Technology & Engineering
Grain Size Strengthening
Grain size strengthening refers to the phenomenon where the strength of a material increases as the grain size decreases. This occurs because smaller grains hinder the movement of dislocations within the material, making it more resistant to deformation. By refining the grain size through processes such as cold working or heat treatment, the material's strength and hardness can be enhanced.
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3 Key excerpts on "Grain Size Strengthening"
eBook - PDFMaterials Science and Engineering
An Introduction
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
Of course, they may be used in conjunction with one another; for example, a solid-solution strengthened alloy may also be strain hardened. It should also be noted that the strengthening effects due to grain size reduction and strain hardening can be eliminated or at least reduced by an elevated-temperature heat treatment (Sections 7.12 and 7.13). In contrast, solid-solution strengthening is unaf- fected by heat treatment. As we shall see in Chapters 10 and 11, techniques other than those just discussed may be used to improve the mechanical properties of some metal alloys. These alloys are multiphase and property alterations result from phase transformations, which are induced by specifically designed heat treatments. As outlined earlier in this chapter, plastically deforming a polycrystalline metal specimen at temperatures that are low relative to its absolute melting temperature produces microstruc- tural and property changes that include (1) a change in grain shape (Section 7.6), (2) strain hardening (Section 7.10), and (3) an increase in dislocation density (Section 7.3). Some frac- tion of the energy expended in deformation is stored in the metal as strain energy, which is associated with tensile, compressive, and shear zones around the newly created dislocations (Section 7.3). Furthermore, other properties, such as electrical conductivity (Section 18.8) and corrosion resistance, may be modified as a consequence of plastic deformation. These properties and structures may revert back to the precold-worked states by appropriate heat treatment (sometimes termed an annealing treatment). Such restora- tion results from two different processes that occur at elevated temperatures: recovery and recrystallization, which may be followed by grain growth.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
It should also be noted that the strengthening effects due to grain size reduction and strain hardening can be eliminated or at least reduced by an elevated-temperature heat treatment (Sections 8.12 and 8.13). In contrast, solid-solution strengthening is unaffected by heat treatment. As we shall see in Chapter 11, techniques other than those just discussed may be used to improve the mechanical properties of some metal alloys. These alloys are mul- tiphase and property alterations result from phase transformations, which are induced by specifically designed heat treatments. As outlined earlier in this chapter, plastically deforming a polycrystalline metal speci- men at temperatures that are low relative to its absolute melting temperature produces microstructural and property changes that include (1) a change in grain shape (Section 8.7), (2) strain hardening (Section 8.11), and (3) an increase in dislocation density (Section 8.4). Some fraction of the energy expended in deformation is stored in the metal as strain energy, which is associated with tensile, compressive, and shear zones around the newly created dislocations (Section 8.4). Furthermore, other properties, such as electrical conductivity (Section 12.8) and corrosion resistance, may be modified as a consequence of plastic deformation. These properties and structures may revert back to the pre–cold-worked states by appropriate heat treatment (sometimes termed an annealing treatment). Such restora- tion results from two different processes that occur at elevated temperatures: recovery and recrystallization, which may be followed by grain growth. Tutorial Video: What Is Annealing and What Does It Do? Recovery, Recrystallization, and Grain Growth During recovery, some of the stored internal strain energy is relieved by virtue of dis- location motion (in the absence of an externally applied stress), as a result of enhanced atomic diffusion at the elevated temperature.
eBook - PDFParticle Strengths
Extreme Value Distributions in Fracture
- Robert F. Cook(Author)
- 2023(Publication Date)
- Wiley-American Ceramic Society(Publisher)
The enhanced strengths associated with enhanced short crack toughness are also unlikely to to affect common particle mechanical performance. Small ceramic particles com- posed of very few grains are a possible exception. The effects of particle size on microstructurally controlled strength can be approached in several ways. At the simplest level of scaling is the expectation that large particles contain large grains and vice versa (e.g. mineral ore vs grinding media) and thus ∼ . The resulting strength behavior follows Figure 13.18 and thus ∼ −1∕2 . The next level of scaling is if the parameters ∗ and are known as a function of , for example as power laws as used earlier. The resulting strength behavior in this case follows Eq. (13.31) and deviations from Figure 13.18 occur, and perhaps initial crack length dependent behavior as in Figure 13.17. The most comprehensive level of scaling, within the analyses presented here, is to combine Eqs. (13.10) and (13.21) such that an additional crack driving force and the initial crack length depend on particle size. The full SIF based equilibrium expression for such a system is given by = ∗ ∕ 3∕2 + 2 ∕ 3∕2 + A 1∕2 = ∞ . (13.32) It is convenient to define a characteristic particle size that scales the microstructural effect by 2 = ∗ ∕ D . (13.33) Particle strength is then given by simple modification of Eq. (13.24) m = 3 4∕3 ∞ ∕4 4∕3 1∕3 ( 2 + 2 ) 1∕3 . (13.34) This is the same analysis used to describe microstructural effects in the strengths of indented extended components (Cook 2015), with particle size parameter 2 replacing indentation load . (Similarly, the same analysis was used to describe local tensile stress effects in Chapter 12 by ∕ 3∕2 .) For an identical strength response of impacted particles, Eq. (13.34) shows a shift to smaller particle sizes in the presence of microstructural effects.
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