interface mechanical properties - · pdf fileinterface mechanical properties fiber push-out...
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INTERFACE MECHANICAL PROPERTIES
Fiber push-in test allows to measure the interface shear strength by loading an individual fiber on a lamina cross-section with a nanoindentor.
Decohesion begins in (1)
P = (nπrEf )u
n2 =2Gm
Ef ln(Re/r)
0
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1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
! c (MPa
) "f,c (M
Pa)
packing factor, Re/ r
S = τc =nPc
2πr2=
n
2σf,c
INTERFACE MECHANICAL PROPERTIES
Fiber push-out test allows to measure the interface shear strength by pushing out an individual fiber from a very thin lamina cross-section with a nanoindentor.
2r
t (≈ 15 µm)
P
δ
plate bending
elastic fiberpush-in
fiberpush-out
S =Pmax
2πrt
References
- K. K. Chawla. Composite Materials. Springer, 1998.
METAL-MATRIX COMPOSITES
Metal-matrix composites are developed to improve the mechanical properties of metallic alloys. Main objectives are to increase specific properties, hardness and mechanical behavior at high temperature.
In addition, materials with tailored properties (stiffness, electrical/thermal conductivity, CTE) can be manufactured for specific applications (thermal management, very low distortion components, etc. )
Particle and fiber-reinforced composites present very different features and properties.
Particle-reinforced MMC are isotropic and most properties are controlled by the matrix. Particle reinforcement modifies properties up to a certain extent. They can processed and machined using techniques similar to those employed for unreinforced metals. This lead to limited cost.
Fiber-reinforced MMC are anisotropic. Unidirectional fiber-reinforcement is normally used. Properties in the fiber direction are controlled by the fibers and by the matrix in the perpendicular direction. Processing routes are different from those used in the metallic matrices, leading to higher cost.
PROPERTIES
Specific stiffness and strength Controlled CTE
Addition of ceramic reinforcements leads to an important reduction in ductility and fracture toughness.
PROPERTIES
TYPOLOGY AND APPLICATIONS
Structural components with high specific stiffness, strength and fatigue resistance for which these features are critical design parameters.
Drive shaft for cars (AlMg1SiCu + 20 vol.% Al2O3 particles)
Bicycle frame
F16 ventral finsrolled 6092 Al + 17.5% SiC particles
TYPOLOGY AND APPLICATIONS
Substrates for electronic packing applications: Electronic substrate materials must conduct heat well and have a CTE close to that of semiconductors used in electronic circuitry, in the range from roughly 3 ppm K−1 to 7 ppm K−1. This can be achieved with Al/SiC composites produced via liquid infiltration.
0.2 mm!
0!
2!
4!
6!
8!
10!
12!
14!
16!
18!
20!
0! 5! 10! 15! 20! 25!
Th
erm
al co
nd
ucti
vit
y @
RT
[W
/cm
K]!
Coefficient of thermal expansion @ RT [ppm/K]!
metals!
ceramics!
diamond composites (Cu-, Al-, and Ag-matrix)!
area of interest!
Al-SiC & Cu-Mo!
Si! GaAs!
Cu!Ag!
Al!
cBN!
SiC!
Diamond!
A new generation of MMCs with Cu, Ag or Al matrix reinforced with diamond particles will provide much higher conductivity and is envisaged for the near future.
TYPOLOGY AND APPLICATIONS
Structural elements with minimum distortion: Tailored composites with minimum CTE and maximum specific stiffness to limit shape changes due to temperature.
6061 Al alloy reinforced with 42 vol. % C fibers (unidirectional)
Eıı = 342 GPaCTEıı = -0.49 10-6 ºC-1
density = 2.5 g/cm3
Hubble space telescope antenna wave guide mast
TYPOLOGY AND APPLICATIONS
Cables for power transmission lines: Al reinforced with Al2O3 fibers have replaced steel cables for power transmission lines because of the lower density, higher strength (1.5 GPa) and lower thermal expansion coefficient.
They are manufactured by liquid infiltration of an Al matrix into a Al2O3 fiber preform.
Al-Al2O3
TYPOLOGY AND APPLICATIONS
Wear/fatigue resistance applications at high temperature in automotive engines (diesel pistons, connecting rods), brakes, etc. They are made of Al2O3 short-fiber or SiC or Al2O3 particles dispersed in Al alloys. They are manufactured by powder metallurgy or liquid infiltration techniques.
Cast MMC brake for a high speed train
A359 + 20% SiC disc car brake
Honda Prelude 2.0 l cast aluminum cylinder block. The cylinder liner inset is made up of MMC.
Al 6061 + SiC connecting rod
TYPOLOGY AND APPLICATIONS
Ultra-hard. wear resistant metals
Tool steels reinforced with 20-45% TiC particles
POWDER METALLURGY
This processing route is used for either particle- o whisker-reinforced MMC. It follows the standard steps of powder sintering of metallic alloys adapted to include ceramic reinforcements in the form of particles or whiskers.
Homogeneous dispersion of matrix (powder) and reinforcement particles or whiskers. It can be carried out by ball milling, ultrasound dispersion in a liquid, or by adding a binder.
Densification by cold isostatic pressing to achieve maximum density. This process is accompanied by degassing.
Consolidation is carried out below the melting temperature by means of pressure (uniaxial, hydrostatic, extrusion) to reduce sintering time and final porosity.
Advantages: - High volume fractions of particles, homogeneously distributed, can be achieved. - Limited interfacial reactions due to limited temperature and time exposure. - Presence of nm oxide particles improves high temperature properties - Near-neat shape final products
Limitations:- High cost, limited component size, discontinuous process.- It cannot be used with long fibers (fiber fracture).
solid state processing
DIFFUSION BONDINGsolid state
processing
Standard processing route for matrices reinforced with SiC or B monofilaments (diameter > 100 µm) and leads to unidirectional or multidirectional laminates. Layers of metal foil are sandwiched with long fibers, and then pressed through to form a matrix.
Advantages - Limited fiber/matrix reaction - No fiber damage, leading to good properties
Limitations - Expensive - Limited to laminates - Discontinuous processing route
Application - Ti/SiC, Al/SiC composites
STIR CASTING liquid state processing
Most economic route to manufacture ingots of particle-reinforced MMC. They are sold to final users for remelting and/or secondary processing (forging, extrusion, etc.). The dispersed phase (ceramic particles, short fibers) is mixed with a molten matrix metal by means of mechanical stirring
Advantages - Similar to conventional casting. - Reduced cost, final parts can be casted. - Ingots can be used for different purposes
after secondary processing.
Limitations - Limited reinforcement volume fraction
due viscosity (< 30%) - Inhomogeneous reinforcement
distribution and residual porosity - Chemical reactions between matrix and
reinforcements
Applications - Ingots of Al-Si alloys reinforced with SiC, Al2O3
particles for various applications. - Disc brakes
STIR CASTING liquid state processing
Clustered and homogeneous SiC particle distributions in an Al/SiC composite
LIQUID INFILTRATION liquid state processing
Liquid metal is injected into the interstices of preform of continuous fibers, short fibers or particles. Commonly, the preform is designed with a specific shape to form an integral part of a finished product in the as-cast form.
Preforms are commonly fabricated by sedimentation of short fibers/particles from liquid suspension. In order for the preform to retain its integrity and shape, it is often necessary for a binder to be used. Various silica- and alumina-based mixtures have been popular as high temperature binders. The binding agent is normally introduced via the suspension liquid, so that it deposits or precipitates out on the fibers, often forming preferentially at fiber contact points, where it serves to lock the fiber array into a strong network.
Full infiltration normally requires the application of pressure, either using a press or gas pressure. The pressure required for infiltration can readily be calculated on the basis of the necessary meniscus curvature and corrections can be made for melt/fiber wetting.
In most cases, fibers do not act as preferential crystal nucleation sites during melt solidification. One consequence of this is that the last liquid to freeze, which is normally solute-enriched, tends to be located around the fibers. Such prolonged fiber/melt contact, often under high hydrostatic pressure and with solute enrichment, tends to favor formation of a strong interfacial bond.
LIQUID INFILTRATION liquid state processing
Squeeze casting Gas-pressure casting
LIQUID INFILTRATION liquid state processing
Advantages - Higher reinforcement volume fractions
can be achieved (up to 50%) - Lower processing time, limiting
interfacial reactions - Low porosity, better mechanical
properties
Al reinforced with 44% vol. % SiC particles Limitations - Higher processing cost due to capital investment - Limited dimensions due to press size and capacity
Applications - Thermal management applications in microelectronics - Reinforcement of engine pistons for high temperature/wear applications - Al/Al2O3 cables for power transmission lines - Connecting rods
PROCESSING - MICROSTRUCTURE
Stir casting Squeeze casting
Powder metallurgySqueeze castingSqueeze casting
Stir casting + extrusion