13.04.17材料概论第06课

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DJTU Materials Science & Engineering
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Types of Processing
• Processing: produces the desired shape of a component from the initial formless material. • Metals can be processed by: 1）casting (铸造) ： liquid metal into a mold; 2）joining (联接) ：individual pieces of metal (welding焊接, brazing铜焊, soldering锡焊, adhesive bonding粘结); 3）forming（压力加工）：the solid metal into useful shapes using high pressures (forging锻压, drawing拉拔, extrusion挤压, rolling轧制, bending 卷扎); 4）compacting（压塑）： tiny metal powder particles into a solid mass (powder metallurgy粉末冶金); 5）heat treatment（热处理）: to high strength levels by thermal cycles heat treatment ； 6） machining（机械加工） removing excess materials by cold machine.
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DJTU Materials Science & Engineering
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2) Binary System Diagrams
二元相图
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Usage of Phase Diagrams
• shows what phases are present where the process boundaries边界 are ; • represents表明 relations between temperature, pressure, compositions and quantities of phases at equilibrium;
EUTECTIC
Steels: eutectoid + hypoeutectoid + hypereutectoid, Cast iron: eutectic + hypoeutectic + hypereutectic.
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A few comments on Fe–Fe3C system
Example: Cu-Ni system -slow cooling along the line with Co = 35wt%Ni.
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CORED VS EQUILIBRIUM PHASES
晶核相与平衡相
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DJTU Materials Science & Engineering
•Generally, all phases are the mixtures混合物 of γ, α and Fe3C;
•C is an interstitial impurity间隙杂质 in Fe, and forms a solid solution with γ, α , d phases of iron; •Cementite is very hard and brittle can strengthen steels.
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DJTU Materials Science & Engineering
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6.2 PHASE DIAGRAM相图
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1) Definitions定义
Component组分: - chemically recognizable species可识别的种类 (e.g. Fe and C in carbon steel, H2O and NaCl in salted water). Phase 相 : –The physically and chemically distinct 截 然 不 同 的 material regions区域. (e.g. water and ice);
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Basic Ideas
When combine two elements at a certain composition (C0), and a temperature (T℃), then... 1. How many phases do we get? 2. What is the composition of each phase? 3. How much of each phase do we get?
•α-ferrite is very soft and ductile, can toughening steels;
• α-ferrite
is magnetic below 768 °C, γ- austenite is non-magnetic.
DJTU Materials Science & Engineering
727° 0.77

Fe3C Cementite
渗碳体
Cementite
a Ferrite
铁素体
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600
0.02
a+ Fe C
3
400
1
2
3
4
5
6
6.7
Weight % Carbon
Fe C 3
23
•Eutectic: 4.30 wt%C, 1148°C, L ⇔ γ (2.14 wt%C)+Fe3C; •Eutectoid: 0.77 wt%C, 727°C, γ ⇔ α(0.022wt%C)+Fe3C; •Pearlite: α+ Fe3C, very fine plate-like or lamellar mixture;
• allows to predict预测 phase transformations转变 during T and t change (e.g. heating or cooling).
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DJTU Materials Science & Engineering
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3) Solid Solution固溶体
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5）EUTECTIC SYSTEMS
共晶系
•Eutectic共晶：systems with a minimum melting point, TE (eutectic means easily melted) . • 3 phases: can equilibrium along isotherm共晶等温线; be in eutectic
eutectoid reaction:
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7）共晶、共析、包晶反应图型与反应式比较
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6.3 IRON-CARBON (Fe-C) System
铁碳平衡相图
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Features of the Fe - Fe3C Diagram
DJTU Materials Science & Engineering
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6.1 Processing
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Structure-Property-Processing-Interaction
• The processing affects the structure. • structure and final properties of casting are very different from formed product . • original structure 原始 组 织 and properties determine process to produce a desired shape.
Introduction to Materials
6 Metallic Materials
DJTU Materials Science & Engineering
6. IRON-CARBON (Fe-C) PHASE DIAGRAM
(铁碳相图)
6.1 Processing 6.2 Phase Diagram 6.3 Fe-C Phase Diagram 6.4 Phases and Structures of Steels 6.5 Heat Treatment
•Eutectic: P P =α+ β •Hypoeutectic: α+ P •Hypereutectic β+ P
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α α α α α α
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6）Eutectoid Reaction共析转变:
• point E: 74 wt%Zn at 560°C; •again 3 phases: δ—γ+ε •but 1 solid transforms to 2 solid phases,
one element dissolved in another to form a single phase structure over a range of compositions