Laser Report by manoj

8/4/2019 Laser Report by manoj

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Laser surface treatment

1 College of Engineering, Ambajogai

CHAPTER 1

INTRODUCTION

The surface treat to its putting in work or its use ments by laser on the piece

confer to the material particular properties adapted to its putting in work or its use.

The laser particularly is indicated in the field of the surface treatments in how much

allows to obtain high energetic concentrations, and the attainment of elevated skin

temperatures in fractions of second, with small thermal alteration of the below

material (Bulk) and with negligibleResidual deformations. According to the energy

density of the incident laser beam, the interaction time, the spatial distribution of the

beam and its wavelength and the thermopysical properties of the material.

It is possible to obtain various effects on the surface of the piece to treat. So

it is possible to obtain as a thermal process type (the quick heating and consequent the

fast cooling of the material interested from the passage of the laser beam can provoke,

second of the caught up values of temperature on the surface of a material, an heat

treatment or a fusion or a vaporization, as a photochemical process type, that removes

thin superficial layers of material or coating or other material because of the

molecular bond breaking provoked by the absorption of the incident laser radiation.


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CHAPTER 2

LASER CLADDING

Drivers for the laser cladding process include laser beam characteristics, filler

material, base material, and thermal properties of the part. The unique capability of

laser cladding enables part processing with reduced heat smaller grain structure

compared to conventional welding. Applications for laser cladding include depositing

a robust surface treatment to salvage and repair used parts. Laser cladding basics

include an understanding of the laser light and the interaction of the laser beam with

the material.

In this article you will be introduced to several of the major components

affecting the cladding process. The key components are integrated to form the laser

cladding system.

2.1 Process Description

Laser cladding uses the high energy density generated by a laser beam to form

a molten pool in a base material for metallurgical bonding with a filler material using

a diffusion type of weld. The interaction between the laser beam and the base material

is primarily a function of the following properties:

1. Laser beam absorption Absorption of the beam generates the molten zone. A

shorter wavelength laser generally absorbs better in metals.

Figure 1 COAX10 in a robot guided 3D cladding system


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2. Laser beam reflection Back reflection from the surface of the metal is high.

3. Laser beam transmission

For metals, penetration of the laser beam (photons) is low. Absorption of the

laser beam results in the heating of the base material. Very high energy densities are

possible with a laser. Different material processing results can be achieved with

increasing the energy density. The following examples are processes that follow a

trend of increasing energy density:

a) Surface heating (low energy density)

b) Soldering

c) Brazing

d) Heat treating (surface hardening for appropriate alloys)

e) Diffusion welding (low penetration)

f) Cladding (diffusion welding plus extra energy for additive mass)

g) Keyhole welding (greater penetration)

h) Cutting (similar or greater keyhole welding energy density plus coaxial

assist cutting nozzle)

i) Drilling (generally pulsed beam)

j) Ablative material removal (very high energy density)Generally the power, pulse length, and beam quality of the laser determines what

material processing techniques are possible. Typical energy densities for cladding or

metal deposition range from 104 to 105 watts per square centimeter (W/cm2). Energy

densities above 105 W/cm2

result in a keyhole welding process producing larger

penetrations than the diffusion process. Diffusion welding of the clad deposit

produces a narrow dilution zone between the clad and the base material. A portion of

the filler material may be preheated by the laser beam just before wetting into the

molten pool. The high energy density enables rapid heating and rapid self-quench

times. One of the key advantages of the laser cladding process over conventional

welding metal deposition (gas metal arc welding (GMAW) or gas tungsten arc

welding (GTAW)) is the smaller dilution zone resulting in a smaller heat-affected

zone (HAZ). Figure 2 shows a magnified view through a metallurgical microscope of

a laser deposit of 420 stainless powder deposited on 4140 steel. The micro hardness

diamond squares show a greater hardness in the deposit (HRC 60+ in the stainless

deposit possible). For an example of the reduced heat possible with pulsed laser


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welding see Fig. 3. Laser cladding is similar to laser welding with filler material

added to the weld pool. The rapid heating and cooling of a laser welded deposition

can result in high hardness being achieved in the deposition

.

Figure 3 Laser beam welding and GTAW visual heat effects.

Table 1: Types of lasers used for cladding

Laser Wavelength Beam Quality Beam Delivery

CO2 10.6 microns High Free space

Nd:YAG 1.06 microns Low Large fiber

(typ.0.4-0.6 mm)

Fiber 1.07 microns High Small fiber

(typ.0.05-0.1mm)

Direct diode 0.8-1 microns low Free space

(typ.rectangular

beam)

Fi ure 2 Laser clad de osit of 420 stainless steel on 4140


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Figure 4 Diagram of laser cladding beam delivery head.

2.2 Applications

With respect to the rising demand within the last years, until now

approximately 30 clad-ding units have been developed for users in different branches.

Noteworthy examples are the repair of turbine blades and seal fins of gas turbines and

aero engines, surface pro-tection of car engine components and wear parts, repair of

metal forming tools and mould inserts as well as the direct manufacturing of complex

shaped sections of tools. The Figures 57 show some of these applications.


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Figure 5 Cladding of oil drilling tools

Figure 6 Repair of car engine crankshafts

Figure 7 Repair of car engine crankshafts


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CHAPTER 3

LASER COATING

3.1 Introduction

Laser coating is an advanced coating technology for improving surface

properties of various components and equipment. Laser coatings are surface coatings

with an extremely dense, crack-free and non-porous structure. Laser coatings show

excellent metallurgical bonding to the base material, have uniform composition and

coating thickness. Laser coating produces also very low dilution and low heat input to

the component. Laser coating of new components gives them surfaces with high

resistance against wear, corrosion and high temperatures. Besides new manufacturing,the process has shown its importance also in maintenance and repair of worn

components, often resulting in component performances superior to those of uncoated

ones. Research and development of laser coating processes, properties of coated

structures, and industrial applications has been very active during the last years in

Finland, primarily due to the rapid development of high power laser technology and

recent launching of industrial laser coating activity. Industrial use of laser coatings is

expected to increase markedly during the following next years.

Table 2: Characteristics of high power lasers for laser materials processing

Laser type

Property CO2 Nd:YAG

lamp-pumped

Nd:YAG

diode-pumped

HPDL

Wavelength

(m)

10.6 1.06 1.06 0.8-0.94

Efficiency (%) 5-10 1-3 10-12 30-50

Power(KW),max 40 5 5 6

Average power

density

( W/cm2

)

106-8

105-7

106-9

103-5

Service period

(h)

1000-2000 200 5000-10000 5000-10000

Fiber coupling No Yes Yes Yes


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High power laser equipment for coating and surface treatment. Several basic

properties of lasers make them very useful for a number of industrial applications

including laser materials processing. These properties include directionality,

monochromaticity, coherence, and high brightness of the laser light. Laser equipment

operating with high power levels, i.e. the high power lasers, can produce highly

energetic and well focusable laser beams that are usable in marking, drilling, cutting,

welding, hardening and laser coating. Table 2 presents the characteristics of different

type of high power lasers available for materials processing.

Carbon dioxide (CO2) lasers are the most traditional high power lasers and are

available in power levels up to several tens of kWs. CO2 lasers have characteristics

of very high power and power density, moderate efficiency, reliable operation and

excellent beam quality (low beam-parameter product number). The high

wavelength of 10.6 m results in a relative low absorption of the laser beam by metals

e.g. steels. It is common that an absorption enhancing pretreatment, such as

graphitizing of the metal surface, is frequently needed in surface hardening by a CO2

laser. Solid-state lasers, e.g. Nd:YAG lasers, operate at a still lower wavelength (1.06

m), which markedly improves the absorption characteristics, i.e. the metal surface

absorbs now significantly better energy from the Nd:YAG laser beam. However,

these lasers operate at significantly lower electrical/optical efficiency, which makes

the equipment bulky and costly to run. Fiber coupling of the laser allows the beam to

be carried easily through optical fibers from the laser beam supply.

3.2 Laser coating process

Among all laser materials processing methods, laser surface engineering is still

significantly less used than for example laser marking, cutting or welding. Surface

engineering by lasers involves primarily transformation hardening of steels, and laser

coating, which is also called laser cladding. Several modifications of laser surface

coating and treatment exist. These can be classified as follows:

1. Laser transformation hardening of steels and cast irons

2. Surface modification: remelting (e.g. cast iron), surface alloying, impregnation (e.g.

with carbides)


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3. Laser coating:

a) 2-step process: remelting of pre-placed or pre-deposited layer

(2-step process, melting/alloying); pre-placed layer of powder,

with/without organic binder

b) 1-step process: laser coating with powder or wire; laser coating with coaxial

or off-axis powder nozzles

4. Laser assisted hybrid processes

a) laser surface cleaning with thermal spraying

b) laser assisted thermal spraying; hybrid spraying

Principle of laser coating: Transformation hardening is a relatively straightforward

process and involves rapid heating of the steel surface to the austenite region, which is

then followed by self-quenching to form a martensitic case of high hardness. Laser

hardening allows hardening of local well-defined areas, high-intensity local heating

and very high self-cooling rates with good hardenability of various ferrous alloys.

Laser coating is an overlay deposition process, where the coating material, a powder

or wire, is applied on the surface of the base material through a melting process.

Figure 8 Principle of laser coating.


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Figure 9 a) and b) show two different laser coating equipment with co-axial and off-

axial powder feeding principles, respectively. In laser coating, a fine powder, e.g. 50-

150 m in size, is injected with a carrier gas to the laser beam traversing on the

surface of the material or component to be coated. The powder absorbs energy from

the laser beam, starts heating and melting in-flight, and deposits on the surface of the

base material. Part of the energy is also absorbed by the surface causing controlled

melting of a thin layer of the base material. This ensures formation of a real

metallurgical bonding between the coating and the base material. In laser coating a

melt pool of the coating material is formed, which in turn results in coatings without

porosity. The mixing between the two materials (coating and base material), i.e.

dilution, must be as small as possible to utilize the properties of the coating material

most effectively.

a) b)

Figure 9 a) 6 kW CO2 laser coating with coaxial powder nozzle and b) 6 kW

diode laser coating process with off-axis


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Table 3 Comparison of thermal spraying, weld surfacing and laser cladding.

Coating process

property

Thermal spraying Weld surfacing Laser cladding

Heat source Combustion flame,

electric or plasma

arc

Combustion flame,

electric arc

High intensity laser

radiation

Bond strength Low to moderate High High

Coating structure Lamellar from

porous to nearly

dense

Dense, cracks and

pores may exist

Dense, cracks and

pore-free layers

Heat load to work

piece

Very low tomoderate

Very high Low to moderate

Dilution Nil Moderate to high Low

Coating thickness 0.05-some mms Several mm Typically 0.5-3 mm

Coating materials Wide range of

metals, alloys, hard

metal, ceramics,

polymers

Metals and alloys,

alloys with hard

particles

Metals and alloys,

alloys with hard

particles

Productivity Low to high Low to very high Low to moderate

3.3 Coating materials and properties:-

Laser coatings can be prepared on several types of base materials. Most

commonly the base materials used are unalloyed steels, alloy steels, hard enable

steels, stainless steels, nickel or cobalt based alloys. Also various cast irons can be

coated successfully by laser process. Laser coating on copper and its alloys, aluminum

alloys and even on titanium alloys have been reported. Laser coating offers a wide

range of possible coating materials. Most commonly used laser coatings= are various

cobalt base hard alloys, e.g. Stellite 6 and 21, nickel based super alloys, e.g. Inconel

625, self fluxing alloys, e.g. NiCrBSi, and stainless steels. In order to improve the

wear resistance, hard carbide particles can be added. Also some hard metals with high

carbide contents can be prepared by the laser coating process. Ceramic coatings can

also prepared, e.g. Al2O3-TiO2on aluminum alloys.


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3.4 Metals and alloys:

Unalloyed and alloy steels Self-fluxing alloys (NiBSi, NiCrBSi, etc.) Stainless

steel (AISI 304, 316, 420, etc.) Nickel and nickel based super alloys (Inconel 625,

Alloy 59, NiCr,NiCrAl,NiCu, etc.) Cobalt alloys (Stellite 6, 12, 21, Triballoys,

Ultimet, etc.) Copper alloys (Aluminum bronze), light metals Carbide containing

alloys and composites; ceramics:

WC, Cr3C2, TiC, SiC + metal alloys - carbide-metal- blends (max. 50 vol. % carbides)

Hard metals WC-Co, Cr3C2-NiCr, TiC-Ni/Co, etc. composites (max 80...90 vol. %

carbides)

Ceramic/metal - composites Al2O3/Ni, TiB2/CrB2-Ni etc. Ceramics Al2O3-TiO2,

Al2O3-ZrO2

Figure 10 Cross section of high chromium Ni-Cr alloy laser coating layer 20 mmwide & 2 mm thick

Figure 11 Micro-structure of high-quality coating a) Stellite 21 b) WC+NiCrBSi

Figures 11.a) and 11.b) show examples of laser coatings. Figure 6 shows an

optical micrograph (cross-section) of a high chromium Ni-Cr alloy laser coating

prepared by the 6 kW HPDL coating process. The laser beam used was 20 mm wide,


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the traverse speed 400 m/min and the powder feed rate 100 g/min. By using

overlapping, large surfaces can be coating effectively. Figure 4 presents the

microstructures of two different laser coatings; Fig.11 a) is an SEM micrograph of a

micro structurally dense Stellite 21 coating on steel; Fig.11. b) is NiCrBSi self fluxing

alloy coating containing hard WC particles as reinforce- resistant base materials

(steels) from corrosion.

.

Figure 12 Laser coated by-pass valve spindle

Figure 13 Laser coating of a large shaft sleeve 1.5 m in diameter


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.

Figure 14 a) Thermally sprayed coating with several detachment due to heavy

corrosion of the coating and the base material beneath the coating,

Figure 14 b) Laser coating of the shaft after removal water (sea water) pump shaft.

Figure 14 c) Laser coated surface ready for post finishing by turning


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CHAPTER 4

LASER GLAZING

4.1 Laser Glazing of Railroad Rails:-

Laser glazing treatment is applied on the gage face of the rails to help

minimize flange and rail wear, reduce fuel consumption, and decrease the likelihood

of derailments caused by flange climb and low-rail rollover.

To maintain the toughness and relative inexpensiveness of rail steel while

reducing wheel/rail friction, an ideal approach is to modify the loading surface of

existing rail in a way that renders it substantially harder yet leaves the substrate

unaffected. Laser treatment can accomplish this by changing the surface

microstructure, and doing so in such a way that the surface layer undergoes a smooth

transition into the substrate and is well bonded to it. One way to harden the surface of

rail steel is by laser surface hardening, i.e. selective austenitization and

martensitization of the local surface region of rail steel by rapid heating and cooling.

The hard surface layer will resist plastic flow and reduce friction and wear. This

simple process has some minor disadvantages. Unlike in the case of hard bulk

materials, like diamond, o thin hard surface when loaded substantially will transmit

these loads to the soft substrate, which can deform even if the surface does not. If the

surface layer has the same elastic modulus as the substrate, it can not mitigate stress

concentrations any differently than an untreated surface. However, a surface layer

with a smaller modulus than the substrate can distribute surface stress concentrations

Figure 15 Laser glazing of railroad rails


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elastically within the layer and mitigate their effect on the substrate. Also, if the hard

surface layer does deform plastically, it will do so in the same manner as untreated

rail steel, producing a damage layer along which separation can eventually occur

leading to delaminating. What is needed then is a surface layer that is hard with

respect to plastic flow is elastically compliant, and, when it does deform plastically,

does not produce a damage layer, Laser glazing can be an ideal treatment to achieve

this goal.

Figure 16 Micrograph of laser-glazed 1080 steel

Figure shows the metal grain structure of the glazed (G), hardened (H) and

substrate (S) regions. In laser glazing, a thin surface layer is melted and rapidly

solidified to produce an amorphous or quasi-amorphous surface film. The lack of

crystalline order in such materials makes them substantially resistant to plastic flow,

and hence very hard. They exhibit about a 30% or greater reduction in elastic

modulus. If they do deform plastically, localized defects are not involved, and the

more open structure tends to be self healing. Consequently, repeated plastic flow is

less likely to result in debris being deposited in a subsurface damage layer. For these

reasons, the laser glazing process alone is sufficient to provide satisfactory reductions

in friction and wear.


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CHAPTER 5

LASER SURFACE MELTING (LSM).

In this technique (also known as laser surface remelting or laser glazing)

melting is induced in the near surface by relatively high intensity, short duration laser

interaction. No additional alloying elements are incorporated. Since the bulk of the

material is unaffected by the laser, a large heat sink is provided for the subsequent

rapid cooling of the melted surface and cooling rates in the region of lo4-lo8 K.S-' can

be obtained. This can result in non equilibrium microstructures which may confer

substantial increases in hardness and wear resistance, the application areas which have

received the most attention, particularly for steels, cast irons and aluminum alloys.

A schematic diagram of the experimental arrangement for LSM treatment is shown in

Figure 17.

Enhanced corrosion properties can be produced by LSM as a result of altering

the surface composition, changing the microstructure of impurities and second phase.

In general the non-equilibrium surface microstructures produced result in finer, more

Figure 17 Experimental arrangement for laser surface melting


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uniform structures with superior homogeneity compared with conventional surfaces.

For example, redissolution of MnS inclusions following LSM resulted in increase in

the critical pitting potential of type 304 stainless steel in 0.1 M NaCl solution.

Deterioration in resistance to pitting in Mo-bearing ferritic stainless steels at low Mo

contents as a result of LSM has been observed. LSM has been applied to sensitized

type 304 and type 316 stainless steels.


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CHAPTER 6

AUTOMOTIVE - HEAT TREATING AND SURFACE

MODIFICATION

Figure 18 Heat Treating And Surface Modification

Laser heat treatment and surface modification are the key technologies

available today to enhance the effective use of materials and achieve the desired

properties of the components used in the automotive industry to improve the

performance of the car.

The high power heat source produced by a laser beam is ideal for surface

modification. Laser heating produces local changes at the surface of the material

whilst, leaving the properties of the bulk of a given component unaffected. The

principle laser surface engineering applications can be divided into three broad areas.

The following processes can also be divided into those relying on metallurgical

changes in the surface of the bulk material i.e. transformation hardening, annealing,

grain refining, glazing and shock hardening, and those involving a chemical

modification to the surface by addition of new material i.e. alloying and cladding.

Heating without melting, commonly know as heat-treating. This involves

solid-state transformation, so that surface of the metal is not melted. The fraction of

the beam power absorbed by the material is controlled by the absortivity of the

material surface. Both mechanical (hardness, abrasion, resistance etc.) and chemical


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properties, (corrosion resistance etc.) can often be greatly enhanced through the

metallurgical reactions produced during these heating and cooling cycles.

Heating with melting, i.e. laser glazing, surface homogenization, remelting.

This method produces very rapid heating, melting and cooling to modify the surface

properties.

Melting with addition of material, i.e. cladding, alloying impregnation, which

involves melting of the surface plus material added to the surface to form a modified

surface layer.

The principles of laser heating are similar to those of conventional through

heating. The time scales involved in the former are, however, typically an order of

magnitude shorter. Whereas heating is conventionally induced by a furnace, flame,

arc or induction coil, the laser beam is focused or shaped into a suitable pattern and

scanned over the component. The high energy density laser beam heats the surface

much more rapidly, reducing the time for conduction into the bulk of the component.

Laser heat treatment and surfacing techniques must compete directly with a wide

range of comparatively low cost conventional processes and must therefore offer

significant advantages. The common advantages of laser surfacing compared to

alternative processes are:

a) Chemical cleanliness and cosmetic appearance

b) No post machining required

c) Non-contact process

d) Ease of integration

The range of alloys that can be transformation hardened by laser techniques covers all

those than can be hardened by conventional methods. The response of steel to

hardening increases with increasing carbon content, and hardness values have

exceeded 700HV for steels containing 0.75% carbon content. In addition because of

the high cooling rates plain carbon steel (0.2%C) will harden. The hardenability of

cast irons is controlled by the amount of pearlite present, and only martensitic


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stainless steels will respond to heat-treating. Transverse section of laser hardened

track in low carbon steel.

Automotive industry has been responsible for much of the laser heat- treatment

process development and some of the applications are listed in below table.

Table 4: Applications in automotive industry

Industry sector Component Material

Automotive Axel bearing seat AISI 1035 steel

Automotive Blanking die Tool steel

Automotive Engine valve Alloy steel

Automotive Gear teeth Steel

Automotive Shaft Steel

Automotive Piston ring Steel

Automotive Steering gear housing Malleable cast iron


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CHAPTER 6

CONLUSION

1) Despite outstanding advantages of laser surface treatment techniques for

enhancement of corrosion resistance; these techniques are not yet widely employed

because of the small area that can be processed in a single pass. Development of large

area treatment techniques would dramatically change this situation.

2) A brief review of laser surface melting, laser surface alloying and laser cladding

techniques on steel substrates has shown that the potential for the production of

corrosion resistant coatings by these means is considerable.

3) A new alloy prototyping technique based on laser cladding via the blown powder

technique which has been developed at Liverpool has been outlined. This should

provide a valuable tool in work aimed at the development of alloys of enhanced

corrosion resistance and other significant materials properties. An advantage of the

technique is that deposition parameters via laser surface cladding for any composition

within the alloy system in question are simultaneously determined.


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23 College of Engineering Ambajogai

Chapter 7

REFERENCES

1. Anubha Bhatla, Y. Lawrence Yao Department of Mechanical EngineeringColumbia University New York, NY 10027

2. Journal De Physique IV Colloque C9, supply Cement au Journal de Physique111, Volume 3, December 1993

3. Dr. Khansaa Dawood Salman* Received on:5/8/2008 Accepted on:31/12/2008

4. X.b. Zhou and J.Th.M. De Hosson Department of Applied Physics, MaterialsScience Centre, University of Groningen, Nijenborgh 4, 9742 AG Groningen,

The Netherlands.

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