Ceramic Casting Technologies for Fine and Coarse Grained TRIP-Matrix-Composites
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The present contribution focuses on the development of composite materials using innovative ceramic casting technologies. Within this work different processing routes, the relevance of their process parameters as well as the resulting mechanical and microstructural characteristics are discussed. The successfully developed TRIP-matrix foams as well as full beads reinforced with 5 and 10 vol.% zirconia achieve higher compressive strengths and energy absorption during deformation in comparison to the pure metal materials as references. The functionally graded beads allowed a compression of up to 20% with corresponding specific energy absorption of 10.7 kJ/kg. In a further approach, metal-matrix composites have been generated via paper-manufacturing technology. The partial replacement of cellulose fibers by commercially available zirconia fibers resulted in fiber reinforced TRIP-matrix composites with an increased tensile strength of approx. 33% as compared to the pure metal material as reference. Large-size ceramic matrix composites with high potential for applications requiring sufficient wear and thermal shock resistance have been successfully prepared via pressure slip casting. The last topic is concerned with the development of yttria-stabilized zirconia fibers with a tailored phase composition (monoclinic-tetragonal-cubic) via electrospinning.
The increasing technological demand within the last decades led to the development of composites significantly enlarging the application field of conventional materials. The research efforts are not only concerned with innovative material systems but also with novel fabrication technologies, always with the aim to create composites with superior mechanical, thermal, thermo-mechanical, wear- and damping-related properties. Within the frame of the Collaborative Research Center 799—TRIP-matrix-composites based on metastable austenitic steel and magnesia partially stabilized zirconia are of interest. The combination of metastable austenitic steel with transformation induced plasticity with magnesia partially stabilized zirconia is advantageous in terms of high strength and specific energy absorption. [1, 2] Both materials exhibit a martensitic phase transformation triggered upon exposure to external stresses.
1.2 Experimental Details
This work is divided into four main parts; the first one deals with the development of TRIP-matrix composites by replica technique, gel casting and paper-processing technology. The second part concerns the metal melt infiltration of ceramic preforms (obtained via replica technique and extrusion). The development of ceramic matrix composites by pressure slip casting was the third part of the study. Finally, an alternative technology for the fabrication of zirconia fibers is introduced. The following section will provide information on the raw materials as well as on the methods of characterization. The sample preparation for the mentioned technologies will be illustrated.
1.2.1 Raw Materials
188.8.131.52 Magnesia Partially Stabilized Zirconia
Chemical compositions of the zirconia powders in wt.%
184.108.40.206 Austenitic Stainless TRIP-Steel
Chemical compositions of the steel powders in wt.%
Calcined and reactive alumina powders were used for the pressure slip casting of alumina based composites. The fine and coarse grained powders had mean particle sizes ranging from 0.2 µm to 3 mm and were provided by Almatis (Ludwigshafen, Germany) and Martinswerke (Bergheim, Germany), respectively.
220.127.116.11 Raw Materials for Electrospinning
For the development of nanofibers via electrospinning high purity zirconyl chloride octahydrate (Sigma Aldrich Steinheim, Germany), yttrium (III) nitrate hexahydrate (Sigma Aldrich Steinheim, Germany) and magnesium nitrate hexahydrate served as precursor materials for the synthesis of zirconia fibers stabilized with 3 mol.% yttria and 8 mol.% magnesia, respectively. Granular polyvinylpyrrolidone (PVP) with an average Mw of 1.3 ×1 06 g/mol (Sigma Aldrich Steinheim, Germany) was employed as polymeric component. The starting materials were dissolved in deionized water and ethanol with a purity of ≥99.8% (Carl Roth Karlsruhe, Germany), respectively. Triton X (Sigma Aldrich Steinheim, Germany) was used as non-ionic surfactant.
1.2.2 Sample Preparation
18.104.22.168 Development of TRIP-Matrix Composites via Powder Metallurgy
Composition of the slurries for replica technique in wt.% 
Austenitic TRIP- steel powder
TLS Technik, GER
Saint Gobain, USA
Axilat DF 581 B
C.H. Erbslöh, GER
Optapix PAF 35
Zschimmer and Schwarz, GER
R.T. Vanderbilt, USA
Otto Dille, GER
Axilat RH 50 MD
C.H. Erbslöh, GER
Composition of the slurries used for gel casting in wt.% 
Austenitic TRIP-steel powder
Saint Gobain, USA
C.E. Roeper, GER
R.T. Vanderbilt, USA
Zschimmer and Schwarz, GER
Composition of the feedstocks excluding water in vol.%
Austenitic TRIP- steel powder
TLS Technik, GER
Saint Gobain, USA
Final GmbH, GER
Zellstoff Pöls AG, AT
Südstärke Chemie, GER
22.214.171.124 Development of TRIP-Matrix Composites via Metal Melt Infiltration of Ceramic Preforms
Open cell foam structures based on magnesia-partially stabilized zirconia for the infiltration with TRIP-steel melts were prepared using the replica technique. The fabrication of these foam structures comprises two coating steps as mentioned before. The impregnation of the polyurethane foams was done according to the description in Sect. 126.96.36.199. The spray coating procedure was modified and performed airstream assisted. The impregnated foam was therefore placed into a tubular sample holder connected to a vacuum unit. The distance between sample holder and spraying gun was set to 27 cm for all experiments; the pressure of the compressed air was maintained at 0.3 MPa. The mass flow of the slurry was set to 80 g/min and the foams were sprayed for 8 s. A detailed description of the experimental setup is given elsewhere . The spraying slurries were prepared with different powder to water ratios. The spraying slurries contained 40 wt.% water, 45 wt.% and 55 wt.% water, respectively After coating, the foams were dried at 110 °C. Debinding and sintering was performed in an oxidizing atmosphere. Debinding took place at 500 °C with a heating rate of 1 K/min and a holding time of 60 min. Sintering was performed at 1600 °C with a heating rate of 5 K/min and a dwell time of 120 min.
The extrusion technology was applied as a further option for the fabrication of porous ceramic preforms, honeycombs and randomly arranged spaghetti-filters, which have been casted with TRIP-steel melt. The preparation and the extrusion of the different plastic feeds are described in detail by Wenzel and Aneziris  and Schärfl et al. . Honeycomb specimens with 196 cpsi (channels per square inch) and a wall thickness of 250 µm as well as randomly arranged full strand-spaghetti-filters with a strand diameter of 1 mm have been prepared. Both extruded ceramic preform types were sintered in an electrical heating furnace with MoSi2-heating elements in oxidizing atmosphere. The heating rate was 1 K/min to 350 °C with a holding time of 90 min and then 3 K/min to 1650 °C with a holding time of 120 min.
Subsequently, the ceramic preforms were infiltrated by a Cast X5CrMnNi16-7-7 steel melt in order to obtain bulk TRIP-matrix composites. Therefore, the preforms were preheated to 1000 °C with a holding time of 10 h and then placed in an unheated sodium silicate bonded SiO2 sand mold. The samples were fixed to the bottom of the mold. The experimental setup is discussed in detail by Weider and Eigenfeld . The steel casting took place with a temperature of 1600 °C in oxidizing atmosphere. A constant height of the feeder was guaranteed due to an inclined drainage for excess steel.
188.8.131.52 Development of Ceramic Matrix Composites via Pressure Slip Casting
Slip preparation comprised several steps, starting with the addition of the organic additives Welan Gum and Konjac flour in deionized water for 10 min using a Heidolph homogenizer DIAX 600 (Heidolph Instruments Schwabach, Germany). Subsequently, the solid fractions and the additive-water mixture have been homogenized for 15 min in an intensive laboratory mixer RV02 (Maschinenfabrik Gustav Eirich Hardheim, Germany) to obtain the slurries. Casting was performed in a modified industrial pressure slip casting device DGM80D (Dorst Technology Kochel am See, Germany). The suspension was pumped from a receiver tank into a polyurethane mould (200 × 200 × 38 mm3) at a pressure of 0.1–0.15 MPa. The pressure was then increased to 2 MPa and held constant for the whole casting time of 25 min. Afterwards, the pressure was released and the green specimens have been demoulded. The casted bodies were subsequently dried up to 110 °C. Debinding took place in an oxidizing atmosphere with a heating rate of 1 K/min up to 400 °C and a dwelling time of 90 min at 400 °C. Sintering was conducted in a XGraphit furnace (XERION Ofentechnik Freiberg, Germany) with a heating rate of 5 K/min to 1450 °C and a holding time of 120 min and an argon flow rate of 2.5 l/min at an excess pressure of 5 mbar.
184.108.40.206 Development of Ceramic Fibers Using Electrospinning
With the aid of the electrospinning technology yttria-stabilized zirconia fibers have been developed. First, a 18 wt.% precursor solution was prepared by dissolving ZrOCl2 · 8 H2O and Y(NO3)3 · 6 H2O in deionized water in a ratio that corresponds to the final composition ZrO2–3 mol.% Y2O3. In a second step, a 7 wt.% polymeric solution was obtained by dissolving the granular PVP in ethanol. The polymeric solution was stirred on a magnetic stirrer at 500 rpm for 30 min. The polymeric solution was then poured stepwise into the precursor solution with a 3:1 weight ratio. Finally, 0.5 wt.% Triton X was added and the stock solution was further stirred at 250 rpm for 240 min. The electrospinning was conducted using an electrospinning device NE 300 (Inovenso Istanbul, Turkey) with a bottom-up configuration and a 4-nozzles feeding unit, each nozzle having an inner diameter of 0.8 mm. The processing temperature and relative humidity were kept constant at 23 °C and 40%, respectively. The stock solution was fed at 3.5 ml/h with a high precision syringe pump (New Era Pump Systems Farmingdale, USA). The electrospinning was carried out at a voltage of 24 kV using a DC power supply at a distance between needle tip and collector of 75 mm. The fibers were collected on a drum that was covered with alumina foil and which was rotating at 300 rpm. The sintering of the nanofibers was performed at different temperature of 700, 1100, 1350 and 1650 °C.
1.2.3 Characterization of the Composite Materials
220.127.116.11 Rheological Characterization of the Slurries
The rheological properties of the slurries developed for the gel-casting of metal beads as well as for the impregnation and spraying of polyurethane foams were investigated using a rotational viscometer Haake RheoStress 150 (ThermoHaake Karlsruhe, Germany). The rheological experiments were carried out under shear control. For the gel-casting the slurries were investigated with a given shear rate of 1–500 s−1 in 150 s. After a holding time of 100 s at 500 s−1 the shear rate was decreased again. The slurries for the impregnation of the polyurethane foams were investigated with given shear rates of 1–200 s−1 or 1000 s−1 in 300 s. After a holding time of 60 s at 200 s−1 and 1000 s−1 respectively it was stepwise decreased to 1 s−1.
18.104.22.168 Thermal Analysis
Highly relevant aspects for the development of composite materials containing TRIP-steel are investigations on the thermal decomposition behavior of the temporary additives. Differential scanning calorimetry (DSC) combined with thermo-gravimetric measurements (TG) were performed using a STA 409 (NETZSCH Waldkraiburg, Germany). During decomposition experiments the DSC/TG device was flushed with synthetic air. For the fabrication of metal beads using gel-casting the decomposition behavior of sodium alginate was of fundamental importance. The chosen heating rate was 10 K/min to 1000 °C. For the paper-derived TRIP-matrix composites the decomposition behavior of the cellulose pulp fibers was investigated up to 800 °C with a heating rate of 1 K/min.
22.214.171.124 Physical Properties
The linear shrinkage after sintering was calculated according to DIN EN 993-10. For the full and hollow metal beads, the pressure slip-casted ceramic matrix composites as well as for the zirconia preforms obtained by extrusion the open porosity, the pore size distribution as well as the bulk density were investigated with the aid of a mercury porosimeter (PASCAL series, Porotec Hofheim am Taunus, Germany). The thickness of the paper-derived TRIP-matrix composites was determined after processing and calendering at five different positions for each sheet using a digital vernier caliper and an analogue dial gauge. The bulk density was determined from weight and volume measurements before and after sintering. The volume of the samples was determined by displacement in mercury volume meter. The theoretical density of the composite mixtures was calculated according to the rule of mixture using the density of the initial powders as measured by helium pycnometry.
126.96.36.199 Mechanical Properties
W is the total energy absorbed during sample deformation, P the load, S the displacement, and Sb is the strain at end of experiment according to Jacob et al. .
The tensile strength of the as-fabricated and calendered paper-derived materials was determined according to DIN EN ISO 1924-2 on a servohydraulic testing machine TT 28100 (TIRA Schalkau, Germany). The clamping length was 65 mm and the sample width was 10 mm. The crosshead speed for the as-fabricated samples was 5 mm/min, and for the calendered samples 3 mm/min. Different crosshead speeds had to be applied in order to ensure sample fracture within 5–30 s as given by the standard.
The tensile strength of the paper-derived TRIP-matrix composites after sintering was determined according to DIN EN ISO 6892-1. It was investigated on as-sintered samples with the following dimensions (before sintering): l0 = 150 mm, lc = 115 mm, b = 20 mm, b0 = 10 mm, with a transition radius of 60 mm (DIN 50125 shape H). Tensile loading tests were also performed on the servohydraulic testing machine TT 28100 (TIRA Schalkau, Germany) at a clamping length of 98 mm. The test length was 70 mm at a crosshead speed of 2.35 mm/min.
Flexural strength (DIN EN 993-6, DIN EN 843-1) and Young’s modulus by static flexure (DIN EN 843-2, Method A) were determined on a servohydraulic universal testing device type TT 28100 (TIRA Schalkau, Germany) with a support distance of 125 mm and a crosshead speed of 0.15 N/mm for the pressure slip casted ceramic matrix composites as well as for the zirconia preforms obtained by extrusion.
188.8.131.52 Microstructural Characterization
Microstructural characterization was conducted by digital microscopy VHX-2000 (Keyence, Germany) and scanning electron microscopy XL30 ESEM (Philips, Germany) equipped with energy dispersive X-ray spectroscopy technology (EDS). Phase identification was done using electron back scatter diffraction (EBSD) analysis (Philips XL30 with EBSD system TSL from Edax/Ametek). For EBSD analysis the samples were polished up to 1 µm grain. Final polishing for 20 h was realized using a VibroMet2 with a SiO2-suspension MasterMet2 (0.02 µm grain size) (Buehler, USA). To avoid electric charging all samples were sputtered with Pt using a sputter coater (Edwards, England). The crystallographic data used for phase determination were taken from ICDD-database. Detailed information are given in Berek et al. , Oppelt et al. [4, 5], Wenzel et al. [10, 15, 16] and Hasterok et al. . Important features of the developed composites have been studied with the aid of a microfocus X-ray computed tomograph CT-ALPHA (Procon X-ray Sarstedt, Germany) equipped with a 160 kV X-ray source and a Hamamatsu detector with 2040 × 2040 pixels. For the open cell foam structure based on magnesia partially stabilized zirconia the homogeneity of the applied spray coatings was studied . In case of the pressure slip casted ceramic matrix composites the homogenous distribution of the steel particles and the coarse alumina grains in the ceramic matrix was evaluated . The deformation behavior of the open cell foam structures based on TRIP-steel and Mg-PSZ was evaluated using of X-ray tomography . With the aid of a Zeiss Xradia 510 Versa X-ray microscope (XRM) the functionally graded beads were investigated with special regard to the formation of transition zones and the formation of cracks between the different layers .
1.3 Results and Discussion
1.3.1 Development of TRIP-Matrix Composites via Powder Metallurgy
184.108.40.206 Open Cell Foam Structures Based on TRIP-Steel/Mg-PSZ
Mass gain of the TRIP-matrix composite foams (mean values of 3 samples, with a standard deviation of less than 5%)
Mass after impregnation
Mass after spraying
Mass after sintering
Bulk density and linear shrinkage of the TRIP-matrix composite foams (mean values of 3 samples, with a standard deviation of less than 3%)
Linear shrinkage in height
Linear shrinkage in width
Chemical composition (EDS) of spot 2 in Fig. 1.3b (oxides in wt.%, spinel-type structure)
Due to the significant differences in particle size between steel (d50 = 30 µm) and zirconia (d50 = 3.0 µm) clusters of zirconia particles were found between the steel particles. Berek et al.  investigated the phase composition of these reinforcing magnesia partially stabilized zirconia particles and found that approx. 80% of the zirconia particles transform into the monoclinic state during thermal treatment up to 1350 °C in argon atmosphere. At the grain boundaries of the zirconia particles precipitates containing Mg are found.
Specific energy absorption (SEA) at 1, 2, 10, 20 and 50% compressive strain
220.127.116.11 Full or Hollow TRIP-Matrix Composite Beads and Functionally Graded Beads Using Gel-Casting
Results of the debinding experiments as a function of the thermal treatment (mean values of 3 measurements)
Dwell time in min at
Carbon content in wt.%
Oxygen content in wt.%
0.049 ± 0.004
11.50 ± 3.61
0.048 ± 0.002
7.13 ± 3.17
0.048 ± 0.003
6.80 ± 1.91
0.053 ± 0.005
7.37 ± 1.55
0.053 ± 0.003
4.23 ± 1.06
0.051 ± 0.006
7.17 ± 1.80
Properties of the TRIP-matrix composite beads, after sintering at 1350 °C
Bulk density g/cm3
Open porosity %
Compressive strength MPa
Strain at failure %
Total specific energy absorption kJ/kg
5.7 ± 0.1
398.3 ± 17.3
29.4 ± 0.8
11.5 ± 0.4
16.7 ± 0.0
344.4 ± 18.1
13.5 ± 0.7
6.3 ± 0.4
22.0 ± 0.1
359.1 ± 15.1
16.6 ± 0.2
7.9 ± 0.4
16.1 ± 0.1
240.3 ± 13.5
16.5 ± 0.2
3.9 ± 0.1
38.7 ± 5.9
61.4 ± 3.2
15.6 ± 3.1
2.4 ± 0.4
26.1 ± 2.6
98.8 ± 12.7
15.3 ± 2.2
3.7 ± 0.2
24.5 ± 5.4
104.0 ± 30.3
10.4 ± 4.5
1.5 ± 0.5
Functionally graded beads (10Z-95Z-0Z)
24.4 ± 4.8
49.6 ± 4.9
4.6 ± 0.8
0.4 ± 0.1
27.0 ± 1.8
551.3 ± 59.3
21.5 ± 3.0
13.7 ± 3.5
Specific energy absorption (SEAm) in kJ/kg at 5, 10, 15 and 20% strain
0.19 ± 0.02
1.11 ± 0.06
2.73 ± 0.18
5.22 ± 0.22
0.74 ± 0.01
3.34 ± 0.13
0.75 ± 0.01
3.39 ± 0.22
7.27 ± 0.18
0.29 ± 0.01
1.27 ± 0.03
3.08 ± 0.3
0.26 ± 0.05
1.14 ± 0.06
2.08 ± 0.40
0.39 ± 0.02
1.45 ± 0.14
3.14 ± 0.30
0.57 ± 0.05
1.51 ± 0.53
Functionally graded beads (10Z-95Z-0Z)
0.34 ± 0.04
0.64 ± 0.19
2.95 ± 0.54
6.89 ± 0.90
10.7 ± 0.23
18.104.22.168 TRIP-Matrix Composites via Paper-Manufacturing Technology
Properties of the TRIP-matrix paper composites in green state
1.00 ± 0.05
0.97 ± 0.05
0.97 ± 0.06
Thickness after calendering
0.31 ± 0.03
0.31 ± 0.01
0.31 ± 0.1
Tensile strength as-fabricated
6.1 ± 0.9
5.3 ± 0.6
5.2 ± 0.5
Tensile strength after calendering
13.2 ± 1.7
14.0 ± 2.9
15.6 ± 3.2
If the thermal treatment was conducted in a non-purified atmosphere, the mechanical properties of the paper-derived metal-matrix composites were deteriorated due to the presence of carbides. The highest tensile strength was determined for the reference material 0Z with 176.6 ± 12.1 MPa at a total porosity of 66%. The composition 5Z (5 vol.% zirconia) showed a lower tensile strength of 123.3 ± 3.1 MPa. For the composite 10Z (10 vol.% zirconia) a tensile strength of 103.3 ± 14.4 MPa was determined. The materials failed at a maximum strain of 0.6% and showed brittle fracture behavior.
In case of the paper-derived TRIP-matrix composites sintered in a purified argon atmosphere significant higher tensile strength has been determined. A purified atmosphere and the optimized composition of the paper-sheets led to tensile strength of 170.6 ± 18.7 for the composition 0Z and 142.4 ± 10.5 MPa for the composition 10Z at total porosities of 26%. The incorporation of commercially available zirconia fibers led to further improvements of the mechanical performance. At a fiber incorporation of 3 vol.% the tensile strength was determined to be 207.0 ± 17.4 MPa at a total porosity of 25%. However, these optimized TRIP-matrix composites showed also a brittle fracture behavior.
1.3.2 Development of TRIP-Matrix Composites via Metal Melt Infiltration of Ceramic Preforms
22.214.171.124 Open Cell Foam Structures Based on Magnesia-Partially Stabilized Zirconia
The influence of the solid content of the spraying slurry on the homogeneity of the spray coating has also been investigated. The slurry with 55 wt.% water had a viscosity of 63 mPas and a yield stress of 13 Pa. Due to the low viscosity the slurry easily penetrates the foam structures.
126.96.36.199 Extrusion Technology for Honeycombs and Randomly Arranged Spaghetti-Filters
1.3.3 Development of Ceramic Matrix Composites via Powder Metallurgy
Mass loss and wear rate of the investigated ceramic matrix composites
Mass loss g
Wear rate 10−2 mm3/Nm
0.015 ± 0.009
0.050 ± 0.024
0.033 ± 0.032
0.103 ± 0.117
0.014 ± 0.009
0.037 ± 0.027
1.949 ± 1.322
49.099 ± 33.318
1.233 ± 0.405
11.828 ± 38.863
0.853 ± 0.421
7.789 ± 3.847
0.008 ± 0.011
0.024 ± 0.025
0.027 ± 0.034
0.081 ± 0.028
0.034 ± 0.001
0.076 ± 0.022
1.3.4 Development of Ceramic Components Using Alternative Technologies
The present work focused on the development of metal matrix composites and ceramic matrix composites using innovative casting technologies that are typically employed for the fabrication of ceramic components.
The ceramic processing route of polyurethane foams at room temperature has been applied for the development of open cell foam structures based on austenitic stainless TRIP-steel and TRIP-steel/zirconia composite materials. Advantages have been achieved in terms of higher compressive stresses as well as energy absorption during deformation. Particularly, the supplement of the TRIP-matrix composite with a dense coating (jacket) at the foam macrostructures led to a light structure design with excellent energy absorption values. Due to EBSD-analysis the stress-induced martensitic phase transformation of metastable tetragonal zirconia has been identified at compressive strains below 2%.
Full and hollow beads based on austenitic stainless TRIP-steel have been developed using the gel casting technology. A major success was the development of functionally graded beads prepared via gel casting in combination with a specific heat treatment. The developed full beads (composition 10Z) as well as the functionally graded beads have compressive strengths of approx. 380 MPa at a compression of 15%. The pure metal reference material (0Z) shows a significantly lower strength of 150 MPa at the same compression. At about 15% compression the full TRIP-matrix beads collapse. The functionally graded beads have a good integrity up to 30% compression and have a significantly higher strength. At small deformation, the stress level of macroscopic bead structures is well above single beads, but then fails due to the poor joining strength. Therefore, the joining between the beads should be optimized to combine the properties of the particle-reinforced beads and functionally graded beads with the good properties of the spherical macrostructures. The functionally graded beads as well as the particle-reinforced beads with 5 and 10 vol.% zirconia show greatest potential within the group of metal beads obtained by gel casting in terms of energy absorption.
Paper-derived metal matrix composites have been developed using the paper-manufacturing technology. Initially sintered TRIP-matrix composites were characterized by a strong carbide formation, resulting in a brittle fracture behavior of these materials. The crack initiation always started from the precipitates and the cracks propagated along the grain boundaries. The highest tensile strength was determined for the zirconia-free reference material with 177 MPa at a total porosity of 66%. A further sintering approach concerned the purification of the flushing gas Argon 5.0 and the improvement of the sealing performance of the furnace. As a result the formation of carbide precipitations was prevented. In a further development, cellulose pulp fibers have been successfully replaced by commercially available zirconia fibers. The resulting fiber reinforced TRIP-matrix composites showed improved tensile strength of 207 MPa, which was approx. 33% higher than for the zirconia-free reference material at a significantly lower porosity. The easy casting technology of the paper-derived metal matrix composites, the possibility to tune the functional properties as well as the raw material selection allows a wide range of applications e.g. as filter material, heat exchanger or catalyst material.
Open cell foam structures based on magnesia partially stabilized zirconia were prepared using the replica technique. If the spray coating procedure was done airstream assisted the homogeneity of the ceramic struts was significantly improved. The optimized slurry based on magnesia partially stabilized zirconia contained 45 wt.% water. After the infiltration of the sintered foam structures the TRIP-matrix composite contained 4.5 vol.% monoclinic zirconia, 49.8 vol.% tetragonal zirconia and 45.7 vol.% cubic zirconia. Thus, approximately 50 vol.% of the ceramic material is able to transform stress-assisted. The steel matrix consisted of 100% austenite.
Another emphasis of the present work was the fabrication of ceramic matrix composites using pressure slip casting. After successful casting the composites were sintered at 1550 °C in argon atmosphere and the homogenous distribution of the steel particles within the matrix materials has been verified. As a result of the casting technology and the sintering temperatures the pressure slip casted ceramic matrix composites had open porosities of ≥27%. Within this work package the wear behavior of the composites has been investigated using a pin-on-disc test. The wear behavior of the pressure slip casted composites was similar to existing results in literature and will be improved if the sintering parameters are optimized. Moreover, the pressure slip casted ceramic matrix composites have a high potential for applications at elevated temperatures, since they show a good resistance to thermal shock .
A further challenge was the development of zirconia fibers with a tailored phase composition via electrospinning. Fibers were successfully prepared from polyvinylpyrrolidone (PVP), ZrOCl2 · 8 H2O and Y(NO3)3 · 6 H2O. Up to a sintering temperature of 1100 °C single zirconia fibers can be obtained. Due to the addition of varying amounts of yttrium (III) nitrate hexahydrate the phase composition was successfully tailored.
The authors gratefully acknowledge the financial support of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) for funding this research project A1 within the frame of the Collaborative Research Center (CRC) 799—TRIP-Matrix-Composites—project number 54473466.
We would like to thank our former colleagues Dr.-Ing. Wolfgang Schärfl and Dipl.-Ing. Manuel Hasterok for their contribution to the subproject A1. For the experimental support we would like to acknowledge the support of Dipl.-Ing. Anna Schneider and M.Sc. Christian Krumbiegel. Moreover, we like to thank our colleagues of the CRC 799, particularly Dr.-Ing. Anja Weidner, Dr.-Ing. Anke Dalke, Dr.-Ing. Katja Pranke and Dipl.-Ing. Christine Baumgart. We greatly appreciate the support of our colleagues at the Chair of Ceramics, in particular Dr.-Ing. Christian Weigelt, Dr.-Ing. habil. Harry Berek, Dr.-Ing Christiane Biermann and M.Eng. Ashish Pokhrel.
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