《材料科学与工程双语》第五次作业讲评

2-39 在温度为912℃时，铁从bcc转变到fcc 。此温度时铁的 两种结构的原子半径分别是0.126nm和0.129nm，（1）求 其结构变化时的体积变化V/O。（2）从室温加热铁到 1000℃，铁的体积将如何变化？ 解：(1)∵ 以四个Fe为例, 即两个bcc晶胞变为一个fcc晶胞, 又因为：bcc时体积 V =2 abcc =2 × (0.126×4/√3)3 =0.0493 nm3 3 fcc时体积 V = afcc = (0.129×4/√2)3 =0.0486 nm3 3 ∴ ΔV / V = (0.0486-0.0493)/0.0493 = - 0.014 = - 1.4% 答： 912℃铁从bcc转变到fcc时，体积缩小1.4% (2) 室温至912℃, 体积增大; 912℃, 体积减小； 912℃至1000℃, 体积增大

2-40固体材料存在哪些结构转 变类型？受哪些因素的影响？ 举例说明。

2-41某熔化的Pb-Sn焊锡具共晶温度，假设 此焊锡50g加热到200℃，则有多少克的锡能 熔进此焊锡中？（参见图2-112）

∵具有共晶温度的50g焊锡中铅的含量为： 50×38.1% = 19.05(g) 200℃时焊锡的总重量则为: 19.05/20% =95.25(g) ∴溶入的Sn重量为 95.25-50 = 45.25(g)

2-43 为什么金属、金属氧化物、无机 化合物（氮化物等）具有高的表面能， 而有机物（包括高聚物）表面能很低？

10.5 Cite the phases that are present and the phase compositions for the following alloys: (a) 90 wt% Zn–10 wt% Cu at 400℃. (b) 75 wt% Sn–25wt%Pb at 175℃. (c) 55 wt% Ag–45 wt% Cu at 900℃. (d) 30 wt% Pb–70 wt% Mg at 425℃. (e) 2.12 kg Zn and 1.88 kg Cu at 500℃. (f ) 37 lbm Pb and 6.5 lbm Mg at 400℃. (g) 8.2 mol Ni and 4.3 mol Cu at 1250℃. (h) 4.5 mol Sn and 0.45 mol Pb at 200℃.

87%

97%

Zn 回到10.9

10.5 解：由相图可知, (a)ε+η; Cε= 87 wt% Zn-13 wt% Cu, (Fig.10.17) Cη = 97 wt% Zn-3 wt% Cu; (b)α+β; Cα=15 wt% Sn-85wt% Pb, (Fig.10.7) Cβ= 97.5 wt% Sn-2.5 wt% Pb; (c) Liquid; CL =55 wt% Ag-45 wt% Cu; (Fig.10.6 ) (d) α; Cα=38 wt% Pb-62 wt% Mg; (Fig.10.18) (e) β+γ; Cβ= 49 wt% Zn-51 wt% Cu, (Fig.10.17) Cγ= 57 wt% Zn-43 wt% Cu; (f) L+Mg2Pb; CL =7 wt% Mg-93 wt% Pb; (Fig.10.18) C Mg2Pb =20 wt% Mg-80 wt% Pb; (g) α; Cα= 63.8 wt% Ni-36.2 wt% Cu (Fig.10.2) (h)β+ L Cβ= 97 wt% Sn-3 wt% Pb, (Fig.10.7) CL =75 wt% Sn-25 wt% Pb;

10.6 For an alloy of composition 74 wt% Zn–26 wt% Cu, cite the phases present and their compositions at the following temperatures: 850℃, 750℃, 680℃, 600℃, and 500℃. 解：由相图可知， 850℃：L 750℃：γ+ L 680℃：δ+ L 600℃：δ 500℃：γ+ε

10.7 Determine the relative amounts (in terms of mass fractions) of the phases for the alloys and temperatures given in Problem 10.5.

(b) Wα= 0.27, Wβ= 0.73; (c) 仅有液相存在，WL = 1.0; (d) Wα= 1.0; (e) Wβ= 0.50, Wγ= 0.50; (f) WL= 0.38, W Mg2Pb = 0.62; (g) Wα= 1.0; (h) Wβ = 0.45 , WL= 0.55

10.9 Determine the relative amounts (in terms of volume fractions) of the phases for the alloys and temperatures given in Problem 10.5a, b, and c. Below are given the approximate densities of the various metals at the alloy temperatures:

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(b) Wa=(97.5-75)/(97.5-15)=0.2727 Wb=(75-15)/(97.5-15)=0.7273 Pa=100/(15/7.22+85/11.20)=10.3446 Pb=100/(97.5/7.22+2.5/11.20)=7.2847 Va=(0.2727/10.3446)/(0.2727/10.3446 +0.7273/7.2847)=0.21