Manufacturing technologies for nanocomposite ceramic structural materials and coatings

Materials Science and Engineering B 148 (2008) 58–64

Manufacturing technologies for nanocomposite ceramic structural materials and coatings R. Gadow ∗ , F. Kern, A. Killinger Universit¨at Stuttgart, Institut f¨ur Fertigungstechnik keramischer Bauteile, D-70569 Stuttgart, Allmandring 7b, Germany Received 1 June 2007; received in revised form 25 July 2007; accepted 3 September 2007

Abstract The new material class of ceramic nanocomposites, containing at least one phase in nanometric dimension, has achieved special interest in previous years. While earlier research was focused on materials science and microstructural details in laboratory scale the subject of developing suitable manufacturing technologies in technical scale is the challenge for the manufacturing engineer. The same high-performance features which make the nanocomposite materials so interesting in their properties are absolutely detrimental if it comes to production of these materials. Extreme hardness, toughness and abrasion resistance make the state of the art cutting-and-machining operations extremely cost intensive so that, from a manufacturing point of view, true near-net-shape manufacturing is mandatory to accomplish reasonable cost targets. Ceramic feedstocks with both, high solid content to reduce shrinkage and warping and stable processing conditions are required to accomplish this aim of near-net-shape processing. Stable and reproducible processing conditions, e.g. favourable rheological properties for injection moulding are essentials for the manufacturing engineer. These prerequisites of ceramic production technologies cannot be reached with pure nanopowders in the 10–20 nm range but materials with a micro-nano architecture can fulfill these requirements, using a mixture of a submicron-sized matrix in the 100–200 nm range and smaller nanosized additives in <20% content which contribute the desired functionality. By using these micronanocomposites near-net-shape ceramic forming technologies such as injection moulding, gel casting and slip casting have been developed which lead to high-performance materials at affordable production cost. Advanced surface technologies include nanoceramic coatings made by thermokinetic deposition processes. Modern ceramic processing, i.e. spray drying leads to fine granulated nanopowders with appropriate flowability for subsequent APS plasma or HVOF supersonic flame spraying projection. Developing high turnover processes for pure nanopowders is a difficult and expensive task especially if safe workplace protection measures have to be applied. Powders of this kind have recently become available but at extremely high price. A novel process named HVSFS, high-velocity suspension flame spraying, has been developed to omit the granulation step and to perform direct spraying of liquid nanoparticle dispersions in a high-velocity oxygen fuel spraying torch with robot controlled kinematics. This process (HVSFS) is well suited to produce dense and, if desired, very thin coatings of various oxide-based nanocomposites and cermets for tribological and further applications in automotive, aerospace and mechanical engineering. © 2007 Elsevier B.V. All rights reserved. Keywords: Nanocomposites; Manufacturing; Ceramic processing; Near-net-shape; Coatings; Thermal spraying; Suspension flame spraying

1. Introduction 1.1. Bulk ceramics Although the first publication of ceramics with nanoscale constituents date back to the late 1980s, the concept of ceramic nanocomposites as a self-contained class of ceramic materials was first introduced by Niihara [1]. An excellent review of the

∗

Corresponding author. Fax: +49 711 685 68299. E-mail address: [email protected] (R. Gadow).

0921-5107/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2007.09.066

potential of nanoceramics including structural and functional aspects was given by Cain and Morell [2]. They pointed out that the most important benefits from the nanoscale approach were the reduction of firing temperature, improvement of optical properties, reduction in microcracking and the ability to obtain better surface finish. Improvements in strength according to the Hall–Petch equation can only be materialized if one succeeds in controlling the critical flaw sizes and the micromechanical stresses in the microstructures. This can be realized by doping with nanoscale constituents which leads to nanocomposites. They also identified some major drawbacks such as the strong agglomeration tendency of nanoparticles, the high powder reac-

R. Gadow et al. / Materials Science and Engineering B 148 (2008) 58–64

tivity especially in the case of non-oxides, the low green density of the compacts and sintering inhibition especially in the case of nanocomposite materials. Viswanathan et al. [3] have reviewed the state of the art of nanocomposite processing. Today we can assume that at least most oxide nanopowders (alumina, zirconia titania, etc.) are available in sufficient amounts and at reasonable cost. In case of non-oxides this is still problematic as neither the quality nor the price and availability of the powders is sufficient to meet the demands of ceramic industry. Assuming that the raw material basis is improving, we have identified three major difficulties in manufacturing and processing of nanocomposites related to: • conditioning and compounding; • forming and shaping; • debindering and sintering. In order to be able to commercially exploit the benefits of nanocomposite ceramics manufacturing routes have to be developed which include a near-net-shape manufacturing step. If milling or grinding operations of ultrahard and abrasionresistant materials are required the processes become absolutely uneconomical. In the scientific literature this aspect is only insufficiently reflected. Compounding of feedstocks for different near-net-shape forming technologies from pure nanopowders is extremely complicated in state of the art technologies equipment. Liquid dispersions of nanopowders have very low solid contents and extremely unfavourable rheological properties. Viscosities are too high and the dispersions are mostly shear thinning. The same is true for thermoplastic compounds which have a low solid content and require very high mixing energies. Pressing requires granulated nanopowder which also includes processing of dispersions with the above mentioned problems. Sintering is an important issue as most novel sintering technologies are not capable of producing near-net-shape components. Summarizing we can state that the processing of purely nanoscale powders to ceramic components up to now is not possible under economical conditions. We therefore decided to seize the suggestion of Niihara to produce nanocomposites with micro-nano-architecture. According to the standard definition, ceramic nanocomposites are composite materials with at least one phase of a size of less than 100 nm. The other components can be larger sized so that it is possible to work with matrices based on submicron-sized powders of 100–500 nm and provide the desired functionality by adding a nanoscale powder of <100 nm. Thereby most of the processing problems can be solved and it is possible to produce ceramic components with modified established manufacturing technologies. Lewis [4] and Sigmund et al. [5] have reviewed several novel-processing routes for ceramics which can be used for nanocomposite materials. After evaluating the literature data we identified gel casting, slip casting and ceramic injection moulding as suitable near net-shape forming technologies. The first two methods have the highest potential to reach good microstructural features and high green densities. There are severe problems concerning surface finish, warping and material handling (in

59

case of gel casting) and a lower degree of freedom in component shape and wall thickness (in case of slip casting). Ceramic injection molding has the clear advantage to be capable to mass produce components with narrow dimensional tolerances and high surface finish in as fired state. Due to the high requirements to compounding of homogeneous feedstocks with suitable rheological properties and high solid contents as well as the high technological needs to optimize machine parameters and mold design, CIM seems to be the most sophisticated forming technology for nanocomposites. The next challenge is to preserve the nanocomposite microstructure in the sintered component in case of structural ceramics or in the coatings. While in case of bulk ceramics the grain growth is initiated by accelerated grain growth in the final stage, the grain growth in thermally sprayed coatings happens as the material is molten in the plasma or flame resulting in droplets of a size between 100 nm and 10 ␮m. In order to conserve the nanostructure different strategies were developed. Hot pressing uses external pressure to speed up the densification and minimize densification time and temperature [6], and SPS technologies [7,8] additionally use pulsed dc current to obtain perfectly dense components at low temperatures and with almost no dwell time. Although the results of these technologies are impressive, from a manufacturing point of view these axial pressing-based techniques suffer from several drawbacks. Large and homogeneous parts are difficult to obtain, manufacturing of complex parts is almost impossible, and the same is true for hot isostatic pressing using glass or sheet metal capsules. Sintering technologies which can be used in combination with near-net-shape forming are pressureless sintering with all its varieties. Two-stage-sintering proposed by Chen [9] combines a fast heating – to a temperature where a certain predensification without grain growth is achieved – with short dwell followed by a prolonged dwell at lower temperatures where the residual porosity is filled by surface diffusion. Two-step sintering [10] proposed by Lin et al. is a combination of a long-dwell at low temperatures to obtain a uniform microstructure combined with a subsequent standard sintering cycle. We found that this method is especially well suited for densification of ZTA nanocomposites with very sluggish densification behaviour at low temperatures [11]. Gas pressure sintering is a state-of-the-art method which also leads to good results provided that the components can be presintered in such a way that the open porosity is closed [12], the method has become a standard for transparent ceramics which require full density. 1.2. Nanocomposite coatings Ceramic and composite coatings can be obtained in a most suitable way by thermokinetic deposition techniques like plasma spraying and supersonic flame spraying. In both cases a dry micropowder or powdermix is injected by a carrier gas under pressure into the hot expanding plasma or gas jet. The microparticles are molten and accelerated to the substrate surface, where the consolidation to a solid film takes place. Shifting from conventional to nanocomposite coatings has attracted rising interest in the surface technology and thermal spray commu-

60

R. Gadow et al. / Materials Science and Engineering B 148 (2008) 58–64

nity in recent years as the down-scaling of the particle size and a much finer and homogeneous microstructure of the coating promises completely different physical properties [13]. As the microstructure controls the physical properties of the coating, a nanoscaled microstructure would lead to improvements in mechanical properties (hardness [14] and abrasion resistance). A large drawback in the use of nanopowders is the missing capability to feed powders of <5 ␮m into a thermal spray device. Conventional powder feeder technologies are not suitable, furthermore any refilling or cleaning would be associated with a potential health hazard as the nanoparticles easily distribute in air and enter the respiratory tract or even the blood circuit [15]. There are now three approaches to solve this problem, spraying of granulated nanopowders [14,16,17], spraying of molecular chemical precursors [18,19] and direct injection spraying of suspensions [20–22]. The technologies have meanwhile found their industrial applications especially in the field of SOFC manufacturing [22]. Cermet coatings with nanosized carbide particles show superior wear behaviour [14,17]. While earlier suspension spraying processes have used plasma-based spray techniques a new high velocity oxyfuel (combustion of hydrocarbon fuel with pure oxygen) spraying process (HVSFS) using dispersions of nanoparticles has extended the potential especially in the field of extremely thin and dense coatings [23]. 2. Experimental To demonstrate some features of ceramic nanocomposites as bulk and coating materials we have chosen ZTA as a reference material and as a case study.

ponents and intermediates was measured using high-pressure mercury porosimetry (Porotec). The textures in injectionmolded components were investigated by polarized light optical texture analysis PLOTA [27,28]. 2.2. Nanocomposite coatings Nanocomposite coatings were produced by the HVSFS process principle described in [23]. The intensive heat and mass transfer during thermokinetic deposition of nanopowders contains the risk of grain coarsening as a consequence of droplet formation in liquid state. This is most evident for single-phase powders under the extreme thermal conditions of plasma spraying. For HVOF flame spraying there is a much higher potential to trigger the heat transfer and dwell time to obtain at least partially the nanostructure of the original powder source. For HV suspension flame spraying with concentric injection of aqueous, organic solvent or even mixture of both with nanodispersions the spraying equipment was modified by using a special conical nozzle geometry to avoid clogging. The dispersion sprayed consisted of a 70/30 mass% mixture of TM-DAR-alumina (150 nm) and Degussa VP-3YSZ (12 nm) dispersed in a 30/70 mass% isopropanol/water mixture. The solid content of the suspension was 20 mass%. Spraying was performed using propane fuel, the nozzle diameter was 3 mm, the spray distance was 90 mm, the length of expansion nozzle/combustion chamber was Ø200/22 mm. The rheology of nanoparticle dispersions was measured by oscillative rheometry. The samples were cut and polished. The microstructure and porosity was investigated by light microscopy and SEM. 3. Results and discussion

2.1. Bulk ceramics

3.1. Bulk ceramics

ZTA nanocomposites were produced by ceramic injection molding and gel casting. The procedure of feedstock preparation, injection molding and debinding was shown elsewhere [11]. Gel cast ZTA samples were produced according the procedures described by Krell et al. [12] using MAA and MBAM as binder and Franks et al. [24] using PVA and DHF as binder. The ZTA nanocomposites were manufactured with Taimicron TMDAR alumina (grain size 150 nm) as submicron scale matrix material with an addition of 0.5–2 vol.% of Degussa zirconia nanopowders (VP-PH or VP-3YSZ (grain size 12 nm) to provide toughening and inhibit grain growth. Homogeneous and deagglomerated mixtures were produced by a wet mixing and milling operation. The rheology of feedstocks was measured by oscillative rheometry (Paar-Physica), the mechanical properties of the samples were determined by either four-point bending tests [25] or ring tests [26] on a Zwick universal testing machine, Hardness and Young’s modulus were measured by microindentation (Fischerscope), the sintering cycles were investigated by dilatometry and thermokinetic analysis (Netzsch). The microstructure of the fracture surfaces of samples was investigated by scanning electron microscopy. The porosity distribution in ceramic com-

Upon measuring the rheological properties of CIM feedstocks of different grain size we observed that the viscosities are strongly dependent on grain size and grain shape. The viscosity of micronscale feedstocks shows a steady value of 106 Pa s over a large shear rate range and a drop down of viscosity at high shear rates. The submicronscale feedstocks show a shear thickening behaviour with viscosities three orders of magnitude higher and no drop down at high shear rates (Fig. 1). Not only the grain size distribution but also the kind of pre-treatment strongly influences the viscosity of ceramic feedstocks. In case of gel casting dispersions ultrasonic treatment and milling of the feedstocks promote deagglomeration of the dispersed particles und thus lead to a decline in viscosity by a factor of 2 (Fig. 2). The information about the rheological behaviour of the nanocomposite feedstocks is essential to be able to form ceramic components. By the high solids loading, high viscosity and the large internal interface the flow behaviour of CIM feedstocks is not comparable to the behaviour of thermoplastic polymers. Plug flow behaviour can often be observed leading to free jet injection if gates are to narrow and to stick-slip effects at the surface of the mould. Texturing of components by orientation

R. Gadow et al. / Materials Science and Engineering B 148 (2008) 58–64

61

Fig. 1. Viscosity of different alumina feedstocks of equal solid content of 57 vol.% for CIM: squares: TM-DAR (150 nm); triangles: HP DBM (400 nm); line: standard feedstock (5 ␮m).

Fig. 4. Tolerable texture in bending bar of submicronscale alumina visualized by polarized light optical texture analysis.

Fig. 2. Gel casting: change of viscosity during compounding process.

of particles in the flow field is much stronger than in the case of standard micron size feedstocks (Fig. 3). Such texture effects in CIM components are almost inevitable but they are tolerable to a certain extent (Fig. 4). If the textures are too pronounced components can be damaged in the green state or they disintegrate during sintering, where the pre-orientation effect during forming is amplified and may lead to microcracks. Fig. 5 shows such an extreme case where an overfilled TMDAR feedstock was injection moulded. The alumina crystallites at the surface (the mould) are arranged perfectly perpendicular to the surface. In the center of the component we have a parallel orientation of crystallites and wall. In between the orientation changes in a very small volume and we can also detect some original turbulences. Sample 2 produced with more favourable moulding parameters is less damaged. If the feedstocks are perfectly tuned and the forming parameters are well adjusted, components with defect-free microstructure can be obtained. Fig. 6 shows that an extremely narrow monomodal pore size distribution with a maximum of 50–60 ␮m is obtained which is

Fig. 3. Flow textures in bending bar (7 mm × 7 mm × 70 mm) filled by a single pin-point gate, visualized by using inhomogeneous nano-spinel S30 CR/carbon feedstock.

equivalent to a dense packing of the alumina powder used (grain size d50 = 150 nm). Sintering of the green component while conserving the initial nanocomposite grain size distribution is one of the most difficult tasks if the choice of sintering is limited to pressureless processes. As ZTA ceramics normally show a very sluggish sintering behaviour pressureless sintering has to be carried out at high final temperatures at the expense of pronounced grain growth which cannot be fully inhibited by the zirconia addition. A two-step sintering process was developed which is capable of obtaining dense and fine-grained materials [11]. Fig. 7 shows the densification under production scale conditions of two ZTA materials with nanosize zirconia (monoclinic and tetragonal) reinforcement. It is evident that under standard conditions the material reaches not more than 97% of theoretical density even at temperatures higher than 1600 ◦ C. The two-step process leads to fully densified materials at temperatures as low as 1375 ◦ C (TM/VP-PH) or 1450 ◦ C (TM/VP-3YSZ). The effect on the grain size can be seen in the two SEM micrographs Figs. 8 and 9. Fig. 8 shows the conventionally sintered material with a grain size of 1–3 ␮m and in some cases abnormal grain growth. Fig. 9 shows the material sintered by two-step sintering. Here the grain size is well below 400 nm, the material is almost fully dense. The secondary phase is clearly visible in Fig. 8, which means that also the zirconia reinforcement is subjected to grain growth, in the two-step sintered material we could conserve the nanosize of the zirconia. 3.2. Nanocomposite coatings Thermokinetic deposition techniques, like plasma and supersonic flame spraying are employed to produce ceramic, metallurgical and cermet coatings on various substrates. The material source is a spray powder in micronsize, which is injected in the hot plasma or in the expanding hot gas jet with a very short dwell time. During the simultaneous heating and

62

R. Gadow et al. / Materials Science and Engineering B 148 (2008) 58–64

Fig. 5. Texture in overfilled nanocomposite CIM component. Note: different color indicates different crystallographic orientation of alumina grains in the microstructure. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

acceleration there is a phase transition from solid to at least partially liquid and finally a solidification of the molten droplets on the substrate. Due to the melting of the particles during the thermal spray process conventional single-phase materials usually lead to micronsize splats. Nanosized oxide powders and metalceramic mixed nanophases can be handled in a suitable way as dispersion in water or organic solvents to be used in direct injection to the torch. A special supersonic suspension flame spray technique has been developed and patented [29], called HVSFS. In case of binary or more complex compositions of immiscible materials, respectively multiphase spray powder dispersions, it is possible to obtain coatings in which the nanocomposite character can be retained. Fig. 6. Pore size distribution of gel cast TM-DAR-alumina presintered at 800 ◦ C/48 h.

Fig. 7. Density vs. sintering temperature of ZTA (TM + 3 vol.% zirconia) produced by CIM during conventional and two-step sintering.

Fig. 8. Conventionally sintered ZTA (TM/2 vol.%VP-PH), 1475 ◦ C/2 h.

R. Gadow et al. / Materials Science and Engineering B 148 (2008) 58–64

Fig. 9. Two-step sintered ZTA (TM/2 vol.% VP-PH), 1375 ◦ C/6 h.

63

One example is the ZTA shown in Fig. 10. The 70/30 mixture of alumina and zirconia macroscopically shows some segregation as the composition is above the percolation threshold. Further examples with partial solubility are Al2 O3 –TiO2 , Cr2 O3 –TiO2 and partially stabilized zirconia. A more detailed SEM image (Fig. 11) reveals that nanoparticulate zirconia is embedded in a matrix of alumina leading to quite unique properties such as high hardness and abrasion resistance. This was achieved as the processing parameters were adjusted in such a way that the alumina (melting at 2050 ◦ C) was completely molten while the perfectly dispersed zirconia (melting point 2550 ◦ C) remained in solid state. As the time between melting and reconsolidation is extremely short, the two components are almost immiscible and the particle-loaded liquid alumina is highly viscous and the nanostructure can be preserved. 4. Conclusion

Fig. 10. Alumina/zirconia nanocomposite coating produced by HVSFS.

It was shown that by adaptation of established manufacturing processes and by novel thermal spray processes it is possible to produce nanocomposite bulk materials and coatings in a costeffective and reproducible way. The key technology in nanocomposite manufacturing is the production of compounds for different forming and coating technologies which are perfectly homogeneous, meet the flowability and rheological requirements and are optimized in solid content, grain size distribution and grain morphology. In order to be able to produce ceramic nanocomposites efficiently it is mandatory to use near-net-shape forming technologies. These technologies need to be adapted to the special features of nanocomposite compounds. In case of, e.g. ceramic injection moulding, designengineering of moulds and proper shaping and placement of gates as well as machine parameters such as injection pressures, processing temperatures need to be optimized to obtain homogeneous components which are free of defects and textures. In case of nanocomposite coatings new process capable of processing a broad variety of ceramic nanopowders was developed. Processing of the nanopowders as a dispersion and not as a as-received powder or granulate has strongly contributed to increased process stability, process safety and ease in safe nanoparticle handling. Acknowledgements We would like to thank Mr. Marc Frischbier, Selahattin Babat, Jochen Ziegler, Johannes Rauch, Martin Wenzelburger, Andreas Vogel, Willi Schwan and Ms. Esther Dongmo for their contributions. References

Fig. 11. HR-SEM image of nanoscale zirconia dispersed in alumina matrix.

[1] K. Niihara, J. Ceram. Soc. Jpn. 99 (10) (1991) 974–982. [2] M. Cain, R. Morell, Appl. Organomet. Chem. 15 (2001) 321–330. [3] V. Viswanathan, T. Laha, K. Balani, A. Agarwal, S. Seal, Mater. Sci. Eng. R 54 (2006) 121–285.

64

R. Gadow et al. / Materials Science and Engineering B 148 (2008) 58–64

[4] J.A. Lewis, J. Am. Ceram. Soc. 83 (10) (2000) 2341–2359. [5] W. Sigmund, N. Bell, L. Bergstr¨om, J. Am. Ceram. Soc. 83 (7) (2000) 1557–1574. [6] S.C. Liao, Y.J. Chen, W.E. Mayo, B.H. Kear, Nanostruct. Mater. 11 (1999) 553. [7] D.D. Jayaseelan, N. Kondo, D.A. Rani, S. Ueno, T. Ohji, S. Kanzaki, J. Am. Ceram. Soc. 85 (11) (2002) 2870–2872. [8] Z. Zhao, V. Buscaglia, P. Bowen, M. Nygren, Key Eng. Mater. 264–268 (2004) 2297–2300. [9] I.W. Chen, X.H. Wang, Nature 404 (2000) 168–171. [10] F.J.T. Lin, L.C. de Jonghe, M. Rahaman, J. Am. Ceram. Soc. 80 (9) (1997) 2269–2277. [11] R. Gadow, F. Kern, J. Ceram. Soc. Jpn. 114 (11) (2006) 958–962. [12] A. Krell, P. Blank, H. Ma, T. Hutzler, M. van der Bruggen, R. Apetz, J. Am. Ceram. Soc. 86 (1) (2003) 12–18. [13] S. Siegmann, M. Leparoux, L. Rohr, Werkstoffe und werkstofftechnische Anwendungen, Band 22, Tagungsband zum 8. werkstofftechnischen Kolloquium, Chemnitz, ISBN: 3-00-106841-9 (2005) 314. [14] Z.G. Ban, L.L. Shaw, J. Therm. Spray Technol. 12 (1) (2003) 112. [15] G. Oberf¨orstner, et al., Environ. Health Perspect. 113 (7) (2005). [16] H. Chen, C. Ding, J. Therm. Spray Technol. 12 (4) (2003) 523. [17] B.H. Kear, R.K. Sadangi, et al., J. Therm. Spray Technol. 9 (3) (2000) 399. [18] C.J. Li, G.J. Yang, Z. Wang, in: E. Lugscheider (Ed.), ITSC Essen 2002 Conference proceedings, DVS Verlag, 2002, pp. 544–549, ISBN 3-87155783-8.

[19] G. Yang, C.J. Li, F. Han, S.F. Mao, in: C. Moreau, B. Marple (Eds.), Thermal Spray 2003: Advancing the Science and Applying the Technology, ASM International, 2003, ISBN: 0-87170-785-3, pp. 675–680. [20] C. Moterubio-Badillo, et al., in: C. Moreau, B. Marple (Eds.), Thermal Spray 2003: Advancing the Science and Applying the Technology, ASM International, 2003, ISBN: 0-87170-785-3, pp. 687–692. [21] T. Poirier, A. Vardelle, et al., J. Therm. Spray Technol. 12 (3) (2003) 393. [22] K. Wittmann, F. Blein, et al., in: K. Berndt, E. Lugscheider (Eds.), Proceedings of the ITSC 2001, Singapore, ASM International, 2001, ISBN: 0-87170-737-3, pp. 375–382. [23] A. Killinger, M. Kuhn, R. Gadow, Surf. Coat. Technol. 201 (2006) 1922–1929. [24] G.V. Franks, F. Chabert, E.S. Carreras, Proceedings of CIMTEC 2006, Acireale Sicily, Advances in Science and Technology, vol. 45, Transtech Publications, 2006, p. 374. [25] DIN EN 843-1, Hochleistungskeramik, Monolitische Keramik, Mechanische Eigenschaften bei Raumtemperatur, Teil 1: Bestimmung der Biegefestigkeit, Deutsche Fassung DIN EN 843-1:2005-01. [26] J.R.G. Evans, Trans. J. Br. Ceram. Soc. 83 (14) (1984). [27] R. Gadow, R. Fischer, M. Lischka, Computer assisted colorimetric optical texture analysis for CIM components, Int. J. Appl. Ceram. Technol. 2 (4) (2005) S271–S277. [28] R. Gadow, F. Kern, J. Rauch, Adv. Sci. Technol. 45 (2006) S1690–S1695. [29] R. Gadow, A. Killinger, M. Kuhn, D. L´opez, Hochgeschwindigkeitssuspensionsflammspritzen, Deutsche Patentanmeldung Nr. DE 10 2005 038 453 A1, 03.08.2005.