Pulsed laser modification of plasma-sprayed coatings: Experimental processing of hydroxyapatite and numerical simulation

Surface & Coatings Technology 201 (2006) 2248 – 2255 www.elsevier.com/locate/surfcoat

Pulsed laser modification of plasma-sprayed coatings: Experimental processing of hydroxyapatite and numerical simulation S. Dyshlovenko a , L. Pawlowski a,⁎, I. Smurov b , V. Veiko c a

c

Service of Thermal Spraying at Ecole Nationale Supérieure de Chimie de Lille, BP 90108, F-59652 Villeneuve d'Ascq, France b Ecole Nationale d'Ingénieurs de Saint Etienne, 58, rue J. Parot, F-42023 Saint Etienne, France St.-Petersburg State University of Information Technologies, Mechanics and Optics, 14, Sablinskaya, str., 197101 St. Petersburg, Russia Received 13 October 2005; accepted in revised form 23 March 2006 Available online 19 May 2006

Abstract A pulsed CO2 laser was used to treat plasma-sprayed hydroxyapatite coatings. Pulses of 0.74 ms duration and powers equal to 41.6 and 45.3 W were focused onto a 300 μm spot of the coatings surface. The laser beam was scanned with speeds of 6.4 and 9.6 mm/s. The morphology of lasertreated deposits was observed by scanning electron microscopy (SEM) and the crystal phases identified using X-ray diffraction (XRD). This technique enabled also the determination of quantitative phase composition. The laser treatment process was modeled using the Fusion-2D, software and the temperature fields and depth of molten material were predicted. The latter were compared with the experimental ones found in metallographically prepared cross-sections. A reasonable convergence between the model and experiment was achieved after careful optimisation of initial material parameters as such coefficient of optical absorption and emissivity. © 2006 Elsevier B.V. All rights reserved. Keywords: Hydroxyapatite; Laser treatment of coatings; Numerical simulation; Plasma-sprayed coatings

1. Introduction Hydroxyapatite (HA, having the chemical formula Ca10 (PO4)6(OH)2) is a bioactive ceramics which owing to chemical composition and crystal structure similar to those of human bone can facilitate integration of prostheses into osseous tissue [1–3]. This ceramics has been used to restore bone tissue and to decrease the negative consequence of surgical operation for many years. Because of its limited mechanical strength, HA is used as coating on surfaces of more resistant metallic prostheses made of, e.g., Ti-6Al-4V alloy [4]. The environment rich of calcium and phosphate at the surface of a prosthesis favors development of bone cells and enhance its adhesion to the bone [1]. Atmospheric Plasma Spraying (APS) is the most widely applied method to deposit HA coating onto titanium alloy prostheses. The method consists of injection of ceramic particles into a high temperature (N 10 000 K) and high velocity ⁎ Corresponding author. Tel./fax: +33 320 33 61 65. E-mail address: [email protected] (L. Pawlowski). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.03.034

Table 1 Runs of laser treatment experiments for samples plasma sprayed using 11 or 24 of electric power, with a working gas Ar + H2 of total flow rate of 50 slpm (volume fraction of Ar was 95% or 97.5%) and carrier gas flow rate of 3 or 3.5 slpm Plasma spray samples abbreviations

Sub11973 Sub11953 Sub24973 Sub24953 Sub119735 Sub119535 Sub249735 Sub249535

Laser power density of 5.9 × 108 W/m2

Laser power density of 6.4 × 108 W/m2

Scan speed

Scan speed

6.4 mm/s

9.6 mm/s

6.4 mm/s

9.6 mm/s

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

17 18 19 20 21 22 23 24

25 26 27 28 29 30 31 32

An example of abbreviation of a sprayed sample: Sub24973 means that powder was sprayed onto substrate, using 24 kW of electric power with 97.5 vol.% of Ar in plasma forming gas and 3 slpm of carrier gas.

S. Dyshlovenko et al. / Surface & Coatings Technology 201 (2006) 2248–2255 Table 2 Laser treatment parameters Parameter

Value

Pulse duration, s Pulse rate, Hz Laser spot dimension, μm Scanning velocity, mm/s Average power, W Pulse power, W Density of the power, W/m2 Overlap the spots, %

7.4 × 10− 4 47 300 6.4 or 9.6 1.47 or 1.6 41.56 or 45.34 5.9 × 108 or 6.4 × 108 32 or 50

(N800 m/s) plasma jet [5]. The high temperature provokes dehydration and decomposition of HA. The dehydration produces oxyapatite (OA, Ca10(PO4)6O) and/or oxyhydroxyapatite (OHA, Ca10(PO4)6(OH)2−xOxVx), in which V means vacancy. The decomposition, in turn, results in different calcium phosphate phases such as, e.g., calcium oxide (CaO), α-tricalcium phosphate (α-TCP, α-Ca3(PO4)2), β-tricalcium phosphate (βTCP, β-Ca3(PO4)2), tetracalcium phosphate (TTCP, Ca4P2O9) and/or the amorphous calcium phosphate (ACP). A spray particle impacting a surface, at plasma spraying using typical processing parameters, is composed of a solid core and liquid shell [6]. Fast cooling of crystal phases in the solid core at impact results in conservation of high temperature phases. The liquid shell is most probably transformed at impact into an amorphous phase. The fractions of HA, OA-OHA, TTCP, α-TCP and ACP phases in sprayed coatings is the most important factor that determines their biological behaviour, such as dissolution of the coating in vivo [7]. Careful control of operational spray parameters may help in predicting the phase content in the coating [8]. On the other hand, post-spray treatment of the coating can modify the phase composition. The treatment can help in transforming amorphous phase ACP back into crystalline HA [9]. This renders possible optimization of plasma spray operational parameters in the way in which most of sprayed powder particles are molten. Consequently, the mechanical integrity of the sprayed coating and its adhesion to substrate would be improved. The physical background of the treatment is based on the observation that atoms and ions of APC are returned easily to the positions corresponding to stable crystalline forms under the action of external factors [10]. Thermal post-spray treatment and, in particular, laser treatment has been tested to allow the recrystallization of the amorphous phase [11–14]. In contrast to annealing, a laser beam does not heat the subjacent substrate. Moreover, it is an efficient and quick technology that allows treatment of selected zones with high spatial resolution. The optimised treatment allows obtaining the desired fraction of amorphous phase and modification of phase composition [9,15]. The phenomena occuring in ceramics such as HA under action of laser irradiation can be categorized as a function of the laser power density as follows [16]: • During laser treatment with low power density (b108 W/m2) phase transformations are likely to take place but material remains solid [9,15]. Treatment under these conditions hardly modifies the coatings surface. It does produce neither

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pores nor fissures at the treated surface. The crystallinity of the irradiated zone increases. These modifications are similar to those produced by furnace annealing [17]. The recrystallization of the amorphous phase takes place at temperatures between 1170 and 1400 K and is accompanied by the formation of TTCP phase and an increase of HA phase [9]. At a temperature above 1400 K, the fractions of the HA phase and of the amorphous calcium phosphate both decrease leading to the formation of TCP and TTCP phases. The following reactions are then likely to occur: Ca10 ðPO4 Þ6 ðOHÞ2 →2Ca3 ðPO4 Þ2 þ Ca4 P2 O9 þ H2 O

ð1Þ

Ca10 ðPO4 Þ6 ðOHÞ2−2x Ox Vx →2Ca3 ðPO4 Þ2 þ Ca4 P2 O9 þ ð1−xÞH2 O

ð2Þ

Ca10 ðPO4 Þ6 O→2Ca3 ðPO4 Þ2 þ Ca4 P2 O9

ð3Þ

On the other hand, recrystallization of the amorphous phase leading to the formation of TCP and TTCP can also occur. • During laser treatment with the power density higher than 108 W/m2 fusion of the coatings surface occurs. This process is called often laser glazing [4]. The surface gets smoother but many cracks will be generated that will weaken the mechanical integrity of the coatings. The cracking results from temperature gradients and residual thermal stresses generated by the laser treatment. Treated ceramics will become denser [18]. Another characteristic phenomenon of this type of treatment is a release of entrapped gases escaping before final solidification and forming of holes in the coating surface [5]. The thickness of the molten layer depends strongly on the energy and the spot size of the laser beam. This type of treatment is realized in the present study by using a pulsed CO2 laser with different power densities. This study examines the effect of laser power density on phase composition and microstructure laser modified coatings. The numerical code Fusion-2D, described elsewhere [19,20], was applied to estimate the depth of molten zone in plasma-

Laser treated surface

As sprayed surface

100 µm

Fig. 1. SEM (secondary electrons) micrograph of separated laser spots obtained at laser power density of 6.4 × 108 W/m2.

2250

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Table 3 Thermophysical data of HA used in modeling Properties

Value HA dense

Melting point Boiling point Latent heat of melting Latent heat of evaporation Density/molar mass Heat capacity Average for solid Average for liquid Heat conductivity Average for solid Average for liquid

Unit

Reference

HA porous 5%

10%

15%

1843 3500 4.87 × 107 1.44 × 109 2.95 × 1027

– – 4.63 × 107 1.37 × 109 2.8 × 1027

– – 4.16 × 107 1.23 × 109 2.52 × 1027

– – 3.54 × 107 1.05 × 109 2.14 × 1027

K K J/m3 J/m3 m− 3

[28] [6] [29,30] [6] [6]

3.34 × 106 4.25 × 106

3.17 × 106 4.04 × 106

2.85 × 106 3.64 × 106

2.42 × 106 3.09 × 106

J/m3 K J/m3 K

[6]

1.867 2.259

1.866 2.257

1.865 2.256

1.863 2.254

W/m K W/m K

[6]

sprayed HA coating. The present paper is a continuation of the study initiated by Cheang et al. [13] by taking into account the crystal phases present in the coatings and a physical understanding of the laser treatment process. • During laser treatment with laser power density higher than 1010 W/m2 evaporation of the ceramics starts. This type of treatment can be applied to modify the morphology of the surface.

by the application of different substrates. The substrates were blasted prior to processing using alumina grit with size in the range +125–250 μm. The powder was pure HA prepared by spray drying and commercialized by Tomita. XRD analysis of the powder only the HA phase. The powder has a mean diameter of d50% = 120 μm and the internal porosity of powder particles is of about 12% [21]. Sprayed coatings had thickness of about 400 μm.

2. Materials and experimental methods

2.2. Laser treatment of sprayed coatings

2.1. Plasma spraying of HA powder

The plasma-sprayed samples were heat-treated with a CO2 laser. The laser used in this study was a single-mode one, working with the TEM00 mode at 10.6 μm wavelength. The principal laser parameters are collected in Table 2. A He–Ne laser helped in aligning the CO2 laser beam. The ZnSe lens focused the beam in a spot of about 300 μm size (Fig. 1). Laser power densities of q = 5.9 × 108 and 6.4 × 108 W/m2 were used in the experiments. A scanning system allowed the laser spot to move across the coating surfaces with linear speeds of v = 6.4 and 9.6 mm/s. For each laser power density two different scan speeds were applied. In total, 32 experiments of laser treatment were realized (Table 1).

Plasma spraying was carried out using a Praxair installation including a SG100 torch with anode type P/N 2083-730 equipped with internal powder injector, cathode type 01083A, manual console type 3710 and powder feeder type 1264. The internal injection of powder was used throughout the experiments. Principal plasma spray parameters were designed in a two level experimental plan, described in details elsewhere [8] and are collected in Table 1 together with laser treatment data. The spray distance was 10 cm and powder feed rate was about 17 g/min. The as-sprayed sample abbreviations, shown in Table 1, include electric power (in kW), fraction of argon in plasma gas (in vol.%), and carrier gas flow rate (in slpm). The spraying was carried out onto aluminum or stainless steel plates with dimensions 15 × 15 × 3 mm. Although titanium alloy Ti-6Al-4V is used typically for prostheses, the coating property tested in the present paper, i.e. phase composition, should not be affected Table 4 Coefficient of optical absorption of HA used in modeling Type of material

Value, 10− 4m− 1

Reference

Hydroxyapatite HA coating HA coating HA coating Enamel composed of HA + 12 wt.% water + 3 wt.% protein and lipids

8.25 10 1.00 ± 0.25 2.01 ± 0.16 8.02

[31] [32] [33] [34] [35,36]

200 µm Fig. 2. Optical micrographs of the sample treated with laser in run 21 (right) and sketch of laser spots used in the treatment (left). The spots' overlapping was equal to 36%.

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3. Modeling Modeling was performed using a numerical code Fusion-2D, described in detail and recently applied to predict the temperature fields in different samples submitted to a continuous wave and pulsed CO2 laser [19,20]. Here, the code was adapted to model pulsed CO2 laser interaction with HA coatings made by APS in order to simulate the experiments described above.

20 µm Fig. 3. Optical micrograph of the surface of the sample treated with laser in run 27.

2.3. Methods of powder and coatings characterizations XRD diagrams were collected with a Guinier Huber 670 imaging camera plate (Ge monochromator, Cu Kα1 radiation of λ = 0.154056 nm). The stepwise 2Θ angle increase was set to 0.005° and step time to 1 s. This resulted in a scan rate of about 0.3°/min. The samples were prepared following the recommendations of French norms [22], i.e. firstly, coatings were detached from the substrate and later, crushed prior to the diffraction experiments. Phase identification was realized by EVA code by superposing experimental X-ray diagrams with those of the data base of International Centre for Diffraction Data. Crystalline phases were identified by the following cards of the data base: • • • •

α-tricalcium phosphate (α-TCP), JCPDS no. 70-0364; tetracalcium phosphate (TTCP), JCPDS no. 70-1379; calcium oxide (CaO), JCPDS no. 75-0264; hydroxyapatite (HA), JCPDS no. 73-1731.

Quantification of the phases was realized by refining the diffraction profiles using PowderCell code [23]. The experimental diagrams were compared with the theoretical ones generated using the data base of Inorganic Crystal Structure Database (ICSD). The structures of following phases from the database were helpful in the generation of theoretical profiles: • • • •

α-TCP, [24]; TTCP, [25]; CaO, [26]; HA, [27].

The shapes of the theoretically generated peaks were modeled using a pseudo-Voigt function. For each diagram, polynomial function with order 8 was applied to modeling of the ground noise. Besides the 8 parameters of the ground noise, scale factor, zero point correction and cell parameters were refined. The effect of micro stresses was not considered. Microscopic observations with a scanning electron microscope JEOL type JSM-5300 and optical microscope Nikon equipped with an electronic camera were made on laser-treated coatings surfaces and cross-sections. The cross-sections were prepared metallographically.

3.1. Optical and thermophysical data The thermophysical data of HA used in numerical simulations are presented in Table 3 and the coefficient of optical absorption is shown in Table 4. This coefficient varies in different bibliographical sources from α = 104 to 105 1/m. Because of different spray conditions resulting in different porosities of HA coatings as well as diverging optical properties, the modeling of laser treatment was made by assuming the data in following ranges: • Porosity from 0% to 15%; • Coefficient of optical absorption α = 2.1 to 8 × 104 m− 1; • Emissivity ε = 0.5 to 1. 4. Results 4.1. Experiments Laser treatment was performed by overlapping of spots ranging from 36% to 50% (Fig. 2). Cracks formation can be observed on treated surfaces. Moreover, some pores on the lasertreated surfaces are probably due to the release of entrapped gases escaping before the melt solidifies [5]. The cracks are likely to be formed as a result of the large temperature gradients and the residual thermal stresses that develop after the laser passes over the surface. A close investigation of melted and solidified surfaces exhibits dendritically shaped crystals (Fig. 3). The crystals crystallized from a laser-generated melt composed initially of amorphous calcium phosphate, HA, and decomposition phases (TCP, TTCP and CaO). The phases were identified using XRD Table 5 Results of quantitative phase analysis related to the entire volume of coatings Plasma spray samples' abbreviations

Phase composition of as-sprayed samples, vol.%

Phase composition of samples laser treated with different power density, vol.% q = 5.9 × 108 W/m2

Sub11973 Sub11953 Sub119735 Sub119535 Sub24973 Sub24953 Sub249735 Sub249535 a

q = 6.4 × 108 W/m2

HA

αTCP

TTCP

HA

αTCP

TTCP

HA

αTCP

TTCP

73 70 74 73 69 65 63 64

19 12 9 10 11 15 11 8

8 18 17 17 20 20 26 26

60 63 53 56 59 56 60 40

13 19 19 16 17 14 13 14

27 18 28 28 24 30 27 44

56 58 47 52 43 43 59 37

16 9 22 24 20 21 17 16

28 33 31 24 37 36 24 45

a All samples of Sub249535 as-sprayed and laser treated in different conditions contain 2% CaO.

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Superficial laser melted zone

Underlying as-sprayed layer

20 µm µm 20 Fig. 4. Optical micrograph of the cross-section of the sample treated with laser in run 25.

analysis. In the analysis should be taken into account that coatings were detached from the substrate and crushed prior to X-ray determination. Consequently, the modifications introduced to the phase composition by laser treatment are related to the entire volume of the coating and not to the laser-treated zone. The XRD of as-sprayed coatings for all used processing parameters is analyzed in detail in previous paper coming from the research group [8]. Table 5 presents the results of quantitative phase analysis for the samples sprayed on the substrate using different spray parameters, and later on, treated by laser with power densities of q = 5.9 × 108 W/m2 and 6.4 × 108 W/m2. A typical cross-section of laser-treated sample is shown in Fig. 4. The laser molten zone can be easily observed. In general, the depth of the molten layer depends on the laser pulse energy, the laser spot size, the scan speed and the degree of overlapping of the laser spots. In the present case, the time interval between laser shots is so long that the laser induced melt can solidify and cool down before the next shot arrives. Consequently, in the present processing conditions, the spots overlapping and scan speed do not influence depth of the molten zone. The latter depends only on laser pulse power and laser spot size, i.e., the laser power density. These depths are shown in Table 6. Their fluctuation for different samples treated with the same laser power density could have resulted from variation in porosity of sprayed coatings. 4.2. Modeling The simulation of laser heating of material with Fusion-2D code allows determining temperatures and phases (solid, liquid, and vapor) fields in 2D. The runs of the code were made by using Table 6 Microscopically determined depths of laser melted zones Plasma spray samples' abbreviations

Laser power density 5.9 × 108 W/m2 (μm)

6.4 × 108 W/m2 (μm)

Sub11973 Sub11953 Sub119735 Sub119535 Sub24973 Sub24953 Sub249735 Sub249535

22 28 29 30 25 23 26 30

36 35 39 30 33 32 37 33

different values of porosity of coatings, optical absorption coefficients and emissivities. The simulated process parameters correspond to those shown in Table 1. The results of all simulations are presented in Fig. 5. The calculated depths of molten zone were compared with the data found experimentally at the coatings cross-sections. As the cross-sections did not reveal any trace of evaporation, all simulations revealing evaporation (Fig. 5c, d, e, and f) which corresponds to absorption coefficient of α = 5 and 8 × 104 1/m were thought to be unrealistic due to the overestimated optical absorption. Moreover, the calculated depths of the molten zone were greater than those observed experimentally. Better convergence was reached with optical absorption coefficient equal to α = 2.1 × 104 1/m. The zones of convergence of experimentally found and simulated depths are inside the rectangles of the Fig. 5a and b. These zones allow also an estimation of coatings emissivity values to be in the range ε = 0.85–1. 5. Discussion The powder used for plasma spraying was composed of pure HA. The plasma-sprayed coatings contained between 63 and 75 vol.% of HA (Table 5). The coatings are relatively porous (Figs. 1 and 3). An increase of electric power input to the plasma torch produces more decomposition phases and less HA. It must be noticed that the XRD analysis does not take into account the formation of amorphous calcium phosphate. This phase is known to be present in the coatings and its formation is discussed elsewhere [8]. The laser treatment associated with melting of the coatings results in smoothing of the surface (Fig. 2) and in a further increase of HA decomposition and in the formation of αTCP and TTCP phases with dendritic structure (Figs. 3 and 5). The decomposition is more pronounced for higher laser power densities (Table 5). The increase of α-TCP and TTCP fraction in the coating volume can be explained using the equilibrium phase diagram. The diagram predicts namely the solidification of αTCP and TTCP from a melt with a composition corresponding to stoichiometric hydroxyapatite. Another effect that can be explained with the diagram is an increase of fraction of TTCP in laser-treated samples (see Table 5). In fact, as P2O5 is an oxide less refractory than CaO, its selective evaporation from the lasergenerated melt is probable. Consequently, at high temperature of the melt associated with laser power density would render its

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Fig. 5. Temperature on treated surface (left side) and depth of molten zone (right side) at the end of laser pulse vs. emissivity for different porosities of coatings calculated for: (a) laser power density q = 5.9 × 108 W/m2 and absorption coefficient α = 2.1 × 104 1/m; (b) laser power density q = 6.4 × 108 W/m2 and absorption coefficient α = 2.1 × 104 1/m; (c) laser power density q = 5.9 × 108 W/m2 and absorption coefficient α = 5 × 104 1/m; (d) laser power density q = 6.4×108 W/m2 and absorption coefficient α = 5 × 104 1/m; (e) laser power density q = 5.9 × 108 W/m2 and absorption coefficient α = 8 × 104 1/m; and (f) laser power density q = 6.4 × 108 W/ m2 and absorption coefficient α = 8 × 104 1/m. The zones of convergence of numerical simulations with experiments are inside the rectangles of depths of molten zone vs. emissivity curves. Symbol “ev” corresponds to evaporation and the figure at the symbol corresponds to the evaporation depth.

composition richer in CaO than that of stoichiometric HA. That is why the formation of TTCP, corresponding to the rich in CaO composition of 4CaO·P2O5 on melt solidification is more probable than that of α-TCP, which corresponds to poorer in CaO composition of 3CaO·P2O5. This is, in fact, confirmed by the quantitative XRD analysis shown in Table 5 for laser-treated samples. The results of this analysis can be interpreted by the increase of the depth of laser molten zone which, in turn, increases the quantity of phases that solidify from the melt and increase their quantity in entire coatings volume. Although P2O5 evaporation happens on the melt surface, the convective move of the liquid homogenizes the chemical composition in the entire molten zone. 6. Conclusions Pulsed laser glazing of plasma-sprayed hydroxyapatite coatings modified the morphology of their surface as well as their phase composition. The surface becomes smoother. The phase content was richer in α-TCP and TTCP, being the products of HA decomposition, than that of as-sprayed deposits. The fraction of TTCP was greater in all samples treated laser. This can be interpreted as the result of modification of the chemistry towards CaO richer compositions. The numerical simulation with the Fusion-2D code allowed predicting the temperatures fields in the treated samples and the depth of the laser molten zone. In

particular, the model should help in predicting the laser treatment condition which results in avoiding of CaO rich phases, which are not recommended by in vivo experiments. The latter was found also experimentally, by microscopic observations of sample cross-sections. The comparison between theoretical and experiment values enabled to estimate the optical coefficients of the actual deposits. Consequently, the optical absorption coefficient was found to be equal to 2.1 × 104 1/m and the emissivity to be in the range of ε = 0.85–1. References [1] L. Sun, C.C. Berndt, K.A. Gross, A. Kucuk, J. Biomed. Mater. Res. (Appl. Biomater.) 58 (2001) 570. [2] J.L. Lee, L. Roubfar, O.R. Beirne, J. Oral Maxillofac. Surg. 58 (2000) 1372. [3] M. Ogiso, J. Biomed. Mater. Res. (Appl. Biomater.) 43 (1998) 318. [4] W. Suchanek, M. Yashima, M. Kakihana, M. Yoshimura, Biomaterials 17 (1996) 1715. [5] L. Pawlowski, The Science and Engineering of Thermal Spray Coating, Wiley, Chichester, 1995. [6] S. Dyshlovenko, B. Pateyron, L. Pawlowski, D. Murano, Numerical simulation of hydroxyapatite powder behaviour in plasma jet, Surf. Coat. Technol., 179 (2004) 110–17 and its corrigendum in Surf. Coat. Technol. 187 (2004) 408. [7] J. Weng, Q. Liu, J.G.C. Wolke, K. de Groot, J. Mater. Sci. Lett. 16 (1997) 335. [8] S. Dyshlovenko, L. Pawlowski, P. Roussel, D. Murano, A. Le Maguer, Surf. Coat. Technol. 200 (2006) 3845.

S. Dyshlovenko et al. / Surface & Coatings Technology 201 (2006) 2248–2255 [9] X. Ranz, L. Pawlowski, L. Sabatier, R. Fabbro, T. Aslanian, in: C. Coddet (Ed.), Thermal Spray: Meeting the Challenges of the 21st Century, ASM International, Materials Park, Ohio, USA, 1998, p. 1343. [10] J. Chen, W. Tong, Y. Cao, J. Feng, X. Zhang, J. Biomed. Mater. Res. 34 (1997) 15. [11] Z. Zyman, J. Weng, X. Liu, X. Li, X. Zhang, Biomaterials 14 (1993) 578. [12] B. Feddes, A.M. Vredenberg, M. Wehner, J.C.G. Wolke, J.A. Jansen, Biomaterials 26 (2005) 1645. [13] P. Cheang, K.A. Khor, L.L. Teoh, S.C. Tam, Biomaterials 17 (1996) 1901. [14] L. Pawlowski, H. Rapinel, F. Tourenne, M. Jeandin, Galvano Organo Trait. Surf. 676 (1997) 433. [15] K.A. Khor, A. Vreeling, Z.I. Dong, P. Cheang, Mater. Sci. Eng. A266 (1999) 1. [16] L. Pawlowski, Dépôts Physiques, PPUR, Lausanne, Switzerland, 2003. [17] S.W.K. Kweh, K.A. Khor, P. Cheang, Biomaterials 21 (2000) 1223. [18] V. Veiko, E. Jakovlev, A. Nikiphorov, V. Chuiko, in: L.L. Hench, J.K. West (Eds.), Chemical Processing of Advanced Materials, Wiley, New York, 1992, p. 919. [19] M. Skrzypczak, P. Bertrand, J. Zdanowski, L. Pawlowski, Surf. Coat. Technol. 138 (2001) 39. [20] L. Pawlowski, I. Smurov, Surf. Coat. Technol. 151–152 (2002) 308. [21] V. Deram, C. Minichiello, R.-N. Vannier, A. Le Maguer, L. Pawlowski, D. Murano, Surf. Coat. Technol. 166 (2002) 153. [22] French norm, Détermination qualitative et quantitative des phases étrangères présentes dans les poudres, dépôts et céramiques à base de phosphate de calcium no. NF S 94-067, AFNOR, Paris, 1993.

2255

[23] W. Kraus, Powder Cell for Windows v.2.3, Federal Institute for Materials Testing, Berlin, Germany, 1999. [24] M. Mathew, L.W. Schroeder, B. Dickens, W.E. Brown, Acta Crystallogr. 33B (1977) 1325. [25] B. Dickens, W.E. Brown, G.J. Kruger, J.M. Stewart, Acta Crystallogr. 29B (1973) 2046. [26] W. Primak, H. Kaufman, R.J. Ward, J. Am. Chem. Soc. 70 (1948) 2043. [27] K. Tomita, M. Kawano, K. Shiraki, H. Otsuka, J. Miner. Petrol. Econ. Geol. 91 (1996) 11. [28] P.V. Riboud, Ann. Chim. 8 (1973) 381. [29] S.J. Yankee, B.J. Pletka, J. Therm. Spray Technol. 2 (3) (1993) 271. [30] Y.C. Tsui, C. Doyle, T.W. Clyne, Biomaterials 19 (1998) 2015. [31] A. Vila Verde, M.M.D. Ramos, R.M. Ribeiro, M. Stoneham, Thin Solid Films 453–454 (2004) 89. [32] A.C. Bento, D.P. Almond, S.R. Brown, I.G. Turner, J. Appl. Phys. 79 (9) (1996) 6848. [33] A.C. Bento, D.P. Almond, Meas. Sci. Technol. 6 (1995) 1022. [34] M. Courouble, E. Lamblin, L. Pawlowski, in: P. Vincenzini (Ed.), 10th International Ceramic Congress, Part C, Techna, Faenza, 2003, p. 45. [35] D. Fried, M. Zuerlein, J.D.B. Featherstone, W. Seka, C. Duhn, S.M. Mccormack, Appl. Surf. Sci. 127–129 (1998) 832. [36] M. Zuerlein, D. Fried, W. Seka, J.D.B. Featherstone, Appl. Surf. Sci. 127– 129 (1998) 863.