Title: Summary Part Annealing

Choose the correct statement.

- The homologous temperature is the ratio of the temperature over the melting temperature of a material, T/Tm, both on the absolute temperature scale. (correct)
- The homologous temperature is the ratio of the temperature over the melting temperature of a material, T/Tm, both on the Celsius temperature scale.
- The homologous temperature is the ratio of the melting temperature of a material over the temperature, Tm/T, both on the absolute temperature scale.

- The temperature at which atomic mobility is suffcient to induce significang diffusion of atoms and hence affect mechanical properties via changes of the microstructure is approximately 0.3 – 0.5 times the homologous temperature. (correct)
- The temperature at which atomic mobility is suffcient to induce significang diffusion of atoms and hence affect mechanical properties via changes of the microstructure is approximately > 0.6 times the homologous temperature.

- Annealing is a heat treatment that reduces hardness and increases ductility in cold-worked alloys. (correct)
- Annealing is a heat treatment that reduces ductility and strength in cold-worked alloys.

- Cold working involves the mechanical deformation of an alloy at a relatively low temperature (below 0.3 T/Tm). (correct)
- Cold working involves the mechanical deformation of an alloy at any temperature.

- Recovery results in a slight reduction in hardness due to a reduction of point defects as a result of the increased atomic mobility at elevated temperatures. (correct)
- Recovery results in a slight reduction in hardness due to grain growth as a result of the increased atomic mobility at elevated temperatures.

- At slightly higher temperatures than those necessary for recovery, a more dramatic reduction in hardness occurs due to recrystallization. The entire cold-worked microstructure is transformed to a set of small, stress-free grains. (correct)
- At slightly higher temperatures than those necessary for recovery, a more dramatic reduction in hardness occurs due to recrystallization. The entire cold-worked microstructure undergoas significant grain growth.

- Grain size d has a major effect on the mechanical properties of (pure) metals. The Hall-Petch relation says that the yield stress is proportional to d^(-1/2). Hence, smaller grains result in an increased strength (but reduced ductility). (correct)
- Grain size d has a major effect on the mechanical properties of (pure) metals. The Hall-Petch relation says that the yield stress is proportional to d^(1/2). Hence, larger grains result in an increased strength (but reduced ductility).
- Grain size d has a major effect on the mechanical properties of (pure) metals. The Hall-Petch relation says that the yield stress is proportional to d^(-1/2). Hence, smaller grains result in an increased strength (but reduced hardness).