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Chapter 7: Problem 36

(a) What is the driving force for recrystallization? (b) For grain growth?

Short Answer

Expert verified
Answer: The main driving force for recrystallization is the reduction of stored energy within the material, while the driving force for grain growth is the minimization of energy associated with grain boundaries. Recrystallization replaces distorted crystals with strain-free ones, and grain growth increases the size of the grains to reduce the number of grain boundaries. Both processes aim to improve the material's properties by minimizing energy.

Step by step solution

01

Define recrystallization

Recrystallization is a process in which deformed, strained, or work-hardened crystals in a material are replaced by new, equiaxed, strain-free crystals. It occurs in materials like metals and ceramics, which have been subjected to mechanical deformation, temperature changes, or other factors that lead to an increase in stored energy within the material.
02

Explain the driving force for recrystallization

The driving force for recrystallization is the reduction of stored energy within the material. During deformation and other processes, the material's crystal structure becomes distorted, and the internal energy increases. Recrystallization allows the material to reduce its stored energy by forming new, strain-free crystals that replace the deformed ones. This results in improved material properties, such as reduced hardness, higher ductility, and better thermal stability.
03

Define grain growth

Grain growth is a process in which the size of the grains or crystals within a material increases over time. It typically occurs after recrystallization has taken place when the new strain-free crystals start to grow larger while consuming adjacent smaller grains. This process leads to a reduction in the number of grain boundaries, which influences the material's mechanical, electrical, and thermal properties.
04

Explain the driving force for grain growth

The driving force for grain growth is the minimization of energy associated with grain boundaries. Grain boundaries represent regions in the material where the crystal lattice is disrupted, leading to a higher energy state compared to regions within the grains. By consuming adjacent smaller grains and increasing their size, the grains effectively reduce the total grain boundary area and, subsequently, the material's overall energy. This results in improved properties such as increased strength and thermal stability.
05

Summarize the main driving forces for recrystallization and grain growth

In conclusion, the main driving force for recrystallization is the reduction of stored energy within the material, whereas the driving force for grain growth is the minimization of energy associated with grain boundaries. Both processes aim to improve the material's properties by minimizing energy, but they focus on different aspects of the material's internal structure: recrystallization focuses on replacing distorted crystals with strain-free ones, while grain growth focuses on increasing the size of the grains, thereby reducing the number of grain boundaries.

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Most popular questions from this chapter

(a) Define a slip system. (b) Do all metals have the same slip system? Why or why not?

List four major differences between deformation by twinning and deformation by slip relative to mechanism, conditions of occurrence, and final result.

Experimentally, it has been observed for \(\sin -\) gle crystals of a number of metals that the critical resolved shear stress \(\tau_{\mathrm{crss}}\) is a function of the dislocation density \(\rho_{D}\) as \\[\tau_{\mathrm{crss}}=\tau_{0}+A \sqrt{\rho_{D}}\\] where \(\tau_{0}\) and \(A\) are constants. For copper, the critical resolved shear stress is \(0.69 \mathrm{MPa}\) \((100 \mathrm{psi})\) at a dislocation density of \(10^{4} \mathrm{mm}^{-2}\) If it is known that the value of \(\tau_{0}\) for copper is 0.069 MPa \((10 \mathrm{psi}),\) compute the \(\tau_{\mathrm{crss}}\) at a dislocation density of \(10^{6} \mathrm{mm}^{-2}\)

Is it possible for two screw dislocations of opposite sign to annihilate each other? Explain your answer.

Two previously undeformed specimens of the same metal are to be plastically deformed by reducing their cross-sectional areas. One has a circular cross section, and the other is rectangular; during deformation the circular cross section is to remain circular, and the rectangular is to remain as such. Their original and deformed dimensions are as follows: $$\begin{array}{lcc} \hline & \begin{array}{c} \text {Circular} \\ \text {(diameter, } \mathbf{m m} \text { ) } \end{array} & \begin{array}{c} \text {Rectangular} \\ (\mathbf{m m}) \end{array} \\ \hline \text { Original dimensions } & 18.0 & 20 \times 50 \\ \text { Deformed dimensions } & 15.9 & 13.7 \times 55.1 \\ \hline \end{array}$$ Which of these specimens will be the hardest after plastic deformation, and why?
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