www.utsi.edu

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: drajput@utsi.edu

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)