Phase Transformation of Materials Phase Transformation of Materials

Phase Transformation of Materials Phase Transformation of Materials

Eun Eun Soo Soo Park Park

Office: 33-316

Telephone: 880-7221

2009 fall

09.01.2009

합금설계 + 공정(工程)

미세조직

(微細組織) 물성(物性)

Materials Science and Engineering

One of the Most Popular Structural Materials

; Iron-Carbon Alloy (or Steel)

Steel frame of building 합금설계 : 재료의 선택

Need of the strongest materials

Application of Iron-Carbon Alloy

K1 – main battle tank of Korea army

합금설계 : 재료의 선택 합금 조성의 변화

Dominant Material for Airplanes

; Aluminum Alloy

B737-800 of Korean Air

합금설계 : 재료의 선택

A Example of Grain Boundary Engineering ; Turbine blade in Aircraft Engine

F100-PW-229

in F-16 fighting falcon

Grain boundaries at high Temperature ; Diffusion path of atoms

Creep

Turbine Blade

합금설계 + 공정 : 재료의 선택 후 공정 조절 특성 최적화

Better Material Properties

Microstructure Control ^of Materials

합금설계 + 공정조절

What is Phase?

A phase is a chemically and structurally homogeneous portion of the microstructure.

Temperature

Pressure (log scale) Phase diagram ;

미세구조 조절: Equilibrium phase Thermodynamics 만 고려

Phase Diagram of Temperature – Composition ;

Temperature(°C)

Liquid solution Liquid solution

+ solid sugar Solubility limit

most useful in materials science & engineering

미세구조 조절: Equilibrium phase Thermodynamics 만 고려

10

Phase Transformation of Iron and Atomic Migration

Pressure (log scale)

Temperature

Face-Centered Cubic Atomic Migration

at 1 atm

미세구조 조절: Phase Transformation Atomic Migration

What is Microstructure in Materials Science ?

Transmission Electron Microscope

Materials ;

Assemblage of Atoms

• periodic

• grain boundaries

Crystals Liquids, glasses

• amorphous = non-periodic

• no grain boundaries

Structure of crystals, liquids and glasses

Perfect Crystal is good in many aspects, But …

‰ 1) Imperfection in Metallic Materials ; Point defect : Vacancies,

Impurity atoms Line defect : Dislocations

Plane defect : Grain Boundaries, Free Surfaces

Bulk defect : Voids, Cracks

‰ 2) Second Phase Particles in Matrix

Mechanical Properties ; Magnetic properties

Electrical properties Etc.

Perfect Crystals without Defect

Carbon Nanotubes

High strength, unique magnetic/electrical properties

1) Imperfection: Dislocations

SR-71

with armor of titanium alloy

It looks perfect.

But….

Edge Dislocation

Line

Burgers vector

Low Carbon Steel

Optical Microscope

Grain Boundary

1) Imperfection: Grain Boundaries

1) Imperfection: Voids

1) Imperfection: Voids

Shrinkage effect

1) Imperfection: Voids

Using of Materials with

Improper Microstructure

성수대교 붕괴 (1994.10.21) Oil tanker

Failures

Phase Diagram of Iron–Carbon Alloy

Temperature (°C)

미세구조 조절: 2) Secondary phase control

22

Equilibrium Phases of Iron-Carbon Alloy

γ phase (FCC)

α phase Fe₃C phase Atomic migration

by diffusion

γ

미세구조 조절: 2) Secondary phase control

Mechanism of Precipitation

(1)

(2) (3)

(1)

(2)

(3)

(2) (3)

(1)

Atomic diffusion Precipitate

Matrix atom

Composition

Temperature

미세구조 조절: 2) Secondary phase control

Effect of Second Phase Particle

on Mechanical Property

Ni₃Si particles in Ni-6%Si single crystal

Dislocations

Second phase particle in matrix material

Obstacle of dislocation slip

& grain growth

High strength

미세구조 조절: 2) Secondary phase control

Precipitates

in aluminum matrix

Boeing 767 by AA7150 T651 alloy

Control of Microstructures by

Precipitation Transformation in Aluminum Alloy

High strength

Hindering dislocation slip 미세구조 조절: 2) Secondary phase control

26

Control of Microstructures ;

Cold Work_

조선시대

김홍도 “대장간”

현대의 단조기 공정조절을 통한 미세구조 조절

Accumulation

Hardening Mechanism by Cold Working

Deformation or

Cold work

Before cold work

Aluminum alloy

공정조절을 통한 미세구조 조절

Changes of Strength and Ductility by Cold Working

Tensile strength Ductility

공정조절을 통한 미세구조 조절

Changes of Microstructure & Mechanical Properties during Annealing

공정조절을 통한 미세구조 조절

Production and Application of Electrical Steel

Hot rolling - cold rolling – 1^st annealing – 2^nd annealing

Transformer Motor

Etc.

Coils Stacked transformer core

합금설계 + 공정조절 특성 최적화

RD 900 μm

Abnormal Grain Growth In Fe-3%Si Steel Sheet produced by POSCO

Abnormally grown grains with Goss texture

Control of grain growth

Control of

magnetic property

Important!!!

Understanding and Controlling

Phase Transformation of Materials

Phase Transformation

G

Metastable

Unstable

Stable barrier

Metastable

하나의 상에서 다른 상으로 변화 비평형 상태

Thermodynamics & Kinetics

structure ^or composition ^or order

How does thermodynamics different from kinetics?

Thermodynamics

says which process is possible or not and never says how long it will take.

The existence of a thermodynamic driving force does not mean that the reaction will necessarily occur!!!

There is a driving force for diamond to convert to graphite but there is (huge) nucleation barrier.

동질이상(同質異像): 화학성분 같고 결정구조 다름

There is no time variable.

How long it will take is the problem of kinetics^.

Phase Transformation

• Solidification: Liquid Solid

• Phase transformation in Solids

1) Diffusion-controlled phase transformation ; Generally long-distance atomic migration

- Precipitation transformation

- Eutectoid transformation ( S S1 + S2) - etc.

2) Diffusionless transformation ; Short-distance atomic migration

Non-Equilibrium Phases

1) Time-Dependency of Diffusion- Controlled Phase Transformation

Need of Controlling

not only Temperature & Composition

but Process conditions (

)

Transformation Kinetics and

Isothermal Transformation Diagram

Logarithm of heating time, t

Fraction of transformation, y

Kinetics of diffusion-controlled solid-state transformation

Temperature (°C)

y = exp(-kt

)

38

Isothermal Transformation Diagram of a Eutectoid Iron-Carbon Alloy

Time

Temperature

Coarse pearlite

Fine pearlite

Rapid cooling

Slow cooling

γ Austenite α Ferrite + Fe₃C ^graphite

Control of Phases by Heat Treatment

Pearlite (Fe₃C+ferrite)

Heat Treatment

Phase & Microstructure Martensite ;

Non-equilibrium phase

( Very hard )

공정조절

Control of Mechanical Properties by

Proper Heat Treatment in Iron-Carbon Alloy

Martensite Tempered martensite

Tip of needle shape grain

Nucleation site of fracture Good strength, ductility, toughness Proper

heat treatment ( tempering )

Very small & spherical shape grain 공정조절

2) Diffusionless Transformation

Martensitic transformation in Ni-Ti alloy ; 55~55.5wt%Ni-44.5~45wt%Ti (“Nitinol”) Martensitic transformation in iron-carbon alloy

Ex) Shape memory alloy

Difference of Deformation Behavior between Conventional Metals and Shape Memory Alloys

일반금속의 응력-변형 곡선 형상기억 합금의 응력-변형 곡선

응력

변형 응력제거

탄성영역 소성영역

영구변형 복원

가열

응력제거 응력

변형

Change of Atomic Array during

Martensitic Transformation in Ni-Ti Alloy

cooling deformation

Twinned martensite

Deformed martensite Austenite

heating

Medical Applications of Shape Memory Alloys

heating After 3 weeks

Shape Memory Alloy's applications can be used in many ways depends on the use of YOUR IDEAS.

Magic spring (climb koala) Magic flower

Application of Shape Memory Alloys Application of Shape Memory Alloys

Contents in Phase Transformation

(Ch1) 열역학과 상태도: Thermodynamics (Ch2) 확 산 론: Kinetics

(Ch3) 결정계면과 미세조직

(Ch4) 응 고: Liquid → Solid

(Ch5) 고체에서의 확산 변태: Solid → Solid (Diffusional) (Ch6)고체에서의 무확산 변태: Solid → Solid (Diffusionless) 상변태를상변태를

이해하는데 이해하는데 필요한필요한 배경배경

대표적인대표적인 상변태상변태

Microstructure

Microstructure - - Properties Relationships Properties Relationships

Microstructure Properties

Alloy design &

Processing Performance

“ “ Phase Transformation Phase Transformation ” ”

“ “ Tailor Tailor - - made Materials Design made Materials Design ” ”

down to atomic scale

2009년 9월

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