Considering handling, costs and metallographic results multifilament alumina fibres were found to lead to best results within the investment casting process.
Starting up with four different matrix alloys the AlZn6Mg1Ag1 showed best results in the MMC in case of best compatibility with the fibres.
For optimisation of the alloy in the reinforced and the unreinforced status parameters and parameter windows for casting and heat treatment were defined:
- Techniques for manufacturing performs for the considered geometries (unidirectional, windings) with defined fibre orientation and fibre content were found and optimised for all specimen and components within the project;
- During the project the process parameters were continuously adapted and optimised on the two following production routes:
a) Gas pressure infiltration (FIBRECAST) and;
b) Autoclave gas pressure infiltration (MIT).
* FIBRECAST: Based on the common investment casting process the requirements of the low gas pressure infiltration lead to an optimised ceramic mould with specially developed layers and to a casting unit. This includes casting in a vacuum chamber, starting the infiltration at a low environmental pressure.
MIT: the autoclave gas pressure infiltration was adapted to ceramic shell moulds. This included the development of a gas-tight sealing for ceramic moulds.
The monitoring of process parameters and comparison with results of mechanical testing and micro structural investigations led to optimised process parameter windows.
A comparison with regard to handling and costs led to the decision to favour the FIBRECAST infiltration route.
Micromechanical models were developed especially for continuous fibre MMCs. The data derived from mechanical testing was used to validate the computed results of the micromechanical modelling.
Based on the verified mechanical properties of the MMCs in the reinforced and unreinforced sections the models were employed for numerical simulation of axial tensions and compressions, torsion, bending and the effects of pressure and temperature. Correlation of mechanical properties predicted by modelling with the data derived from the mechanical testing was used to extend the existing micromechanical models to include more realistic representations of the composite microstructure.
To supply more information to designers of continuous fibre MMCs tests on corrosion behaviour, stress corrosion cracking, coefficient of thermal expansion and fracture mechanisms were executed.
Based on the previously measured mechanical, physical and physico-chemical properties, the micro mechanical modelling and the requirements of the process two real components were defined and designed.
Representing a typical rib structure for aerospace applications an H-shaped MMC part was designed, produced and tested.
A flange connector for an uptake riser for offshore application was selected as the most appropriate candidate for the real tubular component.
* In addition to common ND testing methods such as X-ray radiography, ultrasonic technique and dye penetration the method of 3-D non-destructive testing was scaled up to the geometric requirements making it possible to test longer components and with a higher resolution.
Correlation of measured mechanical properties (especially compression strength) to predicted properties by modelling considering possible infiltration defects and misalignment of fibres led to information about tolerable defects depending on the required properties of the MMC.
On the laboratory scale methods of separation of matrix and fibres by using external forces were successfully applied and showed a very high separation grade. In case of silicon contamination the alloy cannot be reused for MMC production, but can be introduced into the conventional secondary aluminium cycle. All employed procedures need a high technical expenditure. The volume of recyclable MMCs available will define the economic viability.
Objectives and content
A survey of engineering structure materials has shown the
imperative need to save further weight and to increase
performance without increasing the cost beyond reason.
High performance requirements in combination with complex
shapes bring conventional materials as steel, titanium
and aluminium alloys close to their performance limits.
With lot sizes from 500 to 20 pieces those parts are
mostly produced by expensive mechanical milling or die
forging, often as a number of individual pieces to be
assembled later on. Only a minor proportion is made near
net shape by casting. The group of aluminium matrix
composites with a continuous fibre reinforcement is most
efficient for ultra high strength, stiffness and fatigue
requirements. Yet their application is still limited due
to both technologically and economically inefficient
manufacturing processes. The overall objective of the
proposed project is to develop and verify a technically
and economically efficient manufacturing process for
aluminium components with selective reinforcement and to
improve the performance and acceptance of this advanced
material using a tubular and a rib component for
demonstration. The project aims at the industry-scale
verification of a combined filament winding/liquid metal
infiltration process and consequently makes the high
technological potential of fibre MMCs economically
available ensuring highest possible design freedom. The
proposed work programme comprises three main stages:
Elaboration of the materials and the process routes,
Development of a test component and
Production of two real representative components.
The development of components follows an integrated
approach of a 'total life cycle of products', i.e. the
entire component life starting with an appropriate
design, manufacture, post processing, testing under real
service conditions and recycling will be covered by the
tasks of the work programme. Besides others, a new
contactless ND inspection method will be developed and
used. The partnership comprises 5 industrial enterprises
and 2 universities from 5 EU countries (including one
less developed region, Ireland) and CH. Their business
fields reflect the total life cycle of a product starting
with the design through manufacture and testing upon
application and recycling. 6 of the partners
collaborated successfully within the FIBRECAST project
providing an ideal base for a smooth co-operation in the
proposed project. The size of the companies varies from
S1 to S7, involving 3 SMEs. The project will be managed
by Partner 1 who already co-ordinated the FIBRECAST
Funding SchemeCSC - Cost-sharing contracts
SW7 2BP London
6812 AR Arnhem