Lesson

Lesson

Our goal is, that after this lesson, students are able to recognize the importance of affecting wear and corrosion phenomena for material selection.

Note! To ensure proper material selection it is important to recognize the affecting wear phenomenon/ phenomena!

WEAR PHENOMENA FATIGUE WEAR TRIBOCHEMICAL WEAR ABRASIVE WEAR ADHESIVE WEAR JOINT EFFECTS OF WEAR PHENOMENA

Note! Different wear phenomena can affect simultaneously Different wear phenomena can affect consecutively (they can form “chains” of wear phenomena) Numerical values of wear resistance are required to compare the wear resistance of optional materials objectively!

WEAR Main aspects in material selection WEAR Main aspects in material selection MATERIAL PAIR WEAR PHENOMENA SURFACE ROUGHNESS ENVIRON- MENTAL CONDI- TIONS LUBRICATION CONDITIONS MEDIA TYPE OF MOTION - Adhesive - Abrasive - Fatigue wear - Tribochemical wear - HD - EHD - Border - Mixed - Lubricated - Non-lubricated - Self lubricated - Oil - Crease - Slow speed - High speed - Continuous - Cyclic

Surface 1 Surface 2 A surface peak cold welds with the surface peak on the opposite surface. ADHESIVE WEAR MOTION

Surface 1 Harder Surface 2 Sowter A harder abrasive particle wears the softer surface. MOTION ABRASIVE WEAR

TRIBOCHEMICAL WEAR

FATIGUE WEAR

Carburized steel 20NiCrMo 5Polymer PA6.6

FRICTION COEFFICIENT µ T [ºC] TEMPERATURE T [ºC] TEMPERATURE PA 6.6PA % PTFE FRICTION COEFFICIENT µ

Carburized steel 16MnCr5 Centrifugal cast bronze GZ-CuZn12

Wear resistance increases Heavy loads Small loads Thermal coatings Tungsten carbides, cobolt WC/Co Chromium carbides and nitrides CrC, CrN Nitridized steels Carburized steels Ceramic coatings

Heavy loads CrC CrN Thick ceramic coatings Borium steels Carburized steels Nitritized steels Thermal coatings WC/Co Small loads Thermal coatings WC/Co Plasma coating Oxidation:Cr, Al CrC, CrN Nitridized steels Carburized steels Austenic stainless steels Thin ceramic coatings Wear restistance increases

Wear resistance steels are utilized e. g. in crane rails.

Bearing steel 100Cr6

CrNiFeTiCuAlZnSnPbIn Pb Sn Zn Al Cu Ti Fe Ni Cr Highly intensive adhesive reaction Fairly intensive adhesive reaction No adhesive reaction STRENGTH OF ADHESIVE REACTION Mg

Archard’s equation : V =k i ×F × s V= material loss due to wear k i = material pair coefficient F= affecting perpendicular force against the surface s= motion distance The criterion for wear resistance comparison is the material pair coefficient k i

Advanced equations: V =K i ×S C2 × R C3 V = material loss due to wear S = contact stress of the components R = number of loading cycles K i, C2,C3 = coefficient describing the material pair, surface roughness and loading case Advanced equation takes care of the effect of surface profile s and cyclic loading on wear Remember that sometimes the friction coefficient between the materials gives a measureable value for possible wear rate!

Note! To ensure proper material selection it is important to recognize the affecting corrosion phenomenon! It is also necessary to take care of other simultaneous loading conditions with corrosion, such as tensile stress, temperature or wear! Numerical values are needed to evaluate and compare objectively the corrosion resistance of each optional material. See e.g. standards ISO 9223 and ISO 9224 for the corrosion speed of steels.

CORROSION PHENOMENACORROSION PHENOMENA CORROSION PHENOMENACORROSION PHENOMENA Surface corrosion Uniform corrosion Localized corrosion Contact corrosion Galvanic corrosion Mechanical surface loading Corrosion under stress loading Stress corrosion Corrosion fatigue Selective corrosion Intergranular corrosion Selective leaching Pitting corrosion Crevice corrosion High-temperature corrosion Erosion Cavitation Fretting Bronzes Cast irons

UNDER THE GASKET THERE IS THE RISK BOTH OF WEAR AND CORROSION

EXAMPLE OF CRACK AND GALVANIC CORROSION ALUMINIUM BODY FITTING BASED ON CLEARANCE GOLD COATED CENTRE PIN MW-FILTERRESONATOR PINS SMA- CONNECTOR

H6 m6 H6/m6 Clearance in fitting Bearing assembly FRETTING CORROSION

N NUMBER OF LOAD CYCLES STRESS σ ENDURANCE LIMIT FATIGUE WITHOUT CORROSION

CORROSION Aspects to affect material selection CORROSION Aspects to affect material selection MATERIAL PAIR MANUFACTURING TECHNOLOGY CORROSION PHENOMENON STRESS CONDITIONS TEMPERATURE CHEMICAL ENVIRONMENTAL - Coating - Casting - Painting - Uniform corrosion - Localized corrosion - Galvanic corrosion - Erosion and cavitation - Fretting - Intergranular corrosion - Selective leaching - Stress corrosion - Corrosion fatigue

Steel pipes in energy transportation

CABLE JOINT STEEL/STAINLESS STEEL COATED POLYMERS ALUMINIUM ALLOYS COPPER ALLOYS

SURFACE CORROSION OF THE HUB IN A CABLE JOINT

Note! It is not enough to ”select” stainless steel to avoid corrosive damages! There are four different types of stainless steels and they have totally different application areas: Austenitic stainless steels Martensitic stainless steels Ferritic stainless steels Duplex steels

A = AUSTENITIC STAINLESS STEEL B = FERRITIC STAINLESS STEEL C = ZINC COATED STEEL D = CARBON STEEL CORROSION VELOCITY 10 x µm/YEAR x SEASIDECOUNTRY SIDE CONDITIONS