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: Nonuniformity of the Cr-on-steel Sample
Effect of Mass of Cr Powder on
Steel Substrate
Microhardness (Pascal)
Microhardness Vs. Powder Mass
6.00E+09
5.50E+09
5.00E+09
4.50E+09
4.00E+09
3.50E+09
3.00E+09
2.50E+09
2.00E+09
1.50E+09
1.00E+09
0
5
10
15
20
25
30
35
Powder Mass (mg)
40
45
50
55
Milling Time: Effects on Surface
Morphology
Microhardness Vs. Milling-Time
Ten Minutes
Microhardness
(Pascal)
1.20E+10
Tw enty
Minutes
1.00E+10
8.00E+09
6.00E+09
4.00E+09
2.00E+09
0.00E+00
25mg
30mg
40mg
50mg
Powder Mass of the Cr-coating
Heat Treatment
Microhardness
(Pascal)
Heat treatment: Chromium on Steel
1.40E+10
1.20E+10
1.00E+10
8.00E+09
6.00E+09
4.00E+09
2.00E+09
0.00E+00
200 300 400 500 600 700 800 900 100 110 120 130
0
0
0
0
Temperature (C)
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 (Pascal)
Microhardness Vs. Powder Mass
1.40E+10
1.20E+10
1.00E+10
8.00E+09
6.00E+09
4.00E+09
2.00E+09
0.00E+00
0
10
20
30
Powder Mass (mg)
40
50
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