Lecture32-Notes - ME 382 Lecture 32 DEFORMATION MECHANISM...

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ME 382 Lecture 32 1 D EFORMATION MECHANISM MAPS For steady-state creep (ignores microstructural changes, cavitation and elasticity) Different mechanisms can operate simultaneously Fastest mechanism will dominate Depends on temperature, stress and grain size Deformation-mechanism map Dominant mechanisms for stress & temperature Includes lines of constant strain rate Note on this map: “High-temperature” power-law creep is “lattice-diffusion” power-law creep “Low-temperature” power-law creep is “core-diffusion” power-law creep Boundary-diffusion creep d -3 ; lattice-diffusion creep d -2
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ME 382 Lecture 32 2 With small grain sizes, boundary diffusion may dominate for all temperatures Lattice diffusion may dominate at higher temperatures with large grains (because Q l > Q b ) Increase in grain size reduces diffusional creep rate, but not power-law creep Regime of power-law creep dominance increases Example: Cylindrical pressure vessel of pure nickel with grain size of 0.01 mm.
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Lecture32-Notes - ME 382 Lecture 32 DEFORMATION MECHANISM...

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