Advanced Coatings and Surface Engineering Laboratory Surface Engineering Task Repot 2009/2/10

Advanced Coatings and Surface Engineering Laboratory Advanced Coatings and Surface Engineering Laboratory

Surface Engineering Task Repot2009/2/10


Content

• Summary of the mechanical and tribological properties of CrN/AlN superlattice coatings

• High temperature oxidation study of CrN/AlN superlattice coatings

• Updates for the work of AlN ‘smart’ coatings

• Ready to use the Modulated pulse power (MPP) to produce the optimized coating system for the die casting dies


Example of the Multilayered Superlattice Cr/CrxNy/CrN/AlN Coatings

75-500 single layers with bilayer period from 2.5 to 20 nm

2-3 um thickness

substrate

CrN

AlN

Cr/Cr(N) graded

Schematic drawing Typical multilayered structure

Interface between the superlattic layers and the graded adhesion layer

CrN/AlN

Graded CrN

Cr

Bilayer period=22 nm


Deposition system: – Pulsed closed field unbalanced magnetron sputtering (P-CFUBMS);– The Cr and Al targets were installed facing opposite to each other;– The targets were powered by Advanced Energy Pinnacle Plus Dual Channel Power Supply;– The substrate holder was rotated back and forth between Cr and Al targets to deposit CrN

and AlN nanolayers; – The thickness of individual layer thickness were controlled by the target power density and

the settle periods of the substrates facing each target.

– 400-1000 W Target power; 2 mTorr working pressure, 50% N2 flow, -50 V substrate bias

Cryo Pump

Stepping motor

Cr Al

Ar+N2

Substrate


Exaples of the TEM Micrographs

Bilayer period=3 nm Bilayer period=5 nm

CrN

AlN


Mechanical and tribological properties of CrN/AlN coatings as a function of CrN layer thickness

CrN/AlN superlattice coatings exhibit greatly improved mechanical and tribological properties compared to single layer CrAlN coatings


Comparison of the wear track and wear depth of single layer CrAlN coating and CrN/AlN coating

Single layer CrAlN

CrN/AlN superlattice

Test parameters: 3N normal load, WC-Co ball, 5000 testing cycles


Oxidation behavior of CrN/AlN superlattice coatings


LAXRD pattern of CrN/AlN coatings with two different bilayer periods

1 2 3 4 5 6 70

3000

Inte

nsit

y [

arb.

uni

ts]

2-Theta

0

3000

0

3000

0

3000

0

3000

0

3000

1100 oC

1000 oC

900 oC

800 oC

As-deposited

700 oC

1 2 3 4 5 6 7

0

Inte

nsit

y [c

ount

s/se

c]

2-Theta

0

0

0

0

0

1100 oC

1000 oC

900 oC

800 oC

As-deposited

700 oC

3.0 nm 12 nm


SEM micrographs of CrN/AlN coatings of different bilayer periods after annealed at different temperatures

800 oC 900 oC 1000 oC


XRD patterns of CrN/AlN coating with 3.0 nm bilayer period annealed at different temperatures

24 26 28 30 32 34 36 38 40 42 44 46 48 50

Al2

O3(

113)

CrN

(111

)

Sub

CrN(200)C

r2O

3(12

0)

Al2

O3(

104)

Cr2

N(0

02)

Cr2

N(1

10)

Cr2

O3(

110)

Cr2

O3(

121)

Al2

O3(

012)

Cr2

O3(

012)

Inte

nsi

ty [

arb.

uni

ts]

Diffraction angle [ 2]

Cr(

110)

Cr2

N(1

11)

900 oC

1100 oC

1000 oC

950 oC

800 oC

As-deposited

700 oC


Isothermal oxidation test at 800 oC for different periods

60hr 150hr 300hr


Isothermal oxidation test at 800 oC for different periods

60hr 150hr 300hr


Hardness of CrN/AlN coatings measured after thermal annealing tests

0 200 400 600 800 1000 12005

10

15

20

25

30

35

40

45

Har

dn

ess

[GP

a]

Annealling temperature [ oC]

3.0 nm 12 nm Homo


Sumarry

• CrN/AlN superlattice coatings exhibit further improved mechanical and wear resistance to the single layer CrAlN coatings

• CrN/AlN superlattice coatings also show excellent oxidation resistance both for high temperatures and long periods oxidation attack.

• Challenge: for complex shape dies (using MPP is a promising approach)


Progresses in the work for AlN ‘smart’ coatings

• Dr. Fengli Wang has left ACSEL

• Ph.D. student Masood took over the research work on the development of AlN based ‘smart’ coatings.

• New Ph.D. student Ningyi Zhang will work on the other piezoelectric coating material LiNbO3 which is also a potential ‘smart’ coating candidate.


MPP™ - An Alternative HPPMS/HiPIMS Technology

• Modulated Pulse Power - MPP™ – High power pulse magnetron sputtering technique– Heart of technology is the Zpulser™ plasma generator

Produces a multi-step DC pulse First step – ignition of low power discharge Second step – low power discharge Third step – transient stage from low power discharge to high

power discharge Forth step- high power discharge

Zpulser™ now at ACSEL


MPP™ TechnologyModulated Pulse Power (MPP) Provides:

High ionization degree of metal species (see the plasma density)

high deposition rates (for both metal and insulating films)

Deposition of dense and uniform films

Easy scaling up (has moderate peak power, reduced cost)

Influencing film properties and structure by modulated pulse parameters (various controls)

2 4 6 8 10 12 14 16 18 20 22 24

40

60

80

100

120

140

160

180

200

220

240

Average Target Power Density [W/cm2]

Dep

osi

tion

Rate

[n

m/m

in]

MPP Cr DC Cr

The increase rate of the deposition rate

in MPP changes near 11-12 W/cm2

dc

MPP

Dc Cr

MPP Cr

The same power density on the target


MPP System in ACSEL

Hiden electrostatic quadrupole plasma mass spectrometer (EQP)

Unbalanced magnetrons (100 mm x 280 mm)

MPP system and EQP plasma analyzer

Closed magnetic configuration

Zpulser MPP generator


Plasma Characterization

• Hiden EQP mass-energy analysis– Compared conventional DC and MPP power with closed-field

unbalanced magnetrons• Only used one active magnetron

– Measured• Mass peak intensities

– 52Cr+1 (plus isotopes), 40Ar+1, and 26Cr+2

• Ion energy distributions– 52Cr+1, 40Ar+1, and 26Cr+2

EQP

Cr Al

N

N

S

S

N

S

14 cm

Closed Magnetic field

EQP

Cr Al

N

N

S

N

N

S

S

N

S

S

N

S

14 cm

Closed Magnetic field


Comparison of DC and MPP Positive Ion Mass Scans52Cr+1

40Ar+1

52Cr+1

40Ar+1

26Cr+2

• Significant increase in the number of both target metal and gas ions for MPP than dc discharge

• Number of ions much greater for MPP than DC• In MPP, number of ions increased when average-peak power increased

DC sputtering Pave=3.5 kW

MPPTM sputtering Pave=3.5 kW


Microstructure Comparison (DcMS, PMS, MPP)

fN2 =20-30%(h-Cr2N)

DcMS PMS MPP

fN2 =50-60%( c-CrN)

Zone-T columnar grains High density and fine grains High density and fine grains


Wear Resistance

0 10 20 30 40 50 600.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

MPP CrN coatings (Floating bias) dc CrN coatings (-50V bias) PMS CrN coatings (-50V bias)

Coe

ffic

ien

t of

Fri

ctio

n

Nitrogen Flow Rate Percentage [%]

Pin-on-disc test

(3 N, 40 rpm, 5000 cycles, 1mm WC-Co ball)

The COF is lower in the MPP CrN coatings than in dc and PMS CrN coatings.


Using Two Pulse Shapes• Working pressure: 5 mTorr• Nitrogen flow rate percentage: 40%• Two pulse shapes alternating (see the figures below) • Substrate bias: floating

700 s (6/6), 100 Hz rep rateDuration: 1S and 3S

1500 s (6/10), 30 Hz rep rateDuration: 1S and 2S

A

A


Video showing Modulated Pulse Power Pulse


Two pulse shapes with 1s Duration

700 s (6/6), 100 Hz rep rate 1500 s (6/10), 30 Hz rep rate

Denser structure with finer grains Properties:Hardness: 28.7131.615GPaYoung’s Modulus: 314.966 11.87GPaH/E ratio: 0.091COF: 0.25

0 1000 2000 3000 4000 5000 6000 70000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

MPP CrN coating (11)

CO

F

Cycles

COF(ave)=0.25

Pave=0.8 kWDuration: 1S

Pave=3.5 kWDuration: 1S


MPP Summary

• Excellent ionization of sputtered species (denser coating and excellent adhesion)

• High rate process (Cr coating depositions)

• Conducted EQP analysis of MPP and DC plasmas for closed-field UBMs– Number of ions increased when average-peak power increased

• Many more 52Cr+1 ions for MPP than DC

• Significant number of Ar ions

– Average energy for 52Cr+1 ions ~ 2eV• Very small high energy tail

• Almost mono-energetic source of ions

• MPP CrN coatings prepared at a floating substrate bias exhibited denser microstructure, comparable hardness and improved wear resistance to dc sputtered CrN coatings synthesized using -50 V dc substrate bias.

• MPP CrN coatings deposited using multiple pulse shapes exhibit further improved H/E ratio and wear resistance, where a low COF of 0.25 has been identified.

Documents

Advanced Coatings and Surface Engineering Laboratory Surface Engineering Task Repot 2009/2/10