TEXTURE OF TITANIUM AND ITS ALLOYS

Presented by:Gaurav SinghPhD Student,Department of Materials EnggIISc Bangalore

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METALLURGY OF TITANIUM

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β→α Transformation{0001}α ІІ {110}β

<1120>α ІІ <111>β

Dα-Ti=10-19 and Dβ-Ti=10-18 m2/s

β(slow cooling)→α(lamellar)

β(quenching)→α(martensite)Hexagonal α’ martensite

Orthorhombic α’’ martensite

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Classification of Ti alloys

α alloys β alloys α+β alloysNear αMetastable β

α-stabilizer Al,O,N and C

β-stabilizer Mo,V,Ta,Nb,Fe,Mn,Cr,Co,Ni,Cu,Si and H

Neutral stabilizer Sn and Zr

a)lamellar microstructure b) Martensitic microstructure c) Bimodal microstructure

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TEXTURE IN TITANIUM Anisotropy in properties- presence of hcp α

Main textures of Titanium and its alloys Rolling Texture

Annealing texture Transformation texture Solidification texture

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Cold rolling Texture of pure Ti

Initial texture {1013}[1210] basal texture {0001}[0110] Final texture {2115}[0110]

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Annealing texture of Ti after cold rolling

Ti sheet cold rolled upto 90% and then annealed at T=750°C(2115)[0Ī10](before annealing) (Ī013)[1210] (after annealing)

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Hot rolling texture of Ti

Hot rolled upto 96% reduction at a temperature between 700 to 900°C{2115}[0110] below 800°C{2110}[0110] and {2118}[8443] (800<T<850°C){2110}[0110] (T>880°C)

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Hot Rolling Texture in Ti-6Al-4V alloy

{2110}[0110] T< 850 °C{2110}[0110] and {2110}[0001] 850<T<1000°C{1010}[0001] T> 1000°C

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Hot Rolling Texture in high strength Ti alloy

Main alloysTi-4AlTi-5Al-2.5SnTi-6Al-2Sn-4Zr-2MoTi-8Al-1M0-1V

Below β transus it will depend upon dispersion of α and β phase.

Above β transus it will depend upon the transformation property of the alloy.

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Ti-4AlAbove β transus Main component {-2110}[0110]Between β transus and recrystallization T of α {1019}[9092],{0001}[1100]

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Hot rolling texture of Ti-5Al-2.5SnAbove β transus Main component {1010}[1213]Between β transus and Recrystallization T of α {2110}[0110]Below Recrystallization T of α basal texture develop {0001}[1210]

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Hot rolling texture of Ti-6Al-2Sn-4Zr-2MoVolume fraction of β is more.Below Recrystallization T of α (2110)[0110]Between β transus and Recrystallization T of α (2110)[0110] and (2118)[8443]Above β transus (2110)[0110] and (1010)[0001]

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Transformation texture Ti alloys

Amount of cold reduction.Transformation behavior of the alloy , i.e

microstructure.Cooling Rate.Al equivalent. (Al eq= wt %Al +1/3 %Si+1/6%Zr+10%O)

Planar disregistry

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Texture development during ECAP of Ti

During first pass, deformation by glide of dislocation on basal plane and {10-10}twinning.Low dislocation density in first pass (109/cm2)Most shear is accommodated by twinning on {1010} plane.During second ECAP pass deformation on secondary slip system due to• decrease in grain size strain hardening of the slip system.• critical stress for twin nucleation increases.Strong basal texture is observed.

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Texture formation in ECAE of Ti-6Al-4V

Occurs at T=800°C (moderate strain rate)

During First pass, deformation occurs by glide of dislocation and twinning.

During second pass deformation occurs mainly by twinning.

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Nucleation of Mechanical twins- requires very large stress Regions of high stress concentration. Non-planar dissociation of slip dislocation.Deformation by twinning on {1010}plane. low value of critical stress for twin nucleation. separation of twin partial is more.

(0001)Pole figure.a) as received b) one ECAE pass c)two ECAE pass in Ti-64

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Effect of magnetic field on texture of Titanium

Cold rolled Ti to 82% reduction and then annealed at T=750 °C in a magnetic field H=19.4T with varying the orientation of the Sheet.

Major cold rolling texture of Ti (2115)[0110] transform to (1013)[1210] by rotation of 30° about c axis.Two driving force for grain growth curvature effect 2σ/R magnetic driving force H2∆M(cos2θ1- cos2θ2)Growth rate will be more for grain whose <0001> is perpendicular to H. strong basal texture is observed

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Effect of texture on mechanical property of Ti alloy

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Conclusion- Texture of Ti and it alloy strongly depend upon alloying element, cooling rate

transformation behavior , microstructure, prior orientation of the parent phase, amount of cold reduction and cooling rate.

ECAE texture of Ti-64 will depend upon the separation of the twin partial.

Transformation texture will depend upon prior cold reduction, cooling rate, and planar disregistry.

Magnetic field can also effect texture of the Titanium alloy.

Mode of loading and orientation of the crystallite can effect mechanical properties of the Titanium alloy.

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References-1. Cold rolling texture of Titanium by H.Inagaki.2. Texture and mechanical anisotropy in cold rolled Titanium by H.Inagaki.3. Hot rolling texture of Titanium by H.Inagaki.4. Evolution of texture and microstructure in thermomechanical Ti-64 by H.Inagaki.5. Hot rolling texture in High strength Titanium alloys.6. Scripta Materilia ,vol 34,No-8,pp-1281-1286,1996.7. Acta Materialia 51(2003) 983-996 8. Acta Materialia 54(2006) 3755-3771 9. Acta Materialia 52(2004) 4347-4383 10. Material science and engineering A 319-321(2001) 409-414.

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