材料科学基础11PPT课件

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The contents of this chapter
Discuss the basic principles of phase transformations.
Address the role various transformations play in the development of microstructure for alloys and the effects of microstructural changes on mechanical properties
microstructures for Fe-C alloys.
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• Modified phase diagrams are introduced to determine microstructures
• Other microconstituents in addition to pearlite are presented and their mechanical properties are discussed.
number or composition of the
phases present are not change
★ include:
• solidification of a pure metal;
• allotropic transformations;
Light matrix phase:
aluminum solid solution
Small plate-shaped dark precipitate particles: Transitionuilibrium
(MgZn2)
phase 4
Why We Study Phase Transformations ?
In order to develop a set of desirable mechanical characteristics for a material.
Means: by specific heat treatment Based on: modified phase diagrams
it represent time and temperature dependencies of some phase transformations.
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For example:
Tensile strength of Fe-C alloy of eutectoid composition (0.76wt% C) :
Varied 700~2000MPa ※ Depending on the
heat treatment employed
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11. 1 Introduction
☞ One reason is that the metallic materials have wide range of mechanical properties.
Various means are available to manage the mechanical properties.
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Treat crystallization, melting, and glass transition transformations in polymers
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Phase Transformations in Metals
Metallic materials are versatile. Why?
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Development of microstructure ordinarily involves phase transformation
Topics to discuss:
• Basic principles relating to transformation
• transformation rate • development of two phase
Strengthening mechanisms discussed: Grain size refinement, Solid-solution strengthening Strain hardening
Additional technique for strengthening: change mechanical properties by characteristic of microstructure
In a Boeing 767 airplane, above Al alloy used at:
wing skins parts of the internal wing structures selected areas of the fuselage
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TEM of Al alloy
80475
CChahapptteerr 1111 Phase transformations
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PART ONE
前言
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7150-T651 alloy
Al alloy composition:
6.2Zn, 2.3Cu, 2.3Mg, 0.12Zr, the balance Al
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11. 2 Basic Concepts
A variety of phase transformations are divided into three classifications:
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① simple diffusion-dependent
transformations
☀ characteristics:
★ Phase transformations often result in the change of microstructures of materials
☆ microstructures determine the mechanical and other properties of many materials.