Download MM409-coating

Surface Engineered Materials
School of Mechanical and Manufacturing Engineering
Dublin City University
Introduction
The focus of this modules does not include paint, long
established coatings such as those applied by electroplating,
hot dipping (as used in galvanising) and mechanical plating.
Most of these are for low load applications, or for
decorative purposes (and are environmentally costly) .
We do focus on more recent developments such as thermal
barrier coatings, high temperature corrosion and wear
resistant coatings, and biocoatings.
COATINGS
Non-Metallic
Metallic
Chemical
Conversion
Oxide
Anodizing
Phosphate
Glass
Ceramic
Polymer
Vacuum Deposition
Furnace Fused
Chemical Vapour
Deposition
Chromate
Vapour Deposition
Hard Facing
Miscellaneous
Techniques
Coating deposition technologies, adapted from Bhushan & Gupta, (1991), & Stokes, ‘03.
Vapour
Deposition
Hard Facing
Physical
Vapour
Deposition
Chemical
Vapour
Deposition
Evaporation
Ion Plating
Sputtering
Welding
Thermal
Spraying
Flame
Electric Arc
Plasma Arc
Cladding
Miscellaneous
Techniques
Atomised Liquid Spray
DIP Process
Sol-Gel
Fluidized Bed
Brush , Pad, Roller
Chemical Deposition
Chemical Conversion
Intermetallic Compound
Spark Hardening
Electro-Chemical
Deposition
Spin-on
Deformation
Diffusion
Brazing
Welding
Laser
Spray & Fuse
Low Pressure Plasma
Detonation Gun
Electric Arc
Plasma Arc
Flame (HVOF)
Coating deposition technologies, adapted from Bhushan & Gupta, (1991), & Stokes, ‘03.
Increasing resistance to
surface damage
• Creating a smooth, uncracked surface
resistance to nucleation of cracks due to
fatigue, contact loading or corrosion
• Increasing resistance to corrosion
• Increasing resistance to wear
• Increase the threshold value of the stress
intensity factor
Selecting coatings
• Chemical Compatibility
• Mechanical Compatibility- cohesion and adhesion.
• Deposition Process Compatibility – the process used cannot
be such that it compromises the substrate properties (eg. by
exposing it to too high temperatures)
• Component Geometry – some geometries cannot be coated
by ‘line of sight’ techniques, and others cannot
accommodate large sized components.
• Service Environment – the coating must function well within
the service environment, and not be effected by
contamination in process gasses, liquids.
• Repair requirements
Some coatings and modified surfaces
High temperature coatings
• For many key engineering processes efficiency improves with
temperature.
• This is the driving fact behind increasing operating temperatures for a
wide range of engineering components.
• Limiting factor is lack of materials to operate at high temperatures.
• One method used to push up the temperatures by the use of high
temperature coatings.
• Coating in this area is primarily concerned with protecting
components from oxidation, corrosion and erosion by particle debris,
thus prolonging their life.
• Traditionally the coating has developed independent of the substrate
materials, but it is now recognised that as service conditions become
more severe, that the two should be considered as a system.
Degradation
• Degradation modes for components in this service environment include
low cycle thermo mechanical fatigue, foreign object damage, high cycle
fatigue, high temperature oxidation, hot corrosion and creep.
• Damage to the coating itself can occur in one of two ways: surface
damage, and diffusion based changes at the coating/substrate interface.
• The latter can compromise substrate properties, and deplete the coating
of some elements.
• Can be difficult to evaluate interface damage.
3 types of high temperature coatings
1. Aluminide,
2. Chromide and
3. MCrAlY
The substrate generally used with these coatings are Nickel based
superalloys, however these are limited by their melting point for
even higher temperature use.
Ceramic intermetallic and refractory metals are candidates for
replacement, but have very different mechanical, physical and
chemical properties, will still need coating protection, and will be
less tolerant of coating flaws.
For this reason, research continues into the use of graded composition
and multiplayer coating.
Laser modified surfaces
• Lasers or electron beams are used for rapid solidification surface
modification of materials.
• This is done by scanning a high power beam over the material surface,
to induce melting of a thin surface layer.
• Because of the high rate of energy delivery, this is a very efficient
way of melting material, and very little of the energy is wasted in
heating the substrate.
• Because the substrate remains ‘cold’, the melted material cools very
rapidly when the energy input is removed.
• This rapid quenching infers the desired properties on the material.
Application of laser modified surfaces
• This technique has been applied to precipitation hardened nickel based
superalloys, martensitically strengthened steels, and carbide
dispersion strengthened alloys, and generates a refined surface
microstructure which can considerably enhance component life.
• In 304 stainless steel laser glazing effects carbides at grain boundaries,
thus improving resistance to stress corrosion cracking.
• In 614 Al bronze it homogenises the surface, improving its resistance
to corrosion in chloride solutions.
• In high speed steels it generates a uniform fine distribution of hard
carbide particles which improves cutting performance.
• An interesting area of current development is the use of laser glazing,
in combination with powder or reactive gasses to make surface
compositional changes as well as structural ones.
DLC
• Diamond, a crystalline form of carbon, has remarkable characteristics
• It is the hardest material known, has a high stiffness and strength, has
high thermal conductivity and shock resistance, is chemically inert, and
excellent infra-red transmission.
• In the form of a thin coating, diamond-like carbon uses many of these
properties to the benefit of a component.
• While there are several processes used to generate such film, they all
rely on bombardment of a substrate with carbon ions.
• Diamond like carbon refers to a mixture of amorphous and crystalline
carbon phases, and its properties vary with deposition conditions.
• The films are hard, and generally have low coefficient of friction. They
are chemically durable, and abrasion resistant.
• They may have high internal stress, which can limit thickness (which is
of the order of 2-5 m).
Evaluation of Coating
Properties
C
Carbon
Diamond
6.71 Å
6.71 Å
Graphite
DLC
Fullerene C60
Fullerene C70
Diamond (sp3)
Graphite (sp2)
Application of DLC
• Protecting moving parts, components exposed to attack
by oxygen or moisture, optics, optical devices, and in
biomedical components.
•
Tissue can adhere well to carbon implants, and in
blood environment a protein layer forms which stops
clotting at the carbon surface.
• A DLC coating on metal implant combines the strength
of the latter, with biocompatibility of carbon.
Work on DLC at DCU
ADHESION AND COHESION PROPERTIES OF DIAMOND-LIKECARBON COATINGS DEPOSITED ON BIOMATERIALS BY
SADDLE FIELD FAST ATOM NEUTRAL BEAM SOURCE;
MEASUREMENT AND MODELLING
BY
M. M. Morshed (B.Sc.Eng., M.Sc.Eng., PhD)
NCPST
Experimental Procedure
1. Biomaterial
 316L stainless steel (wt%:
2. Sample Preparation
0.03%C,18%Cr,10%Ni, 3%Mo, Fe (balance)
 Grinding
Thickness: 8mm and 0.25mm, Diameter: 25mm
 Polishing (240, 600, 1200 grade emery papers
 Co-Cr and Ti6Al4V alloys (wt%:
69%Co,25%Cr and 5% Mo)
and 0.25 diamond polish)
 Ultrasonic Cleaning
Thickness: 8mm and Diameter: 25mm
0.75mm Thickness Glass substrate
3. Saddle field source
 Neutral beam deposition, energetic molecules
 Also allows deposition on insulating substrates
4. Argon Etching
5. Film Deposition Parameters
In-situ etching - Energetic argon atoms
 Process Gas: C2H2 and C2H2+Ar gas mixture
 Time: 0, 05, 10, 15 and 20 min.
 Voltage: 1-1.7KV
 Voltage: 1 -1.7KV
 Current : 0.6A, 1A
Pressure:
1.5x10-3
 Time: 1 hr.
to
Current: 0.6, 1A
4.8x10-3
mbar
Pressure:1.5x10-3 to 4.8x10-3 mbar
Temperature
 Etching temperature
 Deposition Temperature
NEUTRAL BEAM FAST ATOM SYSTEM
Mechanical Characterization
ADHESION TESTS
F
A) Quantitative Adhesion
Pull-off Adhesion
Stud
Epoxy glue
Coating
Substrate
Normal load
(1471N)
Coated sample
B) Qualitative Adhesion
Rockwell C Adhesion
Rockwell C Adhesion
Better Adhesion
HF1 or HF2
Medium Adhesion
HF3 or HF4
Poor Adhesion
HF5 or HF6
Residual Stress in Film
Deflection, 
Bending beam method
After deposition
Before deposition
z-axis
STONEY EQUATION:
 4 Es t s2

2
31   s l t f
Distance, x-axis (m)
 = Residual stress
Es =Young's modulus of the substrate
(200GPa)
s = Poisson's ratio of the substrate (0.29)
ts = thickness of the substrate
tf = thickness of the film
l =length of the substrate segment and
 = largest deflection (usually the central
deflection) in the segment measured by
surface profilometry after the film deposition
with reference to initial deflection.
Film Thickness
SURFACE PROPHILOMETER