teóricas_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
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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
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