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