outline - tum lvivseptember2014.pdf · 1. introduction: the recent search for new superhard...

NAP , Lviv, September 22

The Recent Search for New Superhard Materials: Go Nano!

S. Veprek

Department of Chemistry, Technical University Munich, Garching, Germany

[email protected]

Outline 1. Introduction: The Recent Search for New Superhard Materials: Go Nano !

2. The role of interfaces for achieving high strength and hardness

3. The nc-TiN/SiNx system – brief summary

4. Other TmN/XY systems, TmN = TiN, ZrN, …; XY = SiC, BN, AlN

DFT & QMD Calculations & Thermodynamic Consideration

5. Summary and Outlook

Acknowledgment Dr. V.I. Ivashchenko Academy of Sci. Kiev,

Prof. R.F. Zhang, Beihang University, Beijing

Dr. M.G.J. Veprek-Heijman, Technical University Munich

Prof. A.S. Argon, MIT, Cambridge, USA

Dr. S.H. Sheng, TUM, now: Beihang University, Beijing

and many more

mailto:[email protected]

“superhard” ≥ 40 GPa “ultrahard” ≥ 70 GPa

c-BN ≈ 48 GPa Diamond ≈ 70 – 90 GPa

Hardness is only one of many properties: “hot hardness”; thermal stability; oxidation

& corrosion resistance; coefficient of friction; fabrication & price

H = average pressure beneath the indenter under conditions of fully developed plasticity H must be load invariant

sufficiently high load and thick coating

H = L/AC AC = contact area of remnant plastic deformation

ε – strain

Size Indentation Effect at low applied load

The meaning of Indentation Hardness

E. Meyer, Zt. D. Vereines Deutscher Ingenieure 52 Nr.17(1908)645 ; D. Tabor, The Hardness of Metals Clarendon Press, Oxford 1951

Load-invariant hardness

In the superhard nanocomposites the plastic flow take place by shear within the

grain boundaries (“G.B. sliding”),

therefore the load-invariant hardness is achieved already at relatively low load

S. Veprek, J. Vac. Sci. Technol. A 31 (2013) 050822

13.8 µm thick coating deposited by plasma

CVD with low biaxial stress of ≤ 0.4 GPa

30.6 µm thick coating deposited by reactive

sputtering with biaxial stress of ≈ 2 GPa

Note the role of the choice of the hardness of Si used for the calibration of the instrument

Many possible mistakes when using the automated load-depth sensing techniques

1 N

In the superhard nanocomposites the plastic flow take place by shear within the

grain boundaries (“G.B. sliding”),

therefore the load-invariant hardness is achieved already at relatively low load

S. Veprek, J. Vac. Sci. Technol. A 31 (2013) 050822

13.8 µm thick coating deposited by plasma

CVD with low biaxial stress of ≤ 0.4 GPa

30.6 µm thick coating deposited by reactive

sputtering with biaxial stress of ≈ 2 GPa

Note the role of the choice of the hardness of Si used for the calibration of the instrument

Many possible mistakes when using the automated load-depth sensing techniques

1 N

Whereas in many intrinsically superhard materials the load-invariant hardness

is reached only at large load

Example: ReB2:

Chung et al. Science 316(2007)436

ReB2 is not superhard !

Load-invariant

H < 30 GPa

Intrinsically Superhard Materials

attain their high hardness from

- strong covalent bonds,

- three-dimentional lattice network and

- electronic stability upon finite shear where plastic deformation occurs

Extrinsically Superhard Materials

attain their high hardness from

their nanostructure which impedes plastic flow

Diamonds are beautiful

Diamond is the hardest material

and sexy

Diamonds are beautiful

Diamond is the hardest material Can a material be harder than Diamond ?

and sexy

Strength of engineering materials << The ideal strength of flaw-free crystal

Ideal strength = The upper limit

1. Ideal Shear Strength:

relevant to plastic deformation

C 0.1G-Shear modulus

2. Ideal Decohesion strength: relevant

for brittle fraction & crack growth

2/1

0

a

Ec

YSurf

C

0.1EY

compres-

sive

tensile

0

Inte

rnal E

nerg

y

Strain

Decohesion Strength

max

0

d E

/dx

Ten

sile R

esis

tan

ce

Strain Large modulus hard material ?

What Determines the Strength & Hardness ?

No !

Elastic moduli describe reversible elastic deformation under infinitesimal strain whereas irreversible plastic deformation occurs at large strain where electronic

instabilities and structural transformation to softer phases may occur

Electronic instability at strain 0.24 Non-binding electron pairs on N interact with C-orbitals

Transformation of c-C3N4 to graphitic-like phase

The story of C3N4

Strain ε 0.1 0.2 0.3

M. Cohen et al., 1985: first principle calculation High B0 High H c-BN < C3N4 ≈ Diamond

Y. Zhang et al. 2006: B0 380 < 423 < 451 GPa

But: measured H(a-C3N4) ≈ 26-28 GPa

Veprek et al., J. Vac. Sci. Technol. A 13 (1995) 2914

c-C3N4 graphitic phase

Y. Zhang et al., Phys. Rev. B 73(2006) 064109

c-BN

Diamond

"Since B0 is related to the strength of a bond, it is

ultimately related to hardness."

“Bond Strength Based Models of Hardness”

M. Cohen et al., 1985, …

B(GPa)= 0.25NC(1971-220λ)/d(Ǻ)3 λ=“ionicity“ 1 for III-V; 2 for II-VI

H of an ideal single crystal ?

“Bond Strength Based Models of Hardness”

M. Cohen et al., 1985, …

B(GPa)= 0.25NC(1971-220λ)/d(Ǻ)3 λ=“ionicity“ 1 for III-V; 2 for II-VI

H of an ideal single crystal ?

“Hardness of an ideal crystal” ??

Hardness is the average pressure beneath the indenter under conditions of fully

developed plasticity no any “ideal crystal”

these “theories” confuse plastic hardness with elastic stiffness

5d transition metals high elastic moduli: Os: B0 ≈ 395-462 GPa

(Diamond 443 GPa) but low H≈ 3-4 GPa due to metallic bonds

Suggestion: “5d metals diborides should be superhard”

HOWEVER:

H(OsB2) ≤ 20 GPa Because of easy shear between Os-Os planes J. Yang, H. Sun, C.G. Chen, J. Am. Chem. Soc. 130(2008)720

H(ReB2) < 30 GPa due to electronic instabilities at finite strain

Zhang, Legut, Niewa, Argon and Veprek Phys. Rev. B 82 (2010) 104104

Veprek, Argon and Zhang, Phil. Mag. 90 (2010) 4101

Shear-induced structural transformations and low shear resistance upon finite strain in ultra-incompressible ReB2 limit its hardness

S. Veprek, A.S. Argon, R.F. Zhang, Phil.Mag. 90 (2010) 4101.

R.F. Zhang, D. Legut, R. Niewa, A. S. Argon and S. Veprek, Phys. Rev. B 82 (2010) 104104

γ

Valence Charge Density

in equilibrium

The boron rings intercalated between the Re planes are holding the structure together; Re-B bonds are weak

Re

B

Bond

breaking

Bond

recovers

γ

Re

B dσ/dγ < 0 inherent instability stress

decreases with increasing strain

0.0 0.5 1.0 1.5 2.0 2.5 3.00.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

VC

DBond distance

B1-B2

=0.0000

=1.1436

=1.5871

=1.9717

B B

Full recovery if stable

The Boron network which has been holding the system

collapsed due to 5d crystal field splitting instabilities

Boron network still strong



R.F. Zhang, D. Legut, R. Niewa, A. S. Argon and S. Veprek, Phys. Rev. B 82 (2010) 104104

γ

Re

B dσ/dγ < 0 inherent instability stress

decreases with increasing strain

0.0 0.5 1.0 1.5 2.0 2.5 3.00.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

VC

DBond distance

B1-B2

=0.0000

=1.1436

=1.5871

=1.9717

B B

Full recovery if stable

The Boron network which has been holding the system

collapsed due to 5d crystal field splitting instabilities

Boron nettwork still strong



R.F. Zhang, D. Legut, R. Niewa, A. S. Argon and S. Veprek, Phys. Rev. B 82 (2010) 104104 Complex changes of the interaction of B-atoms with

the d-orbitals of Re result in large changes of

electronic DOS at Fermi level

The complex transformations to phases with lower plastic resistance are

responsible for the sluggish approach to load-invariant hardness

In the nanocomposites the grain boundaries are

the carrier of plastic flow and, therefore, the

load-invariant hardness is achieved already at

low load of 50 – 100 mN

see above

ReB2

OsB2 & IrB2 Me-double layer yet different deformations paths R.F. Zhang et al. Phys. Rev. B (2014) in press

In equilibrium (strain ε = o) similar

structures with Me double layers only

slightly different inter- and intra-plane

Me-Me distances

IrB2 OsB2

Shear within the weakest slip system

(001)[100]

before and after instability

IrB2

OsB2

Similar structure but different deformation paths

Electronic structure:

Os: [Xe] 4f 14 5d6 6s2

Ir: [Xe] 4f 14 5d7 6s2

Diamond also transforms to Graphite upon (111)[11-2] shear (left) but because of its “simple” electronic structure

this transformation needs very high strain & stress (right)

Note: Diamond is metastable to Graphite, but Eact ≈ 700 kJ/mol

S. Veprek et al. Philos. Mag. 90 (2010) 4101

Diamond

Diamond

ReB2

ReB2

What about BC5 with H = 71 GPa – load invariant ! No such electronic instabilities expected in this material

V. L. Solozhenko, et al., Phys. Rev. Lett. 102(2009)015506

c- BC5 with H = 71 GPa – load invariant ! Synthesis at 24 GPa & 2000 K

V. L. Solozhenko et al., Phys. Rev. Lett. 102 (2009) 015506

Low ideal strength of 37 – 54 GPa < c-BN 58-62, Diamond ≥ 87 GPa

R.F. Zhang, S. Veprek and A.S. Argon, Phys. Rev. B 80 233401 (2009)

Explanation:

The Nanosize Effect

due to 10–15 nm small nanocrystals

The Strongest Size A.S. Argon & S. Yip, Phil. Mag. Lett. 86 (2006) 713

It cannot be

intrinsically superhard

The “Strongest Size” A.S. Argon & S. Yip, Philos. Mag. Lett. 86(2006)713

J. Schiotz & K.W. Jacobsen, Science 301(2003)1357; etc.

10-1

100

101

102

103

104

105

0

5

10

15

20

Grain

Boundary

Shear

Hall - Petch Hardening

H(d) = H0+ k/d0.5

Ha

rdn

es

s (

r.u

.)

Crystallite Size d (nm)

10-1

100

101

102

103

104

105

0,0

0,2

0,4

0,6

0,8

1,0

VG.B./Vtotal ~ 1/d

Vo

lum

e F

rac

tio

n o

f G

rain

Bo

un

da

rie

s (

r.u

.)


Hall-Petch Strengthening:

Decrease of dislocation activity with decreasing crystallite size E.O. Hall, Proc. Phys. Soc. B 64 (1951) 747; N.J. Petch, Iron Steel Inst. 174 (1953) 25.

and other mechanisms of plasticity: slip, twinning, shear …

Below about 10-15 nm strong increase of the material

fraction in Grain Boundaries

Softening due to G. B. Shear

“the Strongest Size”

Generic Mechanism

working almost in any system e.g. TiAlN:

- Pure system d = 110 nm H = 22 GPa

- O-contaminated d = 20 nm H = 30 GPa

But: Fracture Toughness ?

See:

H. Riedl et al., ICMCTF San Diego, 28. April – 2. May 2014

How to Achieve Super- > 40 GPa & Ultrahardnes ≥ 80 GPa?

10-1

100

101

102

103

104

105

0

5

10

15

20

Grain

Boundary

Shear


H(d) = H0+ k/d0.5

Ha

rdn

es

s (

r.u

.)


10-1

100

101

102

103

104

105

0,0

0,2

0,4

0,6

0,8

1,0

VG.B./Vtotal ~ 1/d

Vo

lum

e F

rac

tio

n o

f G

rain

Bo

un

da

rie

s (

r.u

.)


Hall-Petch Strengthening:

Decrease of dislocation activity with decreasing crystallite size E.O. Hall, Proc. Phys. Soc. B 64 (1951) 747; N.J. Petch, Iron Steel Inst. 174 (1953) 25.

and other mechanisms of plasticity: twinning, shear …

Below about 10-15 nm strong increase of the material

fraction in Grain Boundaries

Softening due to Grain Boundary Shear

“the Strongest Size“

“the Strongest Size” Argon & Yip, Phil. Mag. Lett. 86(2006)713

We can reduce the G. B. Shear by

Low-Energy G. B. ?

Examples:

- Stacking Faults in Mg-Alloy prepared by SPD W.W. Jian et al., Mater. Res. Lett. 1(2013)61

- Nanotwinned c-BN H ≈ 108 GPa

Y. Tian et al., Nature 493(2013)385

- Nanotwinned Diamond H ≈ 200 GPa

Q. Huang et al., Nature 510 (2014) 250

Twins and stacking faults = coherent interfaces

10-1

100

101

102

103

104

105

0

5

10

15

20

Grain

Boundary

Shear


H(d) = H0+ k/d0.5

Ha

rdn

es

s (

r.u

.)


-Nanotwinned c-BN

Y. Tian et al., Nature 493(2013)385

Energy of twinned G.B. ≈ 0.1 large-angle G.B.

TB – twin boundaries

STs – stacking faults

▲ - dislocations

It works but many open

questions: H enhancement still limited

to about a factor of 2

The role of other defects ?

▲ twinned c-BN

■ nc c-BN



108 GPa

Martensitic transition

Nanotwinned Diamond Q. Huang et al. Nature 510 (2014) 250


nt- Diamond

natural Diamond

{110} face

{111}

The nt-Diamond shows also high fracture

toughness and oxidation resistance

“One cannot measure hardness larger than the

H of the Diamond indenter” ! e.g. press release of Saxonian Inst. Surf. Mechanics

elementary knowledge missing ∙/∙

ISE

Martensitic transition

Slip-Line Fields theory

R. Hill, The Mathematical Theory of Plasticity, Clarendon Press, Oxford 1950

F.A. McClintock and A.S. Argon, Mechanical Behavior of Materials, Addison-Wesley Publ., Reading 1966

A.Y. Ishlinsky, J. Appl. Math. Mech. (USSR) 8(1944)201

Strength of diamond in compression about 8-times higher than in shear

How can you measure hardness larger than

the H of the Diamond indenter ?

Indenter loaded in

compression

Material being indented

loaded in shear

“Ti-Si-N Films Prepared by Plasma-Enhanced Chemical Vapor Deposition”

Li Shizhi, et al., Plasma Chem. Plasma Process. 12 (1992) 278

H ≤ 70 GPa measured with load ≈ 490 mN on coatings ≈ 5 µm thin

Combined H of the film & soft steel substrate

These values underestimate the correct H(Film)

6.1 µm thick nc-TiN/a-Si3N4/TiSi2, load 1 N

Indent. depth ≈ 2 µm >15% elastic in the coating

S. Veprek & A.S. Argon, J.V.S.T. B 20 (2002) 650

Evaporate Pt strip & focused Ga ion beam etching S. Veprek in C.C. Koch et al. Structural Nanocrystalline

Materials, Cambridge University Press, 2007, Fig. 4.42

Deformation of the Film is Predominantly Elastic

The Hardness of the Films is much Higher

Measure with lower load on thicker coatings

Quasi-ternary nc-TiN/Si3N4/TiSi2 Nanocomposites Prepared by Plasma CVD






Li Shizhi et al.

1992

Tech. Univ. Munich MRS Symp Proc. 581 (2000) 321

Surf.Coat.Technol. 133-134 (2000) 152

Thin Solid Films 522 (2012) 274

nc-TiN/Si3N4/TiSi2

7.3 µm thick










0 50 100 150 200 250 300 350 400 450 500 550

0

20

40

60

80

100

120

FEM Calculations

Ha

rdn

es

s

(G

Pa

)

Load (mN)

Measurements

nc-TiN/Si3N4/TiSi2

7.3 µm thick

┼ measured

○ non-linear Finite Element Modeling M.G.J. Veprek-Heijman & S. Veprek, 2014 Submitted










0 50 100 150 200 250 300 350 400 450 500 550

0

20

40

60

80

100

120

FEM Calculations

Ha

rdn

es

s

(G

Pa

)

Load (mN)

Measurements

nc-TiN/Si3N4/TiSi2

7.3 µm thick

┼ measured

○ non-linear Finite Element Modeling M.G.J. Veprek-Heijman & S. Veprek, 2014 Submitted

Correct harndess of coatings by

Li Shizhi et al. 1992

calculated by non-linear FEM

● Li

3. The quasi-binary are more sensitive to oxygen impurities, but H ≈ 65-70 GPa has

been reported when [O] ≈ 100 ppm.

SEM Micrograph of an indentation into

about 8 µm thick nc-TiN/Si3N4 coatings with

a load of 110 mN

Thin Solid Films 522(2012)274

1. The quasi-ternary nc-TiN/a-Si3N4 /TiSi2 are unstable in long-terms because of the

metastable TiSi2

2. The quasi-binary nc-TiN/Si3N4 are stable for years (measured up to 5 Y)

Why such High sensitivity ?

(a)

High Sensitivity of Interfaces to Impurities 100 ppm Bi in Cu Embrittlement known since > 100 Years

(b)

double-layer at high Bi activity (also in Ni)

J. Luo et al., Science 333(2011)1730

J. Kang et al., Phys. Rev. Lett. 111(2013)055502

A. Kundu et al. Scripta Mater. 68(2013)146J.

a) Theoretically Predicted Structure (V. Vítek et

al., in: Interfaces: Structures and Properties, ed. S.

Ranganathan, Trans. Tech. Publ., New Dehli 1999, p. 3;

Min Yan et al., Phys. Rev. B 47 (1993) 5571)

b) HR TEM image (M. Rühle et al., in: Inst. Phys.

Conf. Series No. 161: Section 1, 1999 IOP Publ. Ltd, ed.

C. J. Kiely, p. 1)

3. The quasi-binary are more sensitive to oxygen impurities, but H ≈ 65-70 GPa has

been reported when [O] ≈ 100 ppm.

SEM Micrograph of an indentation into

about 8 µm thick nc-TiN/Si3N4 coatings with

a load of 110 mN


1. The quasi-ternary nc-TiN/a-Si3N4 /TiSi2 are unstable in long-terms because of the

metastable TiSi2

2. The quasi-binary nc-TiN/Si3N4 are stable for years (measured up to 5 Y)

Questions:

Why no other researchers reproduced these results

for nc-TiN/Si3N4 and other nc-TmN/XY ?

The usual answers:

“Veprek measured incorrectly the hardness”

See: stan.veprek.net

What can be wrong with these measurements ? nothing !!

Questions:

Could there be another explanation of this

“lack of reproducibility of high Hardness of

nc-TiN/Si3N4 and other nc-TmN/XY”?

The answers will come in this lecture

Outline 1. Introduction


3. The nc-TiN/SiNx system – brief summary hardening mechanism?




10-1

100

101

102

103

104

105

0

5

10

15

20

Grain

Boundary

Shear


H(d) = H0+ k/d0.5

Ha

rdn

es

s (

r.u

.)


10-1

100

101

102

103

104

105

0,0

0,2

0,4

0,6

0,8

1,0

VG.B./Vtotal ~ 1/d

Vo

lum

e F

rac

tio

n o

f G

rain

Bo

un

da

rie

s (

r.u

.)


Hard & Superhard nc-TiN/Si3N4 Nanocomposites:

Strong Interface

The G.B. Shear is reduced down to crystalite size of 3-4 nm

by the formation of strong interface

Thin Solid Films 522 (2012) 274; J. Vac. Sci. Technol. A 31 (2913) 050822



nc-TmN/Si3N4

HMax. at 1 ML Si3N4

which is strengthened by valence charge transfer from TiN

at 2 ML the H-enhancement lost due to too much weakening of TiN

1 ML 2 ML

a(TiN) = 4.23 Ǻ

a(VN) = 4.14 Ǻ

a(W2N)= 4.13 Ǻ

Absence of dislocation activity in 3-4 nm size polycrystals

the 1 ML (monolayer) thick interfacial Si3N4 strengthened by valence charge transfer

but weakening of Ti-N bonds adjacent to the Si3N4- like interfacial layer

lost of hardness enhancement at 2 ML Si3N4 because of the weakening of Ti-N bonds adjacent to the SiNx

S. Hao et al. Phys.Rev.Lett. (2006); Phys. Rev. B (2006) – Si3 N4 – like interfaces

R.F. Zhang et al. Phys. Rev. Lett. (2009); Phys. Rev. B (2009); (2010) – pseudomorphic SiN interfaces

Valence Charge Density Difference calculated by DFT


Strong Interface

De-cohesion strength > ideal strength of single crystal




lost of hardness enhancement at 2 ML Si3N4 due to too much weakening of Ti-N bonds



Surf. Coat. Technol. 201(2007)6064 (111) before and after decohesion

a(TiN) = 4.23 Ǻ

a(VN) = 4.14 Ǻ

a(W2N)= 4.13 Ǻ


Strong Interface

1 ML




lost of hardness enhancement at 2 ML Si3N4 due to too much weakening of Ti-N bonds



Surf. Coat. Technol. 201(2007)6064 (111) before and after decohesion

a(TiN) = 4.23 Ǻ

a(VN) = 4.14 Ǻ

a(W2N)= 4.13 Ǻ


Strong Interface

0.00 0.05 0.10 0.15 0.20 0.25-10

0

10

20

30

40

50

60

70

80

90

Str

ess

(G

Pa

)

Strain

Tensile [111] 1ML 2ML

Shear (111)[110] 1ML 2ML

Shear (111)[112] 1ML 2ML

Decohesion of [111] - 2 ML SiN

The 2 ML Interface weaker than 1 ML

R.F. Zhang, A.S. Argon, S. Veprek,

Phys. Rev. B 81 (2010) 245418

The yellow contours show valence charge density of

0.015 electrons/Bohr3 close to bond breaking

1 ML

2 ML

0.00 0.05 0.10 0.15 0.20 0.25-10

0

10

20

30

40

50

60

70

80

90

Str

ess

(G

Pa

)

Strain


Shear (111)[110] 1ML 2ML

Shear (111)[112] 1ML 2ML

Decohesion ! Decohesion of [111] - 2 ML SiN



Phys. Rev. B 81 (2010) 245418



Ti-N bonds

still O.K.

0.00 0.05 0.10 0.15 0.20 0.25-10

0

10

20

30

40

50

60

70

80

90

Str

ess

(G

Pa

)

Strain


Shear (111)[110] 1ML 2ML

Shear (111)[112] 1ML 2ML




Phys. Rev. B 81 (2010) 245418



because of larger weakening of neighbor TiN

Ti-N bonds

still O.K.

0.00 0.05 0.10 0.15 0.20 0.25-10

0

10

20

30

40

50

60

70

80

90

Str

ess

(G

Pa

)

Strain


Shear (111)[110] 1ML 2ML

Shear (111)[112] 1ML 2ML




Phys. Rev. B 81 (2010) 245418




Ti-N bonds

still ±O.K.

0.00 0.05 0.10 0.15 0.20 0.25-10

0

10

20

30

40

50

60

70

80

90

Str

ess

(G

Pa

)

Strain


Shear (111)[110] 1ML 2ML

Shear (111)[112] 1ML 2ML

Decohesion ! Decohesion ! Decohesion of [111] - 2 ML SiN



Phys. Rev. B 81 (2010) 245418




How Can We Understand Such High Hardness ?

see at the end

Limits to the Preparation of Superhard nc-TiN/Si3N4 Nanocomposites


Limits to the preparation of ultrahard nanocomposites:

2a) the nc-TiN/Si3N4 system

- Deposition conditions

The formation of the nanostructure with sharp interface is thermodynamically

driven by high activity of nitrogen and kinetically controlled by the diffusion.

Therefore it requires

Sufficiently high activity of nitrogen (partial pressure) > 0.002 mbar and

sufficiently high temperature of ≥ 550 °C

This has been discussed many times: Veprek & Reiprich, Thin Solid Films 268 (1995) 64

S. Veprek et al., Surf. Coat. Technol. 200(2006)3876

R.F. Zhang & S. Veprek, Mater. Sci. Eng. A 424(2006)128; 448 (2007) 111–119

Reviews: Thin Solid Films 476(2005)1; J. Vac. Sci. Technol. A 31(2013)050822

Very high de-mixing Gibbs free energy of the Ti1-xSixN solid solution at T = 873 K and

different nitrogen pressure as indicated

sharp 1 ML interfacial SiNx layer R.F. Zhang & S. Veprek, Mater. Sci. Eng. A 424(2006)128


2a) the nc-TiN/Si3N4 system

- Impurities: J. Vac. Sci. Technol. B 23(2005)L17

at 0.5 at.% 20 O-related defects per TiN nanocrystal H determined by defects

0.01 at.% 1 O-related defect per 2-3 TiN nanocrystal approaching defect-free system

Published papers of other groups: [O] 0.5 – ≥ 2 at.%

Maximum achievable hardness vs. O-impurities

5 P - CVD & PVD apparatusses from 3 countries

SHM

company

Oxygen impurities are limiting the diffusion and formation of the nanostructure

Si-O bond is the strongest one in the Ti-Si-N system


Temperature needed to complete the

formation of stable nanostructure

O Si

Si is lost above ≈ 1000 °C due to sublimation of SiO

Impossible to form nc-TiN/Si3N4 nanocomposite

Si


see Thin Solid Films 522(2012)274 and references therein

2 ML 1 ML

when H-enhancement maximum at 1 ML but the lost at 2 ML

the Si3N4 –like interfacial layer must be sharp

2b) Other nc-TmN/XY systems:

- absence of spinodal decomposition mechanism

Nucleation & Growth: morphology of

98%B2O3 + 2%PbO glass

J. Zarzycki, Glasses and the Vitreous State,

Cambridge Univ. Press, Cambridge 1991

Spinodally Decomposed Co2TiO4 – CoAl2O4

System

N. Burkert, et al., Ber. Bunsenges. Phys. Chem.

96(1992)1603

100 nm

Sharp interface superhardness possible if

the system is spinodal and

the interfacial layer is strengthened

Hardness enhancement only ≤ 2

See Thin Solid Films 522(2012)274 and references therein

0.0 0.2 0.4 0.6 0.8 1.0-200

-100

0

100

200

300

400

500nc-TiN/a-Si

3N

4

G

ibb

s F

ree

En

erg

y (

kJ

/mo

l)

N2 presure = 0.01 atm

0.001

0.0001

0.00001

0.000002 (0.002 mbar)

mol.% of Si3N

4TiN Si3N

4

600 °C

Spinodal: d2G/dx2 < 0

Gibbs Free Energy of the mixed Ti1-xSixN1+4x/3

interface strain energy ≤ 5 kJ/mol is balanced by the stabilization of the interface

due to negative charge transfer, it cannot hinder the spinodal decomposition

Gde-mixing ≥ 300 kJ/Mol

Strong de-mixing driving force

Different from metallic alloys:

Gde-mixing ≈ 1 – 20 kJ/mol

ABBABBAACBBCAACBA LyayyyyyaRTGyGyGcacaca

)lnln(00

),(

Where to get the T-dependent interaction parameter LAB ?

ab initio DFT calculations

R.F. Zhang & Veprek, Mater.Sci.Eng.A 424(2006)128; Phys.Rev.B 76(2007)174105; Thin Solid Films 516(2008)2264

The Formation of the nanostructure with strong interface?

the TiN/Si3N4 system

Combined DFT & Thermodynamic Calculations

Details if interests

Ti-Si-N Spinodal: R.F. Zhang & Veprek, Mater.Sci.Eng.A 424(2006)128; Phys.Rev.B 76(2007) 174105;


Ti-Al-N Partially Spinodal: R.F. Zhang & Veprek, Mater.Sci.Eng.A 448(2007)111; see also Mayrhofer et al.

Zr-Al-N Nucleation & Growth no interfacial AlN layer:

S.H. Sheng, R.F. Zhang & Veprek, Acta Mater. 56(2008)968

Cr-Al-N Chem. Spinodal, but ΔGDemixing small Nucleation and Growth

more likely: R.F. Zhang & Veprek, Acta Mater. 55(2007)4615

Ti-B-N Nitrogen-rich Ti1-xBxN spinodal, but incoherent TiN/BN interface

Nitrogen-poor TiBxN1-x nucleation & growth R.F. Zhang, S.H. Sheng & Veprek, Acta Mater. 56(2008)4440

Zr-Si-N Nucleation & Growth sharp SiNx interfacial layer unlikely S.H. Sheng, R.F. Zhang, & Veprek, Acta Mater. 59(2011)297

Zr-Al-O Spinodal S.H. Sheng, R.F. Zhang, & Veprek, Acta Mater. 59 (2011) 3498

Al-Si-N Coherency Spinodal unlikely nucleation & growth

S.H. Sheng, R.F. Zhang, & Veprek, Acta Mater. 61(2013)4226

In the majority of the systems the reported H-enhancement is due to smaller crystallite size

not “strong interface” like in nc-TiN/Si3N4







Stability of the 1 ML interfacial XY layer

How to determine the stability of the interfacial layer?

1. “Static” DFT at 0 K manual distortion of the structure what happens with the total energy?

2. First-principles quantum molecular dynamic calculations at elevated temperature temperature-induced structural transformations ?

3. Dynamic (phonon) instability: when instable “negative” frequencies

4. “Soft Modes” as function of the TmN – XY lattice misfit detailed understanding

5. Electronic density of states pseudogap at EF when electronically stable .

“Static” DFT at 0 K: R.F. Zhang et al., Phys. Rev. Lett. 102(2009)015503; Phys. Rev. B 79 (2009) 245426; 81(2010)245418

First-principles QMD & Phonon instability at elevated T: V.I. Ivashchenko et al., Phys. Rev. B 86(2012)014110; Thin Solid Films 545(2013)391; 564 (2014) 284

0,0

0,1

0,20,00 0,05 0,10 0,15 0,20

-150,28

-150,24

-150,20

-150,16

-150,12

-150,08

-150,04

-150,00

To

tal

en

erg

y (

eV

)

[110] x or y direction

[100] xy direction

Distortion of Si atoms along x direction (%)

Dependence of the total energy (eV/supercell) on the displacement of Si-atoms within the (001) interface as

indicated in the inset

The distortion lowers the symmetry and

total energy stabilization well known

Jahn-Teller Effect, Ferroelectric transition, …

DFT calculation at 0 K (001) TiN/1ML SiN/TiN Interface is unstable in its high symmetry octahedral configuration

(a) After full relaxation with Si atoms in symmetric octahedral positions

(b) After displacement of the Si atoms into position with minimum of total energy: Si-four fold coordinated

Confirmed by the Dynamic Phonon Calculations: Alling et al., Phys. Rev. B 78 (2008) 132103

Marten et al., Phys. Rev. B 85 (2012) 104106

R.F. Zhang et al., Phys. Rev. B 79 (2009) 245426

Quantum Molecular Dynamics (QMD) Studies at high T

the TiN/SiNx System

Confirmed the DFT results but the distortion of the (001) interface is random reducing elastic strain energy

V.I. Ivashchenko et al. Phys. Rev. B 85, 195403 (2012)

300 K 1400 300 K

Si 3N4 - like stable to 1100 °C

Experiment: Thin Solid Films 2005; DFT calculations: Hao et al. 2006

Pseudomorphic SiN – DFT Calculations (0 K):

- (111) & (110) stable, - (001) unstable but can be stabilized by 12% distortion of Si in [110] direction

Superhard Nanocomposite with Strengthened Interface

Stability of the SiNx Interfaces - Thermodynamic

Si3N4 stable

Pseudomorphic SiN unstable: 4SiN Si3N4 + Si

however nitriding during deposition at sufficiently high nitrogen activity 3SiN + N Si3N4

1 ML fcc(111) TiN/SiN/TiN is stable at high T

Why? Probably kinetic limitations or

dynamic stabilization (see later)

300 K 1400 300 K

QMD Study:

Surprising stability of the pseudomorphly stabilized (111) SiN

Even heating to 3000 K (melting point 3223 K) did not change the (111) SiN !!

V.I. Ivashchenko et al. Phys. Rev. B 85, 195403 (2012)

Si3N4 – like interfaces QMD

V.I. Ivashchenko et al. 2014 submitted

nc-TiN/BN

a) Stoichiometric TiN & BN is chemically spinodal [R.F. Zhang et al., Acta Mater. 56(2008)4440]

b) H-enhancement at 1 ML BN [P. Karvankova et al., Surf. Coat. Technol. 200(2006)2978]

c) But incoherent interface to TiN [P. Karvankova et al.,ibid.]

First-principles QMD calculations: the interfacial BN layer unstable already at 0 K

V.I. Ivashchenko & S. Veprek, Thin Solid Films 545(2013)391

The BN interfacial layer

unstable alerady at 0 K

annealing to 1400 K and

relaxation at 300 K (right)

a)

b)

c)

Hardening Mechanism the

“Strongest Size” Not “strong interfacial SiNx

layer” like in nc-TiN/Si3N4

TiN/AlN

h(Wurtzite)-AlN - stable; c-AlN (B1-AlN) – high pressure polymorph

≤ 2 nm c-AlN stabilized between TiN slabs [A. Madan et al., Appl. Phys. Lett. 78(1997)1743;

J.W. Kim et al., Appl. Phys. Lett. 78(2001)892] and forms during spinodal decomposition of

Ti1-xAlxN solid solution [P.H. Mayrhofer et al., Appl. Phys. Lett. 83(2003)2049]

1 ML AlN TiN/AlN/ heterostructures stable

at high T(1400 K) V.I. Ivashchenko & S. Veprek, Thin Solid Films 545(2013)391

Can one prepare nc-TiN/AlN nanocomposites? Ti0.9 Al0.1N low de-mixing energy !

R.F. Zhang & S. Veprek, Mater. Sci. Eng. A 448(2007)111

TiN/AlN

h(Wurtzite)-AlN - stable; c-AlN – high pressure polymorph





R.F. Zhang & S. Veprek, Mater. Sci. Eng. A 448(2007)111 as compared with Ti-Si-N

R.F. Zhang & S. Veprek, Mater. Sci. Eng. A

424(2006)128

TiAlN TiSiN



TiN/AlN

h(Wurtzite)-AlN - stable; c-AlN – high pressure polymorph





R.F. Zhang & S. Veprek, Mater. Sci. Eng. A 448(2007)111 as compared with Ti-Si-N

R.F. Zhang & S. Veprek, Mater. Sci. Eng. A

424(2006)128

TiAlN TiSiN



nc-TiN/(1 ML AlN) nanocomposites a Challenge

Worth trying ! But it will probably not work because of the small de-mixing energy of the TiAlN

What about other nc-TmN/AlN systems ?

ZrN/AlN

First-principles QMD

The B1-AlN in ZrN/AlN/ZrN heterostructures is unstable already at temperature ≥ 10 K

V.A. Ivashchenko et al., Thin Solid Films 564 (2014) 284

Broken & distorted bonds

Total energy (ET) as a function of simulation time for

the ZrN-based heterostructures

Unstable AlN interfacial layer already at 10 K

WHY ?

Driving Force for Transformations of the Interfacial Layers?

Soft “Condensed“ Phonon Modes

Central position Stable Unstable imaginary wave vector (‘negative” frequencies)

Phonon “Soft” Mode

driving the transition

Example: Ferroelectric transition in BaTiO3

Ti oscillates around

the centre but in up or down minima

at T>TC = 393 K at T < TC Frequency

Temperature TC 0

-

+ T > TC

T < TC

Instability & Phase Transition in XY interfacial

layer in the TmN/XY heterostructures

Due to Acoustic Soft Modes as function of the lattice parameter of TmN

TmN/AlN nanocomposites ?

Λ3 [2π/a(1/8,1/8,1/8)]

Δ5 [2π/a(1/4,0,0)]

V. A. Ivashchenko et al., Thin Solid Films 564 (2014) 284

aZrN=4.593 Å

B1-AlN is Stable for a < 4.4 Å (TiN, VN, NbN) unstable for a > 4.4 Å (ZrN etc.)

Search for Tm-Al-N system with a < 4.3 Ǻ and High De-Mixing Energy

Can we prepare nc-TmN/AlN nanocomposites with Tm=Ti, V, Nb ?

Probably not because of the low de-mixing energy not spinodal ?

a > 4.4 Ǻ

Unstable

a < 4.4 Ǻ

Stable Ti, V, Nb Zr, …

Driving Force for Transformations of the Interfacial Layers?

Phonon frequencies vs. Lattice Parameter a

B1-BN & SiN unstable, AlN & SiC stable, softening for aTiN

Λ3 [2π/a(1/8,1/8,1/8)]

Δ5 [2π/a(1/4,0,0)]

aAlN aTiN aTiN

aTiN

aBN

aSiC

Instability of B3-BN because it is high-pressure polymorph,;

Instability of B1-SiN because of high electronic DOS above EF;

Destabilization of AlN & SiC for large a

V. A. Ivashchenko et al., Thin Solid Films 545 (2013) 391

●

Instability of B1-BN

interfacial layer at 0 K

because it is the high-P

phase

What about SiC ?

TiN/SiC

Experiment :

a) TiN/SiC/TiN heterostructures, deposited at R.T., no annealing

b) H-enhancement (measurement on only 2 µm thin coatings) M. Kong et al., Appl. Surf. Sci. 253(2007)4734

tTiN = 4.3 nm tSiC = 0.6 nm

TiN/SiC

First-principles QMD calculations & thermodynamics

Transformation at ≥ 600 K poor thermal stability V.I. Ivashchenko et al., Phys. Rev. B 86(2012)014110; Thin Solid Films 545(2013)391

300 K 1400 K 300 K 1400 K

(001) (111)

nc-TiN/SiC nanocomposites?

No because of formation of stable TiN1-xCx Solid solution

nc-TiN/SiC nanocomposites?

No because of formation of stable TiN1-xCx Solid solution S. Veprek et al., Surf. Coat. Technol. 86-87(1996)394

Experiments done in Li Shizi’s laboratury

TiN/SiC

The Hardness follows the Rule-of-Mixtures

Other TmN/XY systems ? Continue ∞

We know from experimental results: 1. The TiN nanocrystals are randomly oriented (XRD, El. Diffraction, HR TEM) 2. The 3-4 nm TiN nanocrystal deform only elastically and 3. The interfaces are the carrier of the plastic flow (high-pressure XRD) 4. We take as an average plastic resistance the shear resistence of the stable

TiN/SiNx heterostructures calculated by QMD (15-32 GPa) at elevated T to be about 20 GPa (see above)

Understanding of Hardness 70 - >100 GPa in nc-TiN/Si3N4 S. Veprek et al., Philos. Mag. Lett. 87 (2007) 955; V. Ivashchenko et al., Thin Solid Films (2014) submitted



5. Accounting for its pressure enhancement during the pressure developed under the indenter

σ(p) = σ0 + · p ≈ 27.8 GPa

p - upon the onset of plasticity

pmax = 2.58∙σ0 Hertzian Theory

β = 0.11 – 0.3 E.F.Oleinik, Polymer Sci. Ser. C 45 (2003) 17

we take β = 0.15




5. Accounting for its pressure enhancement during the pressure developed under the indenter σ(p) = σ0 + · p ≈ 27.8 GPa





6. For randomly oriented polycrystal Sachs average (1928) yields tensile yield strength Y ≈ 2.24·σ(p) ≈ 62 GPa

σ(p) = σ0 + · p ≈ 27.8 GPa


The tensile Yield strength Y of randomly oriented polycrystalline aggregate with plastic slip

resistance of slip planes is increased because all slip systems (even the stronge) have to be active

G. Sachs, Zt. Vereines deutscher Ingenieure 72 (1928) 734

Y = 2.24·σ

A randomly oriented polycrystal is stronger than a single crystal

because all slip systems (also the strongest ones) have to be active

-

Arrows - easy slip system in

randomly oriented crystals





7. H ≈ C·Y, C – constraint factor

σ(p) = σ0 + · p ≈ 27.8 GPa

Constraint Factor:

A.Y. Ishlinsky, J. Appl. Math. Mech. (USSR) 8(1944)201;

R. Hill, The Mathematical Theory of Plasticity, Clarendon, Oxford 1950

M. G. J. Veprek-Heijman et al., Surf. Coat. Technol. 203 (2009) 3385 (non-linear FEM)

For a summary see: S. Veprek, Appendix B in J. Vac. Sci. Technol. A 31 (2013) 050822

C ≈ 2.8

H ≈ 2.8·Y ≈ 173 GPa






7. H ≈ C·Y ≈ 173 GPa

σ(p) = σ0 + · p ≈ 27.8 GPa

8. Why is the experimentally achieved hardness of about 110-115 GPa for quasi-ternary nc-TiN/Si3N4/TiSi2 and 70 GPa for long-term stable quasi-binary nc-TiN/Si3N4 much smaller?


Understanding of Hardness 70 - >100 GPa in nc-TiN/Si3N4





7. H ≈ C·Y ≈ 173 GPa

σ(p) = σ0 + · p ≈ 27.8 GPa

8. Why is the experimentally achieved hardness of about 110-115 GPa for quasi-ternary nc-TiN/Si3N4/TiSi2 and 70 GPa for long-term stable quasi-binary nc-TiN/Si3N4 much smaller?

Impurities

S. Veprek et al., Philos. Mag. Lett. 87 (2007) 955; V. Ivashchenko et al., Thin Solid Films (2014) submitted

Improvement of deposition conditions in industrial coating unit π80

higher Tdep & lower O-impurities life time improvement by > 100 %

S. Veprek, M. Veprek-Heijman (Tech. University Munich), X. Zeng (SIMTech, Singapore), M. Píška (Tech. University

Brno, CZ), A. Bergmaier (Univ. Bundeswehr Munich), Q.F. Fang (Chinese Acad. Sci., Hefei)

Steel DIN C45

C Mn Si P S Cr Ni Fe

0.42-0.5 0.5-0.8 0.17-0.37 0.004 0.004 0.25 0.3 balance

Steel DIN C45

VC = 130 m/min - cutting speed

f= 0.18 mm/revolution

aF = 1.5 mm (depth of cut)

0

10

20

30

40

50

Improved

deposition 2

4 Inserts

Improved

deposition 1

4 Inserts

Standard

To

o L

ife

Tim

e

(min

)

2.2 x

lower O-impurities !

0.2-0-3 at.% Oxygen ≤0.1 at.% Oxygen

Si

Ti Al N

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,00

30

40

50

60

70

80

90

100

110

120

+

[XXX] nc-TiN/a-Si3N

4 P CVD: Cl < 0.5 at.%

Cl = 0.5 - 0.8 at.%

Cl = 1.0 - 3.5 at.%

nc-TiN/a-Si3N

4/a- & nc-TiSi

2 P CVD: Cl < 0.5 at.%

Cl > 0.5 at.%

nc-TiN/a-Si3N

4/a-TiSi

2Li Shizhi 2004, Cl 0.7 - 1.0 at.%

nc-TiN/a-Si3N

4 RMSputt - Centr. Cathode

nc-TiN/a-Si3N

4 RMSputt - Planar Cathode + SiH

4+ H

2

nc-TiN/a-Si3N

4 RMSputt of Ti & Si in N

2 - Planar Cathode & Outgas

nc-TiN/a-Si3N

4 RMSputt of Ti & Si in N

2 - Planar Cathode

+ "Ti-Si-N" Vaz et al. RMSputt

Pla

sti

c H

ard

ne

ss

[G

Pa

]

Oxygen Content [at%]

0

2

4

4 O-defects/Nanocrystal

> 20 O-defects/Nanocrystal

1/C

ov

era

ge

[N

an

oc

rys

tal/

Ox

yg

en

Ato

ms

]

[O] = 100 ppm about 1 O-defects/2.5 Nanocrystals

Detrimental Effect of Oxygen Impurities

S. Veprek, P. Karvankova and M. G. J. Veprek-Heijman, J. Vac. Sci. Technol. B 23 (2005) L17

H determined by strength of

the O-defects

SHM & TUM

Industrial Coating System

“ORM”

Good News

0.07 at.% = 700 ppm

Surface

contamination

Bulk

The great challenge:

Presently ≤ 1000 ppm impurities in every day deposition in “ORM”of SHM and in

Pi80 & Pi300 of PLATIT

We need an improvement only by a factor of 3-4 to reach ≤ 250 ppm in the

industrial coating units!

Selected Examples of Industrial Applications of

Hard and Superhard Nanocomposite Coatings on Tools

Selected Exmples

What are the advantages of the superhard nanocomposites

Advantages of Superhard Nanocomposites:

- Higher Hardness

- Higher oxidation & corrosion resistance

- Lower thermal conductivity lower heat flow into

the cutting edge

- Higher cutting speed & feed Higher Productivity

- Longer Life Time of Expensive Tools

- Dry Cutting – economy, ecology

- Flexibility in the design of “triple Coatings”

Presently Available Superhard Nanocomposite Coatings for

Industrial Applications:

nc-(Ti1-xAlx)N/a-Si3N4 - (“TiAlSiN” or ”AlTiSiN”)

nc-(Cr1-xAlx)N/a-Si3N4 (“CrAlSiN”)

TiCrN/Ni not superhard (H ≈ 15 – 20 GPa) but ductile forming

Hard Dry Milling T. Cselle, PLATIT A.G. (CH)

0 500 1000 1500 2000 2500

0

50

100

150

200

250

Cle

ara

nc

e W

ea

r [µ

m]

Tool Life-Time [m]

nACo-MLH-N nACo-MLH

AlTiN 1 AlTiN 2

nACo-MLH ii nACo-MLH i

T. Cselle & M. Morstein, PLATIT AG

Hard Milling of 57 HRC Steel

Ball nose, cemented carbide end mills, d=10 mm, External Minimum Jet Lubrication

18 500 RPM, fz=0.18 mm, ap=0.25 mm, ae=0.6 mm,

ap-axial -, ae- radial depth of cut

(TiAl)N/Si3N4

1st Generation

Fatigue of "WC/Co" Substrate

2nd Generation:

Improved Design

of Coatings +

higher Si-content

TiSiN-Hitachi

Nanocomposites TiAlN

Coatings

0 500 1000 1500 2000 2500

0

50

100

150

200

250

Cle

ara

nc

e W

ea

r [µ

m]

Tool Life-Time [m]

nACo-MLH-N nACo-MLH

AlTiN 1 AlTiN 2

nACo-MLH ii nACo-MLH i

T. Cselle & M. Morstein, PLATIT AG

Hard Milling of 57 HRC Steel

Ball nose, cemented carbide end mills, d=10 mm, External Minimum Jet Lubrication

18 500 RPM, fz=0.18 mm, ap=0.25 mm, ae=0.6 mm,

(TiAl)N/Si3N4

1st Generation

Fatigue of "WC/Co" Substrate

2nd Generation:

Improved Design

of Coatings +

higher Si-content

TiSiN-Hitachi

Nanocomposites TiAlN

Coatings

ap-axial -, ae- radial depth of cut

Maintenance of Railroads for Fast Trains ≤ 320 km/hr

Shinkansen Japan since 1964

TGV France since 1981

ICE Germany since 1993

Required surface roughness of the rails for given speed

≤ 160 km/h - 0.5 mm

160 – 280 km/h – 0.3 mm

> 280 km/h – 0.2 mm

PRAMET TOOLS & SHM Šumperk Czech Republic 2014

Required surface roughness of the rails for given speed

≤ 160 km/h - 0.5 mm

160 – 280 km/h – 0.3 mm

> 280 km/h – 0.2 mm

Milling tool

D = 600 mm, z = 22 teeths, vC = 220-280 m/min,

n = 120-150 rev./min, f = 700 m/h, aP = 1.5 mm

Steel R350 HT

H = 0.9-1.2 GPa 1.5 GPa (cold work hardening)

(27 – 46 HRC)

Solution: TripleCoatings AlTiSiN Nanocomposite

AlTiN-TiN Multilayers

TiN Adhesion layer

Large-scale tests in large European countries

Life Time increase by 30 % as compared with

the competitor

“life-time” > 2 km !


- Higher Hardness



the cutting edge










Tools: ø7.1-12mm SC step drills - Cooling: 70 bar internal 5% emulsion

Test material: GGG40 - Vc: 140-200 m/min - Vf: 1475 - 2304 mm/min

Source: Sauer Danfoss Steerings, DK

Drill test in cast iron GGG40 UNIMERCO DK

Vc, Surface speed

0

50

100

150

200

250

TiAlN AlTiSiN

Vf, Feed rate

0

500

1.000

1.500

2.000

2.500

TiAlN AlTiSiN

Tool life time

0

5.000

10.000

15.000

20.000

25.000

30.000

35.000

40.000

TiAlN AlTiSiN

Performance improvement at Higher Speed & Feed Rate

Increase in Productivity with AlTiSiN-Nanocomposites 56 % !


- Higher Hardness



the cutting edge










Tool Lifetime: number of sawed parts with tolerance of ± 0.2 mm

Solid Carbide saw blades Diam. 125 mm, Thick. 3.6 mm, z = 100, sintered workpiece material Co1

N = 300 RPM, vf = 800 mm/min, ap = 35 mm, colant: emulsion 7%

Source: Prétat, Selzach & PLATIT AG, CH

Lifetime of Solid Carbide Saw Coated with different Coatings (Precision Metal Cutting)

25x

6.5x

T.Cselle PLATIT AG (CH)

Injection Moulding of Aluminum Alloys for Automotive Industry

after the fabrication of 15 000 parts with different surface treatment. The length and diameter

of several similar tools which were tested was 180-200 mm and 15-25 mm, respectively.

conventional nitriding 2 to 3 µm thick CrAlSiN

nanocomposite coatings Conventionally treated

Many further applications

The superhard nanocomposite coatings

are not the “future nanotechnology”,

they are present reality

Conclusions

1. Low-energy and strengthened interafaces enable one to design strong and

superhard materials

2. The very high hardness of the nc-TiN/Si3N4 nanocomposites fully understood:

it is achieved due to strengthened SiNx interfacial layer

3. Similar H-enhancement possible in other nc-TmN/Si3N4 systems with

a(TmN) < 0.42 nm

4. Impurities hinder this strengthening & formation of the nanostructure and

thus to achieve the high hardness

5. So far no other nc-TmN/XY system was found as candidate because - although many TmN/AlN systems with a(TmN) < 0.44 nm are chemically spinodal

their de-mixing energy is too low

- BN as interfacial layer forms strongly incoherent interfaces to TmN

- SiC as interfacial layer is instable above 600 °C and forms stable TiN1-xCx solution

6. The hardness enhancement reported in many TmN/XY nanocomposites is due

to the “Strongest Size” and not to a strong interfacial XY layer

Thank you for your attention

The pdf of this lecture will be available at stan.veprek.net

outline - tum lvivseptember2014.pdf · 1. introduction: the recent search for new superhard...

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