TAILIEUCHUNG - Engineering Materials 2E VOLUME2 Episode 16

Tham khảo tài liệu 'engineering materials 2e volume2 episode 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 366 Engineering Materials 2 Fig. . c Describe the solidification of an alloy of eutectic composition and the resulting structure. d Compare and contrast this with the formation of a eutectoid structure. A hypothetical equilibrium diagram between two elements A and B shows the following features A has three solid allotropic forms with change temperatures of 800 C and 1150 C and melts at 1980 C. These form solid solutions a p and Y containing B a being the low-temperature one. An intermediate compound A2B3 melts at 1230 C. It has a limited solid solubility for A forming solid solution and no solid solubility for B. B melts at 800 C and has negligible solid solubility for A. Eutectic reactions at 1000 C liquid 55 B p 25 B 60 B at 650 C liquid 90 B A2B3 B. Peritectic reaction at 1300 C Y 8 B liquid 35 B p 15 B . Eutectoid reaction at 600 C p 12 B a 5 B 65 B . Peritectoid reaction at 300 C a 3 B 69 B 8 40 B . Teaching yourself phase diagrams 367 At 0 C the solubilities of B in A and A in A2B3 are negligible and the s phase extends from 35 to 45 B. All percentages given are by weight. The atomic weight of B is twice that of A. Draw the equilibrium diagram assuming all phase boundaries are straight lines. For an alloy containing 30 B describe the changes that occur as it is cooled from 1600 C to 0 C. Give the proportions of phases present immediately above and immediately below each temperature at which a reaction occurs. Answers to questions part 4 Between about and GPa or X 105 - X 105 atm. a See Fig. . b Two-phase region. c a copper-rich solid and p the compound CuZn . d WZn 33 WZn 48 . e Very roughly 50-50 more precisely wt of a 48 - 40 8 . wt of p 40 - 33 7 The solid which first appears on cooling is higher in nickel. Repeated directional remelting and solidification zones the copper up to the end of the bar and leaves most of the bar increasingly pure in nickel. Fig. . 368 Engineering Materials 2 Fig. . a 1. b

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