How to measure the amount of shear fracture in an impact test (ASTM A370 )

8.1 The ratio of diffusion rate of silver in silicon at 1350°C to that at 1100°C was found to be 8 in a doping process. Calculate the activation energy Q for silver diffusion in silicon.

 

8.2 The diffusion rate of A in B was studied at 500°C and 850°C. It was found that, for the same diffusion time, the depths of penetration x1 and x2 in the two experiments were in the ratio of 1 : 4. Calculate the activation energy for diffusion of A in B.

 

8.3 Amorphous selenium used as a semiconductor material exhibits unusual diffusion characteristics. The following is a set of experimental data for self-diffusion in amorphous selenium. Calculate D0 and Q and comment on your results. T, °C D, m2 s–1 35 7.7 10–16 40 2.4 10–15 46 3.2 10–14 56 3.2 10–13

 

8.4 At 900°C, what is the time required to carburize a steel with an initial composition of 0.2% carbon to 1% carbon at a depth of 0.2 mm? Assume a constant surface concentration of 1.4% carbon due to the carburizing atmosphere.

 

8.5 A 1.2% carbon steel is getting decarburized in an atmosphere of 0.0% carbon. After some time t, plot (i) c(x) curve near the surface of the steel, and (ii) J(x) curve below the above curve, using the same x-axis.

 

8.6 A diffusion couple of 95% Cu-5% Zn and pure copper is annealed at 900°C for 50 hr. The zinc concentration at a depth of 2 mm inside the copper bar was found to be 0.3% after the anneal. Determine the diffusion coefficient of zinc in copper.

 

8.7 In a steel, during carburization at 937°C, 0.6% carbon is found at a depth of 0.2 mm after 1 hr. Find the time required to achieve the same concentration at the same depth, if carburization is done at 1047°C.

 

8.8 Compare the diffusivities of hydrogen, nitrogen, and nickel in iron at 300 K and explain the difference between the three values.

 

8.9 Compute the rate at which a vacancy jumps in copper at 20°C. The activation barrier for the jump is 100 kJ mol–l.

 

8.10 An Al-4% Cu alloy is heated to 550°C during heat treatment and quenched to room temperature. Immediately after quench, the diffusion rate of Problems 197 copper (which proceeds by a vacancy mechanism) was found to be 107 times faster than what would be expected from the listed diffusion data. What fraction of vacancies in equilibrium at 550°C is retained at room temperature by the rapid quenching? The enthalpy of motion of vacancy in this alloy is 50 kJ mol–1.