Transcript INSTITUTE OF GENERAL AND INORGANIC CHEMISTRY OF THE

APPLICATION OF MECHANICAL ALLOYING
AND MECHANOCHEMISTRY
NEW METHOD FOR METAL COATING
Speaker: Dr. Aghasi Torosyan
Institute of General and Inorganic Chemistry
National Academy of Sciences of Armenia
Fulbright Scholar at the University of Maryland Baltimore
County & Goucher College
Introduction and Overview
It is well known that mechanical processing, such as
high pressure and shear deformation, ball milling, etc., can
create defects and change the atomic structure, it can be
used to influence the speed, direction and extent of
physical and chemical changes in and between solids,
between solids and liquids as well as solids and gases.
Mechanochemistry investigates the principles of
chemical interactions and conversions in solids under
mechanical influence.
Solid -Phase Systems Under Influence of HP+SD
(Uniaxial Compression)
APPARATUS OF MECHANICHAL PROCESSING
Vibratory Mill
During the milling process , particles are deformed
or broken up using some combination of HP + SD
Fig.2 The principal scheme
of mechanical processing
Important Parameters
Frequency - 
Amplitude - A
Mass of Ball – m
Mass of Loading - ML
Mass of Reactant - MR
Mass Ratio - ML/ MR
Used Particle size - l
The Type of Chemical Transformations Proceeding
Under Ball Milling Conditions
Mechanical Alloying
Two–Me1Me2 (Ex. Ni60Mo40), Three–Me1Me2Me3 (Ex.Al98Y7Fe5)),
or Multicomponent (Me1***Men) ; PbxW1-x
Addition Reactions
Me+2S MeS2, Me+C MeC, Me+Si MeSi
MoO3 + PbO PbMoO4 , **** etc.
Displacement Reaction
Me1O+Me2  Me1+Me2O (Ex. Me1=Cu, Me2=Al)
MeO + H2  Me + H2O (EX. Me= (Cr, Ti, W etc.))
Decomposition Reaction
CuSO4  CuO + SO2  ; CuSO4  Cu +SO2 
C10H8  kC+mCiH(2n+2)+lH2
Theoretical and Applied Mechanochemistry
Practical Applications. Mechanochemical methods were utilized
to prepare carbides, sulfides, amorphous and nanocrystalline materials,
superconductive materials etc. Mechanochemical processing is simple,
environmental friendly, and can be scaled up to tonnage quantities.
The chemical changes take place in the solid state form without a need
for solvents or high temperature.
Theory. In spite of simplicity of practical realization the theoretical
description of ball milling-induced chemical reactions is a difficult
problem due to the complex combination of interrelated processes
on several length and time scales. There is no common theory that
could explain the available data and orient future investigations and
the development of applications. Further progress in this area requires
better fundamental knowledge of the mechanisms of the relevant
chemical interaction and the role of mechanical activation in these
processes.
Application of Mechanochemistry
Mechanochemical Method for Surface modification
and Synthesis of Hard Composite Coating
Deposition of Metallic Coating (Cr, Cu, etc.)
Synthesis of Lubricant Films (MoS2 and WS2 )
Deposition of Amorphous carbon and DLC Films
Method for Mechanochemical (MC) Deposition of
Metallic and Composite Hard and Wear Resistant
Coatings
A novel universal approach to modify metallic
surfaces and deposit multifunctional metallic
coatings, lubricant layers and amorphous carbon
films is proposed and developed based on the
in situ mechanochemical processing of substrate
specimen in the presence of different powdered
compounds and in the environment of various
liquid and gaseous media
The Technology of Coating Deposition
Idea of the method and the Schematic Diagram of the
Coating Form Apparatus
The objects of investigations in traditional Mechanochemistry are
powdered materials. P+PP, P+LP, P+GP, where P-Powder,
L- Liquid and G-Gas. The main idea of the presented method is to
investigate mechanically induced interactions between bulk metallic
specimens (BMS) and various P or L materials.
BMS+PBMS(coated); BMS+L  BMS(coated);
Fig.3; 1-Coating Chamber; 2-Milling balls
3-Coating forming compound
4. Gas supply fitting
5.Metallic Substrate
6 Lever spring
The Process of the Coating Formation
Fig. 4; The Scheme of Deposition
1 - milling balls, 2 – coating form
powder, 3 - coating layer,
4 - sublayer, 5 - substrate.
Fig.5. Distribution of the balls sizes
and the uniformity of Coating
a) The balls have the same diameter
2-substrate, C- coated area
b) The balls have different diameters
2-substrate, C - coated area
Deposition of Metallic Coatings (Cr, Cu)
on the Steel and Al specimens
Two ways of coating deposition

Metal coatings formed due to the mechanical alloying. For
the Cr or Cu coatings, Cr or Cu powders were used only,
The mechanism of coating formation is offered based on
the theory of solids’ deformation and dislocation theory.
Coating-specimen bonding strength is of cold-welding
nature, as was shown by our experiments.
 The coating is formed when initial oxide compounds
containing to-be-coated-metals are mechanochemically
reduced: the Steel-Cr2O3 -H2 system is used for Cr coating
on the Al.
Mechanical Properties of the Coating
Among the General requirement for coatings
obtained by any deposition technique is good
mechanical properties,
as well as knowledge of thickness and microstructure
•
•
•
•
Microstructure
Hardness Characteristics
Adhesion
Roughness
STRUCTURE AND THICKNESS OF
Cr-COATINGS DEPOSITED ON STEEL
Cr
Fig.6a Cross section of steel with Cr
Steel coating,
The thickness of the coating can be
attained to 100 m
Fig.6b Cross section of the etched Cr-coating,
Delineated nature of the interstitial layer indicates
that no diffusion happened between the substrate
and the coating in concern.
60m
Fig.7. Cross section of steel with Cu
coating deposited by electrochemical
method.
Fig.8 XRD Scheme and the Stresses in Cu on Al Coating
M
D
Cu coating
X-ray
Tube
p
z
Al substrate
sp
te
The formation of (Cu-Al
alloy) transition layer
y
x
M –monochromator, D – detector, xyz is the coordinate
system (the x-y plane is parallel to the coating plane ), b ,
b(t) , and b(s) are the biaxial stresses in Cu coating,
transition (interfacial) layer, and Al substrate, respectively.
Table 1. Biaxial and shear stresses in Cu coating
deposited by mechanical alloying method
Model
Young
modulus
E , GPa
Shear
modulus
G , GPa
Poisson
ratio,

Biaxial
stress,
b ,GPa
Shear
stress,
S,Gpa
Reuss
110
40
0.37
0.30
0.21
Voigt
145
55
0.32
0.44
0.26
Improvement of the Mechanical Characteristics
b)
a)
0e Cylindrical samples
Fig.9
(with cross-sectional area-A
and length-lo) for StressStrain testing. Coating - on
the lateral surface
Fig.10 Deformational diagram of
Cylindrical Specimen.
1- specimen without coating
2- specimen with Cr coating.
Stress = F/A, Strain = l-lo/lo
ADHESION TESTING
The value of the critical stretch strain or adhesion
was calculated by means of the following simple
formula:  =Fcr /So ,where Fcr [N] is the critical
load causing the separation of the coating from the
substrate, S0 [mm2] is the lateral surface area of
the Cr coated sample
Fig .11 Scheme of
Adhesion Testing.
1 – cyl. substrate,
2 – coating layer
3 – stretching force
Table 2, The comparative value of adhesion
for Cr coating deposited by different methods
Type of Deposition
Adhesion
[MPa]
Thermal spray (Cr) 80-120
This Method (Cr)
250-300
PVD
300-350
(Cr)
Microhardness (Hv)of the Cr Coatings Formed
by MC method of deposition
Fig.12 Testing Scheme and
the value of HV for the Cr
coating deposited by MC
method
Table 3
Material
Microhardness
HV50 [MPa]
Initial steel substrate
(low carbon steel)
Substrate after mechanical
processing
Steel with Cr-coating layer
2500 – 2700
3500 – 3700
9500 – 10300
Coatings for Tribological Applications
Mo-MoS2 and W-WS2 Lubricant layers
Table 4
1. Mo+Al(subs)Mo on Al
2. Mo+2S = MoS2
1. W+Al(subs)W on Al
2. W+2S = WS2
Material
Microhardness, HV50 [MPa]
Steel substrate (in it initial state)
2500 – 2700
Steel substrate coated by W
7500 – 8000
Steel substrate coated by Mo
9000 – 9500
Mo-MoS2 Coating on Al Substrate
Microstructure and Thickness
The formed coating has porosity microstructure and
can provide self lubrication during the exploitations
Optical microscopic image of
MoS2 coating and the results of
ball catering test
r22 – r12
h = -----------2Rb
Fig 13 The porosity microstructure
of MoS2 coating synthesized
by MC method
r1 = 30 m ; r2=60 m;
R=5mm ; h Mo  0.5m
COATING FOR TRIBOLOGICAL APPLICATIONS
Fig.14, SMC Apparatus for tribological testing
(sliding speed vs=1.5m/c, loading force N=20kg)
The two main important parameters for the
tribological coating, namely the coefficient of
friction – f and durability – I can be defined
by means of Disk-Segment test
Fig 15. The results of segment on disk
testing for W-WS2 (curve 1)
and Mo-MoS2 (curve 2)
coatings.
The comparative results of the mechanochemically deposited
MoS2 coating with the conventional vapor phase deposited
MoS2coating.
Table V
Method of
Synthesis
Friction
coefficient f
Number of
cycles to failure
Treatment of Mo
in S vapor
0.05
50000
Mechanochemical
Mo-MoS2
0.03
70000
Deposition of Amorphous Carbon and DLC Films
DLC films possess high hardness and
resistance to wear, low friction,
chemical inertness to both acids and
alkalis, lack of magnetic response, an
optical gap ranging from 0 to a 3.9eV.
E
EG
ED
Carbon
Source
D
G
The structure of DLC is predominantly amorphous with no longrange order.However,the small (~2 nm) sp2 bonded graphitic
domains are cross-linked by a small number of diamond-like
sp3 bonds.
The precursor powders used for forming the DCL films
coating were pure naphthalene (98.9% pure C8H12).
Raman Spectroscopy is frequently utilizing for
characterizing the bonding structure of the carbon films.
Raman Spectroscopy-Light
loses energy to the molecule
vibration Einc. ph>Eabs
Raman = Laser-  Scattered
l= ±2(Raman),l=0(Raylaigh)
Fig.16; The principle of
Raman Spectroscopy
The scattered from the DLC films
laser beam give resonance peaks
associated with graphitic (G-bands)
and disordered carbon (D-band)
components allow to characterize
the films microstructure.
Fig.17 Raman Spectra of
different Carbon Materials
Raman Spectra of Mechanically Deposited Amorphous
Carbon Films Obtained from C8H12 precursors.
I(D)/I(G) ratio is found to be proportional of the
number of aromatic rings M in the cluster
I(D)/I(G)=1.2 for t=5min
I(D)/I(G)=0.7 for t=5min
Fig.18; Raman spectra of MC
deposited DLC films;
Ar ion Laser, = 514nm
Fig.19 The suggested scheme
for DLC films formation by MC way
AFM Images and Microhardness of the DLC Films
Deposited at 5min and 20 min of Mechanical Processing
Table 6; Microhardness of MC
deposited DLC films
Fig 20 (a), t= 5min
Fig. 20 (b), t=20min
Material
Microhardness
HV50 [GPa]
Initial steel
substrate
2.5 – 2.7
Subs. with DLC
films (5min)
7.6-8.2
Subs. with DLC
films (20min)
8.6-10.3
Conclusions for DLC Films Deposition
Several DLC films on the steel and Al specimens have
been deposited and investigated. The presence of broad
D and G resonance peaks on the Raman spectra along
with the high microhardness indicate that the films have
developed the microstructure typical for DLC films.
The thickness from 100 nm to 300nm was recorded. It
was suggested that the method introduced allow to
manage aromatic microstructure of the precursors thus
providing opportunity to regulate microstructure
during the deposition process.
The Technology of Coating Deposition
A novel approach to metal surface modification and
finishing is proposed and developed based on the in situ
mechanochemical processing of substrate specimen in
the presence of different powdered compounds and in
the environment of various powders and liquids media.
The Ttypes of the Coating Obtained

Metallic coatings based on the pure metals (Cr, Cu, W,
Ni, Ti) and alloys (Ti-Cu, Al-Cr, Ti-Al, Ni-Ti, etc.);

Lubricant Layers, MoS2 and WS2

Amorphous and Diamond-Like Carbon Films .
CONCLUSIONS


A key aspect of the proposed technology is the fact
that mechanochemical processing is simple,
economically profitable and environmentally
friendly. The chemical changes take place in the
solid-state form without a need for complicated
solvents or high temperature.
The authors’ believe that the method presented can
form the basis of an efficient technological coating
process, holding good prospects for such
applications as e.g. corrosion/erosion protective
coating on pipes and steel and aluminum sheet..