Question

120 pts 5. (a) For a given material, is the surface energy to less than, greater than, or the same as, the grain boundary energy? Why is this? b) Why is the grain boundary energy of a small-angle ( grain boundary less than that for a high-angle grain boundary? 20 pts 6. Aluminum-lithium alloys were developed by the aircraft industry to reduce the weight and improve the performance of its aircruft. a) If the desired density of a ercial aircraft skin material is 2.55 gcm', compute the concentration of Li (in wt%) that is required. b) As it turned out, alum inum-lithium alloys were never widely used as aircraft skin materials, speculate why

Answer 1

Answer: 5. (а) Fos dhe given material, dhe Surbace energy is to be greater than che gsaun boundary energg Because, the Swbace atomg have bewer bonds than alom in a gsain boun day ->The Sunbace enegy uantitie dhe disrup tHon ob inter moleculor bond that occur when Surbaa is cseated The Mole cules ob stabace have move enengs compared ω1dh molecules in bulk 06 mateia 5. b → The gain boundary energy ot a small angle gsain boundory is leu than that bes a high angle gsoin boundany Because ob moxe atom bond across boundary tor dhe gmall angle -Thus, dhene ahe bewer unsasbied Bond. n dhis misobientation is less than he about 15 Degree

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