chapter 11 - Chapter 11 Phase transformations Chapter 11...

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Unformatted text preview: Chapter 11 Phase transformations Chapter 11 wing skins parts of the internal wing structures selected areas of the fuselage In a Boeing 767 airplane, In a Boeing 767 airplane, Al alloy composition: 6.2Zn, 2.3Cu, 2.3Mg, 0.12Zr, the balance Al above Al alloy used at: above Al alloy used at: 7150-T651 alloy Light matrix phase: Small plate-shaped dark precipitate particles: Transition η ` phase Remainder: equilibrium η (MgZn 2 ) phase 80475 × TEM of Al alloy aluminum solid solution 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. For example: Tensile strength of Fe-C alloy of eutectoid composition (0.76wt% C) : Varied 700~2000MPa Depending on the heat treatment employed ※ 11. 1 Introduction ★ Phase transformations often result in the change of microstructures of materials ☆ microstructures determine the mechanical and other properties of many materials. Discuss the basic principles of phase transformations. The contents of this chapter Treat crystallization, melting, and glass transition transformations in polymers Address the role various transformations play in the development of microstructure for alloys and the effects of microstruc- tural changes on mechanical properties Phase Transformations in Metals Metallic materials are versatile. ☞ One reason is that the metallic materials have wide range of mechanical properties. Various means are available to manage the mechanical properties. Why? Grain size refinement, Solid-solution strengthening Strain hardening Strengthening mechanisms discussed: Additional technique for strengthening: change mechanical properties by characteristic of microstructure • transformation rate • Basic principles relating to transformation • development of two phase microstructures for Fe-C alloys. Development of microstructure ordinarily involves phase transformation Topics to discuss: • Other microconstituents in addition to pearlite are presented and their mechanical properties are discussed. • Modified phase diagrams are introduced to determine microstructures 11. 2 Basic Concepts A variety of phase transformations are divided into three classifications: ① simple diffusion-dependent transformations ☀ characteristics: number or composition of the phases present are not change ★ include: • solidification of a pure metal; • allotropic transformations; • recrystallization; • grain growth. Basic Concepts ② another type of diffusion-dependent transformation ☀ characteristics: • number or composition of the phases present changes • final microstructure ordinarily consists of two phases ★ include: eutectoid reaction Basic Concepts ③ diffusionless transformation ☀ characteristics: produce metastable phases ★ include: martensitic transformation induced from some steel alloys Basic Concepts 11. 3 The Kinetics of Solid-State Reactions11....
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This note was uploaded on 10/11/2011 for the course ENG 210 taught by Professor Zhang during the Spring '10 term at Tianjin University.

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chapter 11 - Chapter 11 Phase transformations Chapter 11...

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