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 >
Direct LD of Mo on Steel: Problems
> Melting point of Mo (~2623oC) is much higher than that of steel (~1530oC).
> Mo and Fe form high and low temperature intermetallics.
Solution
> Intermediate layers of materials that don>t form intermetallics with Steel and Mo
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
Intermediate layer = Cr + 10.5%CrB2 + 50% binder
Main layer = Mo + 30% MoB + 85% binder
Precursor Deposition
Laser Deposition
Coatings
EDS Analysis
Microhardness: Cr* IML
Microhardness: Mo* ML
Erosion: Cr* IML
Erosion: Mo* ML
Erosion: Comparison
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
