Hideharu Fukunaga

The evaluation of the strength distribution of silicon carbide and alumina fibres by a multi-modal Weibull distribution

The strengh distributions of silicon carbide and alumina fibres have been evaluated by a multimodal Weibull distribution function. This treatment is based on the concept that the fracture of the fibre is determined by competition among the strength distributions of several kinds of the defect sub-population. Since those fibres were observed to have two types of fracture mode, the evaluation of a bi-modal Weibull distribution was performed in comparison with the single Weibull distribution usually employed. The accuracy of the fit for these two distributions was judged from maximum logarithm likelihoods and cumulative distribution curves. The result showed that the logarithm likelihood calculated using the bi-modal Weibull distribution function gave a larger value, as compared with those using the single Weibull distribution function. The curve predicted from the former function was also in good agreement with the data points. In addition, the strength distribution and the average value at a different gauge length were extrapolated from the Weibull parameters estimated at the original gauge length. In this case, also, the bi-modal Weibull distribution gave a more accurate prediction of the data points.

Microstructural study of the interface reaction between titania whiskers and aluminum

Abstract Titania (TiO2) whiskers have been used to react with aluminum to fabricate composite materials. By reaction squeeze-casting, aluminum composites reinforced with the hard phases α Al2O3 and TiAl3 can be fabricated. A characteristic of this process is that the reaction is too drastic to control. Owing to the volume shrinkage during the reaction, the metallographical structure of the composite so prepared is heterogeneous. By squeeze casting at a lower temperature, however, a macroscopically non-reacted TiO 2 Al composite can be fabricated. At the interface there is only a continuous TiO layer with a thickness of ~10–20 nm. After heat-treatment of the TiO 2 Al composite at 800 °C, a new Al 2 O 3 TiAl 3 composite is prepared by the reaction: 3TiO2 + 2Al→3TiO + γAl2O3, 3TiO + 2Al→3Ti+αAl2O3, Ti+3Al→TiAl3. The Vickers hardness increases with heating time, as does the quantity of matrix defects caused by the volume shrinkage accompanying the reaction, and hence the flexural strength degrades with heating time.

Interfacial reaction and its effect on strength of Al18B4O33/Al composites

AbstractAluminium alloy 6061, AC8A, Al–1Mg, Al–9Cu and pure aluminium composites reinforced with aluminium borate whiskers were fabricated by a squeeze casting process. The interfacial reaction in the composites and its effect on the bending strength are discussed, together with the results from SEM, TEM, and X-ray diffraction. A slight interfacial reaction is favourable for composite strength as it has the effect of anchoring the whiskers. A T6 treatment can enhance the strength of an Al–9Cu matrix composite, but is not efficient for magnesium containing 6061 and AC8A matrix composites. Furthermore, if heated at temperatures higher than 793 K for a long time, the composite strength drops rapidly owing to whisker damage and shortening during the interfacial reaction. It is suggested that the interface in an Al18 B4O33 /Al alloy composite is stable below 623 K which is the temperature requirement for automobile engine components.

The whisker-matrix interfacial reactions in SiC, Si3N4 and Al18B4O33 whisker-reinforced aluminium-matrix composites

CHANGSHA INST TECHNOL,CHANGSHA 410073,PEOPLES R CHINA. HIROSHIMA UNIV,DEPT MECH ENGN,HIGASHI KU,HIROSHIMA,HIROSHIMA 724,JAPAN.;NING, XG (reprint author), ACAD SINICA,INST MET RES,ATOM IMAGING SOLIDS LAB,SHENYANG 110015,PEOPLES R CHINA

Reactivity of aluminum borate whisker reinforced aluminum alloys

Abstract One of the important features of aluminum borate whisker reinforced aluminum alloy composites is the interfacial reaction which is considered to play a predominant role in strengthening mechanism and finally affects its mechanical properties. In the present study, pure Al, Mg-contained and Cu-contained alloys were selected as its matrices, Al 18 B 4 O 33w /Al composites were produced by a squeeze casting method. By means of X-ray diffraction analysis, differential thermal analysis (DTA), scanning electron microscope (SEM) and transmission electron microscope (TEM) observations, the characters of the reaction between aluminum borate whisker and aluminum alloys were studied. The results show that pure Al reacts with the whisker to form Al 2 O 3 if temperature is higher than 726.3°C. Magnesium element in aluminum alloy begins to directly affect the whisker at lower temperature of about 517.2°C. The intermediate and final products due to this reaction are Al 2 O 3 and MgAl 2 O 4 , respectively. The present work shows that the mechanism of the interfacial reaction in a Al 18 B 4 O 33W /AC8A composite is divided into two situations and chemical formulas dealt with the interfacial reaction at both low and high temperatures are proposed. However, Cu element in aluminum alloy does not take part in the chemical reaction with Al 18 B 4 O 33 whisker.

Characterization of the whisker-matrix interfacial reactions in K2O center dot 6TiO(2) whisker-reinforced aluminium matrix composites

The interfacial reaction at the whisker–matrix interface in a K2O·6TiO2/6061Al composite was investigated by high-resolution transmission electron microscopy. Magnesium segregation and titanium enrichment at the whisker–aluminium interface was revealed by energy-dispersive X-ray analysis. It was shown that TiO and MgTi2O4 layers and MgAl2O4 particles were formed at the whisker–aluminium interfaces in the composite during the manufacturing of the composite. The thickening of the reaction layer after T6 treatment may result in the decrease of the bending strength of the composite. Specific orientation relationships between MgTi2O4 and TiO, and also between TiO and K2O·6TiO2 whiskers were also found.

Preparation of intermetallic compound matrix composites by reaction squeeze casting

The conventional squeeze casting process has been successfully applied to the manufacture of metal-matrix composites (MMCs) as one of the most effective manufacturing processes of the machine component. For a decade, great interest has been taken in how the reaction could be avoided between the matrix and the reinforcement. In a converse way to the traditional way, reactions were positively promoted to produce new MMCs in this study

Considerations of the reliability of tensile strength at elevated temperature of unidirectional metal matrix composites

Abstract It is well known that the tensile strength of unidirectional metal matrix composites is somewhat decreased at elevated temperatures compared with that at room temperature. In order to elucidate this effect, a Monte-Carlo simulation has been carried out on the tensile fracture of unifirectional metal matrix composites by the use of a finite difference method based on the shearlag model. It was assumed that no reinforcing ceramic fibers were degraded, and only the shear yield stress of the matrix metal changed with temperature. The results showed that the average strength of the composites decreased slightly with temperature, and the variability increased. Such tendencies were also found by the recursion analysis technique based on the chain-of-bundle probability model proposed by Harlow and Phoenix.

The solid particle erosion behavior of Al18B4O33 whisker-reinforced AC4C Al alloy matrix composites

Abstract Steady-state solid particle erosion of squeeze-cast AC4C Al alloy and 19.5 vol.% Al 18 B 4 O 33 whisker/AC4C Al composites was investigated at room temperature. Experiments were performed with angular silica sand having four velocities (55 m s −1 , 140 m s −1 , 198 m s −1 and 243 m s −1 ) and at impact angle in the range 15° to 90°. The eroded surface and subsurface were observed using scanning electron and optical microscopy. The results indicated that erosion characteristics of the composites was affected by the particle velocity and impact angle. Steady-state rate was found to increase with the addition of whisker to the matrix alloy at high particle velocities or upon increasing impact angle. High erosion rate in the whisker reinforced composites can be attributed to reduced ductility. In addition to plastic deformation, flaking, gouging and microcutting, for the composites, fragmentation and dislodgement of Al 18 B 4 O 33 whisker occurred with impact of particles. At low particle velocity and shallow impact angle, the whisker at the surface can act as protective reinforcement to resist the microcutting and microploughing action. The erosion resistance for the Al 18 B 4 O 33 /AC4C Al composites was improved as a result of whisker addition.

A STUDY OF THE ULTRASONIC TECHNIQUE APPLIED IN FABRICATION OF SIC FIBER-REINFORCED ALUMINUM COMPOSITES

By comparing the ultrasonic cavitation in several kinds of transparent liquid mediums, we have investigated the cavitation effect in liquid. It is considered that the shock wave created by the cavitation in aluminum melt induces a high pressure and an elevated temperature field around the fibers, which can promote the wetting between fiber and aluminum and have aluminum melt infiltrate into the fibers. Moreover, the experiment result shows that the fiber resonance matching with the cavitation is also an important factor for SiC/Al composites preparation. There exists a damage of the ultrasonic vibration on SiC fiber, if the fiber is acted long enough.