Question 10.1: Design of an Aerospace Component Because magnesium is a low-......

Design of an Aerospace Component
Because magnesium is a low-density material ($\rho_{Mg}$ = 1.738 g/cm³), it has been suggested for use in an aerospace vehicle intended to enter outer space. Is this a good design?

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The pressure is very low in space. Even at relatively low temperatures, solid magnesium can begin to transform to a vapor, causing metal loss that could damage a space vehicle. In addition, solar radiation could cause the vehicle to heat, increasing the rate of magnesium loss.
A low-density material with a higher boiling point (and, therefore, lower vapor pressure at any given temperature) might be a better choice. At atmospheric pressure, aluminum boils at 2494 °C and beryllium boils at 2770 °C, compared with the boiling temperature of 1107 °C for magnesium. Although aluminum and beryllium are somewhat denser than magnesium, either might be a better choice. Given the toxic effects of Be and many of its compounds when in powder form, we may want to consider aluminum first.
There are other factors to consider. In load-bearing applications, we should not only look for density but also for relative strength. Therefore, the ratio of Young’s modulus to density or yield strength to density could be a better parameter to compare different materials. In this comparison, we will have to be aware that yield strength, for example, depends strongly on microstructure and that the strength of aluminum can be enhanced using aluminum alloys, while keeping the density about the same. Other factors such as oxidation during reentry into Earth’s atmosphere may be applicable and will also have to be considered.

Question: 10.11

Nonequilibrium Solidification of Cu-Ni Alloys Calculate the composition and amount of each phase in a Cu-40% Ni alloy that is present under the nonequilibrium conditions shown in Figure 10-16 at 1300 °C, 1280 °C, 1260 °C, 1240 °C, 1200 °C, and 1150 °C. Compare with the equilibrium compositions and ...

We use the tie line to the equilibrium solidus tem...
Question: 10.10

Design of a Melting Procedure for a Casting You need to produce a Cu-Ni alloy having a minimum yield strength of 20,000 psi, a minimum tensile strength of 60,000 psi, and a minimum % elongation of 20%. You have in your inventory a Cu-20% Ni alloy and pure nickel. Design a method for producing ...

From Figure 10-13, we determine the required compo...
Question: 10.9

Solidification of a Cu-40% Ni Alloy Determine the amount of each phase in the Cu-40% Ni alloy shown in Figure 10-11 at 1300 °C, 1270 °C, 1250 °C, and 1200 °C. ...

● 1300 °C: There is only one phase, so 100% L. ● 1...
Question: 10.8

Application of the Lever Rule Calculate the amounts of α and L at 1250 °C in the Cu-40% Ni alloy shown in Figure 10-12. ...

Let’s say that x = mass fraction of the alloy that...
Question: 10.7

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The vertical line at 40% Ni represents the overall...
Question: 10.5

Design of a Composite Material One method to improve the fracture toughness of a ceramic material (Chapter 7) is to reinforce the ceramic matrix with ceramic fibers. A materials designer has suggested that Al2O3 could be reinforced with 25% Cr2O3 fibers, which would interfere with the propagation ...

Since the composite will operate at high temperatu...
Question: 10.6

Gibbs Rule for an Isomorphous Phase Diagram Determine the degrees of freedom in a Cu-40% Ni alloy at (a) 1300 °C, (b) 1250 °C, and (c) 1200 °C. Use Figure 10-8(a). ...

This is a binary system (C = 2). The two component...
Question: 10.4

NiO-MgO Isomorphous System From the phase diagram for the NiO-MgO binary system [Figure 10-8(b)], describe a composition that can melt at 2600 °C but will not melt when placed into service at 2300 °C. ...

The material must have a liquidus temperature belo...
Question: 10.3