APPLICATION OF MECHANICAL ALLOYING AND MECHANOCHEMISTRY NEW METHOD FOR METAL COATING

1. APPLICATION OF MECHANICAL ALLOYING AND MECHANOCHEMISTRYNEW 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

2. 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 principlesof chemical interactions and conversions in solids under mechanical influence.

3. Solid -Phase Systems Under Influence of HP+SD (Uniaxial Compression)

4. 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

5. 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

6. 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.

7. 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

8. 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

9. 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

10. 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 • The balls have the same diameter • 2-substrate, C- coated area • b)  The balls have different diameters • 2-substrate, C - coated area

11. Deposition of Metallic Coatings (Cr, Cu) on the Steel and Al specimensTwowaysof coatingdeposition • 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.

12. 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

13. STRUCTURE AND THICKNESS OF Cr-COATINGS DEPOSITED ON STEEL Cr Fig.6a Cross section of steel with Cr coating, The thickness of the coating can be attained to 100 m Steel 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. Fig.7. Cross section of steel with Cu coating deposited by electrochemical method. 60m

14. Fig.8 XRD Scheme and the Stresses in Cu on Al Coating M D impact Cu coating X-ray Tube p The formation of (Cu-Al alloy)transition layer te sp z Al substrate y x M –monochromator, D – detector, xyz is the coordinate system (the x-y planeis 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.

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

16. Improvement of the Mechanical Characteristics b) a) 0e 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

17. 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 Table 2, The comparative value of adhesion for Cr coating deposited by different methods Fig .11 Scheme of Adhesion Testing. 1 – cyl. substrate, 2 – coating layer 3 – stretching force

18. Material Microhardness HV50 [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 Table 3

19. 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 Coatings for Tribological Applications Mo-MoS2 and W-WS2 Lubricant layers 1. Mo+Al(subs)Mo on Al 2. Mo+2S = MoS2 1. W+Al(subs)W on Al 2. W+2S = WS2 Table 4

20. 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 ballcatering test r22 – r12 h = ------------ 2Rb r1 = 30 m ; r2=60 m; R=5mm ; h Mo 0.5m Fig 13 The porosity microstructure of MoS2 coating synthesized by MC method

21. 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 – Ican 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.

22. 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

23. Deposition of Amorphous Carbon and DLC Films E EG 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. ED D D Carbon Source G 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.

24. 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 peaks associated 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

25. 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

26. AFM Images and Microhardness of the DLC Films Deposited at 5min and 20 min of Mechanical Processing 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 Table 6; Microhardness of MC deposited DLC films Fig 20 (a), t= 5min Fig. 20 (b), t=20min

27. 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.

28. 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 Ttypesof 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 .

29. 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..