Seminário apresentado pelo doutor Santiago Corujeira Gallo, na UCS (Caxias do Sul, RS) em 28 de setembro de 2009. Público: estudantes, professores e pesquisadores da Pós-Graduação em Materiais (PGMat -UCS)

1. Plasma Surface Engineering
Santiago Corujeira Gallo
Universidade de Caxias do Sul
September 2009

2. Birmingham - UK
Founded in middle age (7th century)
Population ca 2,500,000
Traditional industrial centre
Cultural diversity
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3. University of Birmingham
Founded in 1900
Research oriented
Ranked 12th in UK (RAE)
Multicultural
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

4. Surface Engineering Group (2007)
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
Topics of research:
- Plasma diffusion treatments
- Thermal oxidation
- PVD coatings
- Nanoindentation

5. Active screen plasma surface engineering
of austenitic stainless steel for enhanced
tribological and corrosion properties
• Austenitic stainless steel
• Plasma surface engineering
• Tribological and corrosion properties
• Active screen

6. 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

7. Surface engineering treatments
Benefits of surface engineering
• Improved performance
• Use cheaper materials
• Increase design flexibility
Diffusion treatments:
• No sharp interface - gradient
• Slow (temperature – time)

8. Plasma surface engineering
C or N containing gas
Conventional gas nitriding ~ 550oC
Treated substrate
Conventional gas carburising ~ 950oC
C or N containing gas
at low pressure
- -
Cr23C6
+
Cr1-2N -
Treated substrate - cathode (-)

9. GDOES composition depth profiles

10. XRD - phase identification
S-phase
or
expanded
austenite

11. Micrographs of expanded austenite
Typical cross section
optical micrograph
Typical top view
SEM micrograph

12. Microhardness testing
Typical instrumented
hardness test curves
Typical load
bearing capacity

13. Microhardness indents
Tough carbon
expanded austenite
Brittle nitrogen
expanded austenite

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

15. Wear results
AISI 316 UT AISI 316 PC

16. Morphology of the wear tracks
AISI 316 UT AISI 316 PC

17. Wear track of AISI 316 UT

18. Wear track of AISI 316 PC

19. Wear debris
Untreated sample: metallic debris Treated sample: oxide debris
Wear debris Colour Size Magnetic Possible phases
Treated Red / Orange <20um No alpha-Fe2O3 Hematite
Un treated Black >20um Yes Fe3O4 Magnetite

20. Wear debris – TEM SAD pattern

21. Wear conclusions
• The wear resistance of carbon expanded austenite
is 2 orders of magnitude higher than AISI 316 UT
• The wear mechanism changes from adhesive wear
in AISI 316 UT to oxidational wear in AISI 316 PC
• The layer of carbon expanded austenite reduces
the subsurface deformation and supports the
protective oxide layer

22. Corrosion testing
Immersion corrosion
Boiling H2SO4 (16%)
1 to 20 hours

23. Corrosion results
AISI 316 UT AISI 316 PC
After 1 hour immersed in boiling sulphuric acid (16%)

24. Corrosion mechanisms

25. Corrosion mechanisms - Schematic

26. Macrographs of corroded samples
AISI 316 UT AISI 316 DCPC AISI 316 ASPC
AISI 316 DCPC AISI 316 ASPC
Macrographs
“as treated”

27. Corrosion conclusions
• Carbon expanded austenite exhibits higher corrosion
resistance to boiling sulphuric acid than AISI 316 UT
• The corrosion mechanisms are defect-controlled
(MnS inclusions, slip bands and grain boundaries)
• The AS treated samples performed better than the
DC ones through the elimination of edge effects

28. Active screen plasma treatments
Active Screen experimental
setting inside a conventional
DC plasma furnace / reactor
Nitriding mechanisms of
Active Screen - schematics

29. DC and AS plasma reactors

30. Industrial AS plasma furnace

31. AS typical treatment cycle

32. Processing conditions

33. Benefits of AS treatment
DC – edge effect DC – arcing damage AS – feature less
AS –rusty components before ASPN AS – rusty components after ASPN

34. Active Screen conclusions
• AS plasma treatments can produce superior
surface quality than DC treatments (no edge effect or
arcing damage)
• AS treatments are less sensitive to the surface
condition of components (rust, oil, etc.)
• AS plasma shows potential to further improve the
results obtained with DC or other plasma treatments

35. Acknowledgements
This project was sponsored by:
EU scholarships for Latin America
Techint group
The University of Birmingham
Universidad Tecnológica Nacional

36. Thank you very much indeed