Can someone help me with this extra credit homework?

Due by 10:00 a.m. Wednesday, December 10, 2014, or sooner (Late submissions not accepted unless provisions are made in advance)

Submissions must be a printed copy made in person by 10:00 a.m.

Points added to your Exam 2 score will be ½ the difference between 100 points and the points you earned on the exam times the percentage score you earn on this assignment. For example, if you scored 70 points on the exam, you can earn (100 – 70)/2 = 15 points if you get a perfect score on this assignment. If you score 80% on this assignment, you will earn 12 points. This assignment has a 30 total point basis. You must turn in the assignment by the due date or sooner as a paper document.

This is an open book, open note voluntary assignment to be completed by you alone . By signing below and submitting this assignment or by submitting by email you are certifying that this work is yours and yours alone and that you have not worked with anyone else in completing the assignment. If there is no signature, there will be no credit. If you email this assignment, you are attesting to this certification.

Signature ________________________________Print Name________________________

NOTE: Answers in greater depth than would be the case in a normal exam are expected for full credit!

1. Reproduced below are the isothermal transformation diagram for hypereutectoid steel containing 1.13% C (Fig. 11-49) and the Fe-C phase diagram. We have heated four separate samples of this hypereutectoid steel to 900oC and held them long enough to convert the steel to 100% austenite. (15 points total- you MUST show all work graphically to get full credit!!)

a. If we cool the first sample quickly to 750oC, hold for 1000 seconds, and assume that equilibrium is reached:

What phase(s) will be present? (1 points)

What will the composition of each phase be in wt. % C? (2 points)

How much of each phase will be present (in wt. %)? Show your calculations. (2 points)

b. If we then very rapidly quench this sample to room temperature, what microstructure and phases will be present? (2 points)

c. If we very rapidly cool a second sample from 900oC to 675oC, hold for one hour at that temperature, and then very rapidly quench to room temperature, what microstructure and phases will be present? (2 points)

d. If we very rapidly cool a third sample from 900oC to 400oC, hold for 20-25 seconds at that temperature, what microstructure and phases will be present at that instant of time? (2 points)

g. If we now rapidly cool this third sample to 300oC, what microstructure and phases will be present at that instant of time? (2 points)

h. If we now hold this sample at 300oC for three days, and then very rapidly quench to room temperature, what microstructure and phases will be present? (2 points)

2. Reproduced below is the aluminum-nickel phase diagram. The nickel-rich side of the diagram is the basis of nickel-based superalloys used in gas turbine engines (aircraft and utility gas turbines for electric power) for difficult applications such as turbine blades. The simplest alloys contain aluminum to allow the precipitation of Ni3Al, also called γ’ in the FCC nickel solid solution, called γ. Both γ and γ’ have FCC cyrstal lattices with virtually identical unit cell axes (within ~1% of each other). This allows precipitation of large amounts of γ’ in what is called coherent precipitation. Up to 70% γ’ can be formed if other alloying elements, such as titanium, are included. The result is an alloy with excellent high temperature strength and creep resistance. It is a lot more complicated than that, but this gives us the basis for an interesting assignment. (I could easily lecture for five or more hours on Ni-based superalloys and their use in gas turbine engines.)

It is still desirable to use a “classical” precipitation heat treatment, although cold working of turbines blades is uncommon. However, very careful control of the amounts of γ and γ’ is needed, and the microstructures must be tailored for maximum strength and creep resisitance in the high temperature environment that turbine blades experience. You must show your work graphically and show all calculations to receive full credit. (15 points total)

a. What is the maximum amount of aluminum that can be incorporated in a Ni-Al alloy and still carry out a classical precipitation strengthening heat treatment? (2 points)

b. If we select an alloy of 0.20 fraction aluminum, balance nickel, what temperature would you use for a solid solution heat treatment? (3 points)

c. If we were to do precipitation strengthening at 600oC on this alloy and then cool rapidly to room temperature, how much γ and γ’ would be present, and what would the composition of each of these phases be at equilibrium? (10 points)