BK50A2700 Selection Criteria of Structural Materials

Lesson 22014

REPETITION 2:Material selection based on wear resistanceMaterial selection based on corrosion resistance

Lesson 22014

The goal of this lesson

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

Material selection based on wear resistance

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

JOIN

T EFFECTS O

F

WEAR P

HENOMENA

JOIN

T EFFECTS O

F

WEAR P

HENOMENA

JOINT EFFECTS OF

WEAR PHENOMENA

JOINT EFFECTS OF

WEAR PHENOM

ENA

Note!Different wear phenomena can affect

simultaneouslyDifferent 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!

WEARMain

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 1Harder

Surface 2Sowter

A harder abrasive particle wears the softer surface.

MOTION

ABRASIVE WEAR

TRIBOCHEMICAL WEAR

FATIGUE WEAR

Carburized steel 20NiCrMo 5 Polymer PA6.6

FRICTION COEFFICIENT µ

1

0.8

0.6

0.4

0.2

0

1

0.8

0.6

0.4

0.2

050 150 25050 150 250

T [ºC]TEMPERATURE

T [ºC]TEMPERATURE

PA 6.6 PA 6.6 + 15% PTFE

FRICTION COEFFICIENT µ

Carburized steel16MnCr5

Centrifugal cast bronzeGZ-CuZn12

Wear resistance increases

Heavy loads

Small loads

Th

ermal co

ating

s

Tun

gsten

carbid

es, cob

olt

WC

/Co

Ch

rom

ium

carbid

es and

nitrid

es

CrC

, CrN

Nitrid

ized steels

Carb

urized

steels

Ceram

ic coatin

gs

Heavy loads

CrCCrN

Thick ceramic coatings

Borium steels

Carburized steels

Nitritized steels

Thermal coatingsWC/Co

Small loads

Thermal coatingsWC/Co

Plasma coatingOxidation:Cr, Al

CrC, CrN

Nitridized steels

Carburized steelsAustenic stainless steels

Thin ceramic coatings

Wear restistance increases

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

Bearing steel100Cr6

Cr Ni Fe Ti Cu Al Zn Sn Pb In

In

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

Mg

Archard’s equation : V =ki×F × s

V = material loss due to wear ki = material pair coefficientF = affecting perpendicular force

against the surfaces = motion distance The criterion for wear resistance

comparison is the material pair coefficient ki

Advanced equations: V =Ki×SC2 × RC3

V = material loss due to wear S = contact stress of the components R = number of loading cycles Ki , 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!

Material selection based on corrosion resistance

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

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 BODYFITTING BASED ON CLEARANCE

GOLD COATED CENTRE PIN

MW-FILTER RESONATOR PINSSMA-CONNECTOR

H6 m6

H6/m6

Clearance in fitting

Bearing assembly

FRETTING CORROSION

NNUMBER OF LOAD CYCLES

STRESSσ

ENDURANCE LIMIT

FATIGUE WITHOUT CORROSION

CORROSIONAspects 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 STEELCOATED POLYMERSALUMINIUM ALLOYSCOPPER 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 steelsMartensitic stainless steels Ferritic stainless steelsDuplex steels

A B C D A B C D0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

A = AUSTENITIC STAINLESS STEELB = FERRITIC STAINLESS STEELC = ZINC COATED STEELD = CARBON STEEL

CO

RR

OS

ION

VE

LOC

ITY

10x

µm

/YE

AR xSEASIDECOUNTRY SIDE

CONDITIONS