Introduction

The cold spray process is a relatively new process that uses metallic powders to rapidly

deposit a coating. In the process, metallic powder particles are injected into a de Lavel

type nozzle where they are accelerated to high velocities by a supersonic gas stream [1,

4]. Upon impingement on a substrate, the powder particles are plastically deformed and

form a coating through their bonding to the substrate and to one another. With this spray

process, metallic coatings can be deposited with a high deposition rate, little oxidation,

low residual stress, low porosity and good coating–substrate adhesion. For the present

study, Zinc and Stainless Steel (SS) coatings are prepared using the cold spray process.

Zn coatings are commonly used as protective coatings for ferrous alloys (such as steels),

based on a principle known as cathodic protection [5]. Under most conditions, a Zn

coating is anodic to steels and aluminium alloys so that it can serve as a sacrificial layer

to protect these substrate material from corrosion [6]. Stainless steel is used for corrosion

resistance.

Electron Back Scatter Diffraction (EBSD) is a technique for studying the crystallographic

orientations of grains, as also the grain boundary character distribution. The aim of this

thesis is to obtain an understanding of the microstructure in cold spray coatings using

EBSD. Obtaining good EBSD data is difficult on coatings as compared to bulk materials

due to the inherent porosity and stresses in the coatings. For Zinc coatings, mechanical

polishing is difficult because zinc is a soft material. We observed that the EBSD pattern

quality was poor on specimens that were mechanically polished using diamond paste as

grinding medium. Furthermore, the zinc coatings were getting removed easily in

mechanical polishing. The final stage of fine polishing using diamond as grinding media

was hence replaced with ion beam milling for Zinc specimens. SS coatings were still

polished using diamond pastes as the hardness in this case is relatively high (300 Hv) and

fine polishing using colloidal silica resulted good EBSD data. And EBSD data is

analysed.

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1.1 The thermal spray technique

Thermal Spray is a coating process that provides a functional surface to protect or

improve the performance of an affordable substrate or component. Almost any kind and form of

material can be thermally sprayed - which is why thermal spray has been used worldwide to

provide corrosion protection, protect from wear and abrasion, restore and repair components, and

more. There are many types of thermal spray processes, but all involve the deposition of finely

divided metallic or non-metallic materials in a molten or semi-molten condition on a substrate.

The feedstock material is fed into a gun, which heats the materials to a plastic or molten state and

then accelerates it by a compressed gas to a substrate. The particles strike the surface, flatten, and

form thin platelets or splats that conform and adhere to the irregularities of the prepared surface

and to each other. As the sprayed molten particles impinge upon the substrate, they cool and build

up splat by splat into a lamellar structure, thus forming a coating or spray deposit.

The basic process variations of thermal spraying are the spray feed materials, the

method of heating, and the method of propelling the materials to the substrate. The feed materials

used are in the form of powder, wire, rod, or cord. Fig 1.1.1 shows schematic of the thermal spray

process.

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Fig 1.1.1: Schematic of Thermal spray process

Substrate

Feed material

Why use thermal spray

Thermal spray processes are easy to use, cost little to operate, and have attributes that are beneficial

to applications in almost all industries. The benefits are typically lower cost, improved engineering

performance, and/or increased component life. A substantial cross section, if not all, of the world

industries have coating applications for a wide range of needs including restoration and repair;

corrosion protection; wear protection of many types, such as abrasion, adhesive, fretting and

erosion; thermal barriers or conductors; electrical circuits or insulators; near-net-shape

manufacturing; seals, engineered emissivity, abradable coatings, decorative purposes, and more.

Coating Microstructure

The thermal spray deposited coating microstructure has characteristics typically represented as

lamellar or layered splat structures. The structure is created when molten spherical particles are

accelerated, impact the surface, spread over the substrate, solidify and become interlocked. The

spherical molten particles, at the moment of impact, flatten out into elongated lenticular splats.

These lamellae form the undulating contours of the individual sprayed particles. The different levels

of porosity and the amount of oxide inclusions in the final coating are a function of the velocity of

the molten particles and the environment, air or inert, that is used. Coatings are typically bonded to

the substrate by mechanical interlocks (due to the roughen surface from grit blasting). This bonding

is typical called adhesive bond strength. Particle to particle adhesion is called cohesive bonding.

Fig 1.1.2 shows the thermal sprayed coating microstructure.

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Fig 1.1.2: Thermal sprayed coating microstructure

1.1.2 Thermal Spray Processes

According to the method of heat generation, thermal spray processes may be categorized into

two basic groups, combustion and electrical.

Types of Thermal Spray Processes

Heat Source: Combustion Heat Source: Electrical

Low Velocity Flame Spraying Plasma Spraying

High Velocity Flame Spraying (HVOF) Wire Arc Spraying

Detonation (D-Gun) Induction Plasma Spraying

  Cold Spray

1.1.3 Combustion heat source

Low velocity flame spray

The simplest thermal spray process can be used to deposit material supplied as wire, rod,

or powder. A low velocity flame spray gun is operated by feeding a fine powder or wire

into a combustion flame. This flame is typically acetylene-oxygen, because of the higher

temperatures it permits; but other fuel gases such as propane, natural gas, hydrogen, or

methyl-acetylene can be used as well. The combustion flame melts the powder or wire tip

and propels the molten particles to the substrate to form the coating.

The stream of burning gas carries the particles, molten and atomized, to the work piece or

substrate. Flame spray guns are inexpensive, light, and compact. Compared to other

coating methods, however, particle velocities and temperatures are low, producing more

porous, lower density coatings of lower bond strength. In the simplest form of flame

spraying, oxygen aspirates powder from a canister attached to the flame gun and injects it

into the oxyfuel flame. In some flame spray guns, pressurized inert gas from remote

powder feeders carries the powders into the flame. In this type gun, pressurized air or

inert gas increases the particle velocity for higher bond strength and coating density while

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cooling the substrate. The inert gas also helps in another way; it reduces the oxidation of

the particles and the substrate. When wire or rod is the spray feed material, motor-driven

gears draw, push, or pull the material through the gun into the combustion flame for

melting. Compressed gas, usually air, flows around the flame atomizing the material as it

melts at the tip of the wire or rod, propelling the molten or semi-molten material onto the

substrate or work piece. Powder flame spray can be used to deposit any material that

melts below the flame temperature (4,000° to 5,000° F). Wire flame spray can use any

feed material, usually metals that can be drawn into wire. Ceramic formed into rod can be

sprayed with guns for wire spray, as can powder-filled plastic cord. Typically, flame

spray is used to deposit coatings of low melting metals, low melting metal alloys, self-

fluxing alloys, self fluxing/carbide blends and various plastics. Fig 1.1.3 shows the Low

velocity flame spray process.

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Fig 1.1.3: Low velocity flame spray process

High velocity oxy-fuel (HVOF)

The state-of-the-art High velocity oxy-fuel (HVOF) process uses extremely high kinetic

energy and controlled thermal energy output to produce low porosity coatings with high

bond strength, fine as-sprayed surface finishes and low residual stress. HVOF

combustion spray guns combusts kerosene, propylene, propane, or hydrogen fuel and

oxygen under pressure and accelerates the combusted gas streams down a confined,

cooled tube. Powders are fed axially into the nozzle with carrier gases where the particles

are entrained with the confined, high-pressure combustion gases. The gases undergo

rapid expansion through a restricted nozzle when combusted with oxygen to accelerate

the molten particles to supersonic velocities (up to 4,500 ft/sec). The high gas

acceleration has been shown to increase coating density, increase coating adhesion, and

produce finer coating oxide inclusion distributions. The low residual stress allows for

greater coating thickness, lower porosity, lower oxide content, and higher coating

adhesion. Fig 1.1.4 shows the high velocity oxy fuel spray process.

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Fig 1.1.4: High velocity oxy fuel spray process

Detonation flame (D-gun) spraying

In Detonation flame (D-gun) spraying the energy of explosions of oxygen-fuel gas

mixtures, rather than a steadily burning flame, is used to melt and propel powdered

materials onto the surface of the substrate. The resulting deposit is hard, dense, and

tightly bonded. D-Gun coatings have been used with carbides and metal alloys in order to

develop unique coating systems. Fig 1.1.5 shows the schematic of the detonation spray

process.

1.1.4 Electrical heat source

Plasma spraying processes typically use microwave electromagnetic RF or induction-

coupled fields and AC or DC arcs as energy sources for thermal plasmas. Material in the

form of powder is injected into a very high temperature plasma flame, where it is rapidly

heated and accelerated to a high velocity. The hot material impacts on the substrate

surface and rapidly cools forming a coating.

DC-arc plasma spray uses an inert, high-temperature jet created by heating

inert gases in a confined electric arc. The hot gas jet created by the arc/plasma column

expands, entrains the coating particles, heats the particles, and accelerates the molten or

semi-molten particles to the substrate to form a coating. The high degree of melting and

relatively high particle velocities provides good deposit densities and bond strengths.

Controlled atmosphere plasma spraying using inert gas chambers or inert gas shrouds

have reduced the oxide inclusions and improved coating density.

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Fig 1.1.5: Schematic of detonation spray process

Low-pressure (LPPS) or vacuum (VPS) plasma spraying

Low-pressure (LPPS) or vacuum (VPS) plasma spraying processes have produced clean

coatings with no oxide inclusions, extremely high densities, and significantly improved

bond strengths. The plasma spray process carried out correctly is called a "cold process"

(relative to the substrate material being coated) as the substrate temperature can be kept

low during processing avoiding damage, metallurgical changes and distortion to the

substrate material. The plasma spray gun comprises a copper anode and tungsten cathode,

both of which are water-cooled. Plasma gas (argon, nitrogen, hydrogen, helium) flows

around the cathode and through the anode which is shaped as a constricting nozzle. The

plasma is initiated by a high voltage discharge that causes localized ionization and a

conductive path for a DC arc to form between cathode and anode. The resistance heating

from the arc causes the gas to reach extreme temperatures dissociate and ionize to form

plasma. The plasma exits the anode nozzle as a free or neutral plasma flame (plasma

which does not carry electric current) which is quite different to the plasma transferred

arc coating process where the arc extends to the surface to be coated. When the plasma is

stabilized ready for spraying the electric arc extends down the nozzle, instead of shorting

out to the nearest edge of the anode nozzle. This stretching of the arc is due to a thermal

pinch effect. Cold gas around the surface of the water-cooled anode nozzle being

electrically non-conductive constricts the plasma arc, raising its temperature and velocity.

Powder is fed into the plasma flame most commonly via an external powder port

mounted near the anode nozzle exit. The powder is so rapidly heated and accelerated that

spray distances can be in the order of 25 to 150 mm. RF or induction-coupled plasma

spray has been used to produce thermal plasma jets that provide dense coatings of most

materials using coarser particles. The particles are entrained and heated by the plasma jet

flow, which accelerates slowly toward the exit resulting in increased particle dwell times

in a larger, more uniform heating volume. This allows an increased powder size to be

melted.

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Wire arc spraying

Wire arc spraying processes utilize a DC electric arc to directly melt insulated electrode

wires. As the consumable wire electrodes are advanced to a point, a potential difference

applied across the wire initiates an arc that melts the tips in an atomizing gas. Typically

argon gas is used to atomize the molten material into fine particles and accelerate them to

the substrate. Particles generated by most wire-arc spray processes tend to be larger and

more irregular in size distribution than in power fed thermal spray processes. Typically,

low atomizing-air pressure results in rough coating profiles while high pressure produces

smoother surface textures and finer splats. Oxides can be reduced by boosting feed rates

and by using nitrogen, helium, or argon as an atomizing gas.

lower consumable costs

Benefits of the wire arc spraying process compared to other T/S processes are:

1. Easy to use 2. Simple to learn

3. Portable 4. Easy to maintain

5. High deposition rates 6. Thicker coatings

7. Low operating cost 8. High spray rates

9. Cool substrates.

1.1.5 Applications of thermal spray

For thermal spray processes and materials have a broad range across all industrial sectors.

Thermal spray processes are easy to use, cost little to operate, and have coating attributes

that are beneficial to applications in various industries. Applications include coatings for

wear prevention, dimensional restoration, thermal insulation and control, corrosion

resistance, oxidation resistance, lubrication films, abrasive actions, seals, biomedical

environments, electromagnetic properties, etc., and the manufacturing of free-standing

components; spray formed parts, and nanostructured materials.

Thermal spray processes and deposited materials have resulted in attractive coating

solutions in the aerospace, industrial gas turbine, petrochemical and gas, and automotive

industries. The inherent characteristics of its microstructure can play an important role in

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enhancing performance. For instance, porosity helps reduce the thermal conductivity of

thermal barrier coatings in jet aircraft engines.

In the aerospace market, combustion-spray is used to apply clearance-control coatings. In

the case of abradable systems, the porosity helps to weaken the cohesive strength of the

coating and allows for micro-rupture of particles when in contact with the turbine blade.

Some customers recognize that low-velocity combustion might not be the optimum

choice of processes for an application, but they may select combustion spray anyway

because of its lower cost.

In some cases, design limitations of the manufacturing process may be eliminated or

reduced by thermal spray post-treatments such as spray-and-fuse. In this post-treatment

process, self-fluxing nickel/cobalt alloys are flame sprayed and subsequently fused by

another thermal energy source, such as an oxygen acetylene torch, furnace, induction

coil, or infrared heating. Self-fluxing alloys typically have small amounts of boron and

silicon that help to depress the melting point, which helps these alloys to depress the

melting point, which helps these alloys to fuse and coalesce. As they fuse, the coatings

form a metallurgical bond with the substrate. The coating is dense and low in porosity,

and provides high inter-particle cohesive strength and substrate-to-coating adhesive

strength.

Coatings that are applied by combustion spray processes and then fused are typically

suitable for highly wear-resistant applications. This is important for the agricultural and

glass industries in products such as agricultural blades and glass mould plungers, which

require toughness and wear resistance. Blending carbides into the self-fluxing alloys can

increase coating wear resistance further.

HVOF processes are suitable not only for applying tungsten carbide-cobalt and nickel

chromium-chrome carbide systems, but also for depositing wear and corrosion resistant

alloys such as Inconel (NiCrFe), Triballoy (CoMoCr), and Hastelloy (NiCrMo) materials.

HVOF MCrAlY coatings and some low-pressure plasma (LPPS) coatings are used for

high temperature oxidation/hot corrosion and TBC bond coat applications for repair and

restoration of existing components. Low melting-point ceramics such as alumina and

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alumina-titania are also applied via some HVOF processes for abrasive wear and

dielectric applications.

Wear resistant coatings are used in nearly every industry to extend the surface life of a

component. Because thermal spray coatings offer superior properties, competitive costs,

and environmentally friendly processing, they are increasingly being used in place of

hard chrome plating. Today, HVOF materials are being applied to hydraulic rods, landing

gears, and the internal diameter of large bore cylinders as hard chrome replacements. The

HVOF spraying of carbide materials on the landing gears of commercial airliners has

been approved for use. Although original equipment manufacturers (OEMs) still require

LPPS coatings on critical applications in many aerospace and industrial gas turbine

applications, HVOF MCrAlY usage has increased for repair applications.

The wire arc process is used in aerospace for dimensional restoration and repair of many

different types of jet engine components. Other applications include the spraying of

bridges and marine structures with zinc and aluminium. In the paper and pulp industry,

wire arc sprayed coatings are used to protect boiler tubes against hot corrosion. Medical

applications are being developed such as the spraying of titanium for inert environments

and rapid prototyping. Engine components that require very thick deposits to comply

with specific part restoration requirements such as flanges, lugs, faces, and shafts are

being coated using wire arc spray. Applications also include automotive/marine diesel

components, where low-carbon steel, molybdenum, and other types of corrosion/scuff-

resistant alloys are being considered for valve lifter and piston ring applications.

Applications for LPPS or VPS coatings, which typically have high bond strengths, very

low levels of porosity, and less oxide content, include bond coats for thermal barrier

coatings, oxidation and hot corrosion protection of blades, vanes, and buckets,

biocompatible coatings for medical implants, and tungsten-rhenium x-ray targets.

Carbide coatings have been applied in the aerospace, industrial gas turbine and a variety

of industrial areas by the detonation gun process to components with excellent bond

strength, hardness, and density.

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1.1.6 Coating applications

Coatings for Bearings

Thermal spray coatings for soft bearing surfaces allow the embedding of abrasive

particles and permit deformation to accommodate some misalignment of the bearing

surfaces. These surfaces require adequate lubrication and should be low in cost as they

wear in preference to the mating surface which are usually very much harder. Some of

these coatings are quite porous with the advantage that they act as reservoirs for

lubricants. Thermal spray coatings for soft bearing surfaces commonly used include

aluminium bronze, phosphor bronze, white metal or Babbitt, and aluminium bronze-

polymer composites.

Thermal spray coatings for hard bearing surfaces are hard and have high wear

resistance. Hard bearing materials are used where the embedding of abrasive particles

and self-alignment are not required and where lubrication may be marginal. The inherent

nature of thermal spray coatings seems to provide additional benefits over comparable

wrought or cast materials due to the porosity acting as a lubricant reservoir and the

composite nature of included oxides and amorphous phases increasing wear resistance.

Some coatings show relatively low macro-hardness compared to wrought or cast

materials, but very often show improved wear resistance. Thermal spray coatings used for

hard bearing surfaces typically include cermet coatings like tungsten carbide-cobalt and

chromium carbide-nickel chromium, oxide ceramics like chromium oxide and alumina,

molybdenum, and various hard alloys of iron, nickel, chromium or cobalt.

Abrasion Resistant Coatings

Ideally, the materials for thermal spray coatings for resistance to abrasion should have a

hardness that is in excess of that of the mating surface or abrasive particles. The coatings

commonly used are cermet coatings like tungsten carbide-cobalt, chromium carbide-

nickel chromium (particularly for high temperatures above 540 °C), oxide ceramics like

chromium oxide and alumina, fused self fluxing alloys (NiCrSiB), and various hard

alloys of iron, nickel, chromium or cobalt.

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Wear (scuff/fretting) Resistant Coatings

Coatings resistant to wear caused by repeated sliding, rolling, impacting or vibration are

generally coatings with good toughness and low residual tensile stress. The thermal spray

coatings for resistance to fretting and surface fatigue commonly used include cermet

coatings like tungsten carbide-cobalt, chromium carbide/nickel chromium (particularly

for high temperatures above 540 °C), fused self fluxing alloys, aluminium bronze, copper

nickel indium, and various alloys of iron, nickel, chromium or cobalt.

Erosion Resistant Coatings

The selection of coating for erosive wear is dependent on the severity and type of erosion.

For solid impingement erosion at a shallow angle of attack where the wear is similar to

that of abrasion, high hardness coatings are required. For solid impingement angles near

90°, coating toughness becomes more important. For cavitation and liquid impingement

generally, a coating with good surface fatigue resistance is needed. Thermal spray

coatings for resistance to erosion commonly used include cermet coatings like tungsten

carbide-cobalt, chromium carbide-nickel chromium (particularly for high temperatures

above 540 °C), fused self fluxing alloys, non-ferrous alloys, aluminium bronze, monel,

oxide ceramics like chromium oxide and alumina, and various alloys of iron, nickel,

chromium or cobalt

Corrosion Resistant Coatings

Thermal spray coatings are widely used in preventing corrosion of many materials, with

very often additional benefits of properties such as wear resistance. Thermal spray

coatings for corrosion protection fall into three main groups

Anodic coatings.

Cathodic coatings.

Neutral coatings.

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Anodic coatings for the protection of iron and steel substrates are almost entirely limited

to zinc and aluminium coatings or their alloys. Where coatings anodic to the substrate are

applied, the corrosion protection is referred to as cathodic protection or sacrificial

protection. The substrate is made to be the cathode and the coating the sacrificial

corroding anode. The metallizing process is an excellent means of protecting iron and

steel from corrosion to almost any desired degree, from long life coatings to inexpensive

coatings which are competitive with organic coatings such as paint. Heavy coatings of

zinc or aluminium can be applied to meet the most severe corrosion conditions and give

15 to 50 years life without any further maintenance. Aluminium has been found to be the

most effective metal for protection of steel in offshore structures.

Cathodic coatings comprise a metal coating which is cathodic with respect to the

substrate. A stainless steel or nickel alloy coating would be cathodic to a steel base.

Cathodic coatings can provide excellent corrosion protection. There is a very wide choice

particularly for steel base materials ranging from stainless steel to more exotic materials

like tantalum to cater for the more extreme corrosive environments. However, a

limitation of such coatings is that they must provide a complete barrier to the substrate

from the environment. If the substrate is exposed to the corrosive environment, the

substrate will become the anode and corrosion will be dramatically accelerated resulting

in spalling of the coating. Generally, sealing of these coatings is always recommended.

Processes, which provide the densest coatings, are preferred (HVOF, plasma and fused

coatings). Thick coatings will provide better protection than thin coatings.

Neutral materials such as alumina or chromium oxide ceramics provide excellent

corrosion resistance to most corrosive environments by exclusion of the environment

from the substrate. Generally, a neutral material will not accelerate the corrosion of the

substrate even if the coating is somewhat permeable, but any corrosion of the substrate

interface with the coating should be avoided to prevent coating separation. Again, sealing

of the coatings is recommended. The densest and thickest plasma sprayed coatings are

recommended. When stainless steel type substrate materials are used where the exclusion

of oxygen can cause crevice corrosion, nickel chromium bond coats are required.

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Tool and Die Coatings

Tooling and die costs in metalworking operations contribute significantly to total

production costs. Despite the high investment, wear leads to early failure of

metalworking dies. Thermal spray deposition of wear resistant materials onto the parts of

a die most prone to wear economically extends die life. An example is thermal spray

deposition and high heat flux infrared post-treatment of chrome carbide coatings. Other

coating materials that extend die life include high temperature metallic materials that

have known wear resistance and good fatigue life; oxidation resistant materials known for

their extreme levels of wear resistance; and oxidation resistant materials which provide

protection in thermal environments where wear and oxidation are limiting factors.

Thermal Spray for Resurfacing

Thermal spray is an established industrial method for the surfacing and resurfacing of

metal parts. The benefits are typically lower cost, improved engineering performance,

and/or increased component life. In addition to original equipment applications, thermal

spray coatings are used to repair parts worn and damaged in service, and restore

dimensions to machined parts. Thermal spray coatings are used to restore the dimensions

of components that have been worn or corroded, such as printing rolls and undersized

bearings. Although the thermal spray coating does not add any strength to the component,

it is a quick and economical way to restore the dimensions of parts. Subsequent grinding

operations are often needed to smooth the coating's surface and to bring the final

dimensions into their appropriate tolerances. Thermal spray coatings for dimensional

restoration are being used in every manufacturing industry.

Dielectric Coatings

The aerospace, automotive, and electronic packaging industries are the largest uses of

ceramic dielectric coatings. Dielectric coatings are either pure aluminium oxide or a

spinel. In either case a very high density coating can be created that is capable of

withstanding thousands of volts depending on the coating thickness.

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Release Coatings

Thermal sprayed release coatings use a matrix, which is impregnated with a release agent

of either Teflon or Silicone. Release coatings are used to provide a component with anti-

stick characteristics as well as wear resistance. Components utilizing thermal sprayed

release coatings are typically used in the manufacturing of plastics, adhesives, rubber, or

food products.

Traction coatings

Traction coatings are used on rolls in the printing and papermaking industry to grab and

feed paper. Because the traction of the coating depends substantially on the degree of its

surface roughness, nearly any material can be used to create a traction coating. However,

in most applications where a traction coating is required there is also a great amount of

wear present and, therefore, the most common traction coating materials are carbides,

stainless steels, and nickel alloys.

1.1.7 Summary of thermal spray coatings

Thermal spray processes offer cost-effective manufacturing approaches, which cut across

all industrial sectors solving many industrial problems and providing numerous

applications. Thermal spray solutions are actively used in aerospace, agriculture,

maritime, metal working, papermaking and printing, pumps/motors, electronics,

computers, petrochemicals, geothermal, nuclear power, utilities involving

power/water/sewage, golf, military, offshore oil platforms and submersed pipe lines,

refineries, railroad, automotive, diesel industries. Thermally sprayed chrome oxide and

carbon steel coatings have been used on bearings, piston rings, and hydraulic press

sleeves for adhesive wear. Tungsten carbide, alumina-titania, and steel coatings deposited

by thermal spray processes have been used for guide bars, pump seals, concrete mixer

screws to reduce or eliminate abrasive wear. Tungsten carbide, copper-nickel-indium,

and chrome carbide coatings have been thermal sprayed on dead centres, cam followers,

jet engine fan blades, and land based turbine wear rings to prevent surface fatigue wear.

Thermal spray coatings of tungsten carbide and stellite have been used on slurry pumps,

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exhaust fans, and dust collectors to reduce erosion. Partially stabilized zirconia act as

thermal barriers to provide heat resistance wear on gas turbine burner cans or baskets and

exhaust ducts. Spray deposited aluminium, nickel-chrome, and Hastelloy offer oxidation

resistance for exhaust mufflers, heat treating fixtures, and exhaust value stems. Corrosion

resistance is provided to pump parts, storage tanks, and food-handling equipment by

thermal spray deposited stainless steel, aluminium, Inconel, and Hastelloy. Thermal spray

deposited copper on electrical contacts and ground connectors provide good electrical

conductivity. Deposited alumina coatings as insulation for heater tubes and soldering tips

provide electrical resistance.

Thermal spray processes are easy to use, cost little to operate, and have attributes that are

beneficial to applications in almost all industries. The benefits are typically lower cost,

improved engineering performance, and/or increased component life.

1.1.8 Zinc properties

These include:

high strength

formability

light weight

corrosion resistance

aesthetics

recyclability

low cost

General zinc applications:

Over 7 million tons of zinc is produced annually worldwide. Nearly 50% of the amount is

used for galvanizing to protect steel from corrosion. Approximately 19% are used to

produce brass and 16% go into the production of zinc base alloys to supply e.g. the die

casting industry. Significant amounts are also utilized for compounds such as zinc oxide

and zinc sulfate and semi-manufactures including roofing, gutters and down-pipes. These

first use suppliers then convert zinc into in a broad range of products. Main application

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areas are: construction (45%) followed by transport (25%), consumer goods & electrical

appliances (23%) and general engineering (7%).

For this reason, galvanized steel sheet is an ideal material for a multitude of building and

manufacturing applications - from automobiles to household appliances to residential,

commercial and industrial construction.

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