The paper presents the geometric structure of the surface, hardness and the results of tribological tests for TiO2 layers obtained by the ALD technique. The geometrical structure of the surface before and after the tribological tests was assessed using a confocal microscope with interferometry mode. An instrumental indentation was used to measure nanohardness. Model tribo tests were carried out for reciprocating motion under conditions of dry friction and friction lubricated with artificial saliva and saline. The tests showed that the TiO2 samples showed lower wear and higher hardness

Madej, M.

Piotrowska, K.

English

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665METALURGIJA 61 (2022) 3-4, 665-668K. PIOTROWSKA, M. MADEJINFLUENCE OF TIO2 COATING DEPOSITED WITH THE ATOMIC LAYER DEPOSITION ALD TECHNIQUE ON THE PROPERTIES  OF Ti13Nb13Zr TITANIUM ALLOYReceived – Primljeno: 2021-11-06 Accepted – Prihvaćeno: 2022-03-10Original Scientific Paper – Izvorni znanstveni radThe paper presents the geometric structure of the surface, hardness and the results of tribological tests for TiO2 lay-ers obtained by the ALD technique. The geometrical structure of the surface before and after the tribological tests was assessed using a confocal microscope with interferometry mode. An instrumental indentation was used to measure nanohardness. Model tribo tests were carried out for reciprocating motion under conditions of dry friction and friction lubricated with artificial saliva and saline. The tests showed that the TiO2 samples showed lower wear and higher hardness.Keywords: Ti13Nb13Zr, coating, ALD technique, surface texture, propertiesISSN 0543-5846METABK 61(3-4) 665-668 (2022)UDC – UDK 669.295.293.296:621.794:621.9.015.002.61=111INTRODUCTIONThe atomic layers deposition technique (ALD) is one of most promising technologies of surface treatment for engineering materials. This method is used for deposition of oxide coatings, e.g. Al2O3, TiO2, or ZrO2, as well as of metals - Cu, Co, Fe, Ni, and Ag and also of hydroxyapa-tatite [1-3]. Because of its unique properties, i.e. a high mechanical strength, high hardness, thermal and corro-sion resistance, and good dielectric and insulating prop-erties, the ALD coatings are applied in numerous branch-es of industry: chemical, aviation, electronics, and medi-cine [4-6]. The ALD technique consists in depositing ul-tra-thin layers, up to a few nanometres thick, in a strictly controlled process. The system utilises usually two gase-ous precursor reagents, which are sent to the chamber in an alternating sequence of precisely controlled impulses. Any excessive amount of unreacted precursors in the deposition chamber is blown through with an inert gas - nitrogen [1,7-8]. Solid, liquid or gaseous precursors pro-duce strong chemical bonds, which ensure perfect adhe-sion to the substrate. The temperature of ALD process is 25 - 500 °C and must be high enough to enable the reac-tion between precursors, but low enough to prevent the precursor damage. Gases are released very slowly, in a sequential or impulse mode, causing that a coat consist-ing of atomic monolayers is deposited on the substrate. The advantage of the method consists in a uniform thick-ness of the coating on all faces and openings of the ele-ment subjected to deposition, featuring even very com-plicated shapes, in the repeatability and high productivity of the process [9].K. Piotrowska, (kpiotrowskapsk@gmail.com), M. Madej, Kielce Uni-versity of Technology, Kielce, PolandMATERIALS AND METHODSTitanium and its alloys feature high biocompatibility and fatigue strength, the modulus of elasticity close to the modulus of a human bone, and a high resistance to dissolution in the environment of tissues and systemic fluids [10-12]. A titanium alloy Ti13Nb13Zr consisted of: C ≤ 0,08, H ≤ 0,015, O ≤ 0,016, N ≤ 0,05, Fe ≤ 0,25, Nb 12,5 - 14,0, Zr 12,5 - 14,0. The rest was titanium. The values are presented in wt. %. A TiO2 coating was depos-ited on it by means of the ALD technique to improve its mechanical, tribological, and practical properties.The TiO2 coating was deposited by means of the method of atomic layers deposition from a gaseous phase - ALD, using the Beneq system. Two precursors, Titanium Tetrachloride (TiCl4) and water (H2O), were used during the process, which were alternately intro-duced to the chamber. The process temperature was 150 °C, 1 000 cycles have been applied. The deposited TiO2 coating was 150 - 170 nm thick.A scratch test is the best method to study the adhe-sion of coat to the substrate. The test was carried out on an Anton Paar instrument. It consisted in making a scratch on the surface of the sample by means of a dia-mond sphero-conical indenter, at a load increasing lin-early from 0,03 to 5 mN, at a loading rate of 20 mN/min, and a scratch 3 mm long.The method of instrumental indentation is used to determine the hardness and elasticity of coatings. The hardness of the sample was measured using an Anton Paar hardness tester. An indenter with a Berkovich ge-ometry was used during the tests. The load of 0,05 mN and a pause of 1 s was applied.The tribological tests were carried out using an An-ton Paar nanotribometer. Tests were carried out in a re-666  METALURGIJA 61 (2022) 3-4, 665-668K. PIOTROWSKA et al.: INFLUENCE OF TIO2 COATING DEPOSITED WITH THE ATOMIC LAYER DEPOSITION…Figure 1  Scratch test results - graph of variation of loading force (Fn), coefficient of friction (µ), friction force (Ft)Figure 2  Scratch test results - penetration depth of the indenter (Pd)Table 1 The adhesion tests of Ti13Nb13Zr TiO2Lp. LC1 LC2 LC3 LC4 LC51 2,2 2,84 3,97 4,14 4,542 2,82 3,68 4,15 4,58 4,743 2,68 2,96 3,47 3,91 4,69mean 2,57 3,16 3,86 4,21 4,66std dev 0,32 0,45 0,35 0,34 0,1Figure 3  Load – penetration depth curves from indentation testsTable 2 Mechanical parameters Para-meterUnit SampleTi13Nb13Zr Ti13Nb13Zr TiO2mean std dev mean std devHIT GPa 2,75 0,08 4,46 0,45EIT GPa 89,06 5,93 95,02 5,45Wplast pJ 0,2 0,21 0,14 0,02Welast pJ 0,16 0,01 0,14 0,01Wtot pJ 0,36 0,01 0,28 0,02hm nm 20,56 0,47 16,19 0,63ciprocating motion under conditions of technically dry friction and friction in a Ringer solution environment. The applied loading force was 5 mN and the frequency was 1 Hz.RESULTS AND DISCUSSIONFigures 1-2 presents results of the scratch test. The critical force was assessed based on microscopic obser-vations and recorded changes in the friction force. Table Figure 4  Average friction coefficient obtained under dry friction (TDF) and with the use of Ringer’s solution (RS) as a lubricant.c)a)b)Figure 5  Optical and axonometric views of sample wear track (a, b) and the wear profile on transverse cross-section (c) after the dry sliding of Ti13Nb13Zr—Al2O3 friction pair.667K. PIOTROWSKA et al.: INFLUENCE OF TIO2 COATING DEPOSITED WITH THE ATOMIC LAYER DEPOSITION…METALURGIJA 61 (2022) 3-4, 665-6681 presents values of forces causing chipping of the de-posited coat.The scratch test of the TiO2 coating has shown that as a result of the applied loading the deposited layer was not entirely delaminated. Based on the graph of the fric-tion force (Ft), coefficient of friction (µ), indenter pen-etration (Pd) and microscopic analysis it was found that the coating was chipping only in places marked as LC Ft1—LC Ft5 / mN. At the moment of coating peeling characteristic increases in the value of acoustic force were appearing on the graphs, proving the coating dam-age. The damage to TiO2 layer had a nature of adhesion cracks, featuring local delamination on sides of the scratch trace.Figure 3 presents an example of indenter penetration curve for Ti13Nb13Zr and Ti13Nb13Zr TiO2 at a nomi-nal loading force of 0,05 mN. The maximum value of the loading force is marked on the y axis, for which the value of maximum indent hmax is determined (x axis). The most important mechan-ical parameters were determined based on the measure-ment of indenter penetration depth. Table 2 presents their averaged values obtained from 5 measurements.c)a)b)Figure 6  Optical and axonometric views of sample wear track (a, b) and the wear profile on transverse cross-section (c) after the RS-lubricated of Ti13Nb13Zr —Al2O3 friction pair.c)a)b)Figure 7  Optical and axonometric views of sample wear track (a ,b) and the wear profile on transverse cross-section (c) after the dry sliding of Ti13Nb13Zr TiO2—Al2O3 friction pair.The results of hardness tests presented in Table 2 confirmed the expected increase in mechanical param-eters as a result of coating deposition. In the case of in-strumental hardness an increase of approx. 40 % was recorded, and in the case of Young’s modulus of about 10 %. This is also reflected in the maximum depth of indenter penetration. It was 16,19 nm and was by ap-prox. 20 % smaller as compared with the value obtained for Ti13Nb13Zr titanium alloy.Figure 4 presents results of examples of coefficient of friction μ curves versus the number of cycles regis-tered during the interaction of tested rubbing pairs. Av-erage values of coefficient of friction calculated based on three series of measurements are marked on the graph.The results of tribological tests have shown that the obtained mean values of coefficients of friction were comparable for both studied materials, during the tech-nically dry friction and friction in a lubricating environ-ment as well.After tribological tests the samples were subjected to microscopic observations. An average maximum depth and an average surface area of sample wear on the 668  METALURGIJA 61 (2022) 3-4, 665-668K. PIOTROWSKA et al.: INFLUENCE OF TIO2 COATING DEPOSITED WITH THE ATOMIC LAYER DEPOSITION…c)a)b)Figure 8  Optical and axonometric views of sample wear track (a, b) and the wear profile on transverse cross-section (c) after the RS-lubricated sliding of Ti13Nb13Zr TiO2—Al2O3 friction pair.cross-section were determined based on five series of measurements. Figures 5-8 present the test results.The analysis of studies on the geometrical structure of the surface after tribological tests has shown that the Ti13Nb13Zr titanium alloy featured heavier wear as compared with Ti13Nb13Zr with a TiO2 coating. The rubbed out area of Ti13Nb13Zr on the cross-section was nearly twice larger under conditions of technically dry friction and 15 times larger under conditions of lubrica-tion with the Ringer solution as compared with Ti13N-b13Zr TiO2. It was also noticed that in both cases the ap-plication of a lubricant resulted in reduction of wear.CONCLUSIONThe results of frictional and wear tests have shown that both tested materials featured similar coefficients of friction. For the technically dry friction they amounted to approx. 0,86, and for the friction in the Ringer solution environment – 0,2. In addition, the application of a lubri-cant resulted in decreasing the resistance to motion by ap-prox. 75 %. The mechanical tests have shown that the suggested process of TiO2 coating formation as a result of atomic layers deposition had a favourable effect both for the hardness and Young’s modulus. The curves of load - indenter penetration depth have shown that the deposited layer features smaller elasticity as compared with the ref-erence sample. The analysis of geometrical structure of samples surfaces after tribological tests have shown that the reference sample was the most wearing out material in the frictional connection with a counter-sample of alu-minium (III) oxide. This effect was noticeable both during technically dry friction and friction in the Ringer solution environment. The obtained results of studies have shown that the application of a TiO2 coating results in the im-provement in both mechanical and tribological properties.REFERENCES[1] V. M. Dias, W. Chiappim, M.A. Fraga, H. S. Maciel, F.R. Marciano, R.S. Pessoa, Atomic Layer Deposition of TiO2 and Al2O3 Thin Films for the Electrochemical Study of Corrosion Protection in Aluminum Alloy Cans Used in Be-verage, Materials Research Express 7 (2020), 1–13.[2] H. Im, N.J. Wittenberg, N.C. Lindquist, S.H. Oh, Atomic Layer Deposition (ALD): A Versatile Technique for Pla-smonics and Nanobiotechnology, J Mater Res 27 (2012), 663–671.[3] M. Basiaga, W. Walke, D. 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Szewczenko, Structure and proper-ties of Al2O3 thin films deposited by ALD process, Vacu-um 131 (2016) 319-326.[9] L. A. Dobrzański, A. D. Dobrzańska-Dankiewicz, Obrób-ka powierzchni materiałów inżynierskich, Open Access Library 5 (2011), (online).[10] R. Dąbrowski, The microstructure and properties of Ti13Nb13Zr alloy for biomedical applications, Mechanika w medycynie (2014), 52-62.[11] K. Piotrowska, A. Granek, M. Madej, Assessment of Me-chanical and Tribological Properties of Diamond-Like Carbon Coatings on the Ti13Nb13Zr Alloy, Open Engine-ering 10 (2020), 536-545.[12] G. Gałuszka, M, Madej, D. Ozimina, J. Kasińska, R. Gałuszka, The characterisation of pure titanium for biome-dical applications, Metalurgija 56 (1-2) (2017), 191-194.Note:  The responsible for English language is: Małgorzata Dembińska Lingua Lab.

Influence of TiO2 coating deposited with the atomic layer deposition ALD technique on the properties of Ti13Nb13Zr titanium alloy

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