YSZ multilayer thermal barrier coatings

Accepted Manuscript The effect of laser surface treatment on the thermal shock behavior of plasma sprayed Al2O3/YSZ multilayer thermal barrier coatings

M.S. Ahmadi, R. Shoja-Razavi, Z. Valefi, H. Jamali PII: DOI: Reference:

S0257-8972(19)30278-6 https://doi.org/10.1016/j.surfcoat.2019.03.024 SCT 24432

To appear in:

Surface & Coatings Technology

Received date: Revised date: Accepted date:

26 January 2019 4 March 2019 12 March 2019

Please cite this article as: M.S. Ahmadi, R. Shoja-Razavi, Z. Valefi, et al., The effect of laser surface treatment on the thermal shock behavior of plasma sprayed Al2O3/ YSZ multilayer thermal barrier coatings, Surface & Coatings Technology, https://doi.org/ 10.1016/j.surfcoat.2019.03.024

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ACCEPTED MANUSCRIPT The effect of laser surface treatment on the thermal shock behavior of plasma sprayed Al2O3/YSZ multilayer thermal barrier coatings M. S. Ahmadi1, R. Shoja-Razavi2, Z. Valefi2, H. Jamali*1 1

Faculty of Materials and Manufacturing Engineering, Malek-Ashtar University of Technology, Tehran, Iran

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Department of Materials Engineering, Malek-Ashtar University of Technology, Isfahan, Iran

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*Corresponding author. Tel.: +983145225041; Fax: +983145228530; E-mail address: [email protected]

Abstract:

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The aim of the present research was to investigate the effect of laser surface treatment on the

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thermal shock behavior of plasma sprayed Al2O3/YSZ multilayer thermal barrier coatings. In this regard, specimens of Inconel 718 were sprayed with Ni–22Cr–10Al–Y bond coat and

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Al2O3/YSZ top coat using an atmospheric plasma spraying approach. Then, top surfaces of

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specimens were under exposed to Nd-YAG laser radiation and thereby were glazed. Thermal stabilities of both coatings were evaluated by rising the environment temperature up to 1000 °C,

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keeping at this temperature for 15 minutes, and also rapid cooling of specimens in cold water.

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Using FESEM with EDS and XRD, the microstructure and morphology observations, elemental investigations and also phase identification were carried out. Findings displayed that both

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sprayed and glazed coatings were damaged as a spallation of top coats. Furthermore, by checking the life-time of coatings, the number of thermal cycles led to 20 percent destruction of top surfaces of coatings, increased from 232 cycles in sprayed coating to 325 cycles in laser glazed Al2O3/YSZ multilayer coating which displayed 40% improvement of thermal shock resistance after laser glazing process. This enhancement in resistance to thermal shock was due to strain adaptability improvement via a network of segmented cracks on the top surface produced by laser glazing process.

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Keyword: Laser glazing, Air plasma spray coating, Thermal shock, Al2O3/YSZ multilayer coating, Thermal barrier coating.

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1. Introduction:

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The essential factors of a good performance of components working at high temperatures, such

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as heat transfer parts, vanes and other components of engines are commonly thermal stability and promote operating temperatures [1-3]. Thermal barrier coatings (TBCs) are mainly composed of

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two layers, including a bond coat (MCrAlY) protecting substrates from oxidation, and a top coat

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of zirconia based in order to reduce the substrate temperature [4, 5]. Air plasma spraying (APS( is one of the common methods of applying ceramic top coats [6, 7]. Currently, the best

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combination of zirconia 6-8 wt% yitria (6-8%YSZ) is used as the top coat in TBCs, due to its

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high stability and endurance during thermal cycles [8, 9]. Although most studies have been done to improve the TBC coatings performances, but thermal shock resistance of these structures are

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considered as their poor characteristics [10, 11]. Degradation of TBCs is usually due to the

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formation of stresses and mismatching of thermal expansion coefficients (TEC) and formation of TGO layer between top coat/bond coat. Moreover, spallation and delamination of surface layers

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at operating temperatures and phase transformation of non-equilibrium tetragonal zirconia to monoclinic phase (t' to m) which was associated with 3–6% volume increase during cooling can lead to the cracking and failure of TBCs [12, 13]. The zirconia phases in an equilibrium state, include a monoclinic phase with low yttria amount having a crystalline structure with different lattice parameters (a, b and c), and so, the cubic phase with high yttria amount. In the air plasma spray process, the t' phase is formed due to the diffusionless transformation of the cubic phase at

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ACCEPTED MANUSCRIPT a rapid cooling rate of 106 k/s, which has lower lattice parameters c and c/a than the tetragonal phase (t). Also, the amount of yttria in t phase was less than t' phase [14, 15]. The studying the thermal shock behavior of TBC systems is important to improve mentioned problems. Different studies and investigations have been conducted to enhance the resistance to thermal shock of

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TBCs as follows:

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Improving the resistance to thermal shock using a nanostructured coating [16, 17], coating a

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layer on the top surface such as alumina which enhances the life-time of TBCs under thermal cycling [18] and laser glazing [12]. Liang et al [19], represented that nanostructured zirconia

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coatings has a higher thermal shock resistance in comparison with conventional zirconia coatings

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because of the presence of previous cracks and fine pores with uniform distribution accompanied with a fine structure in nanostructured coatings. Wang et al [20], reported that the resistance to

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thermal degradation of LZ/8YSZ coating was better than 8YSZ coating due to this fact that in

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LZ/8YSZ coating, high thermal insulation, enhanced resistance to sintering and also thermal stresses release was generated between the ceramic coatings and substrates. Ahmadi et al [10],

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showed that laser glazing process with creating a network of continual cracks on the surface led

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to improvement of strain adaptability which led to increase of thermal cycling resistance. According to other researches, most investigations have been focused on thermal shock behavior

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of YSZ plasma sprayed and laser glazed coatings, while thermal shock behavior of Al2O3/YSZ multilayer coatings has not been seriously investigated. Furthermore, examination of thermal shocking behavior of laser glazed Al2O3/YSZ multilayer coating has been done for the first time. Hence, this research was conducted to compare the thermal shock resistance of sprayed and glazed Al2O3/YSZ multilayer coating by the microstructural and elemental evaluations,

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ACCEPTED MANUSCRIPT observations of surface morphology of sprayed and glazed coatings using characterization approaches, FESEM, EDS and x-ray analysis.

2. Materials and Methods

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2.1. Materials

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Inconel 718 nickel-base superalloy with the dimension of 15 mm × 15 mm × 10 mm was used as

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the substrate. Also, Amdry 962 trade mark NiCrAlY powder for bond coat (53-106 µm), Metco 204 NS trade mark YSZ (11–125 µm, 7wt% Y2O3– ZrO2) powder and Amdry 6060 Al2O3

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powder (5-45 µm) for top coat were prepared and coated using an APS process.

2.2. Air plasma spraying and laser glazing processes

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Based on the specifications presented in section 2.1, coatings were APSed on the In718 substrate

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using plasma spraying by a F4-MB gun. The bond coat of NiCrAlY with a thickness of 125 ± 25 µm was sprayed on the substrate. Then, the specimens were plasma sprayed with Al2O3/YSZ

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multilayer coating to a thickness of 50-60 µm /250 µm (multilayer consisting of 50-70 µm Al2O3

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top coat on 250 µm YSZ). The APS parameters were reported in Table 1. In order to increase adhesion strength of coating by increasing outer surface roughness, the substrates were

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completely grit blasted by alumina. The laser surface operation on coated specimens was performed by a Nd:YAG laser with power of 750 W. Laser operation in this work was applied with a wavelength of 1.06 µm. After that, the specimens were placed on a (x–y) two-axes table and then the laser beam scanned their surfaces. Prior to performing the laser treatment, the power was measured using a power-meter (500 W– Lp Ophir). In order to cover the outer surfaces of coatings totally, the specimens were affected

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ACCEPTED MANUSCRIPT by laser radiation according to 25% overlap by several scans performed between the successive tracks, in the same direction continuously. Table 2 presents the laser glazing parameters.

2.3. Thermal shock test

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Thermal shock testing was performed in an air furnace at 1000 °C, keeping at this temperature

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for 15 minutes and also rapid cooling of specimens in cold water. Reaching to 20% spallation of

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coating surfaces, the test was stopped and numbers of cycles performed as the thermal shock resistance were reported. After each 6 cycles, the weights of specimens were measured and

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reported.

2.4. Characterization

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Surface images, microstructural evaluations and chemical analysis of coatings were inspected

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using a FESEM (field emission scanning electron microscopy; TESCAN) along with the EDS (energy dispersive spectroscopy). For surface and sectional morphology studies using SEM, a

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thin-layered Au was sputtered on the surface of specimens to increase the electrical conductivity.

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Elemental identification and chemical analysis of coatings was assessed by EDS. Also, phase analysis of specimens was done by an X-ray diffractometer (AW-XDM300) worked with Cu-Kα

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radiation (λ = 1.54184 nm). The diffraction angle (2θ) was chosen between 20° and 90° (step width of 1°). Moreover, the surface roughness of the ceramic top coat (Ra) was calculated using a roughness tester (Mitutoyo SJ-201P Ver4.00, Japan). The amount of the reported roughness was based on the average of four values from different points of the coating top surface.

3. Results and Discussion 3.1. Specifications of plasma sprayed Al2O3/YSZ multilayer coating before laser glazing

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ACCEPTED MANUSCRIPT Figure 1 displays the polished cross-section and top coat of sprayed Al2O3/YSZ coating. The NiCrAlY, YSZ and Al2O3 layers are visible with proper uniformity in thickness. As observed in Figure 1 (b), the surface of coating was rough. With respect to different flattening parameters of splats deposited on the surface in plasma spraying operation, surface of this coating had a high

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roughness. The roughness of the top surface of the alumina sprayed coating was measured and

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reported about 7.86 ± 0.5 µm.

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The FESEM micrographs of the fractured section of Al2O3 (a), YSZ (b) layers of Al2O3/YSZ coating and XRD pattern (c) of coatings are depicted in Figure 2. As indicated in Figure 2 (a)

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and (b), both types of coatings (Al2O3 and YSZ) displayed a laminar structure composed of

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splats. The columnar grains specified in Figure 2 (b) were caused by oriented solidification at a rapid cooling rate [21]. Furthermore, besides the laminar and columnar structure, defects such as

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porosities, voids and cracks between splats (inter splat) and cracks within splats (intra splat) were

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also visible. As it is evident in Figure 2, alumina layer was denser than YSZ one. The Al2O3 low melting point (2325 K) than YSZ (2950 K), could result in higher density and lower porosities of

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Al2O3 coating [4]. Also, high fluidity of alumina during coating was related to smaller particle

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size of Al2O3 (5-45 µm) with regard to YSZ (11-125 µm). Thus, higher density and lower porosities of Al2O3 splats precipitated was the result of smaller grain size, uniform dispersion of

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grain size, low melting point which was reported above [3, 22]. Figure 3 demonstrates the XRD pattern of sprayed coating containing non-transformable tetragonal zirconia ( t ), rhombohedral phase and cubic of alumina (α and γ – Al2O3). Formation of non-equilibrium tetragonal phase was due to the high solidification rate (∼106 K/s), in plasma spraying treatment. This result was also reported in other investigations [21, 23].

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ACCEPTED MANUSCRIPT 3.2. Specifications of laser glazed Al2O3/YSZ multilayer coating

Figure 4 illustrates top surface and fractured-section of glazed Al2O3/YSZ coating. As seen in Figure 4(a), the surface roughness is reduced more by laser glazing and led to the formation of a dense and smooth top surface. The surface roughness value of the glazed coating was measured

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equal to 2.62 ± 0.5 µm. Therefore, threefold reduction in available roughness was reported. Also,

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the existence of cracks in the layer of glazed was clear. These cracks were created because of the

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thermal stress caused by high temperature gradient and shrinkage. This network of continuous segmented cracks led to an improvement of strain adaptability during thermal cycling. Other

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researches have reported the results [24]. A thickness of about 110 ± 0.5 μm from the surface of

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coating was glazed. Based on Figure 4(b), some cracks is evident in the direction of perpendicular to the top surface in glazed layer.

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Figure 5 illustrates the x-ray pattern of plasma spray Al2O3/YSZ coating after laser treatment.

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This pattern implied the presence of non-equilibrium tetragonal phase and the rhombohedral alumina. The t phase was formed due to rapid cooling rate in laser glazing process (103-104 K/s)

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[21]. Generally, due to rapid solidification rate during the plasma spraying process of alumina,

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the γ and δ-Al2O3 phases were formed as an alumina unstable phase. During the solidification of alumina droplets in plasma spray process, due to the critical free energy of lower γ-alumina

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phase relative to α-alumina, the alumina can precipitate as γ-alumina phase. This phase gives a phase transformation to α-alumina stable phase as an intermediate phase during the thermal cycling and laser glazing process [8, 25]. Therefore, according to Fig. 4, phase γ-Al2O3 not present in the glazed coating.

3.3. Investigation of thermal shock behavior sprayed and glazed Al2O3/YSZ coatings

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ACCEPTED MANUSCRIPT Figure 6 indicates the macroscopic images of the surfaces of sprayed (232 cycles) and glazed (325 cycles) Al2O3/YSZ coatings after the thermal shock test. As seen, spallation of sprayed (Figure 6 (a)) and glazed (Figure 6 (b)) coatings began at the edges of specimens, since the increase of temperature and cooling at the edges were faster than the other places. The effect of

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edge was reported in other researches, too [26]. Therefore, edge effect at the beginning of the

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destruction of the coating is very important.

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Figure 7 illustrates the weight changes according to the number of repetition of cycles performed for sprayed and glazed coatings. As seen, weight changes in coatings were suddenly, which

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shows the destruction mechanism of spallation in both of them.

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As demonstrated in Figure 7, the primary weight increase in coatings was occurred owing to the oxidation of the substrate and the bond coat [16]. Higher resistance to thermal shock in glazed

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coating than sprayed coating is evident in Figure 7. Basically, the destruction of the TBC

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coatings in weight loss assessment is shown in two forms. The specimen gradual weight loss during thermal cycling, which was depicted in FESEM Figs as delamination of top layer and

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reduction of top coat thickness, which presents failure mechanism of delamination. The sudden

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weight loss of the specimen, which was shown in FESEM Figs as complete spallation of top coat in interface of top coat/ bond coat, shows failure mechanism of spallation. These two types of

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destruction mode in weight loss assessment were presented in other studies [10, 17]. According to figure 7, weight loss did not happen gradually, which indicates mechanism of delamination did not occur. FESEM micrographs of polished sections of sprayed (a, b) and glazed (c, d) coatings after thermal cycling test are presented in Figure 8. As seen in figures (a, c), in both coatings, cracks were propagated at the top coat (TC)/ bond coat (BC) interface. Thus, by combining the results obtained from Figures 7 and 8, the destruction mechanism of spallation

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ACCEPTED MANUSCRIPT could be verifiable. According to presented micrographs (Figure 8 (b, d)), due to thermal cycling, the thermally grown oxide (TGO) layer was formed at interface. In general, the destruction of TBCs occurs by two factors. Mismatching of thermal expansion coefficient (TEC) between ceramic TC/ metallic BC during thermal cycling and the formation of TGO layer. These factors

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have been reported in some studies [27, 28].

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3.3.1. Effect of thermal expansion coefficient mismatch in coatings destruction during thermal cycling

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In TBCs, the mismatching of TEC between substrate, bond coat ( 17.2 106 K 1 ) and top coat

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(YSZ = 11.7 106 K 1 and Al2O3 = 9.6 106 K 1 [29]) caused formation of stress and coating failure. The differences in coefficients of TE between the substrate In718 and the bond coat was

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little, as they had similar chemical compositions. However, the incompatibility of TEC between

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the ceramic top coatings and metal components of the system such as the substrate In718 and the bond coat was high, which led to creation of stress and cracks at TC/BC interface during the

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thermal cycling. This result has also been reported in other investigations [25, 26]. Nejati et al

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[30] showed that CSZ/ nano Al2O3 coating was destructed by mismatch of TEC between top

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coat/bond coat, but CSZ/ micro Al2O3 coating was destructed by phase transformation alumina.

3.3.2. Effect of TGO layer in destruction of coating during thermal cycling

The formation and growing of TGO layer, which associated with creation of stress and also the mismatching of TEC between the ceramic TGO layer and the metallic bond coat, led to formation of horizontal cracks expanded near the top/bond coat interface (Figure 9(a) and 8(b)). The formation of this layer in the interface leads to local expansion and stress in the coating YSZ, which results in the creation of horizontal cracks and the failure of the coating. As shown

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ACCEPTED MANUSCRIPT in Figures 9 (b) and 9 (d), this layer is formed on top of the bond coat. The existence of TGO layer at TC/BC interface of sprayed and glazed coatings was confirmed by EDS analysis (Figures 10 (b) and (d)). In general, based on thermodynamic conditions, oxygen can penetrate into the interior and

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aluminum can penetrate into the outside resulting in the formation of Al2O3 phase in interface

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[31]. Soleimanipour et al [26], presented that laser clad and plasma sprayed YSZ/Al2O3 coatings

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were damaged due to stresses of thermal expansion mismatch and the formation of the TGO layer.

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XRD patterns of sprayed and glazed coatings after thermal cycling are displayed in Figure 10.

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Based on the x-ray pattern of sprayed coating after thermal cycling (Figure 10 (b)), t-ZrO2 , δAl2O3 and α-Al2O3 phases were formed. Comparing this pattern with XRD pattern of sprayed

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coating before thermal cycling shows that the γ-Al2O3 phase was transformed into δ-Al2O3. It

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was presented that in a certain range of temperatures about 800-1200 °C, phase transformations could be performed from γ-Al2O3 to δ-Al2O3 [32]. In the XRD pattern related to glazed coating

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(Figure 10(a)), t-ZrO2 , α-Al2O3, and CaZrO3 phases were identified. The formation of CaZrO3

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phase was confirmed by comparing the XRD patterns of glazed coatings before (Figure 5) and

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after (Figure 10 (a)) the thermal cycling. CaZrO3 phase was formed by the reaction of zirconium with calcium in water during the thermal cycling. The formation of CaZrO3 phase on the upper surface leads to the destruction of the coating as delamination [32]. The presence of this phase has been mentioned in other studies, too [17, 33].

3.4. Comparison of thermal shock resistance of sprayed and glazed Al2O3/YSZ multilayer coatings

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ACCEPTED MANUSCRIPT As shown in figure 7, the laser glazed coating suffered more number of cycles than the plasma sprayed coating up to 20% spallation, which presents the suitable performance of glazed coating than sprayed coating in thermal shock test. The differences of the number of cycles applied to 20% failure of sprayed and glazed coatings is presented in Figure 11. As shown in this figure,

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life-time of glazed coating was higher in comparison with sprayed coating. It was visible that

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increasing the resistance to shock in glazed coating was attributed to improvement of strain

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adaptability via the continual cracks network perpendicular to the top surface. Ahmadi et al [10], showed that network of segmented cracks generated by laser glazing process at CYSZ coating

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resulted in improvement of four times in thermal shock resistance. In this research, besides the

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two factors of stress formation by TEC and TGO layer expressed in the previous sections, the other factors producing stress such as transformation of cubic to rhombohedral phase in Al2O3

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associated with volume changes [34] (γ-α, 15%) and the different TEC between Al2O3 (

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9.6 106 K 1 ) top layer and the YSZ ( 11.7 106 K 1 ) ceramic coat resulted in spallation of

Al2O3 layer from YSZ layer in the plasma sprayed Al2O3/YSZ multilayer coating (Figure 9 (a)).

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It was reported that in CSZ/Al2O3 coatings the alumina layer was spalled from the CSZ coating

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by phase transformation of alumina [30]. Basically, the cracks formed in laser glazing process compensated for strains resulted from the TEC mismatching, TGO layer and volume changes

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caused by phase transformation of cubic to rhombohedral in Al2O3 phase, and hence, the destruction of the coating was postponed. This results were also depicted by other investigations for YSZ and CYSZ coatings [10, 24]. Also, the number of cycles until the first spallation (Figures 7 and 11) for sprayed and glazed ones were obtained 65 and 160, respectively. Comparing these numbers, shows the improvement of more than twofold in the initial life-time of sprayed coating by laser surface treatment.

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ACCEPTED MANUSCRIPT 4. Conclusion Al2O3/YSZ ceramic upper layer and NiCrAlY metallic bond coat on substrate of inconel 718 were prepared by an air plasma spraying (APS) process. Then, laser glazing method was performed on the outer surfaces of coatings by Nd:YAG laser. The thermal shock attitude of the

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two types of sprayed and glazed coatings were investigated by rising the environment

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specimens in cold water. Major results could be summarized here:

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temperature up to 1000 °C, keeping at this temperature for 15 minutes, and also rapid cooling of

1. The surface roughness was much reduced by laser glazing and led to the formation of a

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dense and smooth top surface. The value of the top surface roughness of the glazed and

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sprayed coating was measured. The content of surface roughness of sprayed Al2O3/YSZ coating decreased from 7.69 ± 0.5 to 2.62 ± 0.5 µm by laser glaze process.

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2. Findings represented that by checking the life-time of coatings, the number of cycles

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performed to the destruction of 20 percent from the top surface of coatings, increased from 232 cycles in sprayed coating to 325 cycles in laser glazed Al2O3/YSZ coating,

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which displaying 40% improvement of resistance to thermal shock by laser glazing

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process.

3. The improvement of strain adaptability through the segmented cracks which were

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perpendicular to the top surface made by laser glazing resulted in a life-time increase of sprayed TBCs.

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22wt.% Cr-10wt.% Al-1wt.% Y) thermal barrier coatings in cyclic oxidation tests, Surface and

[30] M. Nejati, M. Rahimipour, I. Mobasherpour, A. Pakseresht, Microstructural analysis and

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thermal shock behavior of plasma sprayed ceria-stabilized zirconia thermal barrier coatings with

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micro and nano Al2O3 as a third layer, Surface and Coatings Technology, 282 (2015) 129-138. [31] M. Saremi, A. Afrasiabi, A. Kobayashi, Bond coat oxidation and hot corrosion behavior of

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plasma sprayed YSZ coating on Ni superalloy, Transactions of JWRI, 36 (2007) 41-45. [32] A.N. Khan, J. Lu, Behavior of air plasma sprayed thermal barrier coatings, subject to intense thermal cycling, Surface and Coatings Technology, 166 (2003) 37-43. [33] P. Chraska, J. Dubsky, K. Neufuss, J. Pisacka, Alumina-base plasma-sprayed materials part I: Phase stability of alumina and alumina-chromia, Journal of thermal spray technology, 6 (1997) 320-326.

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ACCEPTED MANUSCRIPT [34] M. Nejati, M. Rahimipour, I. Mobasherpour, Evaluation of hot corrosion behavior of CSZ, CSZ/micro Al2O3 and CSZ/nano Al2O3 plasma sprayed thermal barrier coatings, Ceramics International, 40 (2014) 4579-4590.

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Figure Captions:

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Figure 1. FESEM micrographs of polished cross-section (a) and top surface (b) of as sprayed

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Al2O3/YSZ.

Figure 2. FESEM micrographs of fractured cross-section of (a) Al2O3, (b) YSZ layers of

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Al2O3/YSZ coating.

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Figure 3. XRD pattern of plasma sprayed Al2O3/YSZ coating.

Figure 4. FESEM micrographs of top surface (a) and fractured cross section (b) glazed

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Al2O3/YSZ coating.

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Figure 5. XRD pattern of laser glazed Al2O3/YSZ coating. Figure 6. Macroscopic images of sprayed (a) and glazed (b) coatings during thermal shock

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testing.

glazed coatings.

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Figure 7. Weight changes based on the number of cycles performed for both types of sprayed and

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Figure 8. FESEM micrographs polished cross section of sprayed (a, b) and glazed (c, d) coatings after thermal shock test. Figure 9. EDS analysis of A and B points as shown in Figure 8. Figure 10. XRD patterns of glazed (a) and sprayed (b) coatings after thermal shock test. Figure 11. Comparison of the number of cycles for sprayed and glazed coatings to 20% and initial failure.

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ACCEPTED MANUSCRIPT

YSZ

Al2O3

600

600

600

Primary gas, Ar (L/min)

65

35

35

Secondary gas, H2 (L/min)

12

12

12

Carrier gas, Ar (gr/min)

2.5

3

3

Powder feed rate (gr/min)

20

40

Spray distance (mm)

140

80

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Table 2. Laser glazing parameters.

Value

Current (A)

Distance (mm)

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Pulsed frequency (Hz)

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Average Working Power (W)

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Scanning speed (mm/s)

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Parameter

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Current (A)

15 40 35 12 1

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NiCrAlY

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Parameter

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Table 1. Plasma spraying parameters.

40 80

ACCEPTED MANUSCRIPT

Highlights

1) Improvement of thermal shock resistance of Al2O3/YSZ multilayer coating about 40% by

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laser glazing.

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2) Reduction of roughness from 7.69 to 2.62 µm by laser glazing process.

3) The destruction mechanism of both coatings through the mismatch of TECs and growing of

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TGO layer.

4) The improvement of strain adaptability through cracks produced by laser treatment.

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5) Increase the life-time from 232 cycles in sprayed coating to 325 cycles in laser glazed.

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Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11