MSE 9th assignment

Laser Surface Modification

• The laser has some unique properties for

surface heating

– The electromagnetic radiation of a laser beam is

absorbed within the top atomic layers for opaque

materials, such as metals

– There are no associated hot gas jets, eddy

currents or even radiation spillage outside the

optically defined beam area

– In fact the applied energy can be placed precisely

on the surface only where it is needed

Advantages

• Chemical cleanliness

• Controlled thermal penetration and therefore

distortion

• Controlled thermal profile and therefore shape

and location of heat affected region can be

predicted

• Little-to-no finish machining is required

• Remote non contact processing is usually possible

• Relatively easy to automate

Surface Modification

• Improved components with idealized surfaces

and bulk properties

– Particular parts of surfaces which are vulnerable

to corrosion or wear confined to small areas

– For large areas electroplating will be a better

solution

– for discrete areas the laser has few competitors

and can yield wide variety of surface modification

Surface Modification

• Surface heating for transformation hardening or annealing

• Surface melting for homogenization, microstructure

refinement generation of rapid solidification structures and

surface sealing

• Surface alloying for improvement of corrosion, wear or

appearance

• Surface cladding for wear, corrosion or physical property

manipulation such as melting point or thermal conductivity

• Surface texturing for improved paint appearance

• Plating by Laser Chemical Vapour Deposition (LCVD), Laser

Physical Vapour Deposition (LPVD)

Laser Heat Treatment

• The initial goal of laser heat treatment was

selective surface hardening for wear reduction

• Now it is also used to change metallurgical

and mechanical properties

• There are many competing processes in the

large area surface heat treatment

• The laser usually competitive due to lack of

distortion and high productivity

Laser Surface Applications

• Hardness increase

• Strength increase

• Reduced friction

• Wear reduction

• Increase in fatigue life

• Surface carbide creation

• Creation of unique geometrical wear patterns

• Tempering

Features

• Laser heat treatment is used on steels with sufficient

carbon content to allow hardening and cast irons with

a pearlite structure.

• An absorbing coating is usually applied to the metal

surface to avoid unnecessary power loss by reflection

• The absorption coefficient can also be increased by

allowing a polarised beam with the electric vector in

the plane of incidence, to be reflected at the Brewster

angle (approximately 8° for metals) C)

• This leads to a unique process for transformation

hardening inside small holes - such as valve guides