Deepak Rajput, Kathleen Lansford, Lino Costa, William ...
Transcript of Deepak Rajput, Kathleen Lansford, Lino Costa, William ...
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Deepak Rajput, Kathleen Lansford, Lino Costa, William Hofmeister
Center for Laser Applications
University of Tennessee Space Institute
411 B. H. Goethert Parkway Tullahoma, TN 37388
Interlayer Assisted Molybdenum Coatings on Steel through LISITM
Contact: [email protected]
PHYS 593 Independent Study: Physics Seminar
Properties of Mo
• High melting temperature (~2623oC)• High hardness (~1530 VHN)• No reaction with water and oxygen at RT• Good weldability• Good ductility and fabricability• Good machinability• Good thermal conductivity• Low coefficient of thermal expansion
Why Mo on Steel ?
Improves hardnessImproves corrosion resistanceImproves high temperature strength
Direct LD of Mo on Steel: Problems
• Melting point of Mo (~2623oC) is muchhigher than that of steel (~1530oC).
• Mo and Fe form high and low temperatureintermetallics.
Solution• Intermediate layers of materials that don’t
form intermetallics with Steel and Mo
Mo Fe
Mo FeIML
intermetallics
No intermetallics No intermetallics
Phase diagrams show that Cr, V and Nb are the best intermediate layers (IML)
Chemistry & Stoichiometry
• Cr* = Cr + CrB2 eutectic mixture (9:1) - IML• Mo* = Mo + MoB eutectic mixture (7:3) - ML• B gives additional hardness
tem
pera
ture
CrCrB2
CrB2Cr % CrB2
Cr + 10.5% CrB2
Eutectic: System that melts at a temperature much lower than its constituentsCr-B and Mo-B form eutectic systems
Process: LISITM
• Laser Induced Surface Improvement • Uses pre-placed powder (precursor)• Precursor = Metal powders + Binder• Dry for few hours• Laser process
Intermediate layer = Cr + 10.5%CrB2 + 50% binderMain layer = Mo + 30% MoB + 85% binder
Precursor DepositionPrecursor mixture = Metal Powders + Binder
Precursor mixture
steel
air
Spray gun
250-300 μ
Laser Deposition
SteelCr IML
Mo Layer
Cr* = 165W, 25mm/s, Hatch 0.1mm @ 355mmMo* = 180W, 25mm/s, Hatch 0.1mm @355mm
Coatings
Cr* Intermediate Layer Mo* Main Layer
Cr IMLMo ML
Steel Substrate: 4340 Alloy Steel
SEM pictures
EDS AnalysisCr IML Mo IML
Fe: 11.9 % Fe: 11.5 %Cr: 21 %Mo: 67.5 %
Cr: 88.1 %
We are working !
Microhardness: Cr* IML Cr* on 4340 Steel
0
200
400
600
800
1000
1200
0 100 200 300 400 500 600 700 800 900 1000
Distance Across Sample (microns)
Vick
ers'
Har
dnes
s (1
00 g
f)
0
45
90
135
180
Hardness: 1050 VHN
Microhardness: Mo* MLMo* on Cr* on 4340 Steel
0
200
400
600
800
1000
1200
1400
1600
1800
0 100 200 300 400 500 600 700 800
Distance Across Sample
Vick
ers'
Har
dnes
s (1
00 g
f)
0
100
175
250
325
Hardness: 1200 - 1400 VHN
Erosion: Cr* IML
Erosion Performance: Cr*
0, 0
15, 0.0035
30, 0.0064
45, 0.0088
60, 0.011
75, 0.0125
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0 10 20 30 40 50 60 70 80
Time (min)
Mas
s lo
ss (g
ram
s)
Erosion: Mo* ML
Erosion Performance: Mo*
0, 0
15, 0.0196
30, 0.0268
45, 0.032
60, 0.035875, 0.0396
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0 10 20 30 40 50 60 70 80
Time (min)
Mas
s lo
ss (g
ram
s)
Erosion: Comparison
Comparison of Erosion Performance
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Mas
s lo
ss (g
ram
s)
Cr* IMLMo* ML
Cr* IML
Mo* ML
Summary
• A thick Mo coating• Dilution within permissible range• Very hard ML and IML• Erosion of the ML is worse than the IML
Overall: Good Mo coating! (grade: B)
No conclusion: We are still working !!
Further investigation
• XRD studies for phase determination• Wear studies • Fine tuning of process parameters to
further reduce dilution and continuity of the layers
Questions
Thank You
(I appreciate your patience)