Al2O3 Short Fiber Research Articles

Precipitation behavior of Mg17Al12 in monolithic and Al2O3 short fiber reinforced Mg-Al-Zn alloys

The precipitation behavior of Mg17Al12 in monolithic and Al2O3 short fiber reinforced Mg-Al-Zn alloys was investigated by optical and transmission electron microscopies and hardness measurements. The maximum hardness was obtained when the long and short axes of the platelet type continuous Mg17Al12 precipitates were about 0.3 μm and 0.04 μm, respectively. The area fraction of the discontinuous Mg17Al12 precipitate nodule reached about 0.23. The coarsening behavior of the discontinuous Mg17Al12 precipitate nodule was found to obey the relationship suggested by the Johnson-Mehl-Avrami model. The slope of the Johnson-Mehl-Avrami plot for the Al2O3 short fiber reinforced Mg-Al-Zn alloy was four times larger than that for the monolithic alloy due to the increased number of nucleation sites, i.e. nucleation at the interface between the reinforcing material and the α-Mg matrix as well as at the α-Mg grain boundaries.

Damage and ductility of particulate and short-fibre Al[sbnd]Al2O3 composites

The mechanical behaviour of 2014 and 6061 Al-alloy composites is investigated as a function of matrix treatment (T4 and T6 temper) and reinforcement shape (Al2O3 short fibres and particulates). Comparisons are carried out amongst the composites and with the corresponding unreinforced alloys and are mainly focused on the attained strength and ductility levels as influenced by damage accumulation and fracture mechanisms. Damage is estimated by monitoring the depletion of the elastic modulus as a function of tensile strain. It turns out that the fracture of the reinforcement plays a key role in the failure nucleation mechanism in all composites. Such damage develops in a rate markedly influenced by the matrix condition, the most strengthened and less ductile composites being the most sensitive to damage. Besides, it is suggested that particulates, and their specific interface structure, are more critical with respect to damage than short fibres while unreinforced alloys experience a significantly lower damage rate.

An Experimental Investigation on Infiltration Limit and the Mechanical Properties of Al2O3 Short Fiber Reinforced Metal Matrix Composites Fabricated by Squeeze Casting

Melt infiltration of fibrous preforms is an attractive fabrication route for metal matrix composites. To understand infiltration limits in squeeze casting processes, experimental data are presented for injection of aluminum alloy-based melts into preforms of volume fraction 10%-23% which were composed of δ-alumina fiber with a silica binder. Base alloys used in this study were A16061, A17075, A12024, A1514.0, A356.0 and pure A1. The infiltration distance and deformation of fiber preforms were observed with variation to manufacturing parameters such as preform temperature, die temperature, applied pressure and molten metal temperature. Tensile strength and microstructures were also examined to investigate the effects of processing parameters on infiltration states.

Elevated temperature X-ray measurement of residual stresses in a fibre reinforced Al alloy

Thermal residual stresses have been measured using X-ray diffraction in an Al-2% Mg matrix with 10, 20 or 26 vol % Al2O3 short fibres. Stress measurements were made at room temperature as well asin situ at elevated temperatures up to 250‡C. The thermal stresses arise due to the difference in coefficient of thermal expansion (CTE) between the matrix and the reinforcement. The largest CTE is found in the matrix, resulting in tensile residual stresses after a temperature drop, e.g. after processing or annealing. A high fraction of reinforcement implies higher matrix stresses than a low fibre content. The stresses decrease with increasing temperature for all fibre volume fractions. Measurements are compared with calculations using a modified Eshelby model for equivalent inclusions. Parameters taken into account in the model are coefficient of thermal expansion, Young's modulus, and volume fraction and geometric shape of the reinforcing phase. A good correlation between calculations and experimental results has been found, bearing in mind that no plasticity is taken into account in the Eshelby model. The plastic behaviour of the composites has been described using a model based on a rigid spherical cavity in an elastic-plastic matrix.

金属間化合物の粉末冶金と諸物性 Ｎｉ‐Ｆｅ‐Ａｌ３元素合金の機械的特性と複合材料への適用

NiAl binary and Ni-Fe-Al ternary alloys, with the composition of 40.50at%Al and x ;[Fe]/( [Nil+Fe])=0-0.20, were fabricated by the reactive hot-press sintering. The addition of Fe to NiAl resulted in the decrease of fracture toughness in the case of 50at%AI, however, toughness of 40 and 45at%Al alloys increased to about 30% of the value of NiAl.NiAl and Ni-Fe-45at%Al matrix composites were fabricated successfully. When the proportionality limit of matrices were <500MPa, it increased by the addition of A12O3 short fibers. In the Ni-Fe-45at%Al matrix composites reinforced by β-SiC whisker, the proportionality limit markedly increased with the addition of under 5vol%. The Al2O3 short fiber and the β-SiC whisker reinforced Ni-Fe-45at%Al matrix composites had higher strength at room temperature than the NiAl matrix ones.

Creep features of Al2O3-Al alloy composites

Creep features of two cast aluminium alloy composites reinforced by Al2O3 short fibres randomly oriented in the matrices have been studied at 300 °C and several stress levels. The presence of short-term negative creep in primary creep is an important feature for the composites, which resulted from randomly oriented fibres strongly resisting dislocation creep in the matrix. However, the negative creep magnitude depended on both the applied stress and the nature of the material. There was a critical stress for the presence of the short-term negative creep. When the applied stress had exceeded the critical value, the negative creep disappeared. Fibres traversing grain boundaries can reinforce and resist grain boundary sliding at elevated temperature. The effect of stress on creep rate for the composites is not so strong as that for unidirectional metallic matrix composites. During the creep, some intermetallic phases in the Al2O3/Al-5Si-3Cu-1 Mg composite were precipitated and most of them were segregated at grain boundaries, leading to a small increase of the creep rate.

Thermal Conductivity of Hybrid Short Fiber Composites

A combined analytical/experimental study has been undertaken to in vestigate the effective thermal conductivity of hybrid composite materials. The analysis utilizes the equivalent inclusion approach for steady state heat conduction (Hatta and Taya, 1986), through which the interaction between the various reinforcing phases at finite con centrations is approximated by the Mori-Tanaka (1973) mean field approach. The multiple reinforcing phases of the composite are modeled as ellipsoidal in shape and thus can simulate a wide range of microstructural geometry ranging from thin platelet to con tinuous fiber reinforcement. The case when one phase of the composite is penny-shaped microcracks is studied in detail. Multiphase composites consisting of a Kerimid matrix and Al 2O3 short fibers and Si3N4 whiskers were fabricated and after a careful study of their microstructure, their thermal conductivities were measured. Analytical predictions are shown to be in good agreement with experimental results obtained for the Al2O 3/Si3N4/ Kerimid short fiber composites.

Thermal Diffusivities of Composites with Various Types of Filler

In-plane and out-of-plane thermal diffusivities (conductivities) of Kerimid resin composites reinforced with various types of filler were studied both experimentally and theoretically. The types of filler used are SiO2 particle, Al2O3 short fiber, Boron Nitride (BN) flake, and Si3N4 whisker. The prediction based on our previous model (Eshelby's equivalent inclusion method) agreed reasonably well with the experiment, except for BN flake composite. It was found that the orientation of filler has a strong effect on the overall thermal conductivity of a composite.