Engineering Ceramics

Q: Alumina or zirconia?

Alumina when the part needs hardness, electrical insulation, high-temperature stability or low cost — it is harder, stiffer, a better insulator, and a third of the price. Zirconia when the part must survive a knock: Y-TZP has about three times the fracture toughness and twice the bending strength of alumina, at the cost of lower hardness, no useful electrical insulation at high temperature, and a service limit around 800 °C above which it can degrade in steam.

Q: Why do the tables show flexural strength, not yield?

Ceramics do not yield — they deform elastically and then fracture at a surface flaw. There is no yield point to report, so the industry quotes the bending (flexural) strength from a standard 3- or 4-point test, and that is the "strength" number we list. Compressive strength is typically 5–10× higher; design to keep the ceramic in compression and that is the number that matters.

Q: Can ceramics be machined?

Two answers. Machinable ceramics — Macor, boron nitride, steatite, and any ceramic in its unfired green state — cut with carbide tooling to tight tolerance and are the choice for prototypes and small runs. Dense fired alumina, zirconia, silicon nitride and SiC cannot be machined with a cutting edge at all; every feature is diamond-ground or lapped, which is why finished features on hard ceramics are specified sparingly.

Q: Which ceramic handles thermal shock?

Silicon nitride and cordierite — low expansion, moderate conductivity and good toughness let them survive a quench from red heat. Fused silica and boron nitride are also excellent. Alumina is poor (a 200 °C temperature difference across a thick part can crack it) and zirconia worse; if an alumina part will see fast heating or cooling, ask about a Si₃N₄ or cordierite alternative.

Q: Are technical ceramics expensive?

Per part, usually more than a metal equivalent: the raw powder is cheap, but pressing, sintering and diamond grinding are not, and small runs carry tooling and firing costs. In volume, pressed alumina insulators and substrates are commodity items. The economics work when the ceramic replaces a metal part that would wear, corrode, arc or fail in weeks — the ceramic then lasts years.

Technical ceramics are the materials for the conditions where metals and plastics have both failed: 1,500 °C in air, molten metal, strong acids, hard-particle abrasion, or an electrical insulator that must also conduct heat. Alumina is the workhorse — harder than hardened steel, an excellent insulator, cheap in volume; zirconia is the tough one; silicon nitride survives thermal shock; silicon carbide keeps its strength at 1,400 °C. The rules are different from metal: ceramics have no yield point, so the numbers in the tables are flexural strength, and they fail at a flaw with no warning — design for compression and let the shop grind, never machine, the hard grades.

Ceramics by chemistry

Oxide ceramicsAl₂O₃ (alumina), ZrO₂ (zirconia), ZTA, MgO27350 – 1,000The bulk of technical ceramics: alumina 96–99.8 % for insulators, substrates, wear parts and seals; yttria-stabilized zirconia (Y-TZP) for the toughest ceramic — knives, implants, valve components, bearings.

Nitride ceramicsSi₃N₄, AlN, hexagonal BN750 – 700Silicon nitride for thermal shock, bearings, turbocharger rotors and welding pins; aluminum nitride for substrates that must insulate electrically and conduct heat; boron nitride for machinable, non-wetting crucibles, break rings and high-temperature insulators.

Carbides, borides & cemented carbideSiC, B₄C, TiB₂, ZrB₂ · WC-Co grades (YG / YT / C1–C8 / K-P-M)37—Silicon carbide for seal faces, pump bearings, nozzles, kiln furniture and semiconductor handling — hardness near diamond, strength retained to 1,400 °C, excellent thermal conductivity; boron carbide for armor and blast nozzles; cemented tungsten carbide grades for cutting inserts, dies and wear parts.

Carbon & graphiteIsostatic, extruded and molded graphite · pyrolytic and flexible graphite · carbon brushes, C/C, CVD diamond21—EDM electrodes, crucibles, sintering trays, glass-handling tooling, heating elements, seals and brushes — machines fast and dry, stable to 3,000 °C in inert gas, conducts electricity and heat, but oxidizes above ~450 °C in air.

Silicates & machinable glass-ceramicsMacor, steatite, cordierite, mullite, porcelain1380 – 110Insulators and fixtures that can be machined to tolerance with carbide tooling without firing: Macor for vacuum, optical and precision parts; steatite for low-cost electrical insulators; cordierite for thermal-shock kiln furniture and catalyst supports.

Functional ceramicsPZT, ferrites, titanates, varistor oxides30—Chosen for an electrical property rather than strength: lead zirconate titanate for ultrasonic transducers, sensors and actuators; ferrites for magnetic cores; barium titanate for capacitors.

Other ceramicsVarious8—Composites, cermets, refractory bricks and proprietary grades outside the groups above.

Choose a ceramic for

Insulators and substrates that see heat, plasma or high voltage (alumina, AlN); bearings, seals, nozzles and valve seats in abrasive or corrosive flow (SiC, silicon nitride, zirconia); furnace fixtures, thermocouple sheaths and crucibles (alumina, SiC); wear plates, guides and cutting tools (alumina, zirconia, WC); medical implants and dental restorations (zirconia); and precision insulating fixtures that can be machined to size in-house (Macor, boron nitride, steatite).

Look elsewhere when

The part sees impact, bending or a bolted joint under tension (ceramics are brittle — 10–20× weaker in tension than in compression, and a chipped edge is a failed part), the geometry is thin, threaded or has sharp internal corners, the quantity is one or two of a complex shape (dense ceramics must be formed green, fired, then diamond-ground, so tooling and lead time are high), or a hard-anodized aluminum, tool steel, PEEK or glass-filled polymer would survive the environment for a fraction of the cost.

Hardness (HB equiv.) against thermal conductivity, every ceramic grade

No materials in view have both of these properties.

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Ceramic by application

Hardness and wear: Alumina 96 for most wear liners, guides and seals at the lowest cost; 99.5 % where purity or dielectric strength matters; SiC when the abrasive is hard or the part also runs hot.
Thermal shock and heat: Silicon nitride survives quenching from 1,000 °C that would crack alumina — welding pins, glow plugs, turbo rotors, molten-metal handling; cordierite for kiln furniture and burner parts at lower cost.
Electrical insulation: Alumina for high-voltage and RF insulators, feedthroughs and substrates; steatite for low-cost terminal blocks and resistor cores; AlN when the insulator must also pull heat out of a power device.
Insulator that conducts heat: Power-electronics substrates, laser-diode mounts, heater plates — AlN conducts heat like aluminum while insulating like alumina.
Machinable in the shop: Machine with ordinary carbide tooling to ±0.01 mm and use as-is: Macor for vacuum fixtures, insulators and optical mounts; BN for crucibles, nozzles and plasma-facing parts.
Implants and dental: Yttria-stabilized zirconia for crowns, implant abutments and hip-joint heads; high-purity alumina for bearing surfaces and dental posts.
Sensors and actuators: Ultrasonic cleaning and welding transducers, sonar, fuel injectors, precision positioners and flow sensors — poled PZT discs, rings and plates.

FabAgentAI

AI suggestions — verify with an engineer before ordering. Estimates are indicative; the quote page prices your exact geometry.

Manufacturing notes

Machining and grinding: Dense alumina, zirconia, silicon nitride and SiC are finished only by diamond grinding, lapping and polishing after firing — tolerances of ±0.01 mm and Ra < 0.1 µm are achievable on flats and cylinders, but every feature costs. Macor, boron nitride and steatite are machined green or fully dense with carbide tools like a stiff plastic, which makes them the choice for one-offs and prototypes.
Forming and firing: Production ceramics are pressed, extruded, injection-molded or slip-cast in the green state to near-net shape, then sintered at 1,400–1,800 °C with 15–20 % linear shrinkage. Green machining before firing is far cheaper than grinding after — it is how holes, slots and profiles should be made when the quantity allows a firing run.
Design rules: Load in compression, never in tension or bending if avoidable. Radius every corner (≥ 0.5 mm), avoid sharp thread forms and knife edges, keep wall ratios moderate, and design metal-to-ceramic joints with compliant layers or brazes that tolerate the expansion mismatch. Specify only the surfaces that need grinding.
Joining and metallizing: Alumina and AlN are metallized (Mo-Mn or thin-film) and brazed to Kovar or copper for hermetic feedthroughs and packages; ceramics are also epoxy-bonded, shrink-fitted and mechanically clamped. No welding; adhesives for anything under 150 °C.
Finishing: As-fired (matte), ground, lapped or polished; glazing for porcelain and steatite insulators; thin-film metallization for electrodes. Ceramics need no corrosion coating — the surface is already the most inert thing in the assembly.

Most-quoted ceramic grades

Grade	Chemistry	Yield, MPa	Tensile, MPa	Density, g/cm³	Machinability	Weldability	Best for
Alumina 96	Oxide ceramics	350	190	3.72	Not recommended	Not recommended	Low-cost insulators and wear parts
Alumina 99.5	Oxide ceramics	380	260	3.9	Not recommended	Not recommended	High-purity substrates and high voltage
Zirconia Y-TZP	Oxide ceramics	1,000	450	6.05	Not recommended	Not recommended	Toughest ceramic, implants, knives
Silicon Nitride	Nitride ceramics	700	450	3.22	Not recommended	Not recommended	Thermal shock, bearings, hot metal
Silicon Carbide	Carbides, borides & cemented carbide	380	250	3.15	Not recommended	Not recommended	Seal faces, nozzles, 1,400 °C
Aluminum Nitride	Nitride ceramics	320	200	3.29	Not recommended	Not recommended	Heat-conducting insulator
Macor	Silicates & machinable glass-ceramics	95	34	2.52	Good	Not recommended	Machinable precision insulator

Finishes for ceramic

All 111 finishes

5 of our 111 surface finishes take ceramic: 1 recommended outright, 3 with process care, 1 in limited cases. Each finish opens to its datasheet — thickness, hardness, salt-spray hours, spec codes and the ceramic-specific notes — and the configurator prices it on the grade you pick.

Finish	Group	On ceramic	Thickness, µm	Hardness, HV	Salt spray, h	Cost
Electroless Copper Plating	Plating & metallizing	With care	0.2–5	80–200	—	$$$
Lapping	Mechanical finishing & post-processing	Yes	0	—	—	$$$$
Surface Grinding	Mechanical finishing & post-processing	With care	0	—	—	$$$
Laser Marking	Marking, decoration & colour	With care	0–50	—	—	$
Mechanical Engraving	Marking, decoration & colour	Limited	50–500	—	—	$$

Ceramic — frequently asked

Alumina or zirconia?

Alumina when the part needs hardness, electrical insulation, high-temperature stability or low cost — it is harder, stiffer, a better insulator, and a third of the price. Zirconia when the part must survive a knock: Y-TZP has about three times the fracture toughness and twice the bending strength of alumina, at the cost of lower hardness, no useful electrical insulation at high temperature, and a service limit around 800 °C above which it can degrade in steam.

Why do the tables show flexural strength, not yield?

Ceramics do not yield — they deform elastically and then fracture at a surface flaw. There is no yield point to report, so the industry quotes the bending (flexural) strength from a standard 3- or 4-point test, and that is the "strength" number we list. Compressive strength is typically 5–10× higher; design to keep the ceramic in compression and that is the number that matters.

Can ceramics be machined?

Two answers. Machinable ceramics — Macor, boron nitride, steatite, and any ceramic in its unfired green state — cut with carbide tooling to tight tolerance and are the choice for prototypes and small runs. Dense fired alumina, zirconia, silicon nitride and SiC cannot be machined with a cutting edge at all; every feature is diamond-ground or lapped, which is why finished features on hard ceramics are specified sparingly.

Which ceramic handles thermal shock?

Silicon nitride and cordierite — low expansion, moderate conductivity and good toughness let them survive a quench from red heat. Fused silica and boron nitride are also excellent. Alumina is poor (a 200 °C temperature difference across a thick part can crack it) and zirconia worse; if an alumina part will see fast heating or cooling, ask about a Si₃N₄ or cordierite alternative.

Are technical ceramics expensive?

Per part, usually more than a metal equivalent: the raw powder is cheap, but pressing, sintering and diamond grinding are not, and small runs carry tooling and firing costs. In volume, pressed alumina insulators and substrates are commodity items. The economics work when the ceramic replaces a metal part that would wear, corrode, arc or fail in weeks — the ceramic then lasts years.