material teknik - materi - 3 2015

8/18/2019 Material Teknik - Materi - 3 2015

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Dr. Eko Pujiyanto , S.Si., M.T.Homepage : eko.staff.uns.ac.id/3-material-teknik

Material Teknik


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Ketidaksempurnaan Material Padat

Pendahuluan

Cacat titik

Beberapa jenis cacat lainnya


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Susunan yang sempurna ada dikeseluruhan material kristal pada skalaatom tidaklah ada.

Semua material padat mengandungsejumlah besar cacat atauketaksempurnaan.


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Why are defects important?


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Defects have a profound impact onthe various properties of materials:◦

Defects are responsible for color (&price) of a diamond crystal.

◦ Forging a metal tool introduces defectsand increases strength of the tool.


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Defects can beintroduced/

removedduringprocessing


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Defects in Crystals

A 2D representation of aperfect single crystal withregular arrangement of atoms.

But … structures of realmaterials can be betterrepresented by the schematicdrawing to the left.


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Types of efects

◦ 0 , Point defects: atoms missing or in irregularplaces in the lattice (lattice vacancies,

substitutional and interstitial impurities, self-interstitials)

◦ 1 , Linear defects: groups of atoms in irregularpositions (e.g. screw and edge dislocations)

◦ 2 , Planar defects: the interfaces between

homogeneous regions of the material (e.g. grainboundaries, stacking faults, external surfaces)

◦ 3 , Volume defects: extended defects (pores,cracks)


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Vakansi adalah kekosongan sisi kisi, yaitu sisiyang seharusnya ditempati atom,kehilanganatomnya .

Vakansi terbentuk selama proses pembekuan,dan juga karena getaran atom yangmengakibatkan perpindahan atom dari sisikisi normalnya.

Interstisi-Diri(self-interstitial) adalah sebuahatom dari bahan kristal yang berdesakan kedalam sisi interstisi, yaitu ruang kosong kecildimana dalam kondisi normal tidak diisi atom.


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Impuritas◦ Impuritas adalah atom asing yang hadir pada

material. Logam murni yang hanya terdiri dari

satu jenis atom adalah tidak mungkin.◦ Impuritas bisa menyebabkan cacat titik pada

kristal.


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• Dislokasi adalah cacat linier atausatu dimensi dimana didekatnyabeberapa atom tidak segaris.

• Ada 3 jenis dislokasi yaitu :1. dislokasi sisi2. dislokasi ulir

3. dislokasi campuran.


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1. Dislokasi sisi/pinggir adalah terdapatnyabidang atom ekstra atau setengah bidang,dimana sisinya terputus di dalam kristal.


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2. Dislokasi ulirterbentuk karenagaya geser yangdiberikanmenghasilkan

distorsi sepertiyang ditunjukkanGambar disamping.Daerah depanbagian atas kristaltergeser sebesar

satu atom kekananrelatif terhadapbagian bawah.


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3. Dislokasicampuran : Jika padamaterialdijumpaikedua jenisdislokasidiatas


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3. Dislokasi campuran


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• Cacat antar muka adalah batas yang mempunyaidua dimensi yang biasanya memisahkan daerah-daerah pada material yang mempunyai strukturkristal dan/atau orientasi kristalografi yangberbeda.

• Cacat jenis ini antara lain:1. Permukaan luar2. Batas butir3. Batas kembar4. Kesalahan tumpukan5. Batas fasa.


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Figure 4.16 (a) The atoms near the boundaries of

the three grains do not have an equilibrium

spacing or arrangement. (b) Grains and grain

boundaries in a stainless steel sample. (

Courtesy

r. A. eardo

.)


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• Cacat lainnya yang ada pada semuamaterial padat dimana cacat ini lebihbesar dari yang sudah dibicarakan adalahpori, retak, inklusi benda asing dan fasa-fasa lainnya.

• Cacat-cacat ini timbul biasanya selamatahap-tahap proses dan pabrikasi.


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Difusi

Pendahuluan

Mekanisme difusi

Flux difusi Difusi stabil dan non-stabil

Faktor yang mempengaruhi difusi


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What isdiffusion?

Diffusion ismaterialtransportby atomicmotion

Difusi


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Interdiffusion (or impurity diffusion)occurs in response to a concentrationgradient.

Self-diffusion is diffusion in one-component material, when all atoms thatexchange positions are of the same type.

Difusi


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Difusi


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Difusi

Self-diffusion - The random movement ofatoms within an essentially pure material.

Vacancy diffusion - Diffusion of atoms

when an atom leaves a regular latticeposition to fill a vacancy in the crystal.

Interstitial diffusion - Diffusion of smallatoms from one interstitial position to

another in the crystal structure.


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Difusi


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Difusi


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Difusi

Steady state diffusion: the diffusion flux does notchange with time.

Nonsteady-State Diffusion: In many realsituations the concentration profile and the

concentration gradient are changing with time.

The changes of the concentration profile can bedescribed in this case by a differential equation,Fick’s second law.


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Difusi

Temperature and the Diffusion Coefficient (D)

Types of Diffusion - volume diffusion, grainboundary diffusion, Surface diffusion

Time

Dependence on Bonding and Crystal Structure

Dependence on Concentration of DiffusingSpecies and Composition of Matrix


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Difusi

© 2 0 0 3

B r o o k s / C o l e , a d i v i s i o n o f T h o m s o n L e a r n i n g ,

I n c . T h o m

s o n L e a r n i n g ™

i s a t r a d e m a r k u s e d h e r e i n u n d e r

l i c e n s e .

Figure 5.18 The

diffusion coefficient

as a function of

reciprocal temperature

for some metals and

ceramics. In the

Arrhenius plot,

represents the rate of

the diffusion process. A

steep slope denotes a

high activation energy


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Difusi

Figure 5.19 iffusion

coefficients for different

dopants in silicon. (Source:

From ‘‘ iffusion and

iffusion Induced efects in

Silicon,’’ by U. GÖsele. In R.

Bloor, M. Flemings, and S.

Mahajan (Eds.), Encyclopedia

of Advanced Materials, Vol.

1, 1994, p. 631, Fig. 2.

Copyright © 1994 Pergamon

Press. Reprinted with

permission of the authors

.)


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Difusi


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Difusi


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Difusi


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1. W. D. Callister, Jr. and D. G. Rethwisch, 2010, MaterialsScience and Engineering: An Introduction, 8th edition, JohnWiley.( Chapter 4)

2. Leonid Zhigile, Lecture Note, MSE 209: Introduction to theScience and Engineering of Materials,http://www.people.virginia.edu/~lz2n/mse209/( Chapter 4)

3. Donald R. Askeland and Pradeep P. Phulé, The Science andEngineering of Materials, 4th edition

( Chapter 4)



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1. W. D. Callister, Jr. and D. G. Rethwisch, 2010, MaterialsScience and Engineering: An Introduction, 8th edition, JohnWiley.( Chapter 5)

2. Leonid Zhigile, Lecture Note, MSE 209: Introduction to theScience and Engineering of Materials,http://www.people.virginia.edu/~lz2n/mse209/( Chapter 5)

3. Donald R. Askeland and Pradeep P. Phulé, The Science andEngineering of Materials, 4th edition

( Chapter 5)

Difusi


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Referensi :Callister dan Rethwisch , 2010 , Bab6 - 7


material teknik - materi - 3 2015

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