Wear Mitigation by the Use of Surface Coatings

by Stephen Huse

OutlineAbrasion and adhesion description

Variables that change the wear rateVariables changed by coatings

Surface coating processesPhysical Vapor Deposition (PVD)Chemical Vapor Deposition (CVD)ElectrodepositionThermal Spray

AbrasionPhysical interference of

surface asperitiesTypes:

CuttingCracking (brittle fracture)Ploughing

AdhesionCold weld of surface

asperitiesSimilar materials such as

steel on steel Wear removes oxide layer

Variables That Change the Wear RateFriction

Surface roughnessNormal Forces

Temperature Surface hardness Surface materials Environmental

considerationsH

KN

L

V

NF ksf ,

Variables Changed by CoatingsSurface Hardness

Reduces abrasive wearMay increase brittleness

FrictionReduces force for toolingReduce heat generated

Surface MaterialsReduces adhesive

bondingExample: steel - steel

becomes steel - ceramic coating - steel

Physical Vapor Deposition ProcessVacuum environmentcoating powder is melted and

transported to substrateCathodic arcElectron beamPlasma torchMagnetic

Coating condenses on substrateNASA plasma spray PVDAdvantages

High HardnessLow friction

Disadvantage: requires line-of-sight

Chemical Vapor Deposition ProcessChemically controlled atmospheric

environment. Substrate heated to 2000°FAtmosphere chemically reacts at

surfaceExamples:

Titanium cloride (gas), nitrogen, and hydrogen → titanium nitride coating

Titanium chloride (gas), methane, and hydrogen → titanium carbide coating

Superior adhesion of the coating to the substrate

Used for synthetic diamond growth

ElectrodepositionExample: Chrome platingResists corrosive wearIncreased hardnessReduced friction

Thermal SprayExample: Plasma spraySimilar to PVD, but no vacuumSubstrate is preheated to

remove impurities

Referenceshttp://

www.diamondtc.com/diatiger/about.htmlhttp://www.Gordonengland.co.ukhttp://www.signalplating.comhttp://www.sulzer.comhttp://www.surface.mat.ethz.chhttp://www.pall.comhttp://www.manmadediamondinfo.comhttp://www.ptli.comhttp://www.directindustry.com

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