Felületmódosítás

Korszerű anyagok és technológiák, MSc

2013

A felületi tulajdonságok tudománya: átfogó (interdiszciplináris) terület

• A felület a tiszta fizikai és kémiai tulajdonságok szemszögéből.• Topográfiával kapcsolatos tulajdonságok (felületi érdesség).

• Tágabb értelemben: „surface engineering”: komplex nézőpont• Kapcsolat a felületi tulajdonságok, az alkalmazás és az

alkalmazott technológiák között.

• (Tiszta fizikai és kémiai tulajdonságok: alapkutatás szemszöge.)

• A felületek tulajdonsága a felhasználók szempontjából: „surface engineering”.

Kondenzált anyagok nagy fajlagos felülettel:a „komplexitás” alapja a felület

• Felületi tulajdonságok kialakulása ← klaszterek tulajdonsága (mérethatás):

• „Méretfüggő” tulajdonságok: átmenet az önálló atomtulajdonságok és a termodinamikailag stabil makroszkópos tulajdonságok között;

A redukált ionizációs energia különböző szabadfelületű fémklaszterek esetében a klaszterátmérő reciprokának függvényében

Aim: the local modification of surface properties changing either the local composition or the structure or both of them.

The desired surface properties are often contradict to those in the bulk! (i.e. local hardness, local corrosion resistance)

examples: development of peculiar compositional relations on the surface of semiconductors

The development of hard, wear- or corrosion-resistant surfaces on cutting, drilling tools

Development of optical or decorative layers

Two alternatives:Covering the surface with protective layer (corrosion resistant layers)Structural or compositional changes in the surface layer

Traditional methodsIncrease of non-metallic element concentration in the surface layer, using heterogeneous reaction.i.e. iron/steel heating in appropriate gas-mixture (carbonization, decarbonization, nitridation)

CH4 [C]Fe + 2H2 CH4/H2

2NH3 [N]Fe + 3H2 NH3/H2

Layer deposition using electrochemical or chemical methods Hard chromium-layer (3-500 μm, HV 900-1100)Ni-P amorphous layer (3-30 μm, HV 1300)Surface hardening using inductive heating and subsequent rapid cooling

Inductor

Cog wheel

Inductor

Cog wheel

forrás: Szurdán Szabolcs

Deposition of thin layers by physical methods (Physical Vapour

Deposition, PVD)

• favour:

• High melting point metals can be deposited to low substrat temperature because• T substrat can be low

• The electrical conductivity of substrate not necessary

• Complex multilayers can be deposited

• Alloy deposition is also possible

• „clean technology” (without the formation of products causing environmental pollution)

• limits:

• Expensive (vacuum circumstances)

PVD (physical vapor deposition)The original, traditional technologies: chemical reactions are not included ( i.e. mirror production)

Schematic illustration of the principle

The technical arrangementCrucial in every deposition is the layer duration, which is influenced mainly by the surface preparation

(cleaning)

Heating

Substrate

Source

Vacuum system

Source

Chamber

Window

Layer thickness measure

Substrate holder

Evaporate source

Cover plate

Freezer

Diffusion pump

Pre-vacuum pumps

Valve

Mask

Physical Vapour Deposition

Source: Platit

0,1

Ts/Tm

0,60,50,40,30,2 0,7

The real structure of the deposited layer versus the substrat to melting point temperature

Deposition of TiN layer on the surface of tools for the purpose of surface hardenening

The dimensions

Source: Platit

Some another exmples

Source: Platit

The machined length versus the main machining parameters: cutting speed (a) and feed (b) ( • TiN coated, o TiN coated and newly grinded, □nitride coating ■ without coating

Mac

hin

ed l

eng

th [

m]

Mac

hin

ed l

eng

th [

m]

Cutting speed [m/min] Feed [mm/rev]

Chemical Vapour Deposition, (CVD)basic principles

In the original form, the procedure consist of two isothermal reactions:a.) at T1 temperature M +nXMXn (M layer forming metal , X halogen) At T1 a volatile compound is formedb.) at T2 (T2 > T1 ) MXnM + nX Thermal decomposition of MXn occur on the substrate surface Subsequently the decomposition process, the halogen molecule is circuated (in order to form new volatile molecules)

Typical chemical reactions in the CVD procedure: Metal-halogenides are often used as precursor materials in these techniques.The reason: volatile compounds (high tension even at low temperatures!) (see tables)

Besides the metal-layer depositions, the method also used for compound depositions (refractory carbides, silicides, borides)

Typical CVD reactions

CrI2(g) 800-1000 ºC Cr(s) + 2I(g)

WF6(g) + 3H2(g) 350-1000ºC W(s) + 6HF(g)

WCl6(g) + 3H2(g) 500-1100ºC W(s) + 6HCl(g)

TaCl5(g) +5/2 H2(g)700-1100ºC Ta(s) + 5HCl(g)

(C8H10)2Cr(g)400-600ºC a Cr(s) + 2C8H10(g)

Ni(CO)4 150-200ºC b Ni(s) + 4CO (g)

Al2Cl6(g) + 3H2O(g) 800-1400ºC Al2O3(s) + 6HCl(g)

BCl3(g) + NH3(g) 500-1500ºC BN(s) + 3HCl(g)

TiCl4(g) + CH4(g) 800-1100ºC TiC(s)+ 4HCl(g)

Ga(g) + AsCl3(g) + 3/2H2(g) 750-900ºC GaAs(s) + 3HCl(g)

Typical reactants, processing parameters for a few depositions

Typical reactants, processing

parameters for a few depositions

layer reactant Add. reactant

T (C) pressure(kPa)

Deposition velocity(nm/min)

W WF6

WCl6

WCl6

W(CO)6

H2

H2

------

250-1200850-14001400-2000180-600

0,133-1000,133-2,670,133-2,670,013-0,133

0,127-50,80,254-38,12,54-50,80,127-1,27

Mo MoF6

MoCl5

MoCl5

Mo(CO)6

H2

H2

------

700-1200650-12001250-1600150-600

2,67-46,70,133-2,671,33-2670,013-0,133

1,27-30,51,27-20,32,54-17,80,127-1,27

Re ReF6

ReCl5

NbCl5

NbCl5

NbBr5

H2

---H2

---H2

400-1400800-1200800-12001880800-1200

0,133-13,30,133-26,70,133-1000,133-2,670,133-100

1,27-15,21,27-15,20,076-25,42,540,076-25,4

Nb NbCl5

NbCl5

NbBr5

H2

---H2

800-12001880800-1200

0,133-1000,133-2,670,133-100

0,076-25,42,540,076-25,4

Ta TaCl5

TaCl5

H2

---

800-12002000

0,133-1000,133-2,67

0,076-25,42,54

Zr ZrI4 --- 1200-1600 0,133-2,67 1,27-2,54

Hf HfI4 --- 1400-2000 0,133-2,67 1,27-2,54

Ni Ni(CO)4 --- 150-250 13,3-100 2,54-38,1

Fe Fe(CO)5 --- 150-450 13,3-100 2,54-50,8

V VI2 --- 1000-1200 0,133-2,67 1,27-2,54

Cr CrI3 --- 1000-1200 0,133-2,67 1,27-2,54

Ti TiI4 --- 1000-1400 0,133-2,67 1,27-2,54

The important metals and ceramics produced by the CVD method

Metals Cu, Be, Al, Ti, Zr, Hf, Th, Ge, Sn, Pb, V, Nb, Ta, As, Sb, Bi, Cr, Mo, W, U, Re, Fe, Co, Ni, Ru, Rh, Os, Ir, Pt

Graphite carbides karbon C, B4C, SiC, TiC, ZrC, HfC, ThC, ThC2,VC,

NbC, Nb2C, TaC, Ta2C, CrC, Cr4C, Cr7C3,

Cr3C2, MoC, Mo2C, WC, W2C, VC2, V2C3

Nitrides BN, TiN, ZrN, VN, NbN, TaN, Si3N4

Boron and borides B, AlB2, TiB2, ZrB2, ThB4, ThB, NbB, TaB,

MoB, Mo3B2, WB, Fr2B, FeB, NiB, Ni3B2,

Ni2B

Silicon and silicides Si és Ti, Zr, Nb, Mo, W, Mn, Fe, Ni, Co and varies silicides

Oxides Al2O3, BeO, SiO2, ZrO2, Cr2O3, SnO2

Examples for the compound-layer deposition

• The TiN layer deposition:

• 2 TiCl4 +4 H2 +N2 2 TiN +8HCl

• Al2O3 layer deposition:

• 2AlCl3 +3CO2 +H2 Al2O3 +3CO +6HCl

The scheme of complete unit for CVD technology

Gases

Halide preparatory

Gas mixer

Programming unit

Deposition chambers

Outgoing gas cleaner and neutralizer

Heating bell

Vacuum pump

Hea

tin

g

con

tro

ller

Heating bell

Gas

su

pp

ly

The properties of deposits produced by CVD ,

layer-substrate: the compatibility

Favour: -high temperature: deposit accomodat even the complicated,

irregular surfaces (inner surfaces can be covered)

Another example

Tantállal bevont gégecső

The limits:

• The high substrat temperature (for example for structural or carbon steels is not recommended! 6-800 oC!)

• Expensive reactants

The properties of CVD-produced policrystalline diamond layers:

high chemical resistance, high hardness, high wear resistance, low frictional resistance

Polymer

Diamond

DLC

Graphite

Gyémánt és gyémántszerű amorf rétegek

DLC: Diamond-Like Carbon

Hardness and young moduli of carbon- based coated layers

Me: fém az elektromos vezetőképesség növeléséhez, fém-karbidokH: hidrogéntartalom a C2H2 elbomlásából a: amorf fázis tartalmú rétegSi: szilíciumtartalomi-C: mátrix sp3-as kötésekkel, de amorf

The techniques of plasma spraying

Helium

Hővezetési tényező

Plazmagáz energiatartalma

Shematic drawing of plasma spraying and the SEM photograph of the sprayed coating

Characteristics of plasma-sprayed layers

Improvement of

Succesfully applied for

•Abrasive properties•Hardness•Corrosion resistance•(Especially in those cases, when the base material is low-cost

•improvement of bio-compatibility (implanted parts)

•the surface improvement of carbon-steels

•surface hardness increase •corrosion resistance increase

The modes of plasma welding:inner, outher wire supply, powder supply

The laser surface treatments

The effectivity highly depends on the absorption degree

The absorption degree of various laser beams as a function of wavelengths

Exc

imer

lase

r

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.1 1 10 100Hullámhossz [m]

Ab

szo

rpci

ós

fok

[%

]

Exc

imer

léz

er

Acél

Fe

Mo

Al

Cu

Au

AgN

d:Y

AG

léz

er

CO

2 l

ézer

Dió

da

léz

er

30

20

10

Iron

Wavelength (m)

Ab

so

rpti

on

de

gre

e [

%]

Nd:

:YaG

lase

r

Dio

de la

ser

Exc

imer

lase

r

CO

2 la

ser

The thickness of hardened layer as a function scanning rate on steels with various surface roughness

The absorption degree also depends on the surface roughness

0.4

0.8

1.2

1.6

400 500 600 700

előtolási sebesség [mm/min]

edze

tt r

éteg

vas

tags

ága

[mm

]

mart felület

köszörült felületpolírozott felület

Anyag: CMo4P= 2000 W

Milled surface

Grinded surface

Polished surface

Material: CMo4

Feed [mm/min]

Har

den

ed l

ayer

th

icjn

ess

[mm

]

Laser marking on steel surfaces

The local structural change as the basis of code formation

Depending on the applied energy density various structural changes can be induced

(phase transformation, recrystallisation etc)