题目

一合金之成分为90Pb-10Sn。(a)请问此合金在100℃、200℃、300℃时含有哪几种相?(b)在哪个温度围将只有一相存在?(参看图4-9)Composition of an alloy is 90Pb-10Sn. (a) Which phases is contained at 100℃, 200℃, 300℃? (b) In which temperature range will be only one phase exists? (See Figure 4-9).答:(a)成分为90Pb-10Sn的合金对应的为红色的垂直线,分别在100℃、200℃、300℃作水平线得到交点a,b,c,所以100℃时,交点a位于α+β相区,所以有α和β两相。200℃时,交点b位于α单相区,所有只有α一相。300℃时,交点c位于液相线上,此为两相共存线,所以有液相L和α两相。( )A. Composition of alloy is 90Pb-10Sn alloy which corresponding to the red vertical line, it intersect with the temperature level line at a, B. and C. points. So, there are two phases at 100℃, α and β; there is only one phase at 200℃, α; point c lies on the liquidus line, so there are two phases at 300℃, L and α. D. f, then draw horizontal lines to get the corresponding temperature. So when the temperature is more than 300℃, liquid phase L exists. When the temperature is between 148 ~ 268℃, there is only α p E. and F. G. et three points, d, e and f, then draw horizontal lines to get the corresponding temperature. So when the temperature is more than 300℃, liquid phase L exists. When the temperature is between 148 ~ 268℃, there is only α phase.

一合金之成分为90Pb-10Sn。(a)请问此合金在100℃、200℃、300℃时含有哪几种相?(b)在哪个温度围将只有一相存在?(参看图4-9)Composition of an alloy is 90Pb-10Sn. (a) Which phases is contained at 100℃, 200℃, 300℃? (b) In which temperature range will be only one phase exists? (See Figure 4-9).

答:(a)成分为90Pb-10Sn的合金对应的为红色的垂直线,分别在100℃、200℃、300℃作水平线得到交点a,b,c,所以

100℃时,交点a位于α+β相区,所以有α和β两相。

200℃时,交点b位于α单相区,所有只有α一相。

300℃时,交点c位于液相线上,此为两相共存线,所以有液相L和α两相。

( )

A. Composition of alloy is 90Pb-10Sn alloy which corresponding to the red vertical line, it intersect with the temperature level line at a,
B. and
C. points. So, there are two phases at 100℃, α and β; there is only one phase at 200℃, α; point c lies on the liquidus line, so there are two phases at 300℃, L and α.
D. f, then draw horizontal lines to get the corresponding temperature. So when the temperature is more than 300℃, liquid phase L exists. When the temperature is between 148 ~ 268℃, there is only α p
E. and
F.
G. et three points, d, e and f, then draw horizontal lines to get the corresponding temperature. So when the temperature is more than 300℃, liquid phase L exists. When the temperature is between 148 ~ 268℃, there is only α phase.

题目解答

答案

b

解析

考查要点：本题主要考查对二元相图的解读能力，特别是合金在不同温度下的相组成及单相存在温度范围的判断。

解题核心思路：

  1. 确定合金成分位置：在相图中找到90Pb-10Sn合金的垂直线。
  2. 水平线法：在目标温度处作水平线，观察交点所在的相区。
  3. 相区判断：根据相区类型（单相区或两相区）确定相组成。
  4. 单相范围：找到合金成分垂直线穿过单相区的温度区间。

破题关键点：

  • 相图特征：Pb-Sn相图中，富Pb合金在固相线以下可能经历α单相区和α+β两相区。
  • 液相线特性：温度高于液相线时为液相，温度低于液相线时可能进入两相共存区。

(a) 不同温度下的相组成

  1. 100℃
    • 作水平线至合金垂直线，交点位于α+β相区，因此存在α和β两相。
  2. 200℃
    • 作水平线至合金垂直线，交点位于α单相区，因此只有α相。
  3. 300℃
    • 作水平线至合金垂直线，交点位于液相线，因此存在液相（L）和α相。

(b) 单相存在温度范围

  • 合金垂直线穿过α单相区的温度范围为148℃至268℃，在此区间内仅存在α相。