Micro-Hardness Characteristics and Morphology of Cr-Coating formed due to Mechanical Alloying

A.     Bakhshai, G.S. Dengler, and A.R.Torosyan

Department of Physics, Goucher College, Baltimore, Maryland 21204

What is Ball Milling?

How Does the Reaction Propogate?

                                           

           

                                       

•Increase in Surface to Volume Ratio

•Increase in Heat as a result of the Kinetic energy of the milling balls

•Cold Welding of the Powder to substrate

Key Variables

• Milling Time

• Number and Size of Milling Balls

• Powder Mass

• Powder Mass to Ball Ratio

Initial Experimental Problems

•Downward Curvature of the Substrate

•pressure gradient

•Solution: Insertion of a small hole in substrate prior to milling

Obtaining A Uniform Coating

Ring Formation

Uniformly coated substrate

Atomic Force Microscopy:Uniform Cr coating on Steel

Atomic Force Microscopy: Non-uniformity of the Cr-on-steel Sample

Effect of Mass of Cr Powder on Steel Substrate

Microhardness Vs. Powder Mass

1.00E+09

1.50E+09

2.00E+09

2.50E+09

3.00E+09

3.50E+09

4.00E+09

4.50E+09

5.00E+09

5.50E+09

6.00E+09

0 5 10 15 20 25 30 35 40 45 50 55

Powder Mass (mg)

Mic

roh

ard

ne

ss

(P

as

ca

l)

Milling Time: Effects on Surface Morphology

0.00E+00

2.00E+09

4.00E+09

6.00E+09

8.00E+09

1.00E+10

1.20E+10

Mic

roh

ard

ne

ss

(P

as

ca

l)

25mg 30mg 40mg 50mg

Powder Mass of the Cr-coating

Microhardness Vs. Milling-Time

Ten Minutes

Tw entyMinutes

Heat Treatment

Heat treatment: Chromium on Steel

0.00E+002.00E+094.00E+096.00E+098.00E+091.00E+101.20E+101.40E+10

200 300 400 500 600 700 800 900 1000

1100

1200

1300

Temperature (C)

Mic

roh

ard

nes

s (P

asca

l)

Further Investigations: Cr Coating on Al substrate

•Studied: Powder mass in relationship to microhardness

•Displayed increase in microhardness with increase in powder mass

•Produced same characteristic curve as steel substrate

•Atomic Force Microscopy also showed increases in surface morphology with increased powder mass

Physical Properties of the Coating Powder

Microhardness Vs. Powder Mass

0.00E+00

2.00E+09

4.00E+09

6.00E+09

8.00E+09

1.00E+10

1.20E+10

1.40E+10

0 10 20 30 40 50

Powder Mass (mg)

Mic

roh

ard

nes

s (P

asca

l)

Anomaly: Cu Coating on Al Substrate

•No noticeable coating obtained under equivalent reaction conditions

•Alcohol, Acetone, Silicon oxide were used in an effort to stimulate reaction

•Copper coating obtained by shortening of milling time to 2 minutes

Conclusion