(Model answers will be posted shortly after the due date.)

Question 4.2

Calculate the number of vacancies per cubic metre in gold at 900 C. The energy for vacancy formation is 0.98 eV/atom. Furthermore, the density and atomic weight for gold are 19320 kg/cubic metre and 196.9 gm/mol respectively.

Question 4.7

What is the composition, in atom percent, of an alloy that consists of 92.5% silver and 7.5% copper, by weight?

Question 4.21

Gold forms a substitutional solid solution with silver. Compute the weight percent of gold that must be added to silver to yield an alloy that contains 5.5 x 10²¹ gold atoms per cubic centimeter. (The densities of pure gold and silver are 19320 and 10490 kg/cubic metre respectively.)

Question 4.24

Cite the relative Burgers vector dislocation line for edge, screw, and mixed dislocations.

Question 5.7

A sheet of metal 1.5 mm thick has nitrogen atmospheres on both sides at 1200 C, and is permitted to achieve a steady-state diffusion condition. The diffusion coefficient for nitrogen in steel at this temperature is 6 x 10^-11 m²/s, and the diffusion flux is found to be 1.2x10^-7 kg/m²-s. Also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m³. How far into the sheet from this high-pressure side will the concentration be 2 kg/m³? (Assume a linear concentration profile.)

Question 5.13

Nitrogen from a gaseous phase is to be diffused into pure iron at 700 C. If the surface concentration is to be maintained at 0.1 wt% N, what will be the concentration 1 mm from the surface after 10 h? THe diffusion coefficient for nitrogen in iron at 700 C is 2.5 x 10^-11 m²/s.

Question 5.31

An FCC iron-carbon alloy initially containing 0.1wt% carbon is carburised at an elevated temperature and in an atmosphere in which the surface carbon concentration is maintained at 1.1 wt%. If after 48 hours the concentration of carbon is 0.3 wt% at a position 3.5 mm below the surfce, determine the temperature at which the treatment was carried out.