Jatin Bhatt

Synthesis of Nanostructured Materials by nonequilibrium Processing

by

Jatin Bhatt Assistant Professor Department of Metallurgical & Materials Engineering, Visvesvaraya National Institute of Technology, Nagpur

Classification Discrete nano (dn) materials

0D or 1D

Classification of nanomaterials Nanoscale device (nd) materials Usually 2D some time 1D

Bulk (nc or ns) materials 3D

Problem & Solutions

Fundamental Issue Control of structure at very fine scale

To reduce local entropy density

Two direct consequences 1) Require significant amount of energy /expensive. 2) Thermodynamically unstable and revert back to high entropy state (disordered state)…. Disordered state to desired nanostructured state.

Processes “Such processes are rapid solidification from the liquid state, mechanical alloying, plasma processing , and vapor deposition.

Disordered structure

Regular Atomic structure

Figure shows the basic concept of "energize and quench" to synthesize nonequilibrium materials [Prog. In Mat. Sci., 46(2001)1]

Processes Bulk NanoMaterials by 1) Bottom Up Approach (Pure, Costly, Time consuming) 2) Top Up Approach (Not of high quality but fast & relatively inexpensive) Some process that can defy above broad categorization •

Deposition (CVD/PVD)

•

Consolidation of dn materials

•

Sever Plastic Deformation (SPD)

•

Equal Channel Angular Processing (ECAP)

•

High Pressure Torsion

•

Surface Mechanical Attrition

•

Crystallization from amorphous phase i.e from Bulk Metallic Glasses Recent report by Kumar and Schroers, APL 92(2008)031901 (NEMSs and nanoimprinting-BMG can replicate nanoscale surface feautures)

Nishiyama et al., Mater.Trans JIM 45(2004)1245

BMG prerequisite to nanostructure formation

~10 nm

Nanocrystallization on heating

The HRTEM micrograph of the vit1 BMG annealed at 623 K under 4 GPa for 4 h [Wang et al., , Appl. Phys. Lett. 75 (1999) 2770. ]

HRTEM image of As cast Bulk Metallic Glass

Experiment have demonstrated BMG has Short range ordering (SRO) but long range disordering (LRDO) [Unpublished work]

Case study 1

Zr-Pd Phase Diagram

Journal of Phase Equilibria, 15 (1994) (6)

Rapid Solidification

Argon Atmosphere

Graphite Crucible

Schematic diagram of Melt spinning technique for Rapid Solidification

XRD studies

i

*

5

- i-phase

5i

i

(a) i

*

*

Intensity (a.u)

5 i5

5 5

Zr80Pt20

*

i α− Zr 5 Zr5Pt3 ZrPt

*

(b) (c) (d)

30

40

50

60

70

2θ

XRD patterns of melt spun Zr80Pt20 alloy with various phases at different wheel velocities (a) nanocrystalline at 10m/s, (b) nanoQC at 20m/s, (c) nanoQC + amorphous at 30m/s and (d) amorphous at 40m/s

XRD studies

*

Zr75Pd25

*

*

Intensity (a.u)

*

*

- i-Phase

(a) (b) (c) (d)

30

40

50 2θ

60

70

XRD patterns of melt spun Zr75Pd25 alloy with various phases at different wheel velocities (a) and (b) nanoQC at 10m/s and 20m/s, respectively, (c) nanoQC + amorphous at 30m/s and (d) amorphous at 40m/s.

XRD studies (a)

(b)

wheel side

Zr75Pd25, 40m/s

Intensity (a.u)

Intensity (a.u)

Zr80Pt20, 40m/s

wheel side

air side

30

40

50 2θ

60

air side

70

30

40

50

60

2θ

XRD pattern of the wheel side and air side of the melt spun ribbons at 40m/s for amorphous phase (a) Zr80Pt20 (b) Zr75Pd25

70

Nanoindentation study

250

(i) nanocrystalline (10m/s) (ii) nanoQC (20m/s) 200 (iii) nanoQC + amorphous (30m/s) (iv) amorphous (40m/s) (iv)

Zr80Pt20

150

(ii) (i) 180

100

(i) nanocrystalline (10m/s) (ii) nanoQC (20m/s) 170 (iii) nanoQC + amorphous (30m/s) (iv) amorphous (40m/s)

50

0

(a) 0

200

400

600

800

1000 1200 1400 1600

Displacement into surface (nm)

Load (mN)

Load (mN)

(iii)

Zr80Pt20

160 18nm (iii)

150

140

(iv)

15nm (ii) (i)

130 1200

1240

(b) 1280

Displacement into surface (nm)

(a) Load vs. Displacement (P-h) curves for different phases in melt spun Zr80Pt20 alloy and (b) magnified figure showing small pop in and pop up events in amorphous phase (shown by dotted arrow).

1320

Nanoindentation study 250

(i) nano QC (10 m/s) (ii) nano QC (20 m/s) (iii) nano QC+ amorphous (30 m/s) (iv) amorphous (40 m/s)

Load (mN)

200

(iii)

150

Zr75Pd25

(iv)

(ii) (i) 100

180

Zr75Pd25

(i) nano QC (ii) nano QC 170 (iii) nano QC+ amorphous (iv) amorphous

50

(iii)

0

(a) 200

400

600

800

1000 1200 1400 1600

Displacement into surface (nm)

Load (mN)

0

160

150 15nm

12nm (iv)

140

(ii)

130 1200

(i) 1240

1280

Displacement into surface (nm)

(a) Load vs. Displacement (P-h) curves for different phases in melt spun Zr75Pd25 alloy and (b) magnified figure showing small pop in and pop up events in amorphous phase (shown by dotted arrow)

(b) 1320

Nanomechanical Properties Phase

Melt spun wheel velocity (m/s)

Hardness (GPa)

Elastic Modulus (GPa)

H/E Ratio

Zr80Pt20 Nanocrystalline

10

5.2

60

0.09

NanoQC

20

5.9

70

0.08

NanoQC + Amorphous

30

6.5

93

0.07

Amorphous

40

5.5

65

0.09

Zr75Pd25 NanoQC

10

5.3

66

0.08

NanoQC

20

5.5

68

0.08

NanoQC + Amorphous

30

6.2

81

0.08

Amorphous

40

5.1

62

0.08

Case study 2

Thermodynamic Model: Entropy due to Configuration n

ΔS config = − R ∑ ci ln ci i =1

B 0.00 1.00

0.25

ΔSconfig/R

1.0

0.75

0.9 0.50

0.50

0.75

1.00 A 0.00

0.25

0.25

0.50

0.75

0.00 1.00 C

Isometric contours of ΔSconfig/R

Thermodynamic Model: Enthalpy calculation c c c ΔH chem( ABC ) = ΔH AB + ΔH BC + ΔH AC

ΔH ijc = ci c j (c j ΔH mix (i

in

j)

+ ci ΔH mix ( j

-5 0.00 Zr -7.5 1.00 -10 Δ Hchem -12.5 -15 -17.5 0.25 0.75 -20 -22

0.50

0.50

0.75

0.25

-5

1.00 Cu 0.00

0.25

0.50

0.75

0.00 1.00 Ti

Isometric contours of ΔHchem for Cu-Zr-Ti system

in i

))

Topological Model: Entropy due to atomic mismatch calculation Mansoori et al., J. Chem. Phys. 54(1971)1523-1525.

0.00 Zr1.00 ΔSσ/kB

0.25

0.75

0.50 0.25 0.23 0.22 0.2 0.75 0.175 0.15 0.10 1.00 Cu 0.00

0.50

0.25

0.25

0.50

0.75

0.00 1.00 Ti

Isometric contours of ΔSσ/kB for Cu-Zr-Ti system

Composition Identification

Cu46Zr43Ti11

-5 0.00 Zr1.00 -7.5 ΔSσ/kB -10 Δ Hchem -12.5 -15 Δ Sconfig/R -17.5 0.25 0.75 -20 -22

Cu60Zr30Ti10 0.25 0.23 0.22 0.2 0.175 0.15 0.10

3

0.50

0.50 1

0.75

1.00 Cu 0.00

2

0.25

4

0.50

0.75

0.25

0.00 1.00 Ti

Superposition of isocontours of ΔHchem and ΔSσ/kB, indicating their intersections with in ΔSconfig/R range of 0.9-1.0 for Cu-Zr-Ti system

HRTEM 2Φ x 70mm

3Φx40mm

Bulk Metallic Glassy samples

Typical bright field image and corresponding SADP obtained for Cu60Zr30Ti10 showing amorphous pattern

Thermal History of as cast samples Heating Rate 20K/min

Tx1

Exothermic

Tx2 Relaxed

DSC trace of as cast Cu60Zr30Ti10 BMG 500

600

700

800

Temperature (K)

Sample Name

Condition

As cast

As cast

Relaxed

Annealed in supercooled liquid region (723K for1h)

Tx1

Annealed at the offset of first crystallization peak (795K for1h)

Tx2

Annealed at the offset of second crystallization peak (845 K for 1h)

XRD studies nd i u (a) 2 crystallization

Intensity (a.u)

uCu10Zr7 i Cu8Zr3 5 Cu3Ti2

st

(b) 1 crystallization (c) Super cooled liquid region (d) As Cast

i i u uu u 5

u

45 nm

i

u

u

(a) (b)

u

(c) (d) 20

30

40

2θ

65 nm

50

60

70

Hardness Studies

850

As cast Relaxed structure Tx1 Tx2

800

Hv (VHN)

750 700 650 600 550 500 0

100

200

300

400

500

Load (g)

Hardness (H) vs. Load (P) for as cast, Relaxed, Tx1 and Tx2 samples

Wear Studies 0.5

110

(a)

20 N 40 N

100 90

Wear rate, x10 (kg/m)

-10

0.3

0.2

0.1

80 70 60 50 40 30 20 10 0

0.0

Relaxed

Tx1

As Cast

Tx2

12

8

As Cast

Wear Resistance, x10 (kg/m)

Coefficient of friction, μ

0.4

(b)

20 N 40 N

10

(c)

20 N 40 N

8 6 4 2 0

As Cast

Relaxed

Tx1

Tx2

Relaxed

Tx1

Tx2

Wear vs. Hardeness

12

Relaxed

20N 40N

Wear Resistance

10 8

Archard Equation Q= KW/H

As cast

6

Q= Vol. removed per unit sliding distance.

4 2 Tx2

Tx1

W= Normal Load. H= Indentation hardness.

0 500

550

600

650

700

Hardness (VHN)

Wear resistance dependence on hardness at loads of 20N and 40N

SEM Studies (a) (a)

(b)

SEM micrographs of worn surface of Cu60Zr30Ti10 BMG in (a) relaxed state and (b) annealed at Tx2 at a load of 40N. The arrow marks shows the sliding direction.

SEM Studies

SEM micrographs of worn out fracture surface of Tx2 sample

Conclusions: 1. In case 1, nano composite of nano quasicrystalline and amorphous phase showed excellent combination of hardness and elastic modulus in comparison to monolithic nano crystalline or nano quasicrystalline phase. 2. In case 2, relaxed structure of BMG i.e relaxed SRO showed excellent hardness and wear performance in comparison to nano crystallized phases. 3. Crystallization process in multicomponent glassy alloys is usually quite complicated leading to a number of phases in multiple steps have different sizes/varying volume percentages in matrix of parent phase and contribute differently to the mechanical properties. 4. The nano range should be close to stability limit of crystalline phase on the amorphous matrix which reduces the crack formation and propagation and induces hardness. 5. Close control of nano structure (ns) dimension/ distribution is required to develop ns dimensions- properties relationships.