teóricas_11. co-cr alloys.pdf

7/25/2019 Tericas_11. Co-Cr alloys.pdf

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11. Co-Cr alloys

CoCrMo alloys: cast or wrought are used in

dentistry for many years and artificial joints

CoNiCrMo alloys: usually wrought by hotforging. Used for stems of heavily loaded

joints (knee and hip)

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General properties

High mechanical properties

High Youngs modulus

Good corrosion resistance

Biocompatibility (some concern exists in Ni containing alloys)

Good wear resistance in CoCrMo alloys

High fatigue resistance

High density (8.8 g/cm3)

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! Many similarities between implantable Co alloys and

austenitic stainless steels

!

Hardenable by: solid solution strengthening, carbide

formation, cold working, aging (precipitation hardening)


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Co-Cr alloys

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Alloys based on Co-Cr FCCmatrix

FCC phase is present at roomtemperature because of very

slow transformation to HCP HCP structures may be obtained

by heat treatment or mechanicaldeformation (martensite)

Cr added to improve corrosion

resistance (Cr2O3passive film)

Mo and W act as carbide forming

elements

C and N additions improvestrength

FCC

HCP


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Co-Ni

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Ni added to stabilize FCC phase and improve ductility


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Strength of Co-Cr alloys

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May be hardened by cold working (plastic deformation-strain hardening)


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Co-Cr alloys for implant applications

cast CoCrMo alloy (F75), wrought CoCrMo alloy (F1537) (low

carbon)

wrought CoCrWNi alloys (F90, L-605)

wrought CoNiCrMo alloy (F562)

wrought CoNiCrMoWFe alloy (F563)

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Mechanical properties of Co-Cr alloys

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Co-Cr-Mo alloys

Microstructure contains largecarbides

Large grain size

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No carbides

Smaller grain size

improved wear and fatigue

resistance

F75 cast alloy F1537 wrought alloy (low carbon content)


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Co-Cr-Mo Applications

Cast products are used for complex shapes and applications withmoderate mechanical strength requirements

Cast hip stems are widely used

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Co-Cr-Mo metal-on-metal articulations

Modern metal/metal implants have better dimensionalcontrol a show very low wear

Both cast and wrought materials are in use

Development of materials with improved wearresistance is ongoing, with very low carbon content

and free of second phase particles

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Spinal discreplacement


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Co-Ni-Cr-Mo alloys applications

Forged hip stems

Cables for orthopedic use

Pacemaker/defibrillator leads

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Defibrillator lead contains 3 silver

filled CoNiCrMo cables and a

coiled pacing lead

Corrosion resistance, tensile andfatigue strength are important

properties for this application


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Advantages of Co-Cr alloys for stents

Corrosion resistance

High density aids visibility to X-rays

Wide range of mechanical properties enable design of stents

with thinner walls improving flexibility and ease of deliverability

High elastic modulus with less recoil when balloon is released

(larger opening)

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CoCrWNi alloy

L-605 alloy


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Other applications

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Heart valve support cages, aneurysm clips, blood clot filters,orthodontic wires

CoCrNiFeMo alloys


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Bibliography

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BD Ratner et al, Biomaterials Science, 2nd Ed., Elsevier, 2004.

J Park, RS Lakes, Biomaterials an Introduction, 3rdedition, Springer,2007

teóricas_11. co-cr alloys.pdf

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