材料导论 (11)

Phase diagram1. Hello everybody, Welcome to my class. Today, we will talk about phase diagram, Gibbs phase rule and learn how to calculate the relative amount of liquid phase and solid phase.译文：大家好，欢迎来到我的课程。

今天，我们将讨论相图，吉布斯相律以及如何计算液相和固相的相对含量。

2. We first learn the definition of phase. Phase is defined as a homogeneous part or aggregation of material.This homogenous part differs from another part due to difference in structure, composition, or both. The difference structures forms an interface to difference in structure and composition.这里要注意相的概念，相是指在结构和组成方面与其它部分不同的均匀体。

译文：我们首先学习相的定义，相是指在结构或组成，以及结构和组成与其它部分不同的均匀体，这些不同部分形成界面。

也就是相与相之间的分界面。

3.Some solid material have the capability of changing their crystal structure with varying conditions of pressure and temperature, which cause these materials to change phase.译文：一些固体材料随着不同压力和温度条件的改变，具有改变相的能力。

4. Change phases are depending on the surrounding temperature. As the material absorbs heat: solid completely liquefied.If temperature drops, it cause liquid to solid. Now we should understand some important Conceptions译文：相的改变可基于环境温度，比如固体吸热变成液体，如果温度下降，则液体变成固体。

有缘学习更多驾卫星ｙｇｄ３０７６5. First is Phase diagram. Phase diagram is the graphical representations of a material system under varying conditions of temperature and composition.译文：相图是一个图形，表示材料在不同的温度和组成下相的变化的一个图形。

此外相图中还有一些重要的概念。

6. Next is Cooling curve. Cooling curve is a graphical plot of the structure of a material over the entire temperature range through which it cools under equilibrium conditions. This material is usually a pure metal or metal alloy译文：例如，冷却曲线，冷却曲线是在平衡条件下，在整个温度范围内的组成的一个图。

这里给出的相图是二元合金相图中的一种，也是比较常见的一种完全互溶的合金相图。

7. We now know what the actual composition of the two-phase region is for a particular alloy at a specific temperature. Figure shows a typical phase diagram for two metallic elements that are completely soluble in each other in both liquid and solid phases. The phase diagram contained only two components is known as binary diagrams. 这里给出的相图是二元合金相图中的一种，也是比较常见的一种完全互溶的合金相图。

下面介绍这个相图。

在图中，可看到左边和右边的纵轴以及图中上面弧线和下面弧线。

译文：我们现在知道特定温度下特定合金的两相区的实际组成。

这里给出的相图是二元合金相图中的一种，也是比较常见的一种完全互溶的合金相图。

8. The vertical axis at the left represents a pure metal A with a melting point of Ta. the right represents metal B and has a melting temperature less than metal A. The upper line is the liquidus. The lower line is the solidus.译文：左右两个纵轴分别表示纯A和纯B及其熔点，上面弧线叫液相线liquidus，下面弧线叫固相线solidus，注意液相线单词与液相单词仅差一个后缀，固相同理。

9. The liquidus is the curve that represents the temperatures at which solidification begins. It marks the lower boundary of the liquid phase, and thus it is a solubility curve that shows the limit of solubility of the components A and B in the liquid.译文：液相线是液相的边界，表示固化开始线，同时它是一个溶解度曲线，显示了A 和B在液体中的溶解度极限。

The solidus is the curve that passes through all points at which solidification is completed. It marks the upper boundary of the solid solution phase and therefore it is the solubility limit of both components A and B in the solid solution. 液相线是将所有开始固化的温度点连接起来，固相线指将所有完全凝固的点连接起来。

译文：固相线是凝固完成的曲线。

它是固相的边界，因此它是固体中A和B的溶解度极限。

Between these curves, where a two – phase slushy region of liquid plus solid exists, the process of solidification takes place.译文：在它们之间，是两相区。

所以在相图中，液相线上面是单相区，固相线下面也是单相区，之间是两相区。

下面我们学习在这些相图中每个位置的相态.The pure metals and any composition of the two are in the liquid (melt) phase upon heating above the liquidus. 纯金属和这两种物质的任何组成都在液体线上加热时都处于液态。

译文：纯金属和两种金属的任何组成都是加热到液相之上形成液相。

When an alloy is at a temperature above the solidus but below the liquidus, it exists as part liquid and part solid in a two-phase region labeled L + S. Upon cooling to the solidus, they solidify.译文：当一种合金处于高于固相线，低于液相线的温度，它在两相区是部分液相和部分固相共存，我们把它标为L+s。

冷却到固相线后，它们就完全固化了。

For example: Ni-Cu phase diagramUsing an alloy with a composition of 60% Ni-40% Cu, we will plot this composition on Figure to determine first its chemical composition at any given temperature. Vertical line X-Y represents the alloy.译文：例如镍和铜合金相图。

用60%镍和40%铜合金相图，我们在图上画出这一成分，以确定其在任何给定温度下的化学组成，用直线XY表示合金组成。

Cooling process.At Point 1 at T1: the alloy is in the liquid solution. Point 2 is reached at T2: the alloy is now entering the two –phase region, part is liquid and part has formed a solid solution.译文：冷却过程在温度1处，合金处于液相，在2点处合金开始进入两相区域，部分液相和部分固相。

To determine the composition of these two phases at any point, such as at 3, a horizontal temperature line, called a tie-line, is drawn through point 3. Point 3 at T3, tie-line is used to calculate relative amount of liquid and solid.译文：为了确定这固相和液相的组成，例如3点。