7. The tensile strength of polycrystalline spinel can be approximated using the Hall- Petch relation. If the spinel has a grain size of 5 µm, its tensile strength is 200 GPa. For a grain size of 200...

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Extracted text: 7. The tensile strength of polycrystalline spinel can be approximated using the Hall- Petch relation. If the spinel has a grain size of 5 µm, its tensile strength is 200 GPa. For a grain size of 200 um, the tensile strength decreases to 170 GPa. (a) Determine the Hall-Petch constants (b) Determine the tensile strength if the grain size increases to 250 µm (c) Will the tensile strength from part (b) be higher or lower compared to the tensile strength for grain sizes of 200 um? Explain your answer