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Chap9_2pgs

Chap9_2pgs - =24 in.z t = 4.6 =B(8D4\2 B =4.61(0.333)2 =...

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Princlple\$ uf \$olldlfhntlon 9-10 Suppose that liquid nickel is undercooled until homogeneous nucleation occurs. Ca'tcutate (a) ttri critical radius of the nucleus required,and (b) the number of nickel atoms in the nucleus. Assume that the lattice parameter of the solid FCC nickel is 0.356 nm. Solution: From Table 9-1, Afmsx = 48fC r*= (2)(255 x 10-7 J/cm2)(1453 +273) = 6.65 x l0r8 cm (2756 J/cm3)(480) | =45.118 x t0-24 cm3 %u"l"u. = (4Tc13X6.65 x 10-8 cm)3 = I232x l0-2a cm3 number of unit cells = 1232145.11\$ = 27.3 atoms per nucleus = (4 atomVcellX2T.3 cells) = 109 atoms CHAPTER 9 Principles of Solidification 85 9-31 A 2-in. cube solidifies in 4.6 min. Calculate (a) the mold constant in Chvorinov's rule and (b) the solidification time for a 0.5 in. x 0.5 in. x 6 in. bar cast under the same conditions. Assume that n = 2. Solutlon: (a) We can find the volume and surface area of the cube: V = (2)t= 8 in.3 A

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Unformatted text preview: =24 in.z t = 4.6 =B(8D4\2 B =4.61(0.333)2 = 41.48 min/in.2 (b) For the bar, assuming that B = 41.48 minfn.2: Y= (0.5X0.5)(6) = 1.5 in.2 A = 2(0.5X0.5) + 4(0.5)(6) = 12.5 in.2 1= (41.48)(1.5112.5\2 = 0.60 min Qo=3'56 A 945 A cooling curve is shown in Figure 9-2|.Determine (a) the pouring temperature, (b) the solidification temperature, (c) the superheat, (d) the cooling ratejust before solidification begins, (e) the total solidification time, (f) the local solidification time' and (g) the probable identity of the metal. (h) If the cooling curve was obtained at the center of the casting sketched in the figure, determine the mold constant, assum' ingthatn=2. Solution: (a) Toou , = 47 soc (b) ?Lr = 32oPc (c) 47" = 475 - 320 = 155oC 475 - 320 (d)4nfu1 = ,rr* =1.0oC/s ( e ) f = 4 7 0 s (f) LST = 470 - 170 = 300 s (g) Cadmium (Cd) (h) r, = 470 = B[38 .4t121.612 B - 4713 s/cmz...
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