1. NEWER MATERIAL PROCESSING
1st yr M.Tech(PDM)
HOD & Professor
Mechanical Engg Dept.
Topics: Surface coating - Hardfacing , Thermal Spraying.
PONDICHERRY ENGINEERING COLLEGE
Wear is defined as a progressive deterioration through loss
of material due to prolonged or overly frequent use.
For user, this entails:
• Reduced lifetime and productivity.
• Increased risks to personnel.
• Higher energy consumption and lower yield.
Ex: Adhesion(friction), Abrasion, Erosion, Cavitation etc.
3. Types of wear
low and moderate stress abrasion/Low
Result of particles rubbing/sliding on the
substrate. As pressure from these
abrasives is low, they don’t change size and
don’t break up.
High stress abrasion/Under pressure:
Occurs in equipment where the abrasive is
compressed between two surfaces. The
abrasive is then broken into many
Severe abrasion/Gouging/High impact:
Combination of low, moderate and high
abrasion combined with impact. Large
chips and scratches.
When two metal bodies rub each other and
material is transferred from one substrate
to the other, this is known as “adhesion
Occurs under conditions of high
temperature, high pressure and friction.
This occurs when solid particles or drops of
liquid strike a surface at high speed.
Rate depends on the angle of attack and at
which it is projected.
Caused when there is recurrent rolling or
sliding action between two components.
Under such conditions a sudden loss of
material, in the form of pitting or chipping
will be observed.
Ex: gear teeth, rails, roller presses.
5. Thermal fatigue:
This type of fatigue refers to wear
generated by thermal cycle loads on the
When metal is repeated heated or cooled,
expansion and contraction occurs.
Ex : Forge tools.
Occurs in turbulent liquids in contact with a
Cavities are formed in the liquid and
implode, creating wear.
Combined wear ?
6. SURFACE COATING
An economic method for the production of materials , tools and
machine parts that required the desired surface properties such as
corrosion, erosion and wear resistance.
Different coatings are used to achieve the different properties.
7. Why surface coatings?
Principle of “Better-faster-cheaper”
Either the entire component can be
coated or just the area prone to
attack, which ever best fulfills the
Chrome plated steel pelton turbine nozzle needle after
8. Surface properties
Depends on service environment
• Corrosion resistance
• Thermal insulation
• Electrical insulation
• Improved aesthetic appearance
Usually a combination is present
Hardfacing is the deposition of a surface layer by welding, which
is harder than the base material. Its purpose is to give wear
→ Environmental stresses like corrosion and high temperatures
11. Choosing the Hardfacing process
Function of the
Size and shape
State of repair
12. Benefits of Hardfacing
Following benefits can be obtained
Reduced operation costs
Lower repair costs
Extended equipment lifetime
Gas tungsten Arc welding process
Shielded metal arc welding
Flux cored arc welding
Submerged arc welding
13. Gas Tungsten Arc welding process:
• In TIG process, an electric arc is produced between a
refractory tungsten electrode and the part.
• A metallic filler wire may or may not be used.
• The weld pool is protected from oxidation by an inert
14. Shielded metal Arc-welding(covered electrode):
• The consumable electrode is composed of a solid core wire
and a flux covering.
• An electric arc creates a weld pool between the electrode
core and the part.
• The slag produced by the fusion of the coating protects the
molten metal against oxidation, and can contribute to the
deposit’s chemical analysis.
15. Submerged Arc welding process:
• Molten metal is generated by an electric arc between a wire
and the part, beneath a “blanket” of powdered flux.
• The electric arc is not visible and the welding flames are
mostly absorbed by the flux layer.
• Supports only to flat welding positions on plated and rolls.
• Very high deposit rates.
16. Gas Shielded Metal Arc Welding Process:
• Molten metal is obtained by creating an electric arc between
a wire electrode(solid or tubular cored) and the base metal.
• Metal Inert Gas(MIG)-Metal Active Gas(MAG)
• Easy to automate
Flux cored wires:
Improve fusion characteristics.
Protect the molten metal against excessive oxidation.
Offer a wider range of alloys that can be deposited.
Type Precautions Weld pool
Electric arc Gas 5-15% 0.5-1.5kg/h
Manual Electric arc
Slag 15-30% 1.0-3.0kg/h
Electric arc Gas 15-35% 3.0-10.0kg/h
Automatic Flux Baking Slag 30-50% 5.0-20.0kg/h
Dilution affects the chemical composition of the
deposit, hardness, and quality.
During welding some of the base metal dissolves
into the weld pool, diluting it.
% Dilution =
During surfacing operations, dilution should be limited to
optimize deposit characteristics, whilst ensuring a good fusion
with the substrate.
19. Thermal spraying
“Thermal spray is a generic term for a group of processes in
which metallic, ceramic, cermet, and some polymeric materials
in the form of powder, wire, rod are fed to a torch or gun with
which they are heated to near or somewhat above their melting
Projected against the surface to be coated(substrate).
22. Plasma spray
• DC electric arc generated, plasma gas(He,H2,N2 or
mixtures) acts as spraying heat source
• Copper anode-tungsten cathode
• Plasma plumes temperature can reach 16000 k
• Powder accelerated about 200m/s
• Generation of amorphous calcium phosphate and bio
23. Electric arc wire spray(WAP)
• Two consumable wire electrodes connected to high DC source
for arc generation
• Can also be carried using inert gases or in controlled
• Substrate temperature can be very low
• The process is energy efficient
24. Flame spray
• Use combustible gas as a heat source to melt the coating
• Spray gases-Acetylene, propene, methyl-acetylene-
propadiene (MAPP) and hydrogen along with oxygen.
• Mostly sprayed manually
25. • Flame temperature and characteristics depend on oxygen-to-
• A wide variety of materials can be deposited in rod, wire or
powder form as coatings using this process.
26. High Velocity Oxy-Fuel Spray(HVOF)
• Uses combination of oxygen with various fuel gases like
hydrogen, propene, propylene, kerosene.
• Spray powder is used.
• Flame temperature varies in range 2500c-3200c based on
• Different from flame spray
27. Comparison of several common thermal spray
Heat Source Flame
500-600 2-5 40-70
Wire Electric Arc 5000-
<300 5-10 28-41
3000 <300 5-10 14-21
HVOF Powder Oxy-gas
3200 1200 1-2 >70
28. Energy comparison of thermal spray processes
• Thermal energy–attainable flame temperature
• Kinetic energy–function of gas velocity
30. Gas turbines
Stationary and flight gas turbines.
Thermal sprayed coating.
High temp corrosion resistance,
thermally insulating coatings, repair
of super alloy components.
Salvage and restoration
Repair procedures to restore
components to their dimensions
31. Case study
Thermico GmbH & Co.KG, a German-based company, develops,
produces and distributes robot-based coating centers.
They specialize in plasma and high velocity flame spray systems that
provide coatings for a wide range of products from aircraft turbine
blades to Teflon® frying pans.
Thermico required a new extraction system to handle the dust and
fumes from the plasma and HVOF spray systems that were being
installed in their new premises.
Camfil Air Pollution Control (APC)
32. PRODUCT INFORMATION
Product: Farr Gold Series® dust collector
Size: GS40 ATEX Compliant
Air Volume: 30.000 m3/hr
Application: Thermal spray processes,
Customer: Thermico GmbH & Co.KG,
Installation date: January 2011
Camfil APC addressed the issue by supplying one of their ATEX
compliant Farr Gold Series® GS40 dust collectors, complete with a
supply air system.
Successful handling of thermal spray dust and fumes was
Additionally an energy saving setup that incorporated a heat
exchange system was installed.
Thermico was delighted with the solution which provides
their workforce with a safe working environment meeting all
legislative requirements, whilst saving on energy costs and
34. An interesting fact
According to Centers for Disease control and Prevention,
in 2014 alone there have been approximately 7,19,000 knee
replacements and 3,32,000 hip replacements.
• Fundamentals of Hardfacing by arc welding-Welding alloys group.
• Welding consumables, hardfacing-Afrox product reference manual.
• Thermal spray advanced technology solutions and services –oerlikon
• A review on Thermal spray coating processes by Sagar Amin.
• Case study on Thermal spray by Camfil Air Pollution Control (APC).
• Official website of Centers for Disease control and Prevention.
• Google images.
Notas do Editor
How dilution can be controlled?
Selecting the right welding procedure(particularly heat input).
Choosing the right polarity(DC+;DC-;AC)
Parameters: Gun design, plasma gases, powder injection schemes, and material properties like size, distribution, melting point, morphology, and apparent density.
Dis adv: Mechanical and adhesive instabilities of the coating-generation of amorphous calcium phosphate and bioactive calcium phosphate phase.
The process is energy efficient because all of the input energy is used to melt the metal.
Molten metal is atomized and propelled towards the substrate by a steam of air.
Spray rates are driven primarily by operating current and vary as a function of both melting point and conductivity.
In HVOF process the particles melt completely or only partially based on FLAME TEMPERATURE, PARTICLE DWELL TIME, MATERIAL MELTING POINT AND THEMAL CONDUCTIVITY.
SUPERSONIC JET-results in much higher particle impact on substrate. which is a big benefit.
Mach number>5(results in super sonic)