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Material Type: Exam; Professor: Kim; Class: PHASE TRANSFORMATIONS IN MATERIAL PROCESSING; Subject: Materials Engineering; University: Auburn University - Main Campus; Term: Spring 2010;
Typology: Exams
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held at a temperature of 1400 K in the γ single-phase field and homogenized. These alloys are then instantaneously quenched to a temperature T = 1100 K and allowed to isothermally transform. Consider the growth of precipitates from γ at the 1100 K transformation temperature for each case. Answer the following questions:
(a) Draw the schematic composition profiles for both cases (n and o). Label axes and compositions properly, and determine carbon flux for both cases in the plot. Assume that carbon is moved by bulk diffusion and local equilibrium of the precipitate/matrix interface is obtained.
(b) Draw the schematic composition profiles for both cases (n and o) if the precipitation of a new phase from γ-matrix is not diffusion controlled but interface controlled, i.e. diffusion across the precipitate/matrix interface is very fast.
(c) Assuming the equilibrium condition at 1100 K is reached, fill out the types of equilibrium
(c) Estimate an approximate value for the flux of carbon through the sheet if the thickness is 2 mm (0.8 wt% C = 60 kgm -3^ at 1000 oC)
jump per sec at 500 oC. A technician working for you makes a measurement of the diffusion of A in B at 500 oC. After 100 minutes he finds A has diffused into B a distance of 0.21 cm.
(a) Has your technician made a mistake? Prove why or why not. Be numerical in your explanation!!
(b) What assumptions have you made in your calculations above.