Bab 33 surface treatment, coating and cleaning

surface treatment, coating and cleaning

 Surface Technology outline

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Surface Technology

Surfaces Tribology Surface

Treatment

Fabrication of Microelectronic devices

Surface Treatment, Coating

and Cleaning

Ir Tri Prakosa, M Eng.

Proses Manufaktur II, Januari 2010

1 INTRODUCTION

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1 Introduction

 After a component is manufactured, all or parts

of its surfaces may have to be processed further

or coated in order to impart certain properties

and characteristics

 Surface treatment may be necessary to:

{ Improve resistance to wear, erosion, and indentation

(slideways in machine tools, wear surfaces of

machinery, and shafts, rolls, cams, and gears).

{ Control friction (sliding surfaces on tools, dies,

1 Introduction

{ Improve lubrication (surface modification to retain

lubricants).

{ Improve corrosion and oxidation resistance (sheet

metals for automotive or other outdoor uses, gas turbine components, and medical devices).

{ Improve stiffness and fatigue resistance (bearings

and multiple-diameter shafts with fillets).

{ Rebuild surfaces on worn components (worn tools,

dies, and machine components).

{ Improve surface roughness (appearance,

dimensional accuracy, and frictional characteristics).

{ Impart decorative features , color, or special surface

texture.

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1 Introduction

 Coating of critical surfaces is among important technological developments

 Consider, for example, applications where

temperatures are high and the environment is hostile, such as turbine blades and other

components and surfaces of aerospace

structures

1 Introduction

 In advanced propulsion systems, for example, coatings have important functions

{ First , they act as a thermal barrier to reduce the

temperature to which parts are subjected.

Engine components are expected to withstand

Temperatures are high because the efficiency of gas turbines increases with increasing gas temperature.

{ Second , they protect surfaces from oxidation due to

gases such as hot oxygen, and from hydrogen, used for cooling, which otherwise could form brittle

compounds.

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1 Introduction

 In addition to these physical and chemical

requirements, coatings should also be:

surfaces.

 Several techniques that are suitable and

applicable to certain groups of materials have been developed (see next two Tables)

Perlakuan Permukaan untuk Berbagai Logam

Aluminum Chrome plate; anodic coating, phosphate; chromate conversion coatingBeryllium Anodic coating; chromate conversion coating

Cadmium Phosphate; chromate conversion coating

Die steels Boronizing; ion nitriding; liquid nitriding

High-temperature

steels Diffusion

Magnesium Anodic coating; chromate conversion coating

Mild steel Boronizing; phosphate; carburizing; liquid nitriding; carbonitriding; cyanidingMolybdenum Chrome plate

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Perlakuan Permukaan untuk Berbagai Logam

Nickel- and

cobalt-base alloys Boronizing; diffusion

Refractory metals Boronizing

Stainless steel Vapor deposition; ion nitriding; diffusion; liquid nitriding; nitriding

Steel Vapor deposition; chrome plate; phosphate; ion nitriding; induction hardening; flame hardening; liquid nitridingTitanium Chrome plate; anodic coating; ion nitriding

Tool steel Boronizing; ion nitriding; diffusion; nitriding; liquid nitriding Zinc Vapor deposition; anodic coating; phosphate; chromate chemical conversion coating

1 Introduction

 This lecture describes the methods used to

modify the surface structure and its properties in order to impart these desirable characteristics

 The lecture begins with surface hardening

techniques involving mechanical or thermal

means and continues with different types of

coatings that are applied by various means

 Some of these techniques are also used in the manufacture of semiconductor devices (next

week lecture)

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1 Introduction

 Finally, you'll learn about cleaning techniques for manufactured surfaces, particularly lubricant residues, before components are processed

further, assembled, and the product is placed in service

 Environmental consideration: regarding the

fluids used and the waste material from various surface treatment processes are among

important factors to be considered

2 MECHANICAL SURFACE

TREATMENT AND COATING

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2 Mechanical Surface Treatment and Coating

 Several techniques are available for

mechanically improving the surface properties of finished components

 The more common ones are described as

2.1 Shot peening

 In shot peening, the workpiece surface is hit repeatedly with a large number of cast steel, glass, or ceramic shot (small balls), making overlapping indentations on the surface

 This action causes plastic deformation of

surfaces, to depths up to 1.25 mm (0.05 in.), using shot sizes ranging from 0.125 mm to 5

mm (0.005 in to 0.2 in.) in diameter

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2.1 Shot peening

 Because the plastic deformation is not uniform throughout the part's thickness, shot peening imparts compressive residual stresses on the surface, thus improving the fatigue life of the component

 This process is used extensively on shafts,

gears, springs, oil-well drilling equipment, and jet-engine parts (such as turbine and

compressor blades)

2.2 Roller burnishing

 In roller burnishing, also called surface rolling ,

the surface of the component is cold worked by

a hard and highly polished roller or rollers

 This process is used on various flat, cylindrical,

or conical surfaces (next Figures)

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Roller Burnishing

Roller burnishing pada fillet poros bertingkat guna

memberikan tegangan sisa tekan pada permukaan untuk memperbaiki umur fatigue.

Contoh-contoh roller burnishing

2.2 Roller burnishing

 Roller burnishing improves surface finish by

removing scratches, tool marks, and pits

 Consequently, corrosion resistance is also

improved since corrosive products and residues cannot be entrapped

 Internal cylindrical surfaces are burnished by a similar process, called ballizing or ball

burnishing.

 A smooth ball, slightly larger than the bore

diameter, is pushed through the length of the

hole

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Ballizing (Ball Burnishing)

2.2 Roller burnishing

 Roller burnishing is used to improve the

mechanical properties of surfaces, as well as

the shape and surface finish of components

 It can be used either singly or in combination

with other finishing processes, such as grinding, honing, and lapping

 Soft and ductile, as well as very hard metals,

can be roller burnished

 Typical applications include hydraulic-system

components, seals, valves, spindles, and fillets

on shafts

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 The contact pressures developed can be as high

as 35 GPa (5 x 106 psi), lasting about 2-3 µs

 Large increases in surface hardness can be

obtained by this method, with very little change (less than 5 %) in the shape of the component

2.4 Cladding (clad bonding)

 In cladding, metals are bonded with a thin layer

of corrosion-resistant metal by applying

pressure with rolls or other means

 A typical application is cladding of aluminum

aluminum alloy is clad over pure aluminum

 Other applications are steels clad with stainless steel or nickel alloys

 The cladding material may also be applied

through dies, as in cladding steel wire with

copper, or by explosives

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2.4 Cladding (clad bonding)

 Multiple-layer cladding is also utilized for special applications (see the Figure)

Ilustrasi skematik proses roll

bonding, atau cladding.

2.5 Mechanical plating

 In mechanical plating (also called mechanical coating, impact plating, or peen plating), fine

metal particles are compacted over the

workpiece surfaces by impacting them with

spherical glass, ceramic, or porcelain beads

 The beads are propelled by rotary means

 The process is used typically for hardened-steel parts for automobiles, with plating thickness

usually less than 0.025 mm (0.001 in.)

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3 CASE HARDENING AND

3 Case Hardening and Hard Facing

 Surfaces may be hardened by thermal means in order to improve their frictional and wear

properties, as well as resistance to indentation, erosion, abrasion, and corrosion

 The most common methods are described as:

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3.1 Case hardening

 Traditional methods of case hardening

(carburizing, carbonitriding, cyaniding, nitriding, flame hardening, and induction hardening) were described in Section 4.10 and are summarized

in Table 4.1

 In addition to the common heat sources of gas and electricity, laser beams are also used as a heat source in surface hardening of both metals and ceramics

Outline of Heat Treatment Processes

for Surface Hardening

Process Metals

hardened

Element added to surface

Procedure General

Characteristics

Typical applications

Carburizing Low-carbon steel

(0.2% C), alloy steels (0.08–

0.2% C)

C Heat steel at 870–950 °C

(1600–1750 °F) in an atmosphere of

carbonaceous gases (gas carburizing) or carbon- containing solids (pack carburizing) Then quench.

A hard, high-carbon surface is produced

Hardness 55 to 65 HRC Case depth <

0.5–1.5 mm ( < 0.020 to 0.060 in.) Some

distortion of part during heat treatment.

Gears, cams, shafts, bearings, piston pins, sprockets, clutch plates

Carbonitriding Low-carbon steel C and N Heat steel at 700–800 °C

(1300–1600 °F) in an atmosphere of

carbonaceous gas and ammonia Then quench in oil.

Surface hardness 55 to

62 HRC Case depth 0.07 to 0.5 mm (0.003

to 0.020 in.) Less distortion than in carburizing.

Bolts, nuts, gears

Cyaniding Low-carbon steel

(0.2% C), alloy steels (0.08–

0.2% C)

C and N Heat steel at 760–845 °C

(1400–1550 °F) in a molten bath of solutions

Process Metals hardened Element

added to surface

Procedure General

Characteristics applications Typical

Nitriding Steels (1% Al,

1.5% Cr, 0.3%

Mo), alloy steels (Cr, Mo), stainless steels, high-speed tool steels

N Heat steel at 500–600

°C (925–1100 °F) in an atmosphere of ammonia gas or mixtures of

molten cyanide salts

No further treatment.

Surface hardness up

to 1100 HV Case depth 0.1 to 0.6 mm (0.005 to 0.030 in.) and 0.02 to 0.07 mm (0.001

to 0.003 in.) for high speed steel.

Gears, shafts, sprockets, valves, cutters, boring bars, fuel-injection pump parts

Flame hardening Medium-carbon

steels, cast irons None Surface is heated with an oxyacetylene torch,

then quenched with water spray or other quenching methods.

Surface hardness 50

to 60 HRC Case depth 0.7 to 6 mm (0.030 to 0.25 in.)

Little distortion.

Gear and sprocket teeth, axles, crankshafts, piston rods, lathe beds and centers Induction

hardening Same as above None Metal part is placed in copper induction coils

and is heated by high frequency current, then quenched.

Same as above Same as above

Outline of Heat Treatment Processes

for Surface Hardening

3.1 Case hardening

 Case hardening, as well as some of the other surface-treatment processes, induce residual stresses on surfaces

 The formation of martensite in case hardening causes compressive residual stresses on

surfaces

 Such stresses are desirable because they

improve the fatigue life of components by

delaying the initiation of fatigue cracks

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 Hard coatings of tungsten carbide and

chromium and molybdenum carbides can also

be deposited using an electric arc (spark

4 THERMAL SPRAYING

4 Thermal Spraying

 In thermal spraying processes, coatings such as various metals and alloys, carbides, and

ceramics are applied to metal surfaces by a

spray gun with a stream of oxyfuel flame,

electric arc, or plasma arc

 The coating material may be in the form of wire, rod, or powder, and the droplets or particles

impact the surfaces to be coated at speeds in the range of 100-1200 m/s (300-4000 ft/s)

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4 Thermal Spraying

 The surfaces to be sprayed should be cleaned and roughened to improve bond strength, which depends on the particular process and

techniques used

 The coating has a layered structure of deposited material, and may include porosity (which may

be as high as 20 %) due to entrapped air and

oxide particles due to the high temperatures

involved

4 Thermal Spraying

 The earliest applications of thermal spraying (in the 1910s) involved metals, hence the term

metallizing has also been used.

 Typical applications include the aircraft engine industry (such as in rebuilding worn parts),

structures, storage tanks, tank cars, rocket

motor nozzles, and components requiring

resistant to wear and corrosion

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4 Thermal Spraying

 There are several types of thermal spraying

processes, which we list in decreasing order of performance:

a Plasma, either conventional, high-energy, or

vacuum; it produces temperatures on the order of

b Detonation gun, in which a controlled explosion

takes place using oxyfuel gas mixture; it has a

performance similar to plasma.

4 Thermal Spraying

c Highvelocity oxyfuel (HVOF) gas spraying , which

has a similarly high performance as above, but is less expensive.

d Wire arc , in which an arc is formed between two

e Flame wire spraying (next Figure) in which the

oxyfuel flame melts the wire and deposits it on the

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Operasi Peniupan Panas (a)

Operasi Peniupan Panas (b)

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(b) Peniupan serbuk logam panas

Operasi Peniupan Panas (c)

Example: Repair of a worn turbine-engine

shaft by thermal spraying

 The shaft of the helical-gear for a GE T-38 gas

turbine engine had two worn regions on its

Procedure General

Characteristics

Typical applications

Nitriding Steels (1% Al, 1.5%

Cr, 0.3% Mo), alloy steels (Cr, Mo), stainless steels, high- speed tool steels

N Heat steel at 500–

600 °C (925–1100

°F) in an atmosphere of ammonia gas or mixtures of molten cyanide salts No further treatment.

Surface hardness

up to 1100 HV

Case depth 0.1 to 0.6 mm (0.005 to 0.030 in.) and 0.02 to 0.07 mm (0.001

to 0.003 in.) for high speed steel.

Gears, shafts, sprockets, valves, cutters, boring bars, fuel-injection pump parts

Example: Repair of a worn turbine-engine

shaft by thermal spraying

 The case-hardened depth was 0.3 mm (0.012 in.)

 Even though the helical gears were in good condition, the part was considered scrap

because there was no approved method of

repair

 The worn regions were first machined

undersize, grit blasted, and coated with

tungsten carbide (12% cobalt) using the

high-Example: Repair of a worn turbine-engine

shaft by thermal spraying

 The part was then finish machined to the

dimensions of the original new shaft

 The total cost of repair was a fraction of the cost

to replace the part

 Source: Plasma Technology, Inc.

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5 VAPOR DEPOSITION