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