Metal-Matrix and Ceramic-Matrix Composites
Metal-matrix composites put a ceramic or refractory second phase into a metal so it keeps the ductility and conductivity of the metal with the stiffness, wear resistance or low expansion of the ceramic: aluminum with 10–25 % SiC particulate (6061/SiC/10p, 6092/SiC/17.5p, 2124/SiC/25p) raises the modulus from 69 GPa to 80–115 GPa and cuts thermal expansion by a quarter; tungsten-copper and silver-tungsten pair a refractory skeleton with a conductive infiltrant for contacts, electrodes and heat sinks; oxide-dispersion-strengthened alloys (MA754, MA956, Glidcop AL-15) keep strength to within a few hundred degrees of melting. Ceramic-matrix composites (SiC/SiC, C/SiC, Ox/Ox) go further — fiber-toughened ceramics for 1100–1400 °C hot-section parts — and are bought to shape rather than machined.
Popular metal- and ceramic-matrix composite grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Best for |
|---|---|---|---|---|---|
| 6092/SiC/17.5p | 434 | 483 | 2.8 | Poor | Stiff, low-expansion machinable aluminum MMC |
| 6061/SiC/10p | 296 | 338 | 2.75 | Poor | Entry-level Al/SiC for housings and mounts |
| 2124/SiC/25p | 480 | 620 | 2.88 | Not recommended | Highest-stiffness aerospace aluminum MMC |
| W75Cu25 | 380 | 620 | 14.8 | Poor | EDM electrodes, heat spreaders, matched expansion |
| Glidcop AL-15 | 331 | 413 | 8.9 | Fair | Copper that survives brazing and heat |
| MA956 | 520 | 655 | 7.2 | Poor | ODS Fe-Cr-Al for 1300 °C oxidizing service |
| SiC/SiC | — | 300 | 2.5 | Not recommended | Ceramic-matrix turbine shrouds and liners |
Choose matrix composites for
Optical and metrology mounts that must be stiff and thermally matched; pistons, cylinder liners, brake rotors and wear surfaces in aluminum; heat spreaders, baseplates and EDM or welding electrodes in tungsten-copper; arcing contacts in silver-tungsten; brazed copper hardware that must not soften; furnace, combustor and heat-treatment fixtures in ODS alloys; and turbine, brake and re-entry hardware in ceramic-matrix composites.
Look elsewhere when
A monolithic alloy does the job — 7075 aluminum, Ti-6Al-4V or steel is cheaper and easier to machine than any MMC; the part is a plate or tube where Carbon Fiber gives more stiffness per gram; the geometry is complex and the quantity small (most MMCs are made near-net shape by the producer, with long lead times); pure thermal conductivity is the goal (copper or aluminum carry more heat than W-Cu by volume); or the service is a monolithic ceramic problem — Silicon Carbide or Alumina 99.5 beat a CMC below 1000 °C at a fraction of the cost.
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Metal- and ceramic-matrix composite by application
- Stiff, light precision mounts
- 6092/SiC/17.5p and 2124/SiC/25p for optical benches, gimbal housings and inertial-sensor mounts — 40–65 % stiffer than 6061 at almost the same weight, with expansion closer to steel and glass.
- Wear surfaces in aluminum
- A356/Al2O3/20p and A359/SiC/20p cast rotors, drums and liners; 6061/SiC/10p extruded and machined for pistons and slide ways where a steel insert would be too heavy.
Working with metal- and ceramic-matrix composite
- Machining
- Al/SiC wears carbide in minutes — PCD tooling, rigid setups, moderate speed and flood coolant hold ±0.05 mm and a fine finish, and the higher the SiC loading the slower the cut. W-Cu and Ag-W machine with carbide at low speed and grind well; EDM is the route for fine detail. ODS alloys machine like the base alloy, only harder. Ceramic-matrix composites are ground and diamond-drilled only, and only where the producer has left stock.
- Joining
- Nothing here forms after production. Al/SiC extrusions and plate bond with structural adhesives and bolt; fusion welding is possible with the matrix filler but degrades the reinforcement zone, so it is avoided on precision parts. W-Cu brazes and solders readily to ceramics and copper; Glidcop brazes without softening, which is its whole point. ODS alloys are joined by brazing, diffusion bonding or friction welding — fusion welding destroys the dispersion.
- Heat treatment
- Al/SiC grades take the parent-alloy tempers (T6 for 6061 and 6092, T4 or T8 for 2124) with tighter quench windows; stress relief before final machining matters more than in the monolithic alloy because residual stresses are higher. ODS alloys are used in the coarse-grained recrystallized condition set by the producer and are not re-heat-treated.
- Finishing and surfaces
- Al/SiC anodizes and chem-films, though the exposed SiC leaves a duller, less uniform coat than 6061; nickel plating is the usual finish on W-Cu and Ag-W. CMCs receive environmental-barrier coatings from the producer. Handle AlBeMet AM162 and any beryllium-containing grade under the same dust-control rules as beryllium metal.
Other composite series
Metal-Matrix and Ceramic-Matrix Composites — frequently asked
What is metal- and ceramic-matrix composite?
Metal-matrix composites put a ceramic or refractory second phase into a metal so it keeps the ductility and conductivity of the metal with the stiffness, wear resistance or low expansion of the ceramic: aluminum with 10–25 % SiC particulate (6061/SiC/10p, 6092/SiC/17.5p, 2124/SiC/25p) raises the modulus from 69 GPa to 80–115 GPa and cuts thermal expansion by a quarter; tungsten-copper and silver-tungsten pair a refractory skeleton with a conductive infiltrant for contacts, electrodes and heat sinks; oxide-dispersion-strengthened alloys (MA754, MA956, Glidcop AL-15) keep strength to within a few hundred degrees of melting. Ceramic-matrix composites (SiC/SiC, C/SiC, Ox/Ox) go further — fiber-toughened ceramics for 1100–1400 °C hot-section parts — and are bought to shape rather than machined.
Which grade of metal- and ceramic-matrix composite should I use?
6092/SiC/17.5p and 6061/SiC/10p for stiff, light, wear-resistant aluminum parts that still machine with PCD tooling — optical mounts, brake components, electronics housings, pistons; 2124/SiC/25p for the highest stiffness and lowest expansion in an aerospace aluminum; A356/Al2O3/20p and A359/SiC/20p as the castable versions for rotors and drums. W75Cu25 for EDM electrodes, resistance-welding electrodes and heat spreaders under high-power chips, where its expansion is matched to ceramics; Ag75W25 for arcing electrical contacts. Glidcop AL-15 for copper that must survive brazing or run hot without losing strength. MA956 for furnace and combustor hardware in oxidizing atmospheres to 1300 °C, MA754 for vanes and heat-treatment fixtures. SiC/SiC for turbine shrouds and combustor liners, C/SiC and C/C-SiC for brake discs, nozzles and re-entry components, Ox/Ox for exhaust structure that must survive oxidation without a coating.
Which grade of metal- and ceramic-matrix composite is the strongest?
SCS-6/Ti-6Al-4V has the highest yield strength in the series at 1,100 MPa; B/6061Al follows at 950 MPa. Values are for each grade's default condition.
Which grade of metal- and ceramic-matrix composite is easiest to machine?
AZ91/SiC/15p (machinability fair, 45/100), then Glidcop AL-15 (45/100).
How much stiffer is Al/SiC than plain aluminum?
In proportion to the SiC loading: 10 % particulate (6061/SiC/10p) gives roughly 80–85 GPa against 69 GPa for 6061, 17.5 % (6092/SiC/17.5p) about 100 GPa, and 25 % (2124/SiC/25p) about 115 GPa — a 15–65 % gain at almost the same density, with thermal expansion falling from 23 to about 15–18 ppm/K. Strength rises less and ductility drops to a few percent elongation, so the material is chosen for stiffness, wear and thermal match, not toughness.
Why use tungsten-copper instead of copper for an electrode or heat spreader?
Because copper alone is too soft and expands too much. W75Cu25 keeps about half the thermal conductivity of copper but expands at roughly 9–10 ppm/K, close to alumina, GaAs and silicon carriers, so a chip brazed to it does not crack in thermal cycling; as an EDM or resistance-welding electrode the tungsten skeleton resists the erosion and mushrooming that wear pure copper in minutes. Where expansion match and erosion do not matter, copper or aluminum carry more heat for less weight and cost.