Molybdenum-on-Chromium Dual Coating on Steel





   
Note:  This presentation contains the final results of Interlayer Assisted Molybdenum Coatings on Steel through LISITM. This paper was published in the Surface and Coatings Technology journal. [Surface & Coatings Technology (2009), 203 (9), pp 1281-1287]

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Keywords:

Molybdenum coating, Steel, Metal powders, Laser alloying, Surface engineering, Fiber laser, Galvanic scan mirrors
 




Presentation Transcript:

Molybdenum-on-Chromium Dual Coating on Steel

Molybdenum coating on steel
>> Improves wear resistance (self lubricant)
>> Low coefficient of thermal expansion
>> High resistance to scuffing under sliding contact

>> Problem: low hardness (approx. 160 VHN)
>> Carbon addition improves the hardness of Mo

>> Processes widely used: flame and plasma spraying
>> Problems with thermal spraying: porosity & adhesion
Molybdenum coating on steel
Objective

>> Good wear resistance
>> High hardness
>> Excellent adhesion


Process

>> LISITM (Laser Induced Surface Improvement)
>> LISITM concept: Laser alloying of pre-placed powder
Direct alloying of Mo on Steel: Problems
>> Melting point of Mo (~2623oC) is much higher than that of steel (~1530oC). High dilution !!

>> Mo and Fe form high and low temperature intermetallics.
Dilution
Dilution
Fe-Mo phase diagram
Problems & Solution
>> Intermediate layers of materials that don>>t form intermetallics with Fe and Mo
Fe-Cr phase diagram
Cr-Mo phase diagram
Cr-B phase diagram
Mo-B phase diagram
Chemistry & Stoichiometry
>> Cr* = Cr + CrB2 eutectic mixture (9:1) - IML
>> Mo* = Mo + MoB eutectic mixture (7:3) - ML
>> B gives additional hardness
Process: LISITM
>> Laser Induced Surface Improvement
>> Uses pre-placed powder (precursor)
>> Precursor = Metal powders + Binder
>> Dry for few hours
>> Laser process

IML Precursor = Cr + 10.5 wt.%CrB2 + 50 wt.% binder
ML Precursor = Mo + 30 wt.% MoB + 85 wt.% binder
Precursor Deposition
Laser Deposition
Fiber laser processing
Fiber laser results
Fiber laser results
Fiber laser >> two coatings
Fiber laser >> two coatings
Cr* coating
X-ray Cr* layer
Mo* on Cr* coating
Mo* on Cr* x-rays
Block-on-ring wear tester
Block-on-ring sliding wear
PLINT TE68 Gas Jet Erosion Rig
ASTM G76 dry sand erosion wear
Summary
>> Direct diode fiber laser can effectively perform surface alloying.
>> Cr is an efficient intermediate layer for Mo coatings on steels.
>> Hardness of Mo coating is approx. 1100 VHN.
>> Dry sliding wear resistance of Mo is 10 times that of steel and 4 times that of chromium

Thank You