations for many practical situations dealing with the processing of alloys because when we make them, we typically use new and recycled materials.