Question

Powder Metallurgy

Question 6. Calculate the average molecular weight Mm for a thermoplastic that has the following weight fractions fi for the molecular weight ranges listed:(5 points)

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### Question 22419

Powder Metallurgy

Question 8. Using Pauling's equation (in Chapter 2), compare the percent covalent character of the following compounds: hafnium carbide (HfC), titanium carbide (TiC), tantalum carbide (TaC), boron carbide (BC), and silicon carbide (SiC).(5 points)

### Question 22418

Powder Metallurgy

Question 7. The nose cap and the wing leading edges of the space shuttle may reach temperatures of up to1650°C. (a) Would the silica fiber compound (HRSI) be a suitable candidate for these sections of the shuttle?(b) If not, select a suitable material for this location. (c) List the important properties of the selected material that satisfy the design needs.(5 points)

### Question 22417

Powder Metallurgy

Question 6. Calculate the average molecular weight Mm for a thermoplastic that has the following weight fractions fi for the molecular weight ranges listed:(5 points)

### Question 22416

Powder Metallurgy

Question 5. A metal-matrix composite (MMC) is made of a 6061-Al alloy matrix and continuous boron fibers.The boron fibers are produced with a 15.5 um diameter tungsten-wire core that is coated with boron to make a final 107 um diameter fiber. A unidirectional composite is made with 63 vol % of the boron fibers in the Al6061 matrix. Assuming the law of mixtures applies to isostrain conditions, calculate the tensile modulus of the composite in the direction of the fibers. Data are EB = 370 GPa, Ew = 410 GPa, and EAI = 70.4 GPa. (5 points)

### Question 22415

Powder Metallurgy

Question 4. An austenitized 4340 standard steel bar is cooled at different rates (see Figure 2).Predict what will be the constituents in the microstructure of the bar at 200°C for the following cooling rates:(6 points)
(a) 5°C/s (51-mm from the quenched end of a Jominy bar)
(b) 8°C/s (19.0-mm from the quenched end of a Jominy bar)
(c) 50°C/s (9.5-mm from the quenched end of a Jominy bar)

### Question 22414

Powder Metallurgy

Question 3. Figure 1 illustrates the deformation mechanisms in polymers. (4 points)
(a) Which mechanism is dominant in the stretching of a rubber band?
(b) Which mechanism(s) represent plastic deformation?
(c) Which mechanism is pronounced in polyethylene above its glass transition temperature?
(d) Which mechanism is associated with the highest elastic modulus?

### Question 22413

Powder Metallurgy

Question 2. HFO2 has the CaF2 crystal structure. Calculate the density of HfO2 in kg/m³ if the ionic radii are Hf** = 0.083 nm and O2 =0.132 nm. (4 points)

### Question 22412

Powder Metallurgy

(a) Why is the Fe-Fe3C phase diagram a metastable phase diagram instead of a true equilibrium phase diagram? (1 points)
(b) Define the following phases that exist in the Fe-Fe3C phase diagram: (i) austenite, (ii) a ferrite, (iii)cementite, (iv) 8 ferrite. (2 points)
(c) Write the reactions for the three invariant reactions that take place in the Fe-Fe3C phase diagram. (3points)

### Question 2106

Powder Metallurgy

What is a fence?

### Question 2105

Powder Metallurgy

What is a miter?