APPLICATION OF MECHANICAL ALLOYING AND MECHANOCHEMISTRY NEW METHOD FOR METAL COATING Speaker: Dr. Aghasi Torosyan Institute of General and Inorganic Chemistry.

APPLICATION OF MECHANICAL ALLOYING APPLICATION OF MECHANICAL ALLOYING AND MECHANOCHEMISTRYAND MECHANOCHEMISTRY

NEW METHOD FOR METAL COATINGNEW METHOD FOR METAL COATING

Speaker: Dr. Aghasi TorosyanSpeaker: 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 OverviewIntroduction 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 PROCESSINGVibratory Mill

During the milling process , particles are deformed or broken up using some combination of HP + SD

Fig.2 The principal scheme of mechanical processingImportant ParametersFrequency - Amplitude - AMass of Ball – mMass 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 AlloyingTwo–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

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

Method for Mechanochemical (MC) Deposition of Metallic and Composite Hard and Wear Resistant

Coatings

The Technology of Coating DepositionIdea of the method and the Schematic Diagram of the

Coating Form Apparatus The objects of investigations in traditional Mechanochemistry are powdered materials. P+PP, P+LP, P+GP, 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+PBMS(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.5. Distribution of the balls sizes and the uniformity of Coating

a) The balls have the same diameter 2-substrate, C- coated areab)  The balls have different diameters 2-substrate, C - coated area

Fig. 4; The Scheme of Deposition 1 - milling balls, 2 – coating form powder, 3 - coating layer,

4 - sublayer, 5 - substrate.

Deposition of Metallic Coatings (Cr, Cu) on the Steel and Al specimens

TwoTwo waysways of coatingof coating depositiondeposition

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.

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

Mechanical Properties of the Coating

STRUCTURE AND THISTRUCTURE AND THICKCKNESS OF NESS OF Cr-Cr-COATINGSCOATINGS DEPOSITED ON STEEL DEPOSITED ON STEEL

Fig.6a Cross section of steel with Cr 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.

Cr

Steel

Fig.7. Cross section of steel with Cu coating deposited by electrochemicalmethod.

60m

Cu coating

The formation of (Cu-Al alloy) transition layer

Al substrates

p

te

p

X-rayTube

M D

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. 

Fig.8 XRD Scheme and the Stresses in Cu on Al Coating

x

y

z

impa

ct

Table 1. Biaxial and shear stresses in Cu coating deposited by mechanical alloying method

Model Young modulusE , GPa

Shearmodulus 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 CharacteristicsImprovement of the Mechanical Characteristics

0e

a)

b)

Fig.9 Cylindrical samples (with cross-sectional area-A and length-lo) for Stress-

Strain 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

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

ADHESION TESTING

Type of Deposition Adhesion

[MPa]

Thermal spray (Cr) 80-120

This Method (Cr) 250-300

PVD (Cr) 300-350

Table 2, The comparative value of adhesionfor Cr coating deposited by different methods

Table 3

Material MicrohardnessHV50 [MPa]

Initial steel substrate (low carbon steel)

2500 – 2700

Substrate after mechanical processing

3500 – 3700

Steel with Cr-coating layer 9500 – 10300

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

Coatings for Tribological ApplicationsMo-MoS2 and W-WS2 Lubricant layers

1. Mo+Al(subs)Mo on Al2. Mo+2S = MoS2

1. W+Al(subs)W on Al2. 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

Table 4

Optical microscopic image of MoS2 coating and the results of ball catering test r2

2 – r12

h = ------------ 2Rb

r1 = 30 m ; r2=60 m; R=5mm ; h Mo 0.5m

Mo-MoS2 Coating on Al SubstrateMicrostructure and Thickness

The formed coating has porosity microstructure and can provide self lubrication during the exploitations

Fig 13 The porosity microstructure of MoS2 coating synthesizedby MC method

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

COATING FOR TRIBOLOGICAL APPLICATIONS

Fig 15. The results of segment on disk

testing for W-WS2 (curve 1)

and Mo-MoS2 (curve 2)

coatings.

Fig.14, SMC Apparatus for tribological testing(sliding speed vs=1.5m/c, loading force N=20kg)

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

The comparative results of the mechanochemically deposited MoS2 coating with the conventional vapor phase deposited

MoS2coating. Table V

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.

The structure of DLC is predominantly amorphous with no long-range 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.

CarbonSource

DD

G

E EG

ED

Raman Spectroscopy-Light loses energy to the molecule vibration Einc. ph>Eabs

Raman = Laser- Scattered

l= ±2(Raman),l=0(Raylaigh)

The scattered from the DLC films laser beam give resonance peaksassociated with graphitic (G-bands)and disordered carbon (D-band) components allow to characterize the films microstructure.

Fig.16; The principle of Raman Spectroscopy

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=5minI(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 schemefor DLC films formation by MC way

AFM Images and Microhardness of the DLC Films Deposited at 5min and 20 min of Mechanical Processing

Material MicrohardnessHV50 [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

Fig 20 (a), t= 5min

Fig. 20 (b), t=20min

Table 6; Microhardness of MC deposited DLC films

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.

Conclusions for DLC Films Deposition

The Technology of Coating DepositionA 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.

TThe he TTtypestypes of the Coating Obtainedof 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 .

CONCLUSIONCONCLUSIONSS

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..