SURFACE

ENGINEERING

A.S.Khanna
Corrosion Science & Engineering
IIT Bombay
 Surface Engineering- Scope

Surface
Characterization is
Failure of an External forces The economic perhaps the most
engineering can be benefits - powerful function
Sometimes
component occurs According to a which helps us the
thermal, technological
when its surface report the the UK modify existing
progress and
cannot adequately optical, coating market is surfaces, create
manufacturing
withstand the magnetic and approximately new coatings,
efficiency
external forces or electrical £21.3 b. formulations,
requires surface
environment to understand
wear, or modifications. (RSIC Report,
which it is mechanism of
subjected. corrosion. 2005) surface
degradation and
its improvement
Definition
To make changes to the surface of a material.

Purpose
To gain or improve upon the desired surface
properties of a material. To improve a
components; performance, service lifetime,
aesthetics or economics.

Surface Engineering Processes

There are many processes for modifying
surface properties. These can be grouped
into three categories
Surface Engineering Processes
Surface modification without changing the material chemically

Changes made by thermal or mechanical means, altering metallurgy or

surface texture.

Surface modification by altering surface chemistry

These processes involve diffusion of new elements into the surface of the
material. The original substrate material constituents play an active part in
the modified surface.

Surface modification by adding new material onto the surface

(coating).

These processes essentially add new material to the surface as a coating

and do not involve the substrate material constituents at the surface.
 Surface Modification without Changing
the Material Chemically
• Thermal Processes
Surface Heat treatment, particularly those that undergo phase
transformations like the martensitic reaction hardening of carbon steels, low
alloy steels and cast irons - Laser, Flame, induction

• Mechanical Processes
Cold working - surface by peening, shot blasting, explosive hardening or
other specialised machining processes induce compressive stresses,
increasing hardness and fatigue resistance.
• Changing surface texture using machining and blasting.

• Other Processes
Modification of surfaces by chemical/electro-etching, laser engraving,
various chemical, solvent and ultrasonic cleaning processes could also be
included here.
 Surface Modification by Changing
Surface Chemistry
• Thermochemical Diffusion Processes
– Carburising (carburizing)
– carbonitriding
– nitriding nitrocarburising
– boronising
• In all these processes new element goes into interstitial position.
– aluminising (aluminizing, calorising, alonising)
– chromising (chromizing)
– siliconising (siliconizing)
– In this process new element goes into Substitutional SS
• Electrochemical Processes
– Anodising (anodizing) of aluminium, titanium
• Chemical Conversion Coatings
– Phosphating chemical blacking chromating
• Ion Implantation Processes
Surface Modification by Adding New
Material onto the Surface (Coating)
Welding Type Processes

Thermal Spray Process

Electroplating Electroless plating

Galvanising, molten bath -tin aluminium (Al not aluminide) babbit

PVD Physical Vapour Deposition

CVD Chemical Vapour Deposition

Painting Spin Coating

Powder Coating Lubricants Tiling

Cladding
 Material Properties

Bulk Surface

•Strength
•Density •Hardness
•Ductility •Friction
•Wear
•Corrosion
•Oxidation
Why Surface Treatment ?

To achieve desired
surface properties
which cannot be
achieved by
conventional
alloying process.
What are the surface Properties?
Corrosion

Oxidation

Wear

Erosion/abrasion

Hardness

Conductivity
What are the various modes by which
surface properties can be enhanced ?

• Coatings
Creating a • Cladding
Barrier • Surface Alloying

• Homogenization
Surface • Hardening
treatments • Reflectivity change
 Different Techniques to achieve
Surface Modifications
• Case Hardening
• Slurry
Conventional • Hot Dip
• Quenching
Methods • Hardfacing
• Electrodeposition

• PVD
Advanced • CVD
• Thermal Spray
Methods • Laser Based
Selection of Surface Treatment
Method
Based upon Change in function property

Substrate characteristics
Thickness of the modified surface
Throughput of the process ( slow, fast)
Requirement of vacuum
Geometry of the component
Economics
Thickness as Selection Criteria for Coating
Technique
 Surface Engineering

Gaseous State Solution Molten/semi molten

•PVD Sol-Gel Laser

•Ion Implantation Electroplating Thermal Spray
•Ion Beam Assisted Welding
•CVD
 Classification of Coatings
Types Of Coating
Processes

CVD PVD Thermal spray

Mechanism
Mechanism ofof Coatings
Coatings
B

Mechanical Bonding Types Diffusion Of Coating

Of Coating
 Important parameters to be optimized to control the
properties at substrate coating and its interface

Interface
Coating Surface
Adhesion
•Roughness
Interdiffusion
•Erosion
Cleanliness
•Corrosion/oxidation
Roughness
•Friction
Expansion mismatch
•Porosity
•Electrical properties
Coating

Interface Coating Bulk

Cohesion
Stress
Substrate Adhesion
Cracks/defects
Graded composition
Multilayers
Surface Property Improvement Triangle

Surface
modification
technique
Examples of Surface Modification in Industry
S.No Industry Part/machine Problem for which coating is
. required
1 Aircraft , Turbine Disc, Fretting wear
Gas Turbine Lybrinth seals Friction / Hot Corrosion
Turbine Blades Hot Corrosion and erosion
Rotor Shafts Fretting wear
2 Automobiles Exhaust Nozzles High Temperature Corrosion
Cylinder jackets and Rubbing wear
Liners
Piston Heads and Thermal Fatigue and
crowns Corrosive wear
Camshafts/Crank Fatigue/wear
shafts
3 Textile Yankey Dryers Abrasion and wear
Machinery Grooved rolls Abrasion and wear
Package drive rolls Abrasion and wear
Twisting rolls Abrasion and wear
Yarn guides Abrasion and wear
Tension gates & drives Abrasion and wear
4 Glass Work Scoops and Moulds Hot Corrosion/abrasion
Diamond Work Dies Hot Corrosion/abrasion
Bushing Plates Hot Corrosion/abrasion
Diamond Polishing Pads Abrasive Wear
5 Paper & Pulp Gripper Bars/pads Abrasive wear
Printing Industry Grip Rolls Abrasive wear
Transport Rolls Abrasion
Guide Plates Rubbing wear
Folder Rolls Surface wear
6 Chemical, Oil exploration Shafts Abrasive wear
Petrochemical Well Casing Corrosive wear
Tanks & Vessels Corrosive wear
Impellers Fatigue & Corr. Wear
Plug valves Chemical corrosion
7 Power Plants Gas Turbine Blades Corrosion and abrasion
Boilers Furnace Pipes Heat Corrosion
Superheater tubes Oxidation/sulfidation/erosion/Hot
Corrosion
Boiler Tubes Heat & sulfidation attack
Coat Chuts Abrasive wear
 Plasma & Ion-based Surface Engineering (PISE)
techniques

• Large surfaces are easily treatable

• PISE is based on dry technology, avoiding the use of
harmful solutions
• unlike traditional techniques, the processes are virtually
pollution free
• such processes can be easily automated
• properties such as corrosion and wear resistance,
fatigue strength and biocompatibility, as well as the
combination of these properties, are achievable and
controllable
Electron Beam PVD
MCrAlY-coated blades produced by NTI's EBPVD
process. EBPVD MCrAlY TBC Bond Coats
 HYDROPHOBIC COATINGS

 Plasma Assisted CVD

 Uses scrap teflon
 Used for corrosion resistance
 Also used in textiles as dust
repellant.
 Can be used for water collection
in moist climates
PLASMA ETCHING

 Plasma etching improves adhesion

properties of substrates.
 Cleans & activates surfaces.
 Reduces or eliminates requirements of primers &
toxic chemicals
 Wide applications on materials ranging from metals
to polymers.
 Few of typical examples are:
 Plasma etching of autofacia (improved paintability & service life)
 Plasma etching of TPO profiles
 PLASMA ETCHING – for cars

- One of the futuristic applications of Plasma Etching is ‘Plasma Car Wash’

 PLASMA NITRIDING

Crankshafts
Industrial Scale Plasma Nitriding Facility UHV PN System for Space
For Large size Industrial Jobs Quality Plasma Nitriding

Mould locking plates Connecting rods

Cam chain sprocket
Basic Principal of Thermal Spray Systems
---- Heat Energy
---- Kinetic Energy
Flame Arc

HVOF Plasma
 Comparison of various Thermal Spray Processes
Attributes Flame SPRAY HVOF Detonation Wire Arc Air Plasma Vacuum Cold
Plasma spray
Jet Temp0C 3,200 5,200 5,000 >25,000 15,000 12,000 0-500

Jet Velocities 50-100 500-1200 3000 50-100 300-1000 200-600

M/S
Gas Type O2,Acetylene CH4,C2H2,H2,O2 O2,Acetylene Air,N2,Ar Ar,He,H2,N2 Ar,He,H2 He, N2,
Air
Gas Flow slpm 100-200 400-1100 N/A 500-300 100-200 150-250
Power 20 150-300 N/A 2-5 40-200 40-120 5-25
Input,KW, Eqv.
Particle Temp0C 2500 330 N/A >3800 >3800 >3800
Max.
Particle 50-100 200-1000 N/A 50-100 200-800 20-50 300-
Velocities M/S, 1200
Material Feed 30-50 15-50 N/A 150-2000 50-150 25-150
Rate g/min
DEPOSIT/ COATING
Density Range 85-90 >95 >95 80-95 90-95 90-99 90-99
(%)
Bond Strength 7-18 (1-3) 68 (10) 82 (12) 10-40 (1.5-6) <68 (<10) <68 (<10) 26-62
Mpa, (Ksi)
Oxides High Moderate to Small Moderate to Moderate to None small
dispersed high coarse
 Principle of laser Cladding

Two Step laser Alloying /Glazing

• Single Step laser
Cladding

Laser Beam Powder Feeder Laser Beam

Coating after
Laser Glazing

Already existed Coating Cladding

Substrate Substrate
Performance of laser clad heat exchanger
tube with Ni-25Cr alloy exposed in coal
fired power plant for a year
Optical micrographs showing the fire cracks
on the heat exchanger tube exposed in a
coal-fired power plant

Without Cladding

After Cladding with Ni-25Cr-alloy