Dr. K. Cherian provides a summary of his work researching atmospheric pressure microwave plasma processing technologies. This includes using microwave plasma to carry out processes like sintering, carburizing, nitriding, and brazing of technical ceramics and metals. Some key advantages identified are lower processing temperatures, shorter cycle times, and improved or comparable material properties compared to conventional methods. Specific examples discussed include carburizing gears to greater depths in less time and sintering ceramic cam lobes with better hardness.
IUMRS-ICAM 2015_Deformation Mechansims in IA Medium Mn Steel_OCT 25-29_2015
Dr. K Cherian Atmospheric Pressure Microwave Plasma Processing Technologies
1. Dr. Kuruvilla (Karl) Cherian
Independent Materials Scientist-Consultant
(Diamond and Advanced Materials Processing Technologies)
Home Office: 347 Rose Brier Drive, Rochester Hills, Michigan, USA
Email: kuruvilla.cherian@usa.net, amprayilusa@gmail.com
Excerpts from R&D work in:
Atmospheric Pressure Microwave Plasma Processing
Technologies, Applied Research & Development
(at Disruptive Technologies Group Labs., Dana Corporation)
A.Processing System and Medium
B. Atmospheric Pressure Microwave Plasma Sintering of
Technical Ceramics
C. Atmospheric Pressure Microwave Plasma Carburizing,
Sintering, Nitriding & Brazing of Metallic Objects
C1. Carburizing: Gears
C2. Sintering: Cam lobes
C3. Nitriding: 4140 steel samples
C4. Brazing: Low-Carbon Steel Tube Joint &
Aluminum Tube Joint
D.Related Technical/Research Reports
2. Dr. K. Cherian-MWP1-AB
Atmospheric Pressure Microwave Plasma Processing
Technologies, Applied Research & Development
(at Disruptive Technologies Group Labs., Dana Corporation)
A. Processing System and Medium
Microwave plasma initiated and sustained at atmospheric pressure,
adapted and used successfully for various materials processing applications
A typical AtmoPlasTM
system (left), schematic (center) and close up view of plasma cavity (right)
Features (as numbered in the schematic):
(1): Workpiece(s)
(2): Insulated cavity, microwave transparent material.
(3): Microwave chamber within which the microwave processing cavity is situated.
(4): Working gas/gas mixture that is readily ionized, to be introduced into the cavity.
(5): Magnetrons, fixed outside the chamber, produces microwave radiation that penetrates the cavity
(6): Plasma initiated and sustained within the cavity containing workpiece(s).
Additional feature:
A venting system that is used to:
a): Evacuate & backfill with gases, if needed, for specific processing environment.
b): Remove waste gases from the insulated cavity during and after each processing run.
B. Atmospheric Pressure Microwave Plasma Sintering of
Technical Ceramics
Conventional Sintering Process AtmoPlasTM
Sintering Process
Sintering temp: 1350C Sintering temp: 1100C Sintering temp: 1200C
205min to 1250C +
70min to 1350C +
15min to 1365C +
60min at 1365C +
270min to 200C
Total cycle time: ~10hrs 20min
21 min to 1100C +
120 min at 1100C +
~60 min to Room Temp.
Total time: ~3hrs 21min
60 min to 1200C +
120 min at 1200C +
~60 min to Room Temp.
Total time: ~4hrs
Typical sample - as received,
not sintered
Sample - as received and
sintered 120 min @ 1200 C
Sample – as received and
sintered 120 min @ 1100 C
3. Dr. K. Cherian-MWP2-C1
C. Atmospheric Pressure Microwave Plasma Carburizing, Sintering,
Nitriding & Brazing of Metallic Objects
C1. Carburizing: 8620 steel side gears
Multiple gears in the plasma cavity
prior to plasma processing
Plasma after transitioning from
filamentary to steady modes.
Sintered gears immediately after
plasma switch-off.
Case depth comparison of Conventional Gas Carburized and
AtmoPlasTM
Carburized, 8620 steel side gears.
Conventinal Carburized Gear
Total processing time: 142+110+20 = 272 min
AtmoPlas
TM
Carburized Gear
Total processing time: 112+80+20 =212 min
Comparison of Conventional Gas, Vacuum and AtmoPlas
TM
Carburization
Characteristics /
Properties
Conventional Gas
Carburized
Vacuum Carburized AtmoPlasTM Carburized
Total Carburization
Time
142 min boost + 110 min
diffuse +20 min temp drop
= Total 272 min.
Carburizationn zone time
= 205 min
112 min boost + 80 min
diffuse +20 min temp drop
= Total 212 min
Effective Case Depth ~0.035” ~0.035” ~0.045”
Microstructure (Retained Austenite % and Depth)
Corner Microstructure ~15%- ~30% retained
austenite to a depth of
~0.319 mm.
~10%-15% retained
austenite to a depth of
0.172 mm
~5%-20% retained
austenite to a depth of
0.172 mm
Surface Microstructure ~10%- ~20% retained
austenite to a depth of
~0.119 mm
~5%- ~15% retained
austenite to a depth of
~0.243 mm
~5%-20% retained
austenite to a depth of
0.148 mm
ASTM E112-96 Grain Size No.(Comparison Method)
Case 8-10 (22.5µ -11.2µ) 8-9 (22.5µ - 15.9µ) 10-12 (11.2µ – 5.6µ)
Core 8-9 (22.5µ - 15.9µ) 9-10 (15.9µ – 11.2µ) 10-12 (11.2µ – 5.6µ)
4. Dr. K. Cherian-MWP3-C2C3
C2. Sintering: P/M cam lobes
Multiple cam lobes in the plasma
cavity prior to plasma processing.
Plasma transitioning from
filamentary to steady modes.
Sintered cam lobes immediately
after plasma switch-off.
Processing
Info.
Properties/
Characteristics
Conventional
sintered -
~1150C,
20 min
AtmoPlasTM
sintered -
~1150C,
20 min
AtmoPlasTM
sintered -
~1250C,
20 min
AtmoPlasTM
sintered -
~1350C,
20 min
Hardness (HRB) 89 93.04 93.72 105.96
Decarburization None None None None
Density (g/cc) 6.58 6.42 6.57 7.00
Microstructure
Unetched Etched: 2% Nital. Network of grain boundary ferrite (light regions)
surrounding grains of pearlite (dark regions), the black regions are
porosity voids.
C3. Nitriding: 4140 steel samples
Plasma cavity modified for nitriding trials
(at left)
Samples: 4140 Steel - five
Processing Cycles: Two, A & B:
A.
a) 29 minutes temperature build-up to ~540C
with MW power in 2.5 – 3.6 kW range in N2
b) 200 min nitriding in ammonia at ~540C with
MW power in 3 – 3.6 kW range
c) Cool down to room temp.
B.
a) 41 minutes temperature build-up to ~540C
with MW power 2.5 – 4 kW range in N2
b) 200 min nitriding in ammonia at ~540C with
MW power in 2.9 – 3.3 kW range
c) Cool down to room temp.
5. Dr. K. Cherian-MWP4-C3C4
Post Processing (Nitriding) Microstructural Analysis
Digital image of a cross-section through an atmospheric plasma nitrided sample after etching with 2% Nital..
The structure is typical of this sample. A relatively thick nitride layer is evident. The darker layer (indicated
by bracket) is approximately 0.018” deep and exhibits higher hardness than the rest of the matrix. This
apparently indicates nitride diffusion into the case.
Pre & Post Processing (Nitriding) Microhardness Tests
Cycle &
Sample
No.
Microhardness (HK500) Median Hardness
Change (HK500)Pre-Processing Post-Processing
Min Median Max Min Median Max
A-1 349 373 405 520 558 696 185
A-2 386 403 420 337 465 688 62
B-1 360 372 379 481 594 638 222
B-2 200 223 238 336 354 376 131
B-3 208 230 236 508 522 578 292
Significant changes in the Knoop microhardness values were observed, indicating successes with
the new, faster and environmentally friendly atmospheric pressure microwave plasma nitriding
process.
C4. Brazing: Low-Carbon Steel Tube Joint & Aluminum Tube Joint
Low-Carbon Steel Tube Joint
Low-carbon steel tube joint copper-
brazed with the AtmoPlas process
(Kumar et.al., 2004)
Optical pyrometer data recording the “braze signature” spike
when the copper braze alloy begins to melt (Kumar et.al., 2004)
6. Dr. K. Cherian-MWP5-C4D
Aluminum Tube Joint
Aluminum tube joint brazed with the AtmoPlas
process (Demchak et.al., 2005)
Section view of AtmoPlas aluminum braze joint (no
etch) showing flow of braze alloy into joint.
(Demchak et.al., 2005)
D. Related Technical/Research Reports
Atmospheric Pressure Plasma Microwave Processing
M. J. Dougherty Sr., S. Kumar, D. Kumar, K. Cherian
Proceedings of the 4th World Congress on Microwave and Radio Frequency Applications, Austin, USA (November 2004) 485.
Carburization of Steel Alloys by Atmospheric Microwave Plasma
S. Kumar, D. Kumar, K. Cherian, M. Dougherty,
Proceedings of the 4th World Congress on Microwave and Radio Frequency Applications, Austin, USA, (November 2004) 493
Efficient Brazing with Microwave Plasma at Atmospheric Pressure
Kumar, S. Kumar, M.J. Dougherty Sr., K. Cherian, D.J. Brosky, D. Tasch,
Proceedings of the 4th World Congress on Microwave and Radio Frequency Applications, Austin, USA, (November 2004) 478
Atmospheric Pressure Microwave Plasma P/M Sintering of Cam Lobes
Kuruvilla Cherian, Satyendra Kumar, Devendra Kumar, Mike L. Dougherty, Dominique Tasch, David J. Brosky, Dana M.
Combs,
SAE 2005 Transactions Journal of Materials & Manufacturing (2005) 365.
Braze Signature in Brazing with Atmospheric Pressure Microwave Plasma
Kumar, Devendra, Satyendra Kumar, Kuruvilla Cherian, Mike L. Dougherty, Dominique Tasch, 2005.
2005 SAE World Congress Paper No. 2005 - 01 – 0899, Society of Automotive Engineers, Warrendale, PA, 2005.
Atmospheric Pressure Microwave Plasma Carburization of Steel Alloy Components
Kuruvilla Cherian, Satyendra Kumar, Devendra Kumar, Mike Dougherty, Sr., Dominique Tasch, Greg Fett, Dana Combs,
IMPI 39th Annual Microwave Symposium Proceedings (2005) 68
Use of the AtmoPlas™ Microwave Plasma Process in Brazing Applications
Michael D. Demchak*, Devendra Kumar and Kuruvilla Cherian,
Proceedings of AFC-Holcroft 10th Annual Aluminum Brazing Seminar, 2005
Microwave Carburizing Shows Promise
Kuruvilla Cherian,
Heat Treating Progress, Jan/Feb 2006, 46-47