Jackson M.J. Micro and Nanomanufacturing

Подождите немного. Документ загружается.

Micro- and Nanomanufacturing 663

CP O

-•—<-

zzzn

Dzza

s]_a

Hydrophobic Hydrophilic

Fig. 12.25. Schematic diagram of high-resolution ink jet printing of source and

drain electrodes of

polymer transistor [12]

664 Micro- and Nanomanufacturing

XXX^'^^'^

Dielectric

Rubbed poiyimide

rbi

CUsnnei'^^-jxf:-'

\i\

Fig. 12.26. Schematic diagram of a top-gate ink jet printed transistor showing the

enlargement of the channel region [12]

12.3.7 Nanomanufacturing by Machining

Nanostructured materials such as metals have high hardness,

strength, and ductility. However, their method of manufacture has

inhibited their wider use. Nanostructured metals are typically manu-

factured by condensation from the vapor phase and by high-energy

ball milling. The particulates produced are compacted and sintered

to bulk form. The cost of these materials is typically hundreds of

dollars per pound. Methods to produce a cheaper alternative include

production by severe plastic deformation to achieve microstructural

refinement such as rolling, drawing, equal channel angular extrusion

(ECAE), and high-pressure torsional straining. Machining is one

method to produce nanostructured metals [13-15]. Chip formation

Micro- and Nanomanufacturing 665

produces high shear strains in the range between 2 and 10, strain

rates up to 10^ s"\ and shear plane temperatures up to 0.7 Tm- The

production of chips creates these nanocrystals and is shown via the

quick stop technique in Figure 12.27.

.v'4

••^r ^#5^:;.

-.i^v

•'\'i?J^'^:'^"-''A

—

0.1

Fig. 12.27. Microstructure of partially formed chips produced using the quick

stop device. The superposed Vickers' hardness values show the difference be-

tween bulk and chip material. The lack of visible grain structure in the chip illus-

trates the existence of sub-micron sized grains. Courtesy of

Chandrasekara.

666 Micro- and Nanomanufacturing

AI6061-T6, grain

size:

75 nm

'• • iv.

0.2 M"! %^*

"ft*'''

52100

steel,

grain

size:

330 nm

•Si

Wt!l;Ji;.ih"l

Ti,

grain

size:

90 nnn

lncx)nel-718, grain

size:

90 nm

Fig. 12.28. TEM images of various machining chips showing nanocrystalline

structure. Regions of high dislocation density can be seen. This suggests that

grains are highly deformed. Courtesy of

Chandrasekara.

Figure 12.28 shows bright TEM images of machined chips and

the corresponding selected area diffraction patterns. There are nu-

merous grains with nanostructured features and elongated mor-

phologies. Examination of the image suggests that grains are se-

verely deformed and are under 1000 nm in size. Furthermore, grains

are severely distorted with very high dislocation density. Distinct

changes in aspect ratio have taken place, and convergent beam elec-

tron diffraction images show that nanostructured grains have both

low- and high-angle grain boundaries.

Micro- and Nanomanufacturing 667

Rjre/^uninum

Transition

elongeted grans

ec|uaxiBdgans\A/ith

N^an^e

grain

boundaries

•t '

Fig. 12.29. Bright field TEM images of pure aluminum at increasing shear stains.

Courtesy of

Chandrasekara.

Figure 12.29 shows the bright-field TEM image of aluminum chips

produced under increasing shear strains. The image shows the tran-

sition form elongated grains to equiaxed grains with high angle grain

boundaries. The process of machining at increasing shear strains

also increases the relative hardness of the chip compared to the bulk

of the material. Figure 12.30 shows the difference between the chip

and the bulk of the material. The chip is typically 2-3 times harder

than the bulk material.

668 Micro- and Nanomanufacturing

iL.

E 0)

•i

§?5

£ ^

^ S CD

^ CD "^

0 CO

-CD

Material

Fig. 12.30. Comparison between the hardness of the chip and the bulk material for

various metals. Courtesy of

Chandrasekara.

Conventional turning operations tend to produce chips that cannot

subsequently be processed efficiently for forming nanocrystalline

particulate products. For this purpose, modulation-assisted machin-

ing has been developed to produce unitary chips of the right shape

and size. The process involves modulating the machining process to

produce chips that can be used for infiltrating micro-and macroscale

products. The production of unitary chips is shown in Figure

12.31.

The figure shows the modification a spindle to machine with inter-

mittent cuts. Figure 12.32 shows the effect of modulation on chip

formation processes. The additional of adequate lubrication shows

that segmented chips can be produced with grain sizes in the nano-

meter range. The process can machine a wide range of alloys and

metals, provides an economic way to produce nanostructured prod-

ucts,

eliminates secondary comminution, and provides an economic

way of manufacturing large-scale particulate products.

Micro- and Nanomanufacturing

669

Tuning

with

mxUation

Oonventicrial turning

Fig.

12.31.

Machine tool spindle retrofitted

perform modulation-assisted

machining. Chip segments produced are shown

Dry Cutting

Dry modulation maciiining

Lubricated modulation machining

Fig. 12.32. Images

chips produced

by dry

cutting,

dry

modulation machining,

and lubricated modulation machining. Courtesy

Chandrasekara.

670 Micro- and Nanomanufacturing

The production of chips of different shape and forms can be ac-

complished using modulation-assisted machining. Figure 12.33

shows the types of chips created using modulation. The chips forms

created are needles, platelets, and equiaxed forms and have aspect

ratios between

and 200, and particle sizes ranging from 10 |Lim to 2

mm.

Needles

Ratel^

Particle size

-0.010nnmto2nnm

Aspect ratio

H to 200

Bquiaxed

Fig.

12.33.

Chip forms produced by modulation-assisted machining. Courtesy of

S. Chandrasekara.

The advantages of producing nanostructured metals using these

techniques clearly show how economically viable nanostructured

products can be produced. The direct production of nanocrystalline

particulates produces a wide range of metals and alloys with chip

forms that have variable aspect ratios and sizes. Potential applica-

tions include: structural and wear components, spray applications,

Micro- and Nanomanufacturing 671

thin and thick film coatings, ferromagnetic alloys, and metal and

polymer matrix alloys. Nanostructured metals can be used to manu-

facture a wide variety of products by extrusion, vibratory compac-

tion, cold spray, dynamic compaction, thermal spray, and sintering

techniques. Nanomanufacturing by machining appears to be an ex-

tremely promising and economic way of improving the properties of

micro-and macroscale products using nanostructured metals.

11Hz,300RPM

22Hz,600RPM

44Hz,1200RPM

Control of

particle shape

Fig. 12.34. Control of particle shape using modulation-assisted machining. Cour-

tesy of

Chandrasekara.

672 Micro- and Nanomanufacturing

12.4 Commercialization Issues of Micro- and

Nanotechnologies

This section is devoted to the key issues associated with the

commerciahzation of products and services developed by Micro-

NanoTechnologies (MNT). Research, prototype development,

manufacturing, and marketing are intrinsic to any commercialization

strategy. The availability of an appropriate infrastructure that bridges

the gap between research and manufacture thus providing a seamless

flow from concept to product realization is key to success. Very few

nations have such an ideal infrastructure.

Historically, MNT are a set of enabling technologies that have

evolved from the semiconductor industry, which was based entirely

on silicon as a material. Product based MEMS, microsystems, or mi-

cromachining technologies really came into the market in the early

1980s because of their acceptance by the American automotive in-

dustry for use in automobiles. These products were manifold pres-

sure sensors and fuel injector nozzles. They had to be ultra- reliable

low cost products that could be mass produced and truly commer-

cial. The 1990s gave birth to more commercially successful devices

that sensed, actuated, and were smart. Sensors therefore became the

largest market for microproducts since they pervaded almost every

sector. Integration and packaging technologies had to be developed

to meet market demand for new products such as the air accelerome-

ter and ink-jet print head. The actual assembly, connection, integra-

tion and packaging of components to manufacture a useful product

added a dimension of complexity and presented challenge to the de-

signers and manufacturers. The emergence of nanotechnology and

nanosystems, i.e., a two to three orders of magnitude smaller in di-

mensions greatly increases the magnitude of this challenge. Like mi-

crosystems, nanosystems will be disruptive so new manufacturing

paradigms are required. They will be capable of realizing a limitless

range of new products and systems; some will have a significant im-

pact on societies.

Commercialization is about having a sustainable and marketable

product at the right time. The performance at the technology-product

interface produces the competitive advantage. This first has to

clearly defined and understood by companies if they are to embrace