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Polishing pad conditioning is essential for achieving stable chemical mechanical polishing (CMP). While diamond disk conditioners (DDCs) are often applied, flexible fiber conditioners (FFCs) have been proposed as a new conditioning tool. FFCs are intended for roughening the pad surface appropriately by bundling fine wire fibers. Our previous study demonstrated the fine conditioning characteristics of FFCs for a hard urethane foam pad. In this study, the conditioning characteristics of an FFC are compared with those of a DDC. First, we evaluate the conditioning performance of an FFC using SUS fibers on a soft urethane foam pad. The result indicates that on a soft pad, the SUS-FFC can restore the pad surface asperities more finely, as confirmed via the stabilized number of contact points based on contact image and luminance value distribution analyses. Subsequently, for a metal-contamination-free FFC process intended for semiconductor CMP, we develop an FFC fabricated using polyether ether ketone (PEEK) and verify its performance via the CMP test of a silicon oxide film. It is shown that the hard pad can be conditioned using the developed PEEK-FFC; this implies that a stable removal rate can be realized immediately after pad break-in conditioning.

Carbon fiber-containing refractory high-entropy ceramic matrix composites (C/RHECs) were fabricated through a reaction with carbon powders, transition metal carbides, and Zr–Ti alloys as a novel heat resistant material used for components of hypersonic vehicles cruising at Mach 7–10. With the infiltration of alloys at 1750 °C into a composite preform containing carbon and carbide powders for 15 min, a high-entropy matrix was successfully formed in situ. Arc-jet tests were conducted in the temperature range of 1800–1900 °C. Results showed the formation of an oxidized region composed of complex oxides, such as (Zr, Hf)O2, (Nb, Ta)2(Zr, Hf)6O17, (Zr, Hf)TiO4, and Ti(Nb, Ta)2O7, with an average thickness of ~600 μm, under which an unoxidized region remained. The porous oxidized region resulted from the evolution of CO(g) during oxidation, while a dense oxide region formed as the outermost region. This indicates that the dense oxide region acted as a barrier to oxygen diffusion for the unoxidized region during oxidation.

The degradation behavior of Yb- and Gd-based ternary silicides (YbGdSi) was evaluated in Ar, 50 vol%air-H2O (air-H2O), and 100 vol%H2O (steam) environment and compared with the results obtained in a previous study conducted in air environment. Heat exposure at 1200 °C for 1, 2, 4, and 8 h was carried out in addition to thermogravimetric analysis up to 1200 °C. The results of these studies demonstrated that YbGdSi formed complex oxides in the (Yb- and/or Gd)-Si-O system and Yb2O3 was commonly formed for each environment. In addition, the resultant weight gain for YbGdSi in air, air-H2O and steam decreases by 2–5% in comparison with it for Yb3Si5. These results clearly indicate that the addition of Gd was effective in preventing the degradation of Yb-silicides.

Herein, we prepared 3D-networked porous carbon materials (TNPCs) (porosity ≈ 70%, average pore size ≈ 10 μm, density ≈ 0.37 g cm–3) composed of glassy carbon via pyrolysis of porous phenolic precursors. A compressive test for TNPCs shows that the Young’s moduli and compressive strength of TNPCs ranged from 0.7 to 1.5 GPa and 11 to 30 MPa, respectively, which increased with increasing pore diameter. Although these moduli could not be accurately predicted using conventional periodic unit cell models, the homogenized Young’s moduli predicted using a 3D image-based model acquired by X-ray computed tomography and focused ion beam scanning electron microscopy were in good agreement with the experimental values. These results indicate that the method can be used to reliably investigate the microstructures and evaluate the Young’s modulus using 3D image-based modeling.

Carbon-fiber-reinforced ultrahigh-temperature ceramic (C/UHTC) matrix composites are an attractive candidate for fabricating various hot structures. The present study aimed to establish a Si-free Zr–Ti melt-infiltration method for fabricating C/UHTC matrix composites. To achieve this, the wettability of Zr–Ti alloys on carbon and their reactivity to carbon were examined. The alloys were melted on graphite plates and infiltrated into model preforms, which were made of porous carbon and had median pore diameters of 3 μm. The results showed that the apparent contact angle between Zr–Ti and C measured from melted alloys on carbon in room temperature was ~20–42° and that the alloys infiltrated into the preforms regardless of the Zr or Ti content. However, with an increase in the Zr content in the alloys, carbon disappeared and was absorbed into the alloys since the reactivity of Zr was higher than that of Ti and the specific surface area of the porous preform was higher than that of carbon-fiber-reinforced carbon composites, which are a typical preform of C/UHTC matrix composites. These results clearly indicate that not only the capillary flow during infiltration but also the reactivity of alloys to preforms should be considered in the process design for fabricating high-density composites via Zr–Ti infiltration.

The pulse thermography (PT) technique was applied to the detection of the delamination of a multi-layered coating system composed of mullite/Si onto a reaction-bonded SiC substrate. The potential evaluation was carried out in order to detect internal delamination in multi-layered material system. Moreover, the observation of the cross sections and 3D views obtained by X-ray computed tomography (CT) indicated that the delamination occurred at the interface between the top coat and the bond coat layers. The changes in the temperature distribution obtained by PT indicated the existence of a delamination area in the top coat layer of the mullite. In particular, the lower temperature region corresponded to the delamination area. The experimental results confirmed that the PT technique is effective with respect to the internal delamination of multi-layered coating system.

Recent studies on carbon fiber-reinforced ultra-high temperature ceramic matrix (C/UHTC) composites fabricated by hot-pressing, chemical vapor infiltration, polymer impregnation and pyrolysis, and melt infiltration (MI) are reviewed. Various efforts have been made to improve these preparation processes and to combine two or more of these because they have both the advantages and disadvantages in terms of the processing time, operating temperature, and the porosity of the resulting C/UHTC composites. In addition, the parameters governing the fracture toughness, thermal conductivity, and recession behavior (in oxidizing environments) of these composites have been discussed. This review demonstrates that C/UHTC composites with Zr- or Hf-based UHTC matrices fabricated via MI are potential candidates for advanced heat-resistant structural materials.

Si-rich ytterbium silicide was fabricated by through an arc-melting technique for applying use as a bond coat material in an environmental barrier coating system. Evaluation of its potential was accomplished through oxidation tests in dry air and an inert atmosphere. The experimental results showed that the changes in weight and morphologies of ytterbium silicide observed after the tests depended on the oxygen partial pressure. Extensive oxidation and weight gain occurred after oxidation in air. In order to apply this material for hot structures, improvement of the oxidation resistance is needed.

To improve the oxidation behavior of Yb-Gd-Si, 0.5 and 1 at% of Ti-containing Yb-Gd-Si (denoted as YGTS-0.5 and YGTS-1, respectively) were fabricated by arc melting. The oxidation behaviors of both YGTS specimens were evaluated by oxidation tests performed in a temperature range of 600–1200 °C for 1, 2, 4, and 8 h in air. Additionally, thermogravimetric analysis (TGA) was conducted at the abovementioned temperature range in air and steam. Oxidation tests at 1200 °C revealed no significant changes in the oxidation rate. Moreover, the oxidation tests revealed that Yb-Gd-Si and YGTS-0.5 became powdery after oxidation, whereas YGTS-1 maintained its form. Detailed microstructural observations indicated that the formation of TiO2 and other oxides in the Yb-Ti-O phase and oxide-containing Yb, Gd, Ti, and Si suppressed the formation of Yb2O3, which caused drastic oxidation at intermediate temperatures (600–900 °C). These results indicated that the addition of 1 at% of Ti to Yb-Gd-Si was effective in improving its oxidation behavior.

A mullite/Si multilayer coating was deposited on a SiC substrate using atmospheric plasma spraying. Mud cracking of the protective surface mullite layer was examined using a high-temperature observation system (HTOS). In-plane surface strain distributions were also measured using the digital image correlation (DIC) method. The experimental results showed that mud cracks nucleated in the mullite layer during heating, primarily due to shrinkage of the mullite during crystallization. The cracking event was detectable by mapping the maximum principal strain distribution. We clearly demonstrated that HTOS and DIC are effective tools for investigating the degradation mechanisms of thick coatings at high temperatures.

The oxidation behavior and oxidation mechanisms of monolithic ZrB2 and particulate-ZrB2 matrix composites were reviewed. Dispersion of SiC particles into ZrB2 was found to be an effective way to prevent extensive oxidation. However, the formation of a SiC-depleted layer can become a critical problem because it can lead to spallation and delamination of the protective surface layer. The addition of ZrC in conjunction with rapid heating to temperatures higher than 2000 °C effectively reduced the porosity of the SiC-depleted layer. The formation of a dense surface layer was attributed to large volumetric expansion during the conversion from ZrC to ZrO2. The effect of the ZrC addition depended on the temperature, heating rate, and composition. This review showed that material design for specific applications is required for high-temperature applications to maximize the oxidation resistance of ZSZ composites.

Accepted: 2018-02-03, 資料番号: SA1170294000

Accepted: 2017-10-05, 資料番号: SA1170186000

Rapid oxidation testing for monolithic ZrB 2 and ZrB 2 –SiC binary composites with different SiC contents (0–30 vol%) was performed using an electric heating system above 2000 °C. The system used in this study achieved the high heating rate of 250 °C/s. The experimental results showed that the morphologies of the oxidized specimens depended strongly on the SiC content. The formation mechanism of SiC-depleted layers beneath the surface scale above 2000 °C differed completely from that below 2000 °C. Although the holding time was below 10 s, SiC-depleted layers were formed because the oxygen partial pressure of the air atmosphere was not enough to form SiO 2 by the oxidation of SiC. It was determined that ZrB 2 –20 vol% SiC showed the best oxidation resistance above 2000 °C at high heating rates.

Ytterbium (Yb)- and silicon (Si)-rich ytterbium silicides (Yb5Si3, and Yb3Si5) were successfully fabricated by arc-melting and heat treatment. The degradation behavior of both silicides was evaluated by means of oxidation tests under three different conditions: Air, air-H2O, and steam. The results showed that the degradation of these Yb-silicides in air was accelerated relative to that in air–H2O and in steam. Although Yb3Si5 formed an un-oxidized region in air–H2O and in steam, a complex phase transformation occurred as a result of the decrease in the amount of Yb in Yb3Si5, caused by exposure to heat, while the liquid phase evolved below the melting point of Si. The liquid phases did not form upon exposure of Yb5Si3 to heat, whereas Yb5Si3 was more oxidized and the amount of SiO2 formed during heat exposure in air-H2O and steam is higher than Yb3Si5.

A ternary alloy with an Yb-Gd-Si composition was designed using thermodynamic calculation software. The ternary alloy with two different steady-state phases (Yb:Gd:Si = 25:18:57 and 19:23:58 at%) was successfully fabricated using arc melting. Oxidation tests were carried out at 1200 °C for 1, 2, 4, and 8 h in air. Thermogravimetric and microstructural analyses indicated that weight gain during oxidation at 1200 °C was suppressed compared with that for the Yb–Si alloy (Yb3Si5) owing to the formation of complex oxides in the Yb2O3–Gd2O3–SiO2 system. In addition, the phase stability of Yb-Gd-Si was higher than that of Yb3Si5 because the growth of a eutectic phase in Yb-Gd-Si during oxidation was prevented compared with Yb3Si5. The addition of Gd in Yb–Si alloy was effective in improving phase stability and oxidation behavior.