Conclusions

(6) For the Au-based BMG, the compressive strength and density of the Au49Ag5.5Pd2.3Cu26.9Si16.3 BMG are about 970 MPa and 13.5 g/cm³, respectively.

Therefore, the specific strength of the Au49Ag5.5Pd2.3Cu26.9Si16.3 BMG is 72 MPa.cm³/g.

(7) With the strain rate and the measured stress, the material constant

γ

⁰

^v

⁰ can be determined from by the slope of the curve. Using γ⁰=0.125, the volume of a basic flow unit STZ during shear, v0, is calculated to be 1.29 nm³.

(8) The thermal activation energy of a single STZ, ΔG^m, can be determined from the intercept of the plot. The extracted thermal activation energy ΔG^m for the Au-based BMG is 1.86 eV, corresponding to 179 kJ/mol.

(9) The viscosity values of the Au-based BMG vary from 10⁸ to 10¹¹ Pa.s, higher than the values of 10⁷ to 10⁹ Pa.s for the Mg-based BMG. And that is one reason why the Au-based BMG has higher density and micro-hardness.

(10) From the hot embossing of the micro-lens and V-groove MEMS patterns, the current Au-based BMG shows good forming ability. With the anti-oxidation, anti-corrosion, and good forming ability, the Au-based BMG may be a material with high potential for Micro-Electro-Mechanical Systems (MEMS) applications.

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Table 2.1 Bulk metallic glasses and their developed year [30].

Table 2.2 The composition of representative BMG systems, their glass transition temperature, Tg, onset temperature of crystallization, Tx, and onset melting point, Tm, and glass forming ability represented by reduced glass transition temperature, Trg [30].

Table 2.3 Properties of the elements in the Au-based BMG alloy.

Symbol Atomic

weight Structure Atomic radius (pm)

Melting point (^oC)

Density (g/cm³) Au 197 FCC 135 1064 19.3 Ag 108 FCC 160 962 10.1 Pd 106 FCC 140 1552 12.0 Cu 64 FCC 128 1085 8.9

Si 28 Diamond 110 1410 2.3

Table 2.4 Possible application fields for BMGs [30].

Table 4.1 The composition analyses of the Au49Ag5.5Pd2.3Cu26.9Si16.3 rods by SEM/EDS.

Au (at%) Ag (at%) Pd (at%) Cu (at%) Si (at%)

EDS composition 1 53.9 5.4 2.4 22.7 15.6

EDS composition 2 54.7 5.3 2.3 23.4 14.3

EDS composition 3 54.5 5.7 1.7 25.0 13.0

EDS composition 4 55.0 5.1 2.0 25.0 12.9

Average composition 54.5 5.4 2.1 23.8 14.0

Desighed composition 49.0 5.5 2.3 26.9 16.3

Table 4.2 Summary of the macro-compressive of Au-based BMG at different strain rates.

ε &

~ 5x10^-5 s^-1

ε &

~ 1x10^-4 s^-1

ε &

~ 5x10^-4 s^-1

ε &

~ 1x10^-3 s^-1 Fracture strength

(MPa) 1003 1122 933 827

Fracture elongation

(%) 1.85 1.97 1.59 2.00

Table 4.3 Summary of the micro-compressive of Au-based BMG at different strain rates.

ε &

~ 10^-5 s^-1

ε &

~ 1x10^-4 s^-1

ε &

~ 1x10^-3 s^-1

ε &

~ 1x10^-2 s^-1

ε &

~ 6x10^-2 s^-1 Au base BMG,

1 μm (MPa) -- -- 1657 1941 1948

Input Depth

(Response), nm -- -- 180

(266)

180 (362)

180 (456) Au base BMG,

3.8 μm (MPa) 1409 2020 1689 1761 1629

Input Depth (Response), nm

600 (1230)

600 (2266)

600 (1469)

600 (1880)

600 (812)

Table 4.4 Variation in distance and average height under different conditions for V-groove.

Pressure (MPa)

Time (min)

Band interspacing (μm)

Height (μm)

Mold - - - 94

137 1 143 38

177 K 137 5 148 52

137 10 153 45

62 10 - 11

177 K 137 10 153 45

156 10 147 84

Table 4.5 Variation in height and width under different conditions for micro-lens array.

Width (μm) Height (μm)

Mold 330 24

27 MPa 183 7

62 MPa 315 21

156 MPa 315 22

Table 5.1 The negative heat of mixing in unit of kJ/mol of the Au, Ag, Pd, Cu, and Si elements.

Au Ag Pd Cu Si Au - 0 -9 -30 Ag - -7 2 -20

Pd 0 -7 -14 -55

Cu -9 2 -14 -19 Si -30 -20 -55 -19

Table 5.2 Thermal properties of the Mg65Cu25Gd10 (Mg-based BMG) and Au49Ag5.5Pd2.3Cu26.9Si16.3 (Au-based BMG) obtained from DSC at a heating rate of 10 K/min.

Tg

(K) Tx

(K)

ΔTx

(K) Tm

(K) Tl

(K)

ΔTm

(K) Trg γ γm

Mg-based BMG 410 470 60 679 726 47 0.565 0.414 0.730

Au-based BMG 400 450 50 625 646 21 0.619 0.430 0.774

Figure 2.1 The critical casting thickness versus the year in which alloys were discovered.

Over 40 years, the critical casting thickness has increased by more than three orders of magnitude [19].

Figure 2.2 The picture of as-cast alloy BMG system [30].

Figure 2.3 Relationship between the critical cooling rate for glass formation (Rc), maximum sample thickness for glass formation (tmax) and reduced glass transition temperature (Tg/Tm) for bulk amorphous alloys. The data of the ordinary amorphous alloys, which require high cooling rates for glass formation, are also shown for comparison [31].

Figure 2.4 Relationship between Rc, tmax and the temperature interval of the supercooled liquid region between Tg and Tx for bulk amorphous alloys [31].

Figure 2.5 A comparison of critical cooling rate between reduced glass transition temperature, Trg, among BMG, silicate glasses and conventional metallic glasses [30].

Figure 2.6 The correlation between the critical cooling rate and the parameter γm for metallic glasses [39].

Figure 2.7 Two-dimensional schematics of the atomistic deformation mechanisms proposed for amorphous metals, including (a) a shear transformation zone (STZ), after Argon [40], and (b) a local atomic jump, after Spaepen [50].

Figure 2.8 Scanning electron micrographs illustrating the ‘‘slip steps’’ or surface offsets associated with shear bands in deformed metallic glasses. In (a), a bent strip of Zr57Nb5Al10Cu15.4Ni12.6 illustrates slip steps formed in both tensile and compressive modes of loading, on the top and bottom surfaces, respectively. In (b) the side of a compression specimen of Zr52.5Cu17.9Ni14.6Al10Ti5 is shown, for which the loading axis was vertical; here the slip steps document shear deformation at an inclined angle to the applied compressive load [63].

Figure 2.9 Calculations from the work of (a) Argon and (b) Steif et al. illustrating the process of strain localization in metallic glasses. In (a), a history of strain rate is shown for both the forming shear band and the surrounding matrix; these quantities are normalized by the applied shear strain rate. In (b), the history of strain in the shear band is shown [51, 64].

Figure 2.10 Examples of mechanical test data that illustrate serrated flow of metallic glasses, through repeated shear band operation in confined loading. In (a), the compression response of a Pd77.5Cu6Si16.5 specimen of low aspect ratio is shown, while (b) is an instrumented indentation curve for Pd40Cu30Ni10P20 glass.

Because (a) represents a displacement controlled experiment, serrations are represented as load drops, while the load-controlled experiment in (b) exhibits displacement bursts [65].

Figure 2.11 Average shear band spacings are plotted as a function of characteristic specimen dimensions for a variety of metallic glasses (and some derivative composites) deformed in constrained modes of loading, after Conner et al [67].

Figure 2.12 Amorphous metallic alloys combine higher strength than crystalline metal alloys with the elasticity of polymers [19].

Figure 2.13 Elastic limit σy plotted against modulus E for 1507 metals, alloys, metal matrix composites and metallic glasses. The contours show the yield strain σy /E and the resilience σy2 =E [73].

Figure 2.14 Resilience σy2=E and loss coefficient for the same materials as Figure 2.13 [73].

Figure 2.15 Fracture toughness and modulus for metals, alloys, ceramic, glasses, polymers and metallic glasses. The contours show the toughness Gc in kJ m^-2 [73].

Figure 2.16 Toughness and elastic limit for the same materials. The contours show the process-zone size d in mm [73].

Figure 2.17 Composition dependence of ΔT and dc for (Au58.5Ag6.6Pd2.8Cu32.1)86-xSi14+x for x = 0-6%. A strong dependence on the Si content of both dc and ΔT is observed. No obvious correlation of dc and ΔT is seen [9].

Figure 2.18 Position dependence of ΔT and dc for (Au60.1Ag6.8Cu33.1)83.7-yPdySi16.3 for y = 0-5%. A strong dependence on the Pd content of both dc and ΔT is observed.

No obvious correlation of dc and ΔT is seen [9].

ν

μ/β

Figure 2.19 The relationship between ν and μ/β.

Figure 2.20 The correlation of fracture energy G with elastic modulus ratio μ/B for all the as-cast (unannealed) metallic glasses for which relevant data are available (all compositions in at.%). Elastic constants were used to convert fracture toughness to fracture energy [79].

Figure 2.21 The correlation of fracture energy G with Poisson’s ratio for all the data collected on metallic glasses (as-cast and annealed) as well as for oxide glasses [79].

Figure 3.1 Au-BMG micropillars fabricated by focus ion beam technique: (a) 1 μm in diameter and (b) 3.8 μm in diameter.

(b)

(a)

Figure 3.2 FIB-SEM micrographs of the flat-punch tip: a) top view and (b) side view.

(a)

(b)

Figure 3.3 Triangle marks made by flat punch .

Figure 3.4 Hot embossing set-up for oil hydraulic system [92].

Figure 3.5 Ni–Co mold with gapless hexagonal micro-lens array. [92]

Figure 3.6 Profile of V-groove mold.

Figure 4.1 The appearance of the Au-based BMG rods with 2 and 3 mm.

20 30 40 50 60 70 80

2 mm Au-based BMG rod

2θ

Inte nsit y

3 mm Au-based BMG rod

Figure 4.2 XRD pattern of the 3 mm and 2 mm Au-based amorphous alloys.

Figure 4.3 TEM diffraction pattern of the 3 mm diameter Au-based BMG.

300 400 500 600 700 -80

-60 -40 -20 0 20 40 60

γ_m

=0.774

γ=0.430

T

_rg

=0.619

Au

₄₉

Ag

_5.5

Pd

_2.3

Cu

_26.9

Si

_16.3

Heat flow

Temperature (K) T

_g

=400 K

T

_x

=450 K

T

_l

=646 K T

_m

=625 K

Heating rate: 40 K/min

Figure 4.4 DSC plot of Au-based amorphous alloy with the heating rate of 40 K/ min.

Figure 4.5 The Au-Cu binary phase diagram.

360 450 540 -40

0 40 80

T

x

=442 K T

g

=403 K

Heating rate: 10 K/min Au

49

Ag

5.5

Pd

2.3

Cu

26.9

Si

16.3

Temperature (K)

Heat Flow

Figure 4.6 DSC plot of Au-based amorphous alloy with the heating rate of 10 K/min.

0 1 2 3 4 5 0

400 800

1200

5x10

^-5

s

^-1

1x10

^-4

s

^-1

5x10

^-4

s

^-1

1x10

^-3

s

^-1

S tr ess (MPa)

Strain (%)

Figure 4.7 The compressive stress-strain curves for the Au49Ag5.5Pd2.3Cu26.9Si16.3 BMG.

Figure 4.8 The outer appearance showing fracture plan inclination of the Au-based BMG with a strain rate of 5x10^-5 s^-1.

Figure 4.9 The fracture surface morphology of the Au-based BMG with a strain rate of 5x10^-5 s^-1.

Figure 4.10 The fracture surface morphology of the Au-based BMG with a strain rate of 5x10^-5 s^-1.

Figure 4.11 The outer appearance showing fracture plan inclination of the Au-based BMG with a strain rate of 1x10^-4 s^-1.

50 μm 50 μm 50 μm

Figure 4.12 The fracture surface morphology of the Au-based BMG with a strain rate of 1x10^-4 s^-1.

Figure 4.13 The fracture surface morphology of the Au-based BMG with a strain rate of 1x10^-4 s^-1.

Figure 4.14 The outer appearance showing fracture plan inclination of the Au-based BMG with a strain rate of 5x10^-4 s^-1.

Figure 4.15 The fracture surface morphology of the Au-based BMG with a strain rate of 5x10^-4 s^-1.

Figure 4.16 The fracture surface morphology of the Au-based BMG with a strain rate of 5x10^-4 s^-1.

Figure 4.17 The outer appearance showing fracture plan inclination of the Au-based BMG with a strain rate of 1x10^-3 s^-1.

Figure 4.18 The outer appearance showing fracture plan of the Au-based BMG with strain a rate of 1x10^-3 s^-1.

Figure 4.19 The outer appearance of the Au-based BMG with a strain rate of 1x10^-3 s^-1.

Figure 4.20 The fracture surface morphology of the Au-based BMG with a strain rate of 1x10^-3 s^-1.

Figure 4.21 The fracture surface morphology of the Au-based BMG with a strain rate of 1x10^-3 s^-1.

Figure 4.22 Compression load-displacement curves of the 1 μm Au-BMG at different strain rates.

0 100 200 300 400 500

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Load (mN)

Displacement (nm)

1x10^-3

s

^-1 1x10^-3

s

^-1 1x10^-2

s

^-1

Figure 4.23 Compression load-displacement curves of the 3.8 μm Au-BMG at different strain rates.

0 500 1000 1500 2000 2500 3000 3500

0 3 6 9 12 15 18 21

Load (mN)

Displacement (nm)

5.8 x 10

^-5

s

^-1

1.2 x 10

^-4

s

^-1

1.2 x 10 s

^-3

s

^-1

1.2 x 10

^-2

s

^-1

Figure 4.24 Time-and-displacement curves for the 1 μm Au BMG pillars.

0 20 40 60 80 100

0 50 100 150 200 250 300 350 400 450 500

Displacement (nm)

Time (s)

2.5 nm/s

25 nm/s

150 nm/s

Figure 4.25 Time-and-displacement curves for the 3.8 μm Au BMG pillars.

0 100 200 300 400 500 600 700 800

0 500 1000 1500 2000 2500

Displacement (nm)

Time (s)

0.5 nm/s

1 nm/s

10 nm/s

100 nm/s

500 nm/s

Figure 4.26 SEM micrographs showing the appearance of deformed pillars: (a) 3.8 μm,

~1x10^-3 s^-1, (b) 3.8 μm, ~1x10^-2 s^-1, (c) 3.8 μm, ~6x10^-2 s^-1, (d) 1 μm, ~1x10^-3 s^-1, (e) 1 μm, ~1x10^-2 s^-1, and (f) 1 μm, ~6x10^-2 s^-1.

(a)

(b)

(d)

(c)

(f)

(e)

350 375 400 425 450 475 500 525 550 -50

-40 -30 -20 -10 0

Disp lacement ( μ m)

Temperature (K)

T _finish T _vs

T _onset DTMA

TMA

Figure 4.27 Typical TMA and DTMA curves measured at stress level of 7.1 kPa for the as-cast bulk Au-based BMG.

400 420 440 460 480 500 10⁵

10⁶ 10⁷ 10⁸ 10⁹ 10¹⁰ 10¹¹ 10¹²

10¹³ Au₄₉Ag_5.5Pd_2.3Cu_26.9Si_16.3 Mg₆₅Cu₂₅Gd₁₀

Vi scosi ty ( P a.s)

Temperature (K)

Figure 4.28 Measured viscosities of the Au-based and Mg-based BMG in the supercooled liquid region at a heating rate 10 K/min.

Figure 4.29 Replicated patterns by OM on the Au-based BMG materials imprinted at 177^oC and 137 MPa for 1 min with (a) lower magnification by OM (b) higher magnification.

(a)

(b)

Figure 4.30 Replicated patterns by OM on the Au-based BMG materials imprinted at 177^oC and 137 MPa for 5 min with (a) lower magnification by OM (b) higher magnification.

(b)

(a)

Figure 4.31 Replicated patterns by OM on the Au-based BMG materials imprinted at 177^oC and 137 MPa for 10 min with (a) lower magnification by OM (b) higher magnification.

(a)

(b)

Figure 4.32 Replicated patterns by OM on the Au-based BMG materials imprinted at 177^oC and 62 MPa for 10 min with (a) lower magnification by OM (b) higher magnification.

(a)

(b)

Figure 4.33 Replicated patterns by OM on the Au-based BMG materials imprinted at 177^oC and 156 MPa for 10 min with (a) lower magnification by OM (b) higher magnification.

(b)

(a)

100 200 300 400 500 0

10 20 30 40 50 60 70 80 90

Height ( μ m)

62 MPa 137 MPa 156 MPa

Scanning length (

_μ

m)

Figure 4.34 The morphological curves of V-groove imprinted Au-based BMG at 177^oC and 62 MPa, 137 MPa, and 156 MPa, respectively, for 10 min by the α step.

400 600 800 0

10 20 30 40 50 60 70

Height ( μ m)

Scanning length (

_μ

m)

1 min 5 min 10 min

Figure 4.35 The morphological curves of V-groove imprinted Au-based BMG at 177^oC and 137 MPa for 1, 5, 10 min, respectively, by the α step.

Figure 4.36 Replicated patterns by OM on the Au-based BMG materials imprinted at 177^oC and 28 MPa for 10 min.

Figure 4.37 Replicated patterns by OM on the Au-based BMG materials imprinted at 177^oC and 62 MPa for 10 min with (a) lower magnification (b) higher magnification .

(a)

(b)

Figure 4.38 Replicated patterns by OM on the Au-based BMG materials imprinted at 177^oC and 156 MPa for 10 min with (a) lower magnification (b) higher magnification .

(a)

(b)

400 500 600 0

5 10 15 20 25

Height ( μ m)

Scanning length (

_μ

m)

27 MPa 62 MPa 156 MPa Mold

Figure 4.39 The morphological curves of micro-lens array on the Au-based BMG at 177^oC and 27 MPa, 62 MPa, and 156 MPa, respectively, for 10 min by the α step.

Figure 4.40 Replicated patterns by SEM on the Au-based BMG materials imprinted at 177^oC and 156 MPa for 10 min with (a) lower magnification (b) higher magnification.

(b)

(a)

0.1 1 10 100 1000 1000

1200 1400 1600 1800 2000

m ~39.7

Au-based BMG

Pillar diameter ( _μ m)

Yiel d stre ngth (MPa )

Figure 5.1 The strength-sample size relationship for the Au-based BMG with different

pillar diameters from 2 mm down to 1 μm.

0 20 40 60 80 100 120 140 160 -2.8

-2.6 -2.4 -2.2 -2.0 -1.8 -1.6 -1.4 -1.2

Stress (kPa)

Slope = 9.64 x 10 ^-9 Temperature = 439 K

ln(strain rate)

Figure 5.2 Determination of the STZ size of the Au-based alloys based on the TMA data.

Figure 5.3 Extraction of the activation energy of the Au-based BMG during shear deformation within the supercooled temperature region.

435 440 445 450

0 40 80 120 160

γ = 0.15 s ^-1

Temperature (K)

Shear stress (KPa )

在文檔中 Bulk Metallic Glasses (頁 66-150)