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SURFACE MODIFICATION OF
MATERIALSI. Mechanical surface treatment and coating
II. Case hardening
III. HardfacingBy SHINE GEORGE 27/02/2016
SURFACE MODIFICATION OF MATERIALS
Act of modifying the surface of a material by bringing physical, chemical or biological characteristics different
from the ones originally found on the surface of a material.
Why use a surface treatment?
Improves hardness & durability
Controls Friction
Reduces Adhesion
Improves Lubrication
Rebuild Surfaces
Aesthetics
SURFACE MODIFICATION OF MATERIALSTypes
Mechanical surface treatment and coating Case hardening and hardfacing Thermal spraying Vapour deposition Ion implantation Diffusion coating Electroplating and Electroforming Conversion coating Ceramic and organic coating Diamond coating Advanced surface modification of steels.
SURFACE MODIFICATION OF MATERIALS
Here we are discussing the following
Mechanical surface treatment and coating
Case hardening
Hardfacing
MECHANICAL SURFACE TREATMENT AND COATING
Surface treatment1.Shot peening2.Water-jet peening 3.Laser peening 4.Explosive hardening
Coating1. Mechanical plating
MECHANICAL SURFACE TREATMENTS
Mechanical surface treatments creates a plastically deformed strain hardened layer of
the material itself.
Shot peening (uses tiny balls of metal or ceramic) The surface get plastically deformed. Makes the surface harder.
MECHANICAL SURFACE TREATMENTS
Examples Microstructure of ZK60-T5(Magnesium alloy) before and after
shot peening: (a)unpeened (b) peened
ZK60-T5.
MECHANICAL SURFACE TREATMENTS
Water-jet peening (uses a jet of water at high pressures, e.g. 400 MPa),
MECHANICAL SURFACE TREATMENTS
Water-jet peening (uses a jet of water at high pressures, e.g. 400 MPa), Uses cavitation impacts in the same way as shot peening Used to improve fatigue strength and/or to introduce compressive residual stress. In the case of cavitation peening, cavitation is generated by cavitating jet.
MECHANICAL SURFACE TREATMENTS
Laser peening (surface is hit by tiny impulses from a laser).
MECHANICAL SURFACE TREATMENTS
Laser peeningThe surface of the work piece is subjected to laser
shocks.As a result of which compressive stress is induced in the
component, thus improving the fatigue life.
Specifications Laser intensity - 100-300 J/cm2 Pulse duration - 30 seconds
MECHANICAL SURFACE TREATMENTS
Explosive hardening (layer of explosive coated on the surface is blasted ).
The explosion hardening technique can obviously increase the hardness of metals by severe plastic deformation caused by the shock wave.
Explosive Hardening Applications The most common application of explosive shock hardening is to cast high-manganese steel rail frogs and switchings
MECHANICAL SURFACE TREATMENTS
Features of Explosive Hardening Hardening effects deepen and increase through subsequent applications of the explosive-hardening process.
This effect begins to taper off significantly after four applications of the process.
Hardness values in cast manganese steel components have shown hardness increases of 230 Bhn, and up to 1/4″ deep.
Metallurgical analysis of shock hardened Hadfield’s steel and high-manganese steel have shown a martensitic transformation in the hardened zone.
There are essentially no size or configuration limits to the application of explosive shock hardening.
MECHANICAL PLATING
MECHANICAL PLATING
Also known as,Mechanical coating
Impact plating
Peen plating.
MECHANICAL PLATING
Process: Fine metal particles are compacted over the work-piece surface by
impacting it with spherical glass, ceramic, or porcelain beads. This hammering action causes
plastic flow on the surface work-hardening of the surface layer due to the introduction of
compressive residual stresses.Features: Coating of another metal like cadmium, zinc, nickel. Mechanical /Work-hardening of the surface
Plating thickness usually less than 0.025 µm.
MECHANICAL PLATING
Applications Nails, screws, nuts, washers, stampings, springs,
clips, and sintered iron components , hardened-steel parts for automobiles.
MECHANICAL PLATING
MECHANICAL SURFACE TREATMENT AND COATING
Precautions Overpeening reduces fatigue strength of the product. The surface of the substrate must be thoroughly cleaned before mechanical
coating Adequate cooling must be provided to avoid heating of the work piece while
processing Necessary masking should be provided in the case of products with
complicated cross sections. The work should be free from any cracks. Use of Cadmium and such additives may be subjected to legislation.
CASE HARDENING
Harden the surface only.
Is a chemical heat treatment
Classification of case hardening
CASE HARDENINGCARBURIZIN
G liquid
NITRIDING CARBONITRIDING CYANIDING BORONIZING FLAME INDUCTION
Basically, the component is heated in an atmosphere containing elements (such as carbon, nitrogen, or boron) that alter the composition, microstructure, and properties of surfaces.
Chemical structure manipulation by diffusing the atoms of alternate elements.
Different types includes:
CASE HARDENING
CARBURIZING
Process
CARBURIZING
Process
CARBURIZING
Microstructure of the finished material
CARBURIZING
Microstructure of the finished material
CARBURIZING
Microstructure of the finished material
CARBURIZING
Depth of Carburizing
CARBURIZINGApplications
NITRIDING
Nitrogen is diffused into the surface of the component being treated.
Nitriding Temperature: 500-600°C [2]
NITRIDING
NITRIDING
Application Nitriding is adopted to
increase the fatigue and wear resistance
of the crank shaft.
CARBONITRIDING
Carbonitriding introduces carbon and nitrogen into the austenite of steel.
This treatment is similar to carburizing .
Nitrogen enhances hardenability,
Thus it is possible the use of low-carbon steel to achieve surface hardness equivalent to that of high-alloy carburized steel.
No need for drastic quenching, resulting in less distortion and minimizing potential for cracks.
INDUCTION HARDENING
Power supply delivers current to induction coilCoil currents (ampere-turns) generate magnetic field.
Lines of field always go around the coil turnsAlternating magnetic field flowing through the part cross-section induces eddy current in the part.
Process
INDUCTION HARDENING
Eddy currents generate heat in the part
In each induction system there are at
least 3 closed loops:
1. Induction coil;
2. Eddy current loop in the part;
3. Magnetic flux loop
Process
INDUCTION HARDENING
A special type known as Simultaneous Dual Frequency Hardening is used for the contour hardening of gear teeth
DUAL FREQUENCY HARDENINGDual frequency hardening maybe made by sequential heatingat Low and High frequency intwo inductors or in the sameinductor.
Applications
Contour Hardening of Gears
INDUCTION HARDENING
LF heating brings teeth to atemperature slightly higher thanCurie point and the roots - totemperature close to a finalvalue.
HF heating must be short. Itforms a required austenitizedlayer on the whole gearcircumference
INDUCTION HARDENING
INDUCTION HARDENING
Features and advantages
Induction hardening is characterized by precise energy metering.
Ultra low power consumption. Short process times. Targets surface layer alone. Save energy and reduce rework effort.
Advantages Of Case Hardening Over Through Hardening
Improves properties desirable to surface only such as resistance to surface indentation, fatigue, and wear.
Gives toughness for intended applications.
Prevention of propagation of any surface crack through the part which may otherwise cause total failure.
Case-hardened parts have a hardness gradient. Typically, the hardness is greatest at the surface and decreases below the surface, the rate of decrease depending on the composition of the metal and process variables.
Carburization produces hard, wear resistant layer on the surface.
Typically, case hardens low carbon steel.
Advantages over through hardening
CASE HARDENING
Precautions
Except induction and flame hardening, the substrate should be of low carbon content.
Temperature and duration of heating should be controlled precisely.
Quantity of enriching gas should be adequate. To avoid distortion and cracking of the product,
Quenching must be done carefully
HARD FACING ProcessSurface Hardening by Welding Deposition
In this process, a relatively thick layer, edge, or point consisting of wear-resistant hard metal is deposited on the surface by any of the welding techniques.
Several layers are usually deposited (weld overlay).
HARD FACING
Hard coatings of tungsten carbide, chromium, and molybdenum carbide can also be deposited using an electric arc in a process called spark hardening, electric spark hardening, or electrospark deposition.
Hard-facing alloys are available as electrodes, rods, wire, and powder.
HARD FACING Applications
Typical applications for hard facing include
excavator buckets valve seats, oil-well drilling
tools, and dies for hot metalworking
operations.
Worn parts are also hard faced for
extending their use.
REFERENCES
1. Anon., Surface Treatment, Coating and Cleaning,http://www.ielm.ust.hk/dfaculty/ajay/courses/ieem215/lecs/9_surfacetreatment.pdf,retrieved on 29.12.2012.
2. Kenneth G. Budinski and Michael K. Budinski., (2009) Engineering Materials: Properties and Selection, 9th edition, Prentice Hall Publishers.
3. Anon., Heat Treatment Properties, http://www.tohokusteel.com/en/pages/kirin1.htm, retrieved on 29.12.2012.
4. Hiroshi Yamagatta – “Science and technology of materials” [pg 180 onwards].
5. Induction hardening - http://www.ustudy.in/node/4157
6. Mark davis – “Gear hardening goes green” http://www.eldec.de/fileadmin/00_Dateien/PDF/Veroeffentlichungen/0909_GearSolutions.pdf
REFERENCES
7. Daewei heating machine co., ltd - http://www.dw-inductionheating.com/hardeninginduction-heating-applications.html/hardening-induction-heating, retrieved on 29.12.2012
8. Volume 05 Surface Engineering - Cleaning, Finishing and Coating- by ASM
9. Effect of Shot Peening on Surface Characteristics and Fatigue Properties of T5-Treated ZK60 Alloy- Wencai Liu 1, Jie Dong 1 ;*, Ping Zhang 2, Chunquan Zhai 1 ; 3 and Wenjiang Ding 1 ; 3 1 National Engineering Research Center of Light Alloy Net Forming, School of Materials Science and Engineering,
10.http://mechanicalplating.com/glass_be.htm]
11.H. Soyama and O. Takakuwa, Journal of Fluid Science and Technology, Vol. 6 (2011), pp. 510-521.
Queries