1. Describe the substitutional interstitial diffusion mechanisms in solid metals. 2. What factors affect the diffusion rate in solid metal crystals?

1. Describe the substitutional interstitial diffusion mechanisms in solid metals.

2. What factors affect the diffusion rate in solid metal crystals? 

3. Write the equation for the solution to Fick’s second law for the diffusion of a gas into the surface of a solid metal crystal lattice.

4. The surface of a steel gear made of 1022 steel (0.22 wt % C) is to be gascarburized at 927ºC (1700ºF). Calculate the time necessary to increase the carbon content to 0.30 wt % at 0.030 in. below the surface of the gear.  Assume the carbon content of the surface to be 1.20 wt %. D (C in λ iron) at 927ºC = 1.28 × 10 –11 m2/s.

5. A gear made of 1020 steel (0.20 wt % C) is to be gas-carburized at 927ºC (1700ºF). Calculate the carbon content at 0.90 mm below the surface of the gear after a 4.0-hour carburizing time. Assume the carbon content at the surface of the gear is 1.00 wt %. D (C in λ iron) at 927ºC = 1.28 × 10 –11 m2/s.

6. A gear made of 1018 steel (0.18 wt % C) is to be gas-carburized at 927ºC (1700ºF). If the carburizing time is 7.5 h, at what depth in millimeters will the carbon content be 0.40 wt %? Assume the carbon content at the surface of the gear is 1.20 wt %. D (C in λ iron) at 927ºC = 1.28 × 10 –11 m2/s.