Tyranno Fiber Research Articles

Characterization of CVD Bonded Tyranno® Fibers Oxidized at High Temperatures

The oxidation of highly porous ceramic matrix composites (PCMCs) based on different Tyranno® fibers has been analyzed by means of thermogravimetry and electron microscopy. Both uncoated fibers and PCMC materials exhibit parabolic kinetics between 900°C and 1250°C, these being faster for Ti‐doped than for Zr‐doped Tyranno fibers. Oxide layers in Ti‐doped fibers are porous and partially crystalline, whereas in Zr‐doped materials a significant fraction of relatively coarse β‐SiC grains is still found embedded in the amorphous silica matrix. On the other hand, the CVD‐SiC coatings exhibit higher oxidation rates from the outer surface than from the inner one, a phenomenon that has been associated not only with the more difficult access of oxygen to the inner face but also with the highly <111> textured structure of these coatings, for which very different oxidation rates have been published for the inward and outward directions. Cracking phenomena observed above 1100°C for long dwelling times do not lead to an acceleration of the oxidation process, which could be due to the simultaneous crystallization of the amorphous silica layers.

J043023 CVD法を用いたCNTs析出チラノ繊維複合材料の成形と界面強度評価

J043023 CVD法を用いたCNTs析出チラノ繊維複合材料の成形と界面強度評価

Influence of chemical and physical properties of the last generation of silicon carbide fibres on the mechanical behaviour of SiC/SiC composite

SiC/SiC composites reinforced with near stoichiometric SiC ceramic fibres (Hi-Nicalon S and SA3 Tyranno fibres) are attractive materials to be used in nuclear environment. Netherless, their mechanical properties must be improved and controlled. For example, SA3 Tyranno fibres (TSA3) -reinforced composites exhibit a brittle behaviour whereas composites reinforced by Hi-Nicalon S (HNS) fibres exhibit a conventional damage tolerant response. This difference is related to the nature of the fibre/matrix (F/M) coupling. The aim of this work was to identify the SiC fibres characteristics influencing the F/M coupling and consequently the mechanical properties of the composites. The experimental results point out that the TSA3 fibres exhibit a granular and rough surface leading to an increase of the residual stress and the interfacial shear stress in the SiC/SiC composites. Beside the roughness, the experimental results also point out that the surface chemistry of the SiC fibres significantly influence the F/M bonding.

Oxidation resistance of highly porous CVD-SiC coated Tyranno fiber composites

Oxidation tests have been carried out on highly porous ceramic matrix fiber composites consisting of Tyranno Lox M fibers coated with Pyro C and CVD-SiC thin layers. TGA experiments carried out at 900 °C confirm that mass loss rates are higher for materials with thicker Pyro C layers. At higher temperatures (i.e. 1250 °C) such differences are not significant likely due to the interaction between SiC oxidation and Pyro C burnout. These tests clearly show that the oxidation kinetics of Tyranno fibers are much faster than those of CVD-SiC coatings. Therefore, the CVD-SiC coatings protect the Tyranno fibers against oxidation, although this is less effective as the thickness of the Pyro C layer increases. Finally, it has been found that the oxidation kinetics of the CVD-SiC layers are faster as the coating thickness increases and are different for the inner and the outer coating surfaces.

Effect of heat treatment in air on the thermal properties of SiC fibre-reinforced composite. Part 1: a barium osumilite (BMAS) matrix glass ceramic composite

The thermal properties have been studied on a glass ceramic composite comprised of a barium osumilite (BMAS) matrix reinforced with SiC (Tyranno) fibres which has been subjected to a heat treatment in air in the range of 700–1,200 °C. Microstructural studies were carried out especially on of the interface between fibre and matrix. The presence of a carbon thin layer in the interface is a typical observation in SiC fibre-reinforced glass ceramic matrix composite systems. The microstructural evaluation and thermal properties showed a degradation of interfacial layer occurred at low heat treatment temperatures, (700–800 °C) this was attributed to the fact that, at those heat treatment temperatures the carbon rich layer formed during processing was oxidised away leaving voids between fibre and matrix, which were linked by isolated silicon-rich bridges. After heat treatment at higher temperatures of 1,000–1,200 °C, the thermal properties were retained or even enhanced by leaving a thick interfacial layer.

Low cycle fatigue behavior in an orthogonal three-dimensional woven Tyranno fiber reinforced Si–Ti–C–O matrix composite

The low cycle fatigue tests of an orthogonal three-dimensional (3-D) Tyranno fiber reinforced Si–Ti–C–O (SiC) matrix composites were conducted with a sine wave form under stress and strain controls at room temperature. It was shown that the asymmetric response of strain or stress occurs between tension and compression. There is no stress ratio ( R) effect on fatigue life between R=0.1 and −1 at 0.02 Hz. The reduction of Young’s modulus and sliding stress of interface during fatigue was analyzed to interpret experimental results.

Characterization of the medium-range structure of Si-Al-C-O, Si-Zr-C-O and Si-Al-C Tyranno fibers by small angle X-ray scattering

The medium-range structures of Si-Al-C-O, Si-Zr-C-O and Si-Al-C Tyranno fibers, which were prepared by pyrolysing polymetalocarbosilane organic fibers, were observed by means of small angle X-ray scattering using a point-collimated Cu Kα incident beam and a two-dimensional imaging plate detector. Single Si-Al-C-O and Si-Zr-C-O Tyranno fibers of a few μm in diameter have an anisotropic structure comprising thousands of fine filaments of about 10 nm in diameter bundled together along with the long axis of the fibers. The anisotropic structure is not sensitive to the pyrolysing temperature during the organic-to-inorganic conversion process. However, the anisotropic structure of the Si-Al-C-O fibers is totally modified to an isotropic one in Si-Al-C fibers prepared by heating the Si-Al-C-O fibers above 1700°C in an argon gas stream, because of the formation of an aluminum oxide-rich phase at the grain boundaries of β-SiC nanoclusters.

916 HAp-チラノ繊維複合体の内部構造観察

Hydroxyapatite has been used as implant material, because it has the character of excellent organism affinity. But it lacks mechanical strength, for example bending strength and elasticity. So, we try to composite HAp powder with Tyranno fiber to increase mechanical strength and to curb the destruction action. Tyranno fiber has the heat resistance and the oxidation resistance. In this study, we evaluated mechanical strength of the specimen by three point bending test and observed the breaking surface by SEM.

３次元織物チラノ繊維強化ＳｉＣ基複合材料の疲労挙動に及ぼす周波数の影響

３次元織物チラノ繊維強化ＳｉＣ基複合材料の疲労挙動に及ぼす周波数の影響

Fracture behavior of notched unidirectional Si-Ti-C-O/BMAS composite

Experimental and modeling studies on tensile fracture behavior of notched unidirectional Si-Ti-C-O (Tyranno fiber) reinforced BMAS (barium magnesium aluminosilicate) glass matrix composite were carried out. The longitudinal crack arose at the tip of the transverse notch before overall fracture. The critical energy release rate around at initiation of the longitudinal cracking was estimated to be nearly 100 J/m2 by application of the present model to the experimentally observed relation between the stress of the composite in the very early stage of longitudinal cracking and the notch size. The notched strength was higher than that predicted by the fracture mechanical criterion due to the blunting arising from the premature longitudinal cracking, but it was lower than that predicted by the net stress criterion due to the constraint effect arising from the bridging of the fibers and the spalling of the segmented matrix into the longitudinal crack.

ゾルゲル法酸化物を添加した新規なプレセラミックポリマーを前駆体とするSi-M-C-(O)繊維の開発

A new SiC-based continuous fiber containing a small amount of sol-gel-derived oxide material(zircon) has been developed. The new inorganic continuous fiber has a better oxidation resistance in dry and wet air at high temperatures than those of the current SiC-based continuous fibers (Tyranno ZMI). The precursor polymer was prepared by polymerizing the current precursor polymer with a sol-gel-derived alcoholic solution. The production process of the newly developed Si-M-C-(O) fiber (Tyranno ZX) from its precursor polymer was almost the same as that of the currently available Tyranno Fiber (ZMI). Although the productivity is open to improvement, fiber diameter, tensile strength and tensile modulus of Tyranno ZX fiber were 11 μm, 3.0 GPa and 190 GPa, respectively. The oxidation resistance of Tyranno ZX at 1273-1773 K in wet air was excellent, compared to the current polymer-derived SiC-based fiber (Tyranno ZMI). Since the addition of an oxide material to the SiC-based fibers was shown to improve the fiber properties, we are currently investigating the addition of other oxide material, Al2O3, in order to achieve fibers with much higher thermal stability by using the sol-gel method.

Critical load of reversible thermal expansion of tyranno fiber.

To develop the high temperature shape memory bi-ceramics, the thermal expansion test was performed for Si-C-O glassy tyranno fiber which shows high resistant to heat and oxygen. The reversible shape change can be observed for Si-C-O glassy fiber sample under 1573K and below 25MPa.

Analysis of SiC fibres and composites using raman microscopy

The application of Raman spectroscopy in the analysis of the microstructure of SCS-6 silicon carbide fibres using a Renishaw Raman microscope is described. It is demonstrated that the technique allows a detailed study to be made of the point-to-point variation in microstructure across a fibre section. It has been possible to monitor the variation of the concentration of SiC and carbon in the fibre microstructure and to detect differences in the forms of carbon present. It is also shown that Raman spectroscopy can be used to follow the micromechanics of both the deformation of silicon carbide fibres and of the fibres within a model composite. Well-defined Raman spectra have been obtained from a variety of Nicalon and Tyranno fibres and the positions of the Raman bands shown to shift on the application of stress or strain. From such stress-induced Raman band shifts, the point-to-point variation of axial fibre stress or strain along an individual fibre in an epoxy matrix can be determined. An example is given of the use of the technique to map the distributions of axial fibre strain in a Nicalon/epoxy fragmentation test specimen and to model the failure processes at the fibre/matrix interface.

Thermodynamic Considerations on the in-situ Formed Interface Structure Observed in Si-Ti-C-O-Fiber/SiO2-Glass Composite.

Si-Ti-C-O-fiber/SiO2-glass composite was prepared by oxidation of the fibers at ambient temperature and subsequent hot-pressing at 1750°C (50-70MPa). The matrix was built by a silica layer on the fiber surfaces formed during initial oxidation. High-resolution transmission electron microscopy (HRTEM) revealed the in-situ formation of a graphitic interface with both turbostratic and cellular configuration in addition to TiC crystallites, also precipitated within the silica matrix. Thermodynamic considerations indicate the possibility of active oxidation of SiC in the Tyranno fiber yielding gaseous silicon monoxide and solid carbon.

Mechanical properties of Si-T-C-O fibre-bonded ceramic using satin weave

Tensile and compressive properties of fibre-bonded ceramic (Tyrannohex) are reported along with the relationship between fibre orientation and flexural strength. In this study, Satin-Tyrannohex was produced by hot-pressing an oxidized satin-woven Tyranno fibre. The Satin-Tyrannohex showed the most well-balanced mechanical properties in all directions from the fibre axis at room temperature compared with crossplied- or 0 °/±45 °/90 °-Tyrannohex. The Satin-Tyrannohex maintained excellent strength up to 1400°C, which is comparable to or greater than the strength at room temperature. Decreases in tensile and compressive strengths at 1500°C could be due to an increase in the critical length of the fracture fibre and a decrease in the capability to support the fibre, respectively, because of the slight “softening” of the matrix.

Mechanical properties and fracture behaviour of SiTiCO fibre/SiAlON composite

Unidirectional SiTiCO fibre (Tyranno fibre®) reinforced SiAlON (Si 2Al 4O 4N 4) was fabricated by the filament winding method. The fibre/matrix green sheets were stacked and hot-pressed at 1773 K for 1.8 ks under a nitrogen atmosphere. The composite with a fibre content of 42 vol% showed significantly higher flexural strength (800 MPa) than that of monolithic SiAlON ceramics (570 MPa). A strength decrease due to the matrix degradation was observed at high temperature (1273 K and 1473 K). The fracture toughness of the composite measured by SENB (single edge notched beam) method was 8.0 MPa·m 0.5, being two times higher than that of monolithic ceramics (4.0 MPa·m 0.5). The work-of-fracture of the composite measured by static and dynamic methods was 9.62 kJ/m 2 and 8.29 kJ/m 2, respectively. 1998 Elsevier Science Limited and Techna S.r.l.

Radiation response of SiC-based fibers

Loss of strength in irradiated fiber-reinforced SiC/SiC composite generally is related to degradation in the reinforcing fiber. To assess fiber degradation, the density and length changes were determined for four types of SiC-based fibers (Tyranno, Nicalon CG, Hi Nicalon and Dow X) after high temperature (up to 1000°C) and high dose (up to 80 dpa-SiC) irradiations. For the fibers with nonstoichiometric compositions (the first three types in the list), the fiber densities increased from 6% to 12%. In contrast, a slight decrease in density (<1%) was observed for the Dow X fiber with a quasi-stoichiometric composition. Fiber length changes (0–5.6% shrinkage) suggested small mass losses (1–6%) had occurred for irradiated uncoated fibers. In contrast, excessive linear shrinkage of the pyrocarbon-coated Nicalon CG and Tyranno fibers (7–9% and 16–32%, respectively) indicated that much larger mass losses (11–84%) had occurred for these coated fibers. Crystallization and crystal growth were observed to have taken place at fiber surfaces by SEM and in the bulk by XRD, moreso for irradiated Nicalon CG than for Hi Nicalon fiber. The radiation response of the quasi-stoichiometric Dow X fiber was the most promising. Further testing of this type fiber is recommended.

Fabrication of three-dimensional tyranno fibre reinforced sic composite by the polymer precursor method

A three-dimensional Tyranno fibre reinforced SiC composite was fabricated by infiltration of molten polycarbosilane into three-dimensional textile preform (volume fraction; 39%) in an autoclave followed by pyrolysis in argon up to 1200 °C. An attempt to improve the density of the composite was done by repeated infiltration and pyrolysis. As a result of 10 times repetition, the density of the composite was increased to 2.4 g cm −3 (relative density; 83%, open porosity; 5%). Bending strength and fracture toughness were 420 MPa and 11.5 MPa m 1 2 , respectively. The composite showed semistable fracture behaviour because of bridging of fibre parallel with the tensile direction.

Microstructural evolution of the latest generation of small‐diameter SiC‐based fibres tested at high temperatures

The new generation of silicon‐carbide‐based fibres made from organosilicon precursors, cross‐linked by electron irradiation, have been compared with the earlier fibres which have undergone cross‐linking in air. The latest fibres, known as Tyranno Lox‐E and Hi‐Nicalon, possess a lower oxygen content (≈5 wt% and ≈0.5 wt%) whereas the NLM202 fibres contain 12 wt% and the Tyranno Lox‐M 13 wt% of oxygen. The Tyranno fibres have been produced with a precursor similar to that used to produce the Nicalon fibres, but modified by the addition of titanium. All fibres possess a structure composed of β‐SiC grains, free carbon aggregates, with no crystallized titanium compounds in the Tyranno fibres and an oxygen‐rich intergranular phase, except in the Hi‐Nicalon fibre. The Hi‐Nicalon fibre has the largest grain size and its free carbon content is higher than in the NLM202 fibres. For all the fibres, the β‐SiC grains grow when the temperature increases, whilst the strengths and Young's moduli decrease. The NLM202 shows the least change in grain size and tensile properties. The Hi‐Nicalon is stiffer and stronger than the others at high temperature. TEM results show that grain growth is isotropic, even during creep tests. The growth depends on the nature and amount of the intergranular phase. Mechanical changes as a function of temperature can be explained by external oxidation during tensile tests in air and internal oxidation facilitated by the nanoporosity, which is greater in the Tyranno than in the Nicalon fibres. The presence of the oxygen‐rich phase in the three fibres containing the most oxygen decreases the creep resistance. Titanium does not improve the mechanical properties and the creep resistance beyond 1523 K and does not have any positive influence in limiting the SiC grain growth. Tyranno fibres are less well stabilized than the Nicalon fibres. The Hi‐Nicalon fibres have been shown to possess consistently better mechanical properties at all temperatures, including creep resistance, than the other fibres studied. All the fibres are sensitive to external oxidation at high temperature.

In situ carbon formation within a Si--Ti--C--O-fibre SiO2-glass composite

This paper reports on a detailed interface characterization performed by high-resolution transmission electron microscospy (HRTEM) of a Si-Ti-C-O (Tyranno) fibre composite. The micromechanisms of fracture, which are strongly influenced by the interface structure, are discussed in light of the TEM observations. Moreover, the in situ formation of such a weak interface structure, i.e. the formation of carbon, is discussed