Question 23:

(a) Consider a diffusion couple that is made by joining a bar of 1010 steel to a bar of 1040 steel and annealed at a temperature in the single phase y region.

(a-1) Write an expression to describe C(x,t) during interdiffusion in this couple.

(a-2)Which way would markers placed at the original interface move? (Note: D_c >D_Fe)

(b) A pure iron sample is carburized at 915C under conditions that maintain a 1.0 wt.% surface carbon composition. After 30 minutes the carbon level at a point 0.1 mm into the iron is 0.5 wt.%. How long would it take to reach 0.5 wt.%C at 0.1 mm if the temperature were 1150C where the diffusivity is 20 times that at 915C. The surface carbon concentration at 1150C is 1.0 wt.%.