Name the microstructural products of eutectoid iron carbon alloy

Chapters 9-10-11 – Homework To be discussed in class on 3/30/16

Bring a hardcopy of your solutions to class, and mark-up the solutions as described in the self- reflection template. Submit your self-reflection along with your marked-up solutions in class prior to RAA-4 (Quiz) on 4/1/16). 1. Consider the cooling of (a) pure lead, (b) the lead-tin eutectic alloy, and (c) the hypoeutectic Pb-

30at% Sn alloy. Sketch the cooling curves for these alloys as they are cooled from the liquid phase, showing how temperature changes with time and temperatures at which solidification starts and at which solidification is complete. Hint: Refer to Figure 9.8 and handout for Class on 3-14-16.

2. The solidus and liquidus temperatures for the germanium-silicon system.

a. Construct the phase diagram for this system and label each region. No hand sketches please.

b. For an alloy of composition 30 wt% Si, what are the compositions and amounts of phases present at 1200°C?

Composition (wt% Si) Solidus Temperature (°C) Liquidus Temperature (°C)

0 938 938 10 1005 1147 20 1065 1226 30 1123 1278 40 1178 1315 50 1232 1346 60 1282 1367 70 1326 1385 80 1359 1397 90 1390 1408

100 1414 1414 3. The NaCl-H2O phase diagram is shown below.

a. Using the NaCl-H2O phase diagram explain how spreading salt on ice at 0°C (32°F) causes the ice to melt.

b. What is the lowest temperature to which NaCl can be used to melt ice?

Note: Brine is a liquid solution of NaCl in water

4. Consider a 0.25 wt % C steel. (refer to Figures 9.24 and 9.29)

a. Upon cooling from the austenitic phase region of phase diagram, at what temperature will the first ferrite appear and what is its composition?

b. What temperature will the alloy completely transform to ferrite + cementite? c. What are the compositions and amounts of the phases present just above the eutectoid

temperature of 727°C d. How much (total) ferrite will be found in the microstructure at 400°C? e. How much ferrite was formed during the eutectoid transformation?

5. Is it possible to have a copper–nickel alloy that, at equilibrium, consists of a liquid phase of

composition 20 wt% Ni–80 wt% Cu and also an α phase of composition 37 wt% Ni–63 wt% Cu? If so, what will be the approximate temperature of the alloy? If this is not possible, explain why.

6. If homogeneous nucleation occurs at 900°C in copper (Tmp=1085°C) a. Calculate the critical radius size given that the latent heat of fusion is –1.77 × 109 J/m3 and

surface free energy is 0.200 J/m2. b. Knowing copper has an fcc structure with lattice constant of 0.3597 nm, estimate the

number of atoms in the nucleus 7. For a particular solid state transformation having kinetics that obey the Avrami equation (Equation

10.17), the parameter n is known to have a value of 1.7. If, after 100 s, the reaction is 50% complete, how long (total time) will it take the transformation to go to 99% completion?

8. Name the microstructural products of eutectoid iron–carbon alloy (0.76 wt% C) specimens that are first completely transformed to austenite, then cooled to room temperature at the following rates:

a. 200°C/s, b. 100°C/s, and c. 20°C/s.

9. Is it possible to produce an oil-quenched and tempered 4340 steel that has a minimum yield

strength of 1400 MPa and a ductility of at least 42%RA? If this is possible, describe the tempering heat treatment (tempering temperature and time). If it is not possible, explain why. (refer to Figure 10.34)

10. The surface of forging made from 4140 steel was unexpectedly subjected to a quench rate of 70°C/s (at 700°C). The forging is specified to have hardness between Rockwell Hardness (HR) C46 and C48. Is the forging within specifications? Briefly explain your answer. (refer to Figure 11.15)

11. It is desired to create a 2014-T4 aluminum alloy with yield strength of at least 350 MPa and

ductility of at least 12.5% EL. Assume the alloy is solution heat treated and quenched. Specify a precipitation heat treatment process involving time and temperature to obtain the desired properties. (refer to Figure 11.28)