chapter  5
10 Pages

Nanostructured.Titanium.Alloys.for.Implant.Applications

Titanium. and. its. alloys. have. become. one. of. the. most. attractive. classes. of. biomedical. implant. materials.owing.to.their.light.weight,.superior.biocompatibility.and.biocorrosion.resistance,.good. mechanical.properties,.and.low.elastic.modulus..Commercial.pure.(CP).titanium,.Ti-6Al-4V,.and. Ti-6Al-7Nb.alloys.have.been.widely.used.in.biomedical.applications.to.replace.stainless.steel.and. cobalt-based.alloys..Pure.titanium.has.a.hexagonal.close-packed.(HCP).crystal.structure.at.low.temperature,.but.this.changed.to.body-centered.cubic.(BCC).above.882°C..Alloy.phases.based.on.these. two.structures.are.denoted.as.α.and.β,.respectively..Broadly.speaking,.simple.metals.(Al,.Ga).and. interstitials.(C,.N,.O).are.α-stabilizers,.and.most.transition.metals,.such.as.Nb,.Mo,.and.V,.act.as.βstabilizers..Depending.on.composition,.titanium.alloys.can.generally.be.classified.as.near-α,.α+β,. and.β.type..For.biomedical.applications,.the.primary.requirements.of.an.alloy.include.high.strength,. good.corrosion.and.wear.resistance,.low.elastic.modulus,.and.no.toxicity..Although.α+β.alloys.such. as.Ti-6Al-4V.and.Ti-6Al-7Nb.have.adequate.strength,.they.are.far.from.ideal.in.satisfying.other. stringent.requirements.for.implant.applications..In.order.to.overcome.the.long-term.health.problem. caused.by.the.release.of.Al.and.V.ions.from.these.alloys.[1,2].as.well.as.stress.shielding.related.to. elastic.modulus.which.is.still.inadequately.large.as.compared.to.that.of.the.surrounding.human.bone. [3-5],.novel.β-type.titanium.alloys.with.greater.biocompatibility,.lower.elastic.modulus,.and.better. processability.have.been.developed.in.the.past.decade.[6,7].