Evaluation of the mechanical behaviour at high temperature (150 - 350C ) of the Al-Cr-X (X = Fe, Mn, Mo, Ni, V) alloys rapidly solidified by centrifugal atomization and consolidated by hot extrusion. Investigation about the influence of the nature and the concentration of the X element upon the mechanical properties. Selection of one or two alloys capable of an industrial development.
Rapid solidification and consolidation by extrusion was used to produce alloys based on aluminium-chromium-X mix where X was utilised in various percentages (1% and 3% iron; 1% and 2.6% magnesium; 0.3% molybdenum; 1% and 3% nickel). New alloying elements were also added and evaluated (1% cerium, 1, 2 and 3% silicon; A 2% silicon, 1% vanadium mix).
The microstructure, hardness, tensile strength and thermal stability of the alloys were assessed and compared with a known alloy produced by Allied Signal Incorporated. Improved tensile properties were a result of the formation of stable, small precipitates (with a structure of Al13(CrX)2 formed at temperatures up to 300 C. At higher temperatures other complexes were formed which did not perform so well.
An aluminium-chromium-vanadium alloy was further strengthened by the addition of silicon. It appears that the presence of silicon favoured the nucleation of smaller Al13(CrV)2 precipitates. To overcome the problems of high temperature processing giving rise to an inferior product, the chromium and vanadium content were increased (while maintaining the ratio of Cr:V at 3:1) and the silicon content was optimized to encourage the production of Al13(CrV)2 and to restrict the production of undesirable precipitates.
The cerium alloy was found to have a high thermal stability but poor tensile strength. A similar adjustment of the chromium and cerium content and ratio should lead to improved tensile strength.
Nonimpregnated thermoplastic preforms manufactured by coweaving or comingling thermoplastic and carbon fibres processed into high quality composites. Mechanical properties were on the samel level as composites manufactured by using impregnated tapes with the exception of the longitudinal tensile strength of unidirectional laminates. For processing of complex shaped parts, the nonimpregnated preforms showed significant advantages due to the good drape properties of the textile preforms. Moreover, it was shown by means of physiochemical methods and single fibre tests that most mechanical properties of the composites investigated depend on the fibre matrix interfaces and interphases.
High performance thermoplastic based composites have the potential for improving the performance of these materials and simultaneously simplifying the manufacture of parts made out of these materials.
CONVENTIONAL ALUMINIUM ALLOYS LOSE THEIR STRENGTH ABOVE ABOUT 150 CELSIUS DEGREES. IN AIRCRAFT APPLICATIONS TITANIUM ALLOYS ARE USED FOR A HIGHER OPERATING TEMPERATURE, UP TO 450 CELSIUS DEGREES; IN THE RANGE OF OPERATING TEMPERATURE 150-350 CELSIUS DEGREES THOSE ALLOYS ARE STRUCTURALLY AN OVERDESIGN. SO THE DEVELOPMENT OF NEW ALUMINIUM ALLOYS TO BE USED IN THIS OPERATING TEMPERATURE RANGE PRESENTS SIGNIFICANT BENEFITS: SAVINGS IN FABRICATION COST AND MATERIAL, REDUCED COMPONENT WEIGHT, REDUCED CONSUMPTION OF TITANIUM.
THESE ALLOYS ARE FORESEEN FOR A WIDE RANGE OF AEROSPACE APPLICATIONS: GAS TURBINE ENGINES (LOW TEMPERATURE FAN, IMPELLER, COMPRESSOR CASES, VANS AND BLADES).
THE METHODS TO BE IMPLEMENTED ARE RAPID SOLIDIFICATION AND POWDER METALLURGY. THE APPROACH IS TO ADD ALLOYING ELEMENTS SUCH AS TRANSITION METALS OR RARE EARTH ELEMENTS WITH LOW SOLUBILITY AND LOW DIFFUSIVITY IN THE ALUMINIUM ALLOY.