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HW4+solutions (2)

# HW4+solutions (2) - MechEng 382 Winter 2010 2009 Homework#4...

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MechEng 382 Homework #4 Solutions 1. [ A&J-2 , Ex. 3.1] Explain brieﬂy what is meant by the following terms. (a) a eutectic reaction; Solution A eutectic reaction is one in which a single-phase liquid simultaneously changes into two solids upon cooling. (b) a eutectoid reaction. Solution A eutectoid reaction is one in which a single-phase solid simultaneously changes into two (diferent) solid phases upon cooling. 1 2010

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MechEng 382 Homework #4 Solutions 2. [ A&J-2 , Ex. 3.2] The phase diagram for the copper-antimony system is shown below. The phase diagram contains the intermetallic compound marked “X” on the diagram. Determine the chemical formula of this compound. The atomic weights of copper and antimony are 63.54 and 121.75, respectively. Solution With a given weight composition W X Sb 0 . 49 and atomic weights, the atomic composition can be obtained using the formula: X Sb = W Sb /a Sb W Cu /a Cu + W Sb /a Sb = 0 . 51 / 121 . 75 0 . 49 / 63 . 54+0 . 51 / 121 . 75 =33% = X Cu =67% . Since X Sb /X Cu =67 / 33 2, there are approximately 2 Sb atoms for every Cu atom. This implies a chemical formula of Cu 2 Sb . Figure 1: Cu-Sb phase diagram, Prob. 2 . 2 2010
MechEng 382 Homework #4 Solutions 3. [ A&J-2 , Ex. 3.4] A copper-antimony alloy containing 95 weight% antimony is allowed to cool from 650 C to room temperature. Describe the diFerent phase changes which take place as the alloy is cooled and make labeled sketches of the microstructure to illustrate your answer. Solution : Temperature Description Microstructure 650 C Alloy is single-phase liquid (L). L 610 C Regions of δ -solid begins to form in L. ± ± ± ± ± ± ± L > 526 C Primary phase δ -solid with L at eutectic composition.

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HW4+solutions (2) - MechEng 382 Winter 2010 2009 Homework#4...

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