ISSN 1062-8738, Bulletin of the Russian Academy of Sciences: Physics, 2016, Vol. 80, No. 9, pp. 1161–1164. © Allerton Press, Inc., 2016. Original Russian Text © A.V. Kostuchenko, S.V. Kannykin, S.B. Kuschev, V.A. Dybov, 2016, published in Izvestiya Rossiiskoi Akademii Nauk, Seriya Fizicheskaya, 2016, Vol. 80, No. 9, pp. 1275–1278.
Synthesis of Composite Calcium-Phosphate Coatings via Pulsed Photon Processing A. V. Kostuchenkoa, S. V. Kannykinb, S. B. Kuscheva, *, and V. A. Dybova aVoronezh
State Technical University, Voronezh, 394026 Russia Voronezh State University, Voronezh, 394018 Russia *e-mail:
[email protected]
b
Abstract⎯The phase composition and mechanical properties of coatings generated on a Ti surface via the ion sputtering of a hydroxyapatite (HA) target and a compound (hydroxyapatite and Ti) target with subsequent pulsed photon processing (PPP) with incoherent xenon lamp radiation are investigated. It is found for the first time that pulsed photon processing accelerates the crystallization of amorphous films of Ca–P–O–H and Ca–P–O–H–Ti compositions, during which tricalcium phosphate Ca3(PO4)2, titanium oxide TiO2 (rutile, anatas), and perovskite CaTiO3 are formed, depending on the radiation dose and the ratio between Ti and Ca phases (Ti/Ca) with hydroxyapatite structure. It is found that pulsed photon processing of initial amorphous coatings greatly increases their hardness (up to 10.9 GPa) and adhesion (up to 29.0 MPa). DOI: 10.3103/S1062873816090264
INTRODUCTION It is possible to produce medical implants with properties adaptive to operating conditions (strength and solubility) by synthesizing composite coatings on their surfaces. Coatings consist of phases insoluble in an organism’s medium (e.g., biocompatible metals and their oxides, crystalline hydroxyapatite (GA) Ca10(PO4)6(OH)2) and bioresorptive calcium phosphates (tricalcium phosphate (TCP) Ca3(PO4)2, and amorphous phases of hydroxyapatite). The first of these form insoluble matrices that ensure the required strength under long-term operation, while the second ones ensure coating bioactivity. One way of forming such compositions is to activate the solid-phase interaction between crystalline calcium phosphate (CP) and titanium. It is known that solid-phase interaction is activated at the interphase titanium–hydroxyapatite boundary upon thermal processing. As a result, simple (TiO2) [1] and complex (CaTiO3) oxides [2] are formed, the strength of volumetric bioceramic [3] is increased, and the adhesion of hydroxyapatite to Ti is improved. However, high temperatures and long periods of thermal processing greatly increase the strength of the metallic substrate. The second way of forming such compositions is to synthesize a coating of appropriate composition during growth. In [4], it was shown that we can obtain nanocrystalline composite coatings via the joint magnetron sputtering of ZrN and hydroxyapatite onto heated Ti substrates. If the coating is formed on the unheated substrates of compound titanium–hydroxyapatite targets [5, 6], and if two targets of hydroxyapatite and Ti are sputtered jointly [7], the coating’s structure is amorphous. This is why thermal annealing is necessary. As a result, the composite
coating is crystallized, and phases of hydroxyapatite, СаО and TiO2 [7], and CaTiO3 [6] are formed. A promising way of crystallizing coatings and activating solid-phase reactions at a substrate–coating boundary is photon processing. In [8, 9], it was shown that if hydroxyapatite coatings on the metallic substrates are processed with the KrF monochromatic radiation of an eximer laser, they recrystallize [9] and a developed surface with a column structure is formed [8]. Laser processing of hydroxyapatite coatings can result in the formation of tetracalcium phosphate and tricalcium phosphate [10]. At high efficiencies of coating crystallization, laser processing is not adaptable to treating large surfaces. One of the most promising ways of activating structural variations and solid-phase reactions is pulsed photon processing (PPP) with broadband light radiation at energy pulse durations of tenths of seconds up to ten seconds. This type of processing is effective for synthesizing silicides and oxides [11–13]. Our information on the structure and phase variations in calcium phosphate films caused by broadband light radiation is very poor. In [14], as a result of the prolonged (up to 100 h) processing of hydroxyapatite ceramic doped with titanium using low-power ultraviolet radiation (1 mW cm−2), activation of solid-phase reaction of Ti oxidation due to interaction between the oxygen of the OH– groups of hydroxyapatite was observed. At the same time, there are no works on investigating solid-phase processes in composite calcium-phosphate-coatings activated by quick photon processing. The aim of this work was to investigate patterns of structure formation and the mechanical properties of a heterostructure Ti-coating with Ca–О–Н–Ti composition after pulsed photon processing by incoherent light.
1161
1162
KOSTUCHENKO et al.
Table 1. Phase composition of heterostructures Ti-coating after pulsed photon processing Elemental composition of initial coatings, at % Crystalline phases in coatings Еk, J cm–2 Ca P O Ti Ti/Ca 22 15 63 0 0 170 Hydroxyapatite, α-tricalcium phosphate 16 6 68 10 0.6 280 Hydroxyapatite 13 5 69 13 1.0 280 Hydroxyapatite, CaTiO3, Ti6O 12 5 69 14 1.2 280 Hydroxyapatite, CaTiO3, TiO2 (rutile), Ti6O
EXPERIMENTAL Coatings of Ca–Р–О–Н–Ti composition 1.0– 1.5 μm thick were formed on unheated plates of polished Ti (VT1-0) and mono-Si by means of high-frequency magnetron spattering (HFMS) (gas, argon; operating pressure, Р = 10–1 Pa; specific power of the high-frequency discharge, ~60 W cm–2) of a compound target made of Ti and hydroxyapatite. The compound target allowed ud to synthesize a coating with Ti : Са atomic ratios of 0.6, 1.0, and 1.2. Coatings without Ti (composition Ca–Р–О–Н) were formed on unheated plates of polished titanium via ion-beam spattering (IBS, Ar, Р = 0.5 × 10−2 Pa) of a ceramic target made of hydroxyapatite1. Post-condensation processing of the heterostructure Ti-coating was performed using pulsed photons from xenon lamps (wavelength, 0.2–1.2 μm) in an Ar atmosphere at t = 1.5–2.6 s. The energy density of the light flux incident on a sample’s surface (Еr) ranged from 170 to 280 J cm−2. The elemental composition of each coating was estimated by means of local X-ray spectral analysis (JEOL JSM-6380LV). The phase composition of the heterostructure substrate coating was examined via X-ray diffractometry (ARL X’TRA Thermo Techno D2 Ti Ca10(PO4)6(OH)2 α-Ca3(PO4)2 TiO2(p) * CaTiO3 Ti6O
Intensity 350 300 *
250 200
*
150 100 50 0 20
30
40
4 3 2 1 50 2Θ, deg
X-ray diffractograms of the (1) initial and post–pulsed photon processing (Еr = 280 J cm−2) heterostructure Ticoating of Ca–Р–О–Н–Ti composition with Ti : Ca of (2) 0.6; (3) 1.0; and (4) 1.2.
Phaser, Bruker). The elastic–plastic properties of the coating were examined by means of measurement nanoindenting (Nano Hardness Tester, CSM Instruments) using a Berkovich diamond indenter. The maximum loading was selected by assuming that the indenter penetrated no deeper than 20% of the depth of the examined coating. The Meyer hardness of the samples’ near-surface layers was determined according to Oliver and Pharr [15], and was calculated as the mean value for a series of measurements (not less than 5). The coatings’ adhesion to titanium was measured by shift testing (RPM-10MG4 test unit) according to [16]. The surface morphology obtained as a result of coating failure was examined via atomic force microscopy (Solver 47 unit). RESULTS AND DISCUSSION X-ray diffractometry revealed that independent of composition, the initial coatings on Ti were characterized by amorphous structures. The pulse photon processing of our heterostructure Ti-coating at Еr < 170 J cm−2 did not result in appreciable structural variations. Table 1 presents information on the phase composition for coatings on Ti after pulse photon processing. At Еr ≥ 170 J cm−2 (t = 1.5 s) the pulse photon processing of our heterostructure Ti-coating of Ca–Р–О–Н composition led to the formation of crystalline phases of hydroxyapatite and α-tricalcium phosphate. This finding agrees with the information presented in [17], where the structural transformation of a hydroxyapatite lattice into a tricalcium phosphate lattice was observed in the near-surface layer of a hydroxyapatite ceramic enriched with phosphor during its diffusion to the free surface upon high-temperature annealing (1050°C; t = 1 h) in a vacuum. As can be seen from Table 1, as a result of the pulsed photon processing of our heterostructure Ticoating of Ca–Р–О–Н composition at Еr = 280 J cm−2, crystalline phases of hydroxyapatite, CaTiO3, TiO2 (rutile), and Ti6O with a hexagonal lattice were formed. We analyzed the peak intensities in the X-ray diffractograms and found that if the Ti : Ca ratio is increased, the share of crystalline phase of perovskite CaTiO3 grows and rutile TiO2 is formed (see figure). To understand which phase formed at the boundary of the titanium coating as a result of pulse photon processing, we performed a phase analysis of a hetero-
BULLETIN OF THE RUSSIAN ACADEMY OF SCIENCES: PHYSICS
Vol. 80
No. 9
2016
SYNTHESIS OF COMPOSITE CALCIUM-PHOSPHATE COATINGS
1163
Table 2. Phase composition of heterostructures Si–SiO2 coating of Ca–Р–О–Н–Ti composition after pulse photon processing Ti/Ca in the coating
0.6
1.0
1.2
Еr, J cm−2
Crystalline phases in the coatings
170
Hydroxyapatite
210
Hydroxyapatite, α-tricalcium phosphate
240
Hydroxyapatite, α-tricalcium phosphate, TiO2(rutile)
170
No
210
Hydroxyapatite, α-tricalcium phosphate, CaTiO3, TiO2(rutile), TiO2(anatase)
240
Hydroxyapatite, α-tricalcium phosphate, CaTiO3, TiO2(anatase)
170
No
210
TiO2(rutile), α-tricalcium phosphate, hydroxyapatite, CaTiO3
240
TiO2(rutile), TiO2(anatase), hydroxyapatite, CaTiO3
structure Si–SiO2–coating of Ca–Р–О–Н–Ti composition after pulse photon processing (Table 2). The minimum Еr at which we see substantial structural transformations in the coatings of Ca–Р–О–Н–Ti rises if the Ti : Ca ratio is increased: at Ti : Ca = 0.6, crystalline phases form when Еr = 170 J cm−2; at Ti : Ca = 1.0 and 1.2, they form when Еr = 210 J cm−2. Let us compare the phase composition of a coating on Ti and one on oxidated silicon after pulse photon processing. We find that Ti6O formation is a result of solid-phase interaction at the boundary of a titanium substrate coating of Ca–Р–О–Н–Ti composition. We investigated the mechanical properties of Ti coatings via nanoindenting and found that independent of a coating’s composition, pulsed photon processing greatly increases its hardness (Table 3). From Table 3, it is seen that the hardness of the coating after pulsed photon processing depends on the Ti : Ca ratio: the higher it is, the greater the hardness. This could be due to internal stresses growing weaker in the coating, since the proportions of titanium oxides and the perovskite increase inside it. Atomic force microscopy revealed that as a result of shift tests, the heterostructure of our Ti-amorphous coating failed over the coating volume (cohesion mechanism). The value of adhesion R of our amorphous coating was in this case no higher than 2.5 MPa (Table 3). Pulsed photon processing greatly improves adhesion (up to 29.0 MPa). This could be due to coating crystallization (improved strength of cohesion) or the emergence of chemical bonds at the interphase boundary as a result of solid-phase reactions (improved strength of adhesion). CONCLUSIONS It was found for the first time that pulsed photon processing with incoherent radiation from xenon
Table 3. Mechanical properties of heterostructures titanium-coating after pulse photon processing Ti/Ca Е , J cm−2 in the coating r
Mechanical properties of the coatings Н, GPa
R, MPa
No
4.4
2.5
170
7.2
14.0
No
4.9
2.1
280
9.1
14.9
No
5.4
1.0
280
10.6
29.0
No
3.2
1.6
280
10.9
14.8
0.0
0.6
1.0
1.2
lamps accelerates the crystallization of amorphous films of Ca, P, O, H, Ti composition, during which tricalcium phosphate Ca3(PO4)2, titanium oxide TiO2 (rutile, anatas), and perovskite CaTiO3 are formed, depending on the radiation dose and the ratio between the Ti and Ca phases (Ti : Ca) with hydroxyapatite structure. It was established that pulsed photon processing of initial amorphous coatings greatly improves their hardness (up to 10.9 GPa) and adhesion (up to 29.0 MPa). ACKNOWLEDGMENTS This work was supported by the RF Ministry of Education and Science, project no. 523; and by the Russian Foundation for Basic Research, project no. 15-03-09186.
BULLETIN OF THE RUSSIAN ACADEMY OF SCIENCES: PHYSICS
Vol. 80
No. 9
2016
1164
KOSTUCHENKO et al.
REFERENCES 1. Ozeki, K., Aoki, H., and Masuzawa, T., Biomed. Mater. Eng., 2011, vol. 21, no. 3, p. 179. 2. Gross, K.A., Gross, V., and Berndt, C.C., J. Am. Ceram. Soc., 1998, vol. 81, p. 106. 3. Shishkovsky, I.V., Zhuravel’, L.V., Petrov, A.L., and Tarasova, E.Yu., Tech. Phys. Lett., 2001, vol. 27, no. 3, p. 211. 4. Nathanael, A.J., Lee, J.H., and Hong, S.I., World J. Eng., 2010, vol. 3, p. 849. 5. Desai, A.Y., Fabrication and characterization of titanium-doped hydroxyapatite thin films, Ph.M.Dissertation, Cambridge Univ., 2007. 6. Proc. 11th Asia Pacific Industrial Engineering & Management Systems Conf. (APIEMS 2010), Melaka, p. 556. 7. Lee, B.-H. and Koshizaki, N., Nanotecnology, 2008, vol. 19, no. 41, p. 5303. 8. Teixeira, S., Monteiro, F.J., Ferraz, M.P., Vilar, R., and Eugenio, S., J. Biomed. Mater. Res. A, 2007, vol. 81, no. 4, p. 920. 9. Queiroz, A.C., Santos, J.D., Vilar, R., et al., J. Biomater., 2004, vol. 25, p. 4607.
10. Dyshlovenko, S., Pawlowski, L., Smurov, I., and Veiko, V., J. Surf. Coat. Technol., 2006, vol. 201, p. 2248. 11. Ievlev, V.M., Kushev, S.B., and Soldatenko, S.A., Funct. Mater., 1999, vol. 6, no. 5, p. 920. 12. Ievlev, V.M., Kushchev, S.B., Soldatenko, S.A., and Gorozhankin, Yu.V., Inorg. Mater., 2008, vol. 44, no. 7, p. 705. 13. Ievlev, V.M., Kannykin, S.V., Kushchev, S.B., et al., Fiz. Khim. Obrab. Mater., 2011, no. 4, p. 18. 14. Wakamura, M., Fujitsu Sci. Tech. J., 2005, vol. 41, no. 2, p. 181. 15. Oliver, W. and Pharr, G., J. Mater. Res., 1992, vol. 7, no. 6, p. 1564. 16. GOST R (Russian State Standard) 52641-2006: Implants for Surgery, Moscow: Standartinform, 2007, p. 10. 17. Nakano, T., Kaibara, K., Umakoshi, Y., et al., Mater. Trans., 2002, vol. 43, no. 12, p. 3105.
BULLETIN OF THE RUSSIAN ACADEMY OF SCIENCES: PHYSICS
Translated by Yu.V. Zikeeva
Vol. 80
No. 9
2016
