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Aluminium matrix composite reinforced with boron fibres
Many mechanical properties of structural materials e.g. strength, hardness, can be improved by proper alloying or thermal treatment. However, there are only very limited possibilities how to improve the modulus of elasticity. The most efficient way is to combine metallic matrix with some ceramic reinforcement (particles, fibres) exhibiting substantially higher modulus of elasticity.
Various routes can be used to prepare such composite including solid state as well as liquid state technologies.
Aluminium matrix composites reinforced with boron fibres combine low density Al matrix with high strength and high elastic modulus B fibres. They are prepared by vacuum diffusion bonding technique.
Al-B composites provide unique structural material with extraordinary specific strength and stiffness. The composite can be prepared in the various kinds of profiles including tubes.
The experimental tests confirmed the tensile strength of Al/B composite reinforced with 60 vol. % of unidiretionally aligned boron fibres as high as 1400 MPa and the elastic modulus 266 GPa with the overall density of 2 565 kg.m-3
. This means that the elastic modulus is higher than that of steel while the density is lower than that of aluminium.
Depending on the parameters of diffusion bonding composites with different interfacial strengths can be prepared. In optimal conditions composites exhibit cumulative failure modes i.e. the crack that appears in boron fibre proceeds to the next fibre where it is stopped and turned off its course along the interface. The composite breaks only after accumulation of critical failure events (fibre breakage).
Structure of B fibre
Structure of Al-B composite
Unique combination of properties predetermine the application of Al/B composites in most heavily loaded dynamic constructions. Typical examples include:
- compressor turbine blades
- frames of space vehicles (space shuttle)
K. IŽDINSKÝ – P. MINÁR – J. IVAN: The effect of Isothermal Exposure and Thermal Cycling on the Properties of Boron Fibre/Aluminium Alloy Composite Material. In: Metal Matrix Composites, Key Engineering Materials, Vol. 104-107, pp. 845 - 853.