Cobalt-Chrome (CoCrMo, ASTM F75)

Material Profile: Cobalt-Chrome (CoCrMo, ASTM F75) for Binder Jetting

Binder Jetting Engineering Material Technical Report Series

Compiled from manufacturer technical datasheets and peer-reviewed literature

Abstract—Cobalt-chromium-molybdenum (CoCrMo, ASTM F75) is a biocompatible, wear-resistant, high-temperature superalloy used predominantly for orthopaedic and dental implants and gas-turbine components. It was qualified on the Desktop Metal Shop System as one of the first medical-targeted binder-jet alloys, enabling cost-effective production of patient-specific implants and dental crowns at much lower cost than laser PBF. The HCP ε-Co matrix provides exceptional wear resistance (the metal-on-metal hip joint baseline), while the 27–30 wt% Cr content provides corrosion resistance superior to even 316L stainless steel in body fluids. As-sintered binder-jet CoCrMo achieves UTS ≈ 900 MPa and yield ≈ 600 MPa; HIP at 1200 °C / 100 MPa is mandatory for fatigue-critical implants, raising UTS to ≈ 1100 MPa.

Index Terms—additive manufacturing, binder jetting, cobalt chrome, CoCrMo, ASTM F75, biomedical, dental, orthopaedic implant.

I.  MATERIAL IDENTIFICATION

This section establishes the canonical names and commercial designations under which the material is supplied.

A.  Designation

Trade names: Desktop Metal Cobalt Chrome (Shop System); ExOne CoCr; Digital Metal DM CoCr. Wrought / cast equivalents: ASTM F75-18 (cast CoCrMo for surgical implants), ASTM F1537 (wrought low-carbon CoCrMo), ASTM F1241 (CoCr for dental). UNS R30075. Common trade names: Vitallium®, Stellite® 21.

B.  Full Chemical Name

Cobalt-chromium-molybdenum HCP/FCC dual-phase superalloy. Composition (wt%, ASTM F75): Cr 27.0–30.0, Mo 5.0–7.0, Ni ≤ 1.0, Fe ≤ 0.75, C 0.35 max (or ≤ 0.05 for low-carbon F1537), Mn ≤ 1.0, Si ≤ 1.0, W ≤ 0.20, P ≤ 0.020, S ≤ 0.010, N ≤ 0.25, Co — balance. Primary phase: HCP ε-Co at room temperature; transforms to FCC γ-Co above ~ 970 °C (martensitic-like transformation on cooling).

C.  Aliases and Alternative Designations

II.  COMPOSITION AND MOLECULAR STRUCTURE

A.  Empirical Chemical Formula

Co(balance, ≈ 60–65%) — Cr(27–30%) — Mo(5–7%) — minor (Ni, Mn, Si, C, Fe, W). Primary phase: HCP ε-Co + FCC γ-Co dual; carbides M₆C (CoMo₂C) and M₂₃C₆ (Cr-rich) at grain boundaries.

Fig. 1.  Repeating unit / structural schematic of the polymer matrix.

Fig. 2.  Schematic of the single-phase polymer (no reinforcement).

B.  Composition Breakdown

TABLE I
 COMPOSITIONAL BREAKDOWN OF COBALT-CHROME (DESKTOP METAL SHOP SYSTEM) (TYPICAL / PER SUPPLIER DATASHEET)

III.  MECHANICAL PROPERTIES — XY BUILD DIRECTION (HORIZONTAL)

In the XY orientation the tensile load is applied parallel to the powder-bed plane. Binder-jetted (BJ) parts in the as-sintered state generally show modest in-plane vs build-axis anisotropy because sintering occurs near the solidus and re-distributes the porosity left by the binder-removal step. For metal BJ, post-sintering treatments (HIP, solution-anneal, age) are commonly applied to bring properties to wrought-equivalent and to eliminate residual closed porosity.

TABLE II
 MECHANICAL PROPERTIES — XY ORIENTATION (COBALT-CHROME (DESKTOP METAL SHOP SYSTEM))

IV.  MECHANICAL PROPERTIES — Z BUILD DIRECTION (VERTICAL)

In the Z orientation the tensile load is applied perpendicular to the printed layers. Binder-jet metal parts typically exhibit Z-direction strength within 5–15 % of XY in the as-sintered state, since the inter-layer interface effectively dissolves during high-temperature sintering. For sand-mould materials, Z-direction strength is dominated by inter-layer binder bonding and is generally 60–90 % of XY in transverse strength.

TABLE III
 MECHANICAL PROPERTIES — Z ORIENTATION (COBALT-CHROME (DESKTOP METAL SHOP SYSTEM))

Binder-jet CoCrMo is essentially isotropic after sintering and HIP. The high sinter temperature (~1280 °C) and slow cooling allow the ε ↔ γ phase transformation to occur uniformly, yielding a fine-grained microstructure with grain-boundary carbides. HIP (1200 °C / 100 MPa / 4 h) is mandatory for ASTM F75-compliant implants — closes residual porosity and ensures the mandatory ≥ 99.5 % density for fatigue-loaded applications.

V.  RECOMMENDED PROCESS PARAMETERS

Values summarised below give consensus operating windows from public datasheets (Desktop Metal, ExOne, voxeljet, cprint3d). Specific machines and parameter sets may differ within ±10 %; the supplier's verified parameter sheet always supersedes this table. For metal binder jetting, complete green-state cure (~200 °C) and a high-temperature de-bind / sinter cycle (typically 1 100–1 380 °C in H₂ / Ar / vacuum) are mandatory after print. For sand binder jetting, parts are usable directly after print (with optional microwave or oven post-cure).

TABLE IV
 RECOMMENDED BINDER-JETTING PROCESS PARAMETERS FOR COBALT-CHROME (DESKTOP METAL SHOP SYSTEM)

VI.  GLASS TRANSITION TEMPERATURE (TG)

Reported / typical Tg: Not applicable (metallic alloy).

Critical thermal limits: ε (HCP) ↔ γ (FCC) transformation at ~ 970 °C; service temperature limit ~ 870 °C (oxidation); melting range 1290–1410 °C. Note that for orthopaedic implant service, the 'thermal limit' is autoclave sterilisation at 132 °C — far below any metallurgical concern.

VII.  HEAT DEFLECTION TEMPERATURE (HDT)

Heat deflection temperature is the temperature at which a standard bar deflects 0.25 mm under a specified flexural load (ASTM D648 / ISO 75).

TABLE V
 HEAT DEFLECTION TEMPERATURE OF COBALT-CHROME (DESKTOP METAL SHOP SYSTEM) UNDER STANDARD TEST LOADS

VIII.  DISTINGUISHING CHARACTERISTICS AND STANDARDS

A.  Biocompatibility — ASTM F75 compliant

CoCrMo passes ISO 10993 cytotoxicity, sensitisation, intracutaneous reactivity, and chronic implantation testing. Approved by FDA for permanent orthopaedic implants (hip femoral heads, knee femoral components, dental crown copings). Ni content < 1 wt% accommodates Ni-allergic patients.

B.  Exceptional wear resistance

The HCP ε-Co matrix has the highest wear resistance of any binder-jettable metal — historically the standard metal-on-metal hip articulation surface. Carbide volume fraction ~ 5 % gives wear rates ~ 100× lower than 316L in metal-on-metal sliding contact.

C.  Corrosion resistance superior to 316L

27–30 wt% Cr (vs 17 wt% in 316L) provides chloride-pitting immunity in body fluids, sweat, and saline. Pitting Resistance Equivalent Number (PREN) ≈ 60 — among the highest of biomedical alloys.

D.  High elastic modulus (~ 230 GPa)

Nearly 2× the modulus of Ti-6Al-4V (~113 GPa) — desirable for some implant applications (e.g. dental copings requiring stiffness) but undesirable for hip/knee (causes stress shielding of cortical bone, ~ 20 GPa). Implant designers must balance with geometric compliance features.

E.  Cost-effective vs investment casting

Traditional CoCrMo dental crown manufacturing uses lost-wax investment casting from individually carved wax patterns — labour-intensive. Binder jetting batches hundreds of patient-specific crowns per build at ~1/3 the per-crown labour cost. Already disrupting dental laboratory workflows globally.

IX.  REPRESENTATIVE APPLICATIONS

Cobalt-Chrome (Desktop Metal Shop System) is typically deployed in the following applications:

1)  Dental crowns and bridges (CoCrMo): Patient-specific copings produced from intraoral-scan CAD data; sintered and HIP'd to F75 compliance; veneered with porcelain.

2)  Orthopaedic implants — femoral components: Hip femoral heads, knee femoral components requiring high wear resistance + biocompatibility (FDA cleared with full F75 + HIP traceability).

3)  Spinal cages and fusion devices: Patient-specific lumbar / cervical interbody cages with porous lattice for osseointegration.

4)  Gas turbine components (industrial): Stator vanes and combustor components for industrial gas turbines requiring high-temperature wear and corrosion resistance.

5)  Mining and pump industry wear parts: Erosion-resistant pump impellers, slurry valve seats — exploiting carbide-rich microstructure.

X.  REFERENCES

[1]  Desktop Metal, “Cobalt-Chrome — Material Data Sheet,” 2024.

[2]  ASTM F75-18, “Standard Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Castings and Casting Alloy for Surgical Implants,” 2018.

[3]  ASTM F1537-20, “Standard Specification for Wrought Cobalt-28-Chromium-6-Molybdenum Alloys for Surgical Implants,” 2020.

[4]  ASTM F1241-18, “Standard Specification for Wrought Co-26Cr-6Mo Alloy for Hand-Held Surgical Instruments,” 2018.

[5]  ISO 5832-4:2014, “Implants for surgery — Metallic materials — Part 4: Cobalt-chromium-molybdenum casting alloy,” ISO, 2014.

[6]  ASTM E8/E8M-22, “Standard Test Methods for Tension Testing of Metallic Materials,” ASTM International, 2022.

[7]  ASTM B962-17, “Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes' Principle,” ASTM International, 2017.

[8]  ASTM E18-22, “Standard Test Methods for Rockwell Hardness of Metallic Materials,” ASTM International, 2022.

[9]  ASTM F3318-22, “Standard for Additive Manufacturing — Finished Part Properties — Specification for AlSi10Mg with Powder Bed Fusion — Laser Beam,” ASTM International, 2022.

[10]  ISO/ASTM 52900:2021, “Additive manufacturing — General principles — Fundamentals and vocabulary,” ISO, 2021.

[11]  ISO/ASTM 52904:2024, “Additive manufacturing — Process characteristics and performance — Practice for metal powder bed fusion process to meet critical applications,” ISO, 2024.

[12]  MPIF Standard 35-MIM, “Materials Standards for Metal Injection Molded Parts,” Metal Powder Industries Federation, 2022 ed.

[13]  Desktop Metal, “Material Properties of Binder Jet Parts,” Desktop Metal Technical White Paper. [Online]. Available: https://www.desktopmetal.com/resources/material-properties-of-binder-jet-parts

[14]  Desktop Metal, “Why Binder Jetting?” Desktop Metal Application Note. [Online]. Available: https://www.desktopmetal.com/resources/why-binder-jetting-1

[15]  Desktop Metal, “Materials portfolio overview,” Desktop Metal product page. [Online]. Available: https://www.desktopmetal.com/materials/

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