Molybdenum-on-Chromium Dual Coating on Steel www.utsi.edu   Center for Laser Applications University of Tennessee  Space I...
Molybdenum coating on steel <ul><li>Improves wear resistance (self lubricant) </li></ul><ul><li>Low coefficient of thermal...
Molybdenum coating on steel <ul><li>Objective </li></ul><ul><li>Good wear resistance </li></ul><ul><li>High hardness  </li...
Direct alloying of Mo on Steel: Problems <ul><li>Melting point of Mo (~2623 o C) is much higher than that of steel (~1530 ...
Dilution Precursor mixture Substrate  Laser beam Pores  Capillary action fills up the pores with the molten metal from the...
Dilution Substrate Substrate 1) Composite coating: unmelted precursor particles embedded in the substrate 1 2 T p  >> T s ...
Fe-Mo phase diagram
Problems & Solution <ul><li>Intermediate layers of materials that don’t form intermetallics with Fe and Mo </li></ul>Mo Fe...
Fe-Cr phase diagram
Cr-Mo phase diagram
Cr-B phase diagram 1630 o C
Mo-B phase diagram 2180 o C
Chemistry & Stoichiometry <ul><li>Cr* = Cr + CrB 2  eutectic mixture (9:1) -  IML </li></ul><ul><li>Mo* = Mo + MoB eutecti...
Process: LISI TM <ul><li>Laser Induced Surface Improvement  </li></ul><ul><li>Uses pre-placed powder (precursor) </li></ul...
Precursor Deposition Precursor mixture = Metal Powders + Binder Precursor mixture steel air Spray gun
Laser Deposition Cr* = 165W, 25mm/s, Hatch 0.1mm @ 355mm Mo* = 180W, 25mm/s, Hatch 0.1mm @355mm Steel Cr IML Mo Layer
Fiber laser processing Scan head Fiber Water-cooled chamber View port Hopper
Fiber laser results Substrate: AISI 4130 steel
Fiber laser results Cr* layer at high magnification
Fiber laser – two coatings
Fiber laser – two coatings Mo* layer at high magnification
Cr* coating Microhardness test of chromium layer
X-ray Cr* layer X-ray diffractogram of chromium layer
Mo* on Cr* coating Microhardness test of molybdenum coating
Mo* on Cr* x-rays X-ray diffractogram of molybdenum coating
Block-on-ring wear tester ASTM G77  (4 lb load)
Block-on-ring sliding wear Sliding wear performance
PLINT TE68 Gas Jet Erosion Rig ASTM G76  (silica 2 gm/min at 52 m/s)
ASTM G76 dry sand erosion wear Solid particle erosion performance
Summary <ul><li>Direct diode fiber laser can effectively perform surface alloying. </li></ul><ul><li>Cr  is an efficient i...
<ul><li>Thank You </li></ul>
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Molybdenum-on-Chromium Dual Coating on Steel

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A presentation on Molybdenum-on-Chromium Dual Coating on Steel made by Deepak Rajput at the Center for Laser Applications, the University of Tennessee Space Institute.

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Molybdenum-on-Chromium Dual Coating on Steel

  1. 1. Molybdenum-on-Chromium Dual Coating on Steel www.utsi.edu Center for Laser Applications University of Tennessee Space Institute 411 B. H. Goethert Parkway Tullahoma, TN 37388 Surface & Coatings Technology (2009), 203 (9), pp 1281-1287 Implementation of fast scanning diode pumped fiber laser to surface modification Deepak Rajput [email_address] / http://drajput.com
  2. 2. Molybdenum coating on steel <ul><li>Improves wear resistance (self lubricant) </li></ul><ul><li>Low coefficient of thermal expansion </li></ul><ul><li>High resistance to scuffing under sliding contact </li></ul><ul><li>Problem: low hardness (approx. 160 VHN) </li></ul><ul><li>Carbon addition improves the hardness of Mo </li></ul><ul><li>Processes widely used: flame and plasma spraying </li></ul><ul><li>Problems with thermal spraying: porosity & adhesion </li></ul>
  3. 3. Molybdenum coating on steel <ul><li>Objective </li></ul><ul><li>Good wear resistance </li></ul><ul><li>High hardness </li></ul><ul><li>Excellent adhesion </li></ul><ul><li>Process </li></ul><ul><li>LISI TM (Laser Induced Surface Improvement) </li></ul><ul><li>LISI TM concept: Laser alloying of pre-placed powder </li></ul>
  4. 4. Direct alloying of Mo on Steel: Problems <ul><li>Melting point of Mo (~2623 o C) is much higher than that of steel (~1530 o C). High dilution !! </li></ul><ul><li>Mo and Fe form high and low temperature intermetallics . </li></ul>
  5. 5. Dilution Precursor mixture Substrate Laser beam Pores Capillary action fills up the pores with the molten metal from the substrate
  6. 6. Dilution Substrate Substrate 1) Composite coating: unmelted precursor particles embedded in the substrate 1 2 T p >> T s T p > T s or not enough Laser power 2) Partial melting of the precursor: coating contains alloy and unmelted particles
  7. 7. Fe-Mo phase diagram
  8. 8. Problems & Solution <ul><li>Intermediate layers of materials that don’t form intermetallics with Fe and Mo </li></ul>Mo Fe Mo Fe IML intermetallics No intermetallics No intermetallics Phase diagrams show that Cr , V and Nb are the best intermediate layers (IML)
  9. 9. Fe-Cr phase diagram
  10. 10. Cr-Mo phase diagram
  11. 11. Cr-B phase diagram 1630 o C
  12. 12. Mo-B phase diagram 2180 o C
  13. 13. Chemistry & Stoichiometry <ul><li>Cr* = Cr + CrB 2 eutectic mixture (9:1) - IML </li></ul><ul><li>Mo* = Mo + MoB eutectic mixture (7:3) - ML </li></ul><ul><li>B gives additional hardness </li></ul>temperature Cr CrB 2 CrB 2 Cr % CrB 2 Cr + 10.5% CrB 2
  14. 14. Process: LISI TM <ul><li>Laser Induced Surface Improvement </li></ul><ul><li>Uses pre-placed powder (precursor) </li></ul><ul><li>Precursor = Metal powders + Binder </li></ul><ul><li>Dry for few hours </li></ul><ul><li>Laser process </li></ul><ul><li>IML Precursor = Cr + 10.5 wt.%CrB 2 + 50 wt.% binder </li></ul><ul><li>ML Precursor = Mo + 30 wt.% MoB + 85 wt.% binder </li></ul>
  15. 15. Precursor Deposition Precursor mixture = Metal Powders + Binder Precursor mixture steel air Spray gun
  16. 16. Laser Deposition Cr* = 165W, 25mm/s, Hatch 0.1mm @ 355mm Mo* = 180W, 25mm/s, Hatch 0.1mm @355mm Steel Cr IML Mo Layer
  17. 17. Fiber laser processing Scan head Fiber Water-cooled chamber View port Hopper
  18. 18. Fiber laser results Substrate: AISI 4130 steel
  19. 19. Fiber laser results Cr* layer at high magnification
  20. 20. Fiber laser – two coatings
  21. 21. Fiber laser – two coatings Mo* layer at high magnification
  22. 22. Cr* coating Microhardness test of chromium layer
  23. 23. X-ray Cr* layer X-ray diffractogram of chromium layer
  24. 24. Mo* on Cr* coating Microhardness test of molybdenum coating
  25. 25. Mo* on Cr* x-rays X-ray diffractogram of molybdenum coating
  26. 26. Block-on-ring wear tester ASTM G77 (4 lb load)
  27. 27. Block-on-ring sliding wear Sliding wear performance
  28. 28. PLINT TE68 Gas Jet Erosion Rig ASTM G76 (silica 2 gm/min at 52 m/s)
  29. 29. ASTM G76 dry sand erosion wear Solid particle erosion performance
  30. 30. Summary <ul><li>Direct diode fiber laser can effectively perform surface alloying. </li></ul><ul><li>Cr is an efficient intermediate layer for Mo coatings on steels. </li></ul><ul><li>Hardness of Mo coating is approx. 1100 VHN . </li></ul><ul><li>Dry sliding wear resistance of Mo is 10 times that of steel and 4 times that of chromium </li></ul>
  31. 31. <ul><li>Thank You </li></ul>

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