Plasma Surface Engineering

Universidade de Caxias do SulSeptember 2009

Santiago Corujeira Gallo

Founded in middle age (7th century)

Population ca 2,500,000

Traditional industrial centre

Cultural diversity

Birmingham - UK

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Founded in 1900

Research oriented

Multicultural

Ranked 12th in UK (RAE)

over 4000 Intl students

from 150 countries

Colleges

Arts and Law

Engineering and Physical Sciences

Life and Environmental Sciences

Medical and Dental Sciences

Social Sciences

University of Birmingham

Composition of the group:

1 Professor

1 Senior Lecturer / Reader

2 Research fellows

1 Visiting research fellow

7 PhD students

2 MSc students

2 Undergraduate students

Surface Engineering Group (2007)

Topics of research:

- Plasma diffusion treatments

- Thermal oxidation

- PVD coatings

- Nanoindentation

Active screen plasma surface engineering of austenitic stainless steel for enhanced

tribological and corrosion properties

• Austenitic stainless steel

• Tribological and corrosion properties

• Plasma surface engineering

• Active screen

Austenitic stainless steel• Typical composition: 18% Cr – 8% Ni

• AISI 316: 17% Cr – 12% Ni – 2% Mo

Typical properties:

• Excellent corrosion resistance

• Non-magnetic

• No ductile-to-brittle transition• Poor mechanical properties• Low wear resistance

Surface engineering treatments

• Improved performance• Use cheaper materials• Increase design flexibility

Benefits of surface engineering

Diffusion treatments:

• No sharp interface - gradient• Slow (temperature – time)

Plasma surface engineering

Conventional gas nitriding ~ 550oC

Conventional gas carburising ~ 950oC

Cr23C6

Cr1-2N

Treated substrate - cathode (-)

-

- -

+

C or N containing gas

Treated substrate

C or N containing gas

at low pressure

GDOES composition depth profiles

XRD - phase identification

S-phase

or

expanded

austenite

Micrographs of expanded austenite

Typical cross section optical micrograph

Typical top view SEM micrograph

Microhardness testing

Typical instrumented hardness test curves

Typical load bearing capacity

Microhardness indents

Tough carbon expanded austenite

Brittle nitrogen expanded austenite

Wear testing

Dry sliding pin-on-disc test, 10 N normal load, WC counterpart, 0.03 m/s sliding speed; 4.5 hours

Wear resultsAISI 316 UT AISI 316 PC

Morphology of the wear tracks

AISI 316 UT AISI 316 PC

Wear track of AISI 316 UT

Wear track of AISI 316 PC

Wear debris

Wear debris Colour Size Magnetic Possible phases

Treated Red / Orange <20um No alpha-Fe2O3 Hematite

Un treated Black >20um Yes Fe3O4 Magnetite

Untreated sample: metallic debris Treated sample: oxide debris

Wear debris – TEM SAD pattern

Wear conclusions

• The wear resistance of carbon expanded austenite is 2 orders of magnitude higher than AISI 316 UT

• The layer of carbon expanded austenite reduces the subsurface deformation and supports the protective oxide layer

• The wear mechanism changes from adhesive wear in AISI 316 UT to oxidational wear in AISI 316 PC

Corrosion testing

Immersion corrosion

Boiling H2SO4 (16%)

1 to 20 hours

Corrosion resultsAISI 316 UT AISI 316 PC

After 1 hour immersed in boiling sulphuric acid (16%)

Corrosion mechanisms

Corrosion mechanisms - Schematic

Macrographs of corroded samplesAISI 316 UT AISI 316 DCPC

AISI 316 DCPC

Macrographs

“as treated”

AISI 316 ASPC

AISI 316 ASPC

Corrosion conclusions

• Carbon expanded austenite exhibits higher corrosion resistance to boiling sulphuric acid than AISI 316 UT

• The AS treated samples performed better than the DC ones through the elimination of edge effects

• The corrosion mechanisms are defect-controlled (MnS inclusions, slip bands and grain boundaries)

Active screen plasma treatments

Active Screen experimental setting inside a conventional DC plasma furnace / reactor

Nitriding mechanisms of Active Screen - schematics

DC and AS plasma reactors

Industrial AS plasma furnace

AS typical treatment cycle

Processing conditions

Benefits of AS treatmentDC – edge effect DC – arcing damage AS – feature less

AS –rusty components before ASPN AS – rusty components after ASPN

Active Screen conclusions

• AS plasma treatments can produce superior surface quality than DC treatments (no edge effect or arcing damage)

• AS plasma shows potential to further improve the results obtained with DC or other plasma treatments

• AS treatments are less sensitive to the surface condition of components (rust, oil, etc.)

Acknowledgements

This project was sponsored by:

EU scholarships for Latin America

Techint group

The University of Birmingham

Universidad Tecnológica Nacional

Thank you very much indeed