Ceramic Alumina 96% vs. Steel AISI 4340

Compare Ceramic Alumina 96% vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Ceramic Alumina 96%Sintered ceramic (pressed and fired)

Mechanical
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Yield strength	not given (tensile used)	1,035MPasourcetypical, transverse
Ultimate tensile strength	221MPasourcetypical tensile strength, 25 °C (ACMA Test #4)	1,140MPasourcetypical, transverse
Compressive strength	2,068MPasourcetypical, 20 °C (ASTM-C773)	not sourced
Flexural strength	358MPasourceflexural strength (MOR), 20 °C (ASTM-F417)	not sourced
Elongation at break	not sourced	18%sourcetypical, transverse
Young's modulus (stiffness)	303GPasourcetypical, 20 °C (ASTM-C848)	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	3,720kg/m³sourcetypical (ASTM-C20)	7,840kg/m³sourcetypical
Strength to weight	59.4kN·m/kg	132kN·m/kg2.22x higher
Stiffness to weight	81.5MN·m/kg3.19x higher	25.5MN·m/kg
Poisson's ratio	0.21sourcetypical, 20 °C (ASTM-C848)	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	125GPa1.65x stiffer in shear	75.7GPa
Bulk modulus	174GPa	185GPa
Speed of sound	9,025m/s	5,049m/s
Thermal
Thermal conductivity	24.7W/m·Ksourcetypical, 20 °C (ASTM-C408)	37.5W/m·Ksourcetypical
Thermal expansion	8.2µm/m·Ksourcemean, 25-1000 °C (ASTM-C372)	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	41µm growth38% less	56.5µm growth
Specific heat	880J/kg·Ksourcetypical, 100 °C (ASTM-E1269)	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	7.55mm²/s	10.7mm²/s41% faster
Thermal shock resistance	1,736W/m	11,678W/m6.73x more resistant
Values for	CoorsTek AD-96, nominal 96% Al2O3 sintered alumina, typical values; CoorsTek "Ceramic Seal Material Properties" (© 2018, 01899 F). AD-96 is the general 96% grade, not the ADS-96R substrate grade.	Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level

Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Is Ceramic Alumina 96% stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against tensile strength 221 MPa for Ceramic Alumina 96% (4.68x).

Which is lighter, Ceramic Alumina 96% or Steel AISI 4340?

Ceramic Alumina 96% is lighter: 3,720 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Ceramic Alumina 96% or Steel AISI 4340?

Ceramic Alumina 96% is stiffer: Young's modulus 303 GPa against 200 GPa for Steel AISI 4340, so the same part in Ceramic Alumina 96% deflects less under the same load.

Which is lighter for the same job, Ceramic Alumina 96% or Steel AISI 4340?

For the same stiffness or strength: Ceramic Alumina 96% is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate; Steel AISI 4340 is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Ceramic Alumina 96%	Steel AISI 4340
Stiff rod or tie (tension)	lighter	3.19x heavier
Stiff beam (bending)	lighter	2.59x heavier
Stiff panel or plate	lighter	2.42x heavier
Strong rod or tie	2.22x heavier	lighter
Strong beam	33% heavier	lighter
Strong panel or plate	3% heavier	lighter

For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).

Which conducts heat better, Ceramic Alumina 96% or Steel AISI 4340?

Steel AISI 4340 conducts heat better: 37.5 W/m·K against 24.7 W/m·K for Ceramic Alumina 96%.

Which expands less with temperature?

Ceramic Alumina 96% expands less: 8.2 µm/m·K against 11.3 µm/m·K for Steel AISI 4340.

Among 72 materials

Stiffness against density

Strength against density