单组元相图及纯晶体的凝固1.ppt

Ch3 单组元相图及纯晶体的凝固 3.1 基本概念 3.2 单元相图 3.3 纯晶体的凝固 3.1 基本概念 一、相变 二、相图 三、材料热力学基本概念与定律 四、相律 一、相变 1.定义 2.类型 The Fundamentals of Phase Transformations As a metallurgist, or most other types of materials engineer, one’s main activity is to manipulate the structure of materials to control their properties.? This manipulation involves the selection of the material itself and the ways in which this is processed.? Thus processing - structure - property relationships lie at the heart of metallurgy and other branches of materials science/engineering.? One of the principal tools (arguably the most important tool) for controlling the structure of materials, is to use processing (heating, forming etc.) techniques to manipulate the phases that are present in the material and how these are distributed. 1.定义 相变是指当温度、压力或成分等因素改变到某一临界值时,材料的相所发生的改变. 通过相变可以改变材料微观的成分、组织和结构,从而达到改变材料宏观性能的目的. 2.类型（宏观） 序号 主 要 类 型 举 例 Ⅰ 气体→液体 水汽的凝结 Ⅱ 气体 →固体 窗霜的形成 Ⅲ 液体 →晶体 结冰 Ⅳ 晶体1→晶体2 析出(脱溶)转变 (固态相变) 同素异构转变 有序转变 再结晶转变等 2.类型（微观） 序号 变化的复杂程度 举 例 或 说 明 Ⅰ 结构变化 纯铁凝固或熔化 Ⅱ 结构变化＋ 合金的凝固或熔化 成分变化 Ⅲ 结构变化＋ 多数固态相变因相的 产生畸变 比容不同,产生畸变 Ⅳ 结构变化＋ 多数固态相变属此类 产生畸变＋ 成分变化 What are Phase Transformations and Why Do These Matter? Pure iron has three different solid phases (a, g and d-Fe) at different temperatures.? Thus, as iron is heated from room-temperature to above its melting point, the following changes in phase occur: a transforms to g; g transforms to d; d transforms to liquid iron. Each of these changes is an example of a “phase transformation”.? The key point is that, by controlling phase transformat