plasma surface engineering
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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
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