The Influence of the Diffusion on Adherence of the 60T Deposits Obtained through Thermal Spraying in Electric Arc

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1 Applied Mechanics and Materials Online: ISSN: , Vol. 371, pp doi: / Trans Tech Publications, Switzerland The Influence of the Diffusion on Adherence of the 60T Deposits Obtained through Thermal Spraying in Electric Arc TOMA Stefan Lucian 1,a, GHEORGHIU Diana Antonia 1,b, RADU Steluta 2,c and BEJINARIU Costica 1,d 1 Technical University Gh. Asachi, Fac Mat. Sci& Engineering Iasi, Bd. Dimitrie Mangeron no. 67, , Iasi, Romania 2 UnivAgrSci & Vet Med Ion Ionescu Brad, Fac. Agr. Iasi, Aleea Mihail Sadoveanu, no. 3, , Iasi, Romania a stl_toma@yahoo.com; b dagheorg@tuiasi.ro; c stelaradu2010@yahoo.com; d costica.bejinariu@yahoo.com. Keywords: thermal spraying, adherence, arc spraying process and coatings. Abstract. The physic-chemical and mechanical properties of steel deposits obtained by thermal spraying depend on technological parameters of the spraying process. Generally, wear resistance of the deposits depends on the degree of porosity and the adhesion of the layer to the substrate. In the case of the deposits obtained by spraying, studies have shown that between deposited layer (SD) and substrate (S) there are the following types of adhesions: mechanical, metallurgical, superficial, physical and diffusive. Each type of adherence, enumerated above, works through a well-defined mechanism so that it can be said that the adhesion of the obtained deposits by thermal spray is a sum of mechanisms which interacting. How these mechanisms interact, as well the percentage of the influence is determined by: operating parameters, by the deposit material and thermal treatments after the deposit obtaining. This paper proposes to determine the influence of thermal treatment on adherence of 60T deposits obtained by thermal spraying in electric arc- as a thermal processing method after metallization. The assessment of adherence deposit 60T, in conjunction with the investigations of electron microscopy (SEM), XRD analysis, and image analysis performed at both the zone: Coating - Interface - Substrate (CIS) has revealed the presence of diffusion and the structural constituents. The graphics of the adherence variation for 60T deposits with the concentration gradient experimentally obtained by investigations carried out on the substrate have demonstrated the role of the secondary thermal treatment on the adherence of the deposit. Introduction Developed as a reconstruction method of surfaces obtained by arc spraying process (ASP), it has the advantage of creating hard or soft layers, dense or porous - depending on the exploitation environment requirements. The deposit properties depend on the nature of input material, metallization procedure used, technological parameters and heat treatment applied after the coating [1,2].The experimental studies have shown that in the case of coatings obtained by spray deposition, between the deposited layer (SD) and the substrate (S) there are following types of adhesions: mechanics, metallurgical, superficial, physical and diffusive, [3,4]. Each type of adherence above, works through a well-defined mechanism so that it can be said that Fig. 1. The schematically structure of a coating adherence of coatings, obtained by thermal spraying deposition, is a sum of mechanisms that interact [5,6]. How these mechanisms interact as well as the influence percentage of each of them All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-10/05/16,19:53:47)

2 Applied Mechanics and Materials Vol are influenced by: the operating parameters, substrate material, and the subsequent thermal treatments metallization (or realization deposit), [7,8]. The purpose of this work is the diffusion realization of some chemical elements from the deposit in the substrate with the formation of new chemical compounds and the determining their influence on the coating adherence. Investigations, carried out on the system of protection obtained, were performed in the coating-interface-substrate (CIS) zone- see Fig. 1 Experimental Procedure Materials and Equipment. To observe how influence the diffusion of the elements, from the deposit in the substrate, on the steel coatings adherence; I realized deposits of alloyed filler material on cylindrical and flat samples - made of a low alloy material, [9]. Tests were performed on cylindrical samples (diameter 36x300 mm) and flat samples (40 x 40x 30mm), made of C15-DIN steel, with the following composition C-0.14, Mn 0.43, Cr-0.3, Ni-0.3, Si- 0.15, P- 0.04, S-0.04 (wt%). The specimens cylindrical were prepared by applying a metric screw thread with normal step of 1 mm and were chemically cleaned in order to eliminate the traces of oxides, dust and grease. Flat sample surface was blasted with shots (granulation silica 2-3mm) and then chemically cleaned with pure acetone, [10,12]. For spraying, a 60T metallization wire produced by Tafa, was used, with the following chemical composition C 0.3, Mn 0.1, Si 0.08, and Cr 14, balance Fe (wt.%), [13]. The wire was deposited on a 75B anchorage layer, with 93.2% Ni content, [13]. The cylinder samples were metallized through depositions of successive layers to avoid the tension issuing caused by exposure to high temperature, [14]. Arc Spraying Process Parameters. The experiments in this paper were done with the spray device Tafa 9935 with console, equipped with automatic advance mechanism wire, data acquisition system and gun. In table 1 there are presented the ASP parameters. Coatings Characterisation. The 60T layers, obtained by arc spraying were microscopically examined with stereomicroscope Optika SZM 2 made by Optika - Italy, for the purpose of excluding coatings containing defects. The structural characterization was performed with a scanning electron microscope (SEM), Vega Tescan LMH II model, made by Tescan Company, Czech Republic. The deposit porosity was calculated by image analysis on SEM micrographs using an IQ Materials image analysis software. Qualitative phase analysis was performed on an X-Ray diffractometer type X PERT PRO MRD produced by PANalytical Holland, which works in 2θ angle range from 0 0 to 90 0, and a High Score Plus software. The adherence of the obtained deposits was determined by two methods: - by tensile test of the coatings deposed on the frontal flat surface of the samples (the determination of tensile adherence strength R H ) in accordance with EN by shear test of the coatings deposed on the cylindrical surface of the samples (the determination of shear resistance τ ad ) in accordance with DIN 27201/2005. Results The metallizing tests by thermal spraying where subdued to a very attentive control macroscopic with a lentil having a power 10 x, to eliminate during the researching the tests with surface faults like a exfoliation. Table 1. Arc spray parameters Parameters Value Current, (A) 160 Voltage (V) 32 Compressed air flow, (Nm 3 h -1 ) 130 Rotational speed of the samples for cylindrical sample (rpm) 45 Motion speed of the gun, (m/s) 0,15 Spraying distance (mm) 150 Fig. 2. Thermal treatment diagram

3 272 Innovative Manufacturing Engineering After metallization the samples were subdued to a thermal treatment the diffusion see diagram Fig. 2, in an electrical furnace with induction heating. The thickness of the deposits obtained was determined by measurement using the accuracy of a micrometre as well as with the electronic microscope SEM according with SR EN 9920/. In the table no. II you will find the values of the thickness (g) of the layers attained. Microstructural analysis allowed the determination of porosity deposit by using the method of image analysis - see Table 2 as well as the method of alloying elements distribution on the samples section. From Fig. 3.a it can be seen that the 60T deposit has a high contain (concentration) of chromium and the anchor coating is high alloyed in nickel. The substrate has a low contain of chromium, manganese and nickel. The quantitative analysis of the chemical composition made in transversal section of the samples after diffusion - see Fig. 3.b as well as the X-ray difractographic analysis of samples subjected to diffusion treatment, demonstrates that the manganese and the chromium migrate into the substrate to form complex chemical compounds. No. samples Type of sample Table 2. g P [mm] [%] 6 cylindrical plate cylindrical plate cylindrical plate cylindrical plate Fig. 3. Scanning electron micrographs (secondary electrons) of the cross-section of the 60 T layer, obtained by ASP, in these conditions I=160A, p=6 bar: a) before the thermal diffusion; b) after the thermal diffusion, t = 30h The images in Fig. 4 are retrieved from the CIS area at mm from the interface deposit - substrate. It can be seen that manganese diffuses into the substrate after a holding time of over 10 hours. Compared with it, chromium diffuses into the substrate after a holding time greater than 30 h. The influence of the thermal treatment diffusion on steel coatings deposited by thermal spraying in electric arc is described by the voltage variation curves of shear (τ ad ) and by blood breaking through traction (R H ) experimentally obtained on cylindrical and flat samples for different diffusion times- Fig. 5 and Fig. 6. Fig. 4. XRD pattern of the cross section of the sample exposed in air at 900 C

4 Applied Mechanics and Materials Vol By analysing Fig. 5 and Fig. 6 it can be seen that the values of shear stress (τ ad ) and breaking tensions by traction (RH) significantly increase with increasing diffusion time. This is due to the fact that by the exposure to high temperature, T = 9000C, long time in the CIS chemical bonds formed by diffusion of Cr and Mn and the formation of new chemical compounds (Mn, Fe) 3 O 4, MnCr 2 O 4, Mn 2 O 3 and Cr 2 O 4, contribute to the increasing of τ ad and RH stress and thus of the coatings adherence. The adhesion of the coatings increases with diffusion time till when the region inside the substrate located in the CIS area becomes saturated in chemicals compounds based on Cr and Mn which will prevent the elements diffusion in the substrate volume (see Fig. 4, Fig.5 and Fig. 6 - PTR t 30h). The Analyse of the graphs 4, 5 and 6 demonstrates that the chemical compounds based on Cr are forming in a diffusion time greater comparing with the Fig. 5. Variation shears strength of the 60 T steel coatings with the chemical compounds based on thickness coatings. The abbreviation mean: CSBD cylindrical Mn. The adherence of coatings samples before diffusion and CSAD represent cylindrical sample after diffusion. increases significantly when in the substrate appear chemical compounds based on chrome. It can observe that the adherence of steel deposits decreases with the increasing of the deposit thickness. The aspect is due to the presence of pores in excess which, in the case of the increasing of deposit thickness may constitute breaking primers. It can be affirmed that these increases of tensions τ ad and R H with values above 12% - see Fig. 5 and Fig. 6, due to the phenomenon of diffusion Fig. 6. Variation tensile strength of the 60 T steel coatings with the represent the increasing of the thickness coatings. The abbreviation mean: FSBD flat samples before diffusion and FSAD - flat sample after diffusion. diffusive component of total adherence of the coating. Conclusions The experimental analysis of the influence of diffusion thermal treatment on adherence of steel deposits, obtained by thermal spray in electric arc, revealed the following conclusions: - by applying the thermal treatment diffusion to the coatings average alloyed with chromium and manganese, occurs in the substrate the diffusion alloying elements and the formation of new chemical compounds complexes (Mn, Fe) 3 O 4, MnCr 2 O 4, Mn 2 O 3 and Cr 2 O 4 ; -both the quantity of chemical compounds and the obtained values τ ad and RH stresses, are dependent on the time of thermal treatment - see Fig. 4, Fig. 5 and Fig.6;

5 274 Innovative Manufacturing Engineering -the diffusion thermal treatment significantly improves the adherence of the deposit and the stresses values τ ad and R H increasing by over 12%. A better adhesion of the 60T steel coating on the substrate, combined with a low degree of porosity, and a smaller size of the sprayed particles allows the obtaining of steel coatings with wear resistant and oxidation resistance at high-temperature. References [1] A.P. Newbery, P.S. Grant, J. Therm. Spray Technol. 18 (2009) 256. [2] D.E. Crawmer, in: J.R. Davis (Ed.), Handbook of Thermal Spray Technology, ASM International, 2004, p. 54. [3] E.R. Sampson, M.P. Zwetsloot, Arc spray process for the aircraft and stationary gas turbine industry J. Therm. Spray Technol. 6 (1997) 150. [4] L. Pawlowski, in: 2nd ed., The Science and Engineering of Thermal Spray Coatings, Ed. Wiley, Chichester, England, 2008; [5] St.L. Toma, The influence of jet gas temperature on the characteristics of steel coating obtained by wire arc spraying, Surf & Coat. Technol. 220 (2013) [6] Giovanni Bolelli, Luca Lusvarghi, Roberto Giovanardi, Surf. Coat. Technol. 202,(2008) [7] St.L. Toma, C. Bejinariu, R. Baciu, S. Radu, The effect of frontal nozzle geometry and gas pressure on the steel coating properties, obtained by wire arc spraying, Surf & Coat. Technol. 220 (2013) [8] G. La Barbera-Sosa, Y.Y. Santana, C. Villalobos-Gutiérrez, S. Cabello-Sequera, M.H. Staia, E.S. Puchi-Cabrera, Effect of spray dist. on the corrosion-fatigue behavior of a medium-carbon steel coated with a Colmonoy 88 alloy deposited. by HVOF thermal spray Surf. Coat. Technol. 205 (2010) [9] V.V. Sobolev, J.M. Guilemany, A.J. Martín, Flattening of composite powder particles during thermal spraying, Surf. Coat. Technol. 89 (1997) p [10] H. Kaβner, R. Vaβen, D. Stöver, Suspension plasma spraying of TiO 2 for the manufacture of photovoltaic cells Surf. Coat. Technol. 202 (June 15, 2008), p [11] L. Latka, A. Cattini, A ; L. Pawlowski, S Valette, B. Pateyron, JP. Lecompte, R. Kumar, A. Denoirjean, Thermal diffsi. and conduc. of yttria stabilized zirconia coat. obt. by suspension plasma spraying, Surface & Coatings Technology Vol 208, 2012, pag: [12] M. Agop, V.P.Paun, T. Dandu-Bibire, Chaos via fractality in gravitational systems dyn. a new approach (I), Int. Jour of bifurcation and chaos Vol 22, (2012), DOI: / S [13] Technical Data Buletin Praxair & Tafa, File T, (K10624), [14] St. Toma, Contribution Regarding the Steels Metallization Through Activated Thermal Spraying, PhD Thesis, Technical University Gheorghe Asachi from Iasi, Romania, 2009.

6 Innovative Manufacturing Engineering / The Influence of the Diffusion on Adherence of the 60T Deposits Obtained by Thermal Spraying in Electric Arc / DOI References [1] A.P. Newbery, P.S. Grant, J. Therm. Spray Technol. 18 (2009) /s y