Ti alloys
- 1. Thermo-mechanical processing of Ti alloys SUBMITTED TO PROF. B. P. KASHYAP PROFESSOR-IN-CHARGE SUBMITTED BY ADARSH BHARTI MP19MT002 DEPARTMENT OF METALLURGICAL & MATERIALS ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY JODHPUR
- 2. Abstract Titanium alloys is used in many engineering applications. It is very strong and high corrosion strength and can perform well at high temperature up to 600°C. Because of its high strength, low weight ratio and corrosion resistance ratio it is used in many aerospace and marine applications. The specific properties of titanium is very good so that it is cost effective. In engineering applications, titanium takes over heavier, serviceable and less cost effective materials. It has excellent mechanical properties and machinability. Titanium has very high application in medicine. Also, the biocompatibility of Ti alloys is very good so it is used in body implants where it has direct contact with bone and muscles.
- 3. Introduction Crystal structure – BCC, FCC Density(g/cc) - 4.54 Melting point - 1667°C Atomic diameter - 0.32A° Properties • Experiences allotropic transformation at 882.5°C. • React with oxygen, nitrogen, carbon and hydrogen. • Extraction is difficult & costly. • High strength and toughness. • Used in advance application.
- 4. Advantages of Ti alloys Advantages • More used in aircraft because of its high-strength to weight ratio. • Used in engines (fans and compressor) because of high temperature resistance. • High corrosion resistance • Low specific gravity. • Non-magnetic property. • High specific strength. • Bio-compatible material • Fatigue property is more than steel. • Good fabrication ability.
- 5. Application of titanium alloys a)Titanium cladded museum b)hip-joint component c)Turbine blades Aerospace • Civil • Military • Space Medical • Orthopedic Implants • Bone screws • Trauma Plates • Dental fixtures • Surgical instruments Industrial • Petrochemical • Offshore • Subsea • Metal Finishing • Pulp & Paper • General Engineering Specialist • Body jewelry • Ultrasonic welding • Motor racing • Marine • Bicycle • Sport equipment
- 7. 882.3°C Transformation Alloying elements • Alpha stabilizers- Al, O, N • Beta stabilizers- • Neutral- Zr, Si, Sn 1. Isomorphous – Mo, V, Wb, Nb, Ta 2. Eutectoid – Fe, Cr, Cu, Ni, Co, Mn Phase diagram of Ti alloys
- 8. Classification of titanium alloys Titanium alloys Commercially pure titanium alloys Alpha-beta titanium alloys Beta titanium alloys Generally non-heat treatable and weldable Medium strength Good creep resistance Good corrosion resistance Heat treatable Good forming properties Medium to high strength Good creep resistance Heat treatable formable Very high strength Low ductility
- 9. Classification with examples •Commercially Pure – ASTM grades 1,2,3,4 •Ti/Pd Alloys- ASTM grades 7 and 11 Alpha Alloys •Ti-2.5%Cu- IMI 230Alpha + compound •Ti-8%Al-1%Mo-1%V •Ti-6%Al-5%Zr-0.5%Mo-0.2%Si- IMI 685 •Ti-6%Al-2%Sn-4%Zr-2%Mo-0.80%Si Near alpha Alloys •Ti-6%Al-4%V •Ti-4%Al-4%Mo-2%Sn-0.5%Si •Ti-6%Al-4%Mo-4%Sn-0.5%Si –IMI 551 Alpha-Beta Alloys •Ti-3%Al-8%V-6%Cr-4%Zr-4%Mo- Beta C •Ti-15%Mo-3%Al-0.2%Si- Timetal 21 S Metastable Beta Alloys
- 10. Classification by strength •ASTM grades 1,2,3,7 and 11Low strength •ASTM grades 4,5 and 9 •Ti-2.5%Cu •Ti-8%Al-19%Mo-0.1%V Medium strength •Ti-3%Al-8%V-6%Cr-4%Zr-4%Mo •Ti-4%Al-4%Mo-2%Sn-0.5%Si •Ti-6%Al-6%V-2.5%Sn High strength •Ti-10%V-2%Fe-3%Al •Ti-4%Al-4%Mo-4%Sn-0.5%Si Very high strength
- 11. Heat treatment It is applied to α/β and β Ti alloys due to α-β transformation Heat treatment diagram for β-titanium alloys Effect • Strength of annealed alloys increases with alloys contents • Quenching from β phase gives a martensitic transformation with improved strength. • For lowly alloyed Ti alloys, rapid quenching from the β phase gives maximum strength. • For highly alloyed Ti alloys, rapid quenching from β phase gives lowest strength but after aging gives maximum strength. • For highly alloyed Ti alloys, rapid quenching from β phase gives lowest strength but after aging gives maximum strength.
- 12. Commercially pure titanium alpha/near alpha alloys Microstructure contains HCP α phase and can be divided into:- Commercially pure titanium alloys Alpha titanium alloys Near alpha titanium alloys Characteristics Non-heat treatable weldable Medium strength Good notch toughness Good creep resistance Phase diagram of α- stabilized Ti alloy
- 13. Microstructure of CP titanium alloys HCP alpha phase structure a) Purity of 99-99.5% b) HCP structure c) Main elements are Fe and interstitial elements like C,O,N and H d) O content determine the grade and strength. e) C,N,H are impurities.
- 14. Properties and application of CP Ti Lower strength depending on content of O & N Corrosion resistance to nitric acid, moist chlorine. Less expensive 0.2% Pd addition improves corrosion resistance Applications airframes Surgical implants chemical marine Heat exchanger
- 15. Alpha Titanium Alloys 1. Al and O are the main alloying elements, which provide solid solution strengthening. O and N gives interstitial hardening. 2. The amount of α stabilizers should not exceed 9%. %𝐴𝑙 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 = 𝐴𝑙 + 0.33𝑆𝑛 + 0.167𝑍𝑟 + 10 𝑂 + 𝐶 + 2𝑁 ≤ 9% 3. 5-6% Al can lead to finely dispersed, ordered phase (α2), which is coherent to lattice. 4. Sn and Zr are also added to stabilize the phase and give strength.
- 16. Microstructure, properties and application •Moderate strength •Strength depend on O and Al content. •Al reduces the density. •Good oxidation resistance PROPERTIES •Aircraft engine compressor blades •Sheet metal parts •High pressure cryogenic vehicle at -423°C. APPLICATION •Ti-5%Al-2.5%Sn alloy in sheet form •Sn is added to improve ductility. MICROSTRUCTURE
- 17. Heat treatment of CP and alpha titanium alloys Annealing of CP Ti at high temperature gives HCP 𝛼-phase Quenching of CP Ti alloy from β phase change the HCP structure to hexagonal martensitic phase with remaining β phase. Air cooling of CP Ti from β phase field produces widmanstatten plates.
- 18. Near alpha Titanium Alloys 1. Small amount of β stabilizer(Mo, V) is added for microstructure of β phase dispersed in α- structure. 2. Sn and Zr are added to compensate Al contents while maintaining strength and ductility. 3. Show greater creep strength than fully α Ti alloy up to 400°C. 4. Ti-8Al-1Mo-1V and Ti-6Al-2Sn-4Zr-Mo alloys are the most commonly used for aerospace applications, i.e., airframe and engine parts. a) Duplex annealed Ti-8Al-1Mo-1V b) Forged compressor disc made from neat alloy IMI 685
- 19. Heat treatment of near alpha titanium alloys Heat treatment of 𝛼 + 𝛽 phase field • Alloys should contain high amount of 𝛼 stabilizers without severe loss of ductility. • Small amount of Mo or V are added to promote the response to heat treatment. • The alloy is heated up to T to obtain equal amount of 𝛼 and β phases. • Air cooling gives equi-axed primary 𝛼 phase Widmanstätten formed by nucleation and growth from the β phase. • Faster cooling transforms β in to martensitic 𝛼 to give higher strength. Pseudo-binary diagram for Ti-8%Al with Mo and V addition. Air cooled from 𝛼 + 𝛽 phase to primary 𝛼 and windmanstattan 𝛼.
- 20. Heat treated from 𝛽 phase field • Quenching from the β phase field produces laths of martensitic α’ , which are delineated by thin films of β phase. • Aging causes precipitation of fine 𝛼 phase dispersion. • Air-cooling from the 𝛽 phase field gives a basket weave structure of 𝛼 phase delineated by 𝛽 phase. (a) Near 𝛼-Ti oil quenched (b) Quenched from 𝛽 phase field and aged at 850°C Near 𝛼-Ti air cooled from the 𝛽 phase field.
- 21. Effect of cooling rate from 𝛽 phase field in lamellar microstructure Increasing cooling rate
- 22. Properties And Application Properties • Moderately high strength at RT and relatively good ductility (~15%). • High toughness and good creep strength at high temperatures. • Good weld-ability. • Good resistance to salt-water environment Application • Airframe and jet engine parts requiring high strength, good creep and toughness. • Parts and cases for jet engine compressors, air- frame skin components.
- 23. Alpha beta titanium alloys • Alpha-beta titanium alloys contains both 𝛼 𝑎𝑛𝑑 𝛽. • 𝛼 stabilizers are used to give strength with 4-6% 𝛽 stabilizers to allow the β phase to retain at RT after quenching from β or 𝛼 + 𝛽 phase field. • Improved strength and formability to 𝛼-Ti alloys. • Microstructure depends on chemical composition, processing history and heat treatments i.e. annealing, quenching and tempering. • Heat treatment can be done to achieve desired microstructure and properties.
- 24. Annealing from 𝛽 and 𝛼 + 𝛽 phase field Annealing from β phase field causes a transformation from β to 𝛼 microstructure containing lamellar structure of similar crystal orientation Annealing from 𝛼 + 𝛽 phase field produces microstructure approaching equilibrium equi-axed primary 𝛼 phase surrounded with retained 𝛽 phase.
- 25. Air Cooling from 𝛽 and 𝛼 + 𝛽 phase field • Air cooling provides intermediate cooling rates. • Air cooling from the 𝛽 phase field produces fine acicular 𝛼, which is transformed from the 𝛽 phase by nucleation and growth. • Air cooling from 𝛼 + 𝛽 𝑝ℎ𝑎𝑠𝑒 𝑓𝑖𝑒𝑙𝑑 provide equi-axed primary 𝛼 𝑝ℎ𝑎𝑠𝑒 in a matrix of transformed 𝛽 phase. Air-cooled from β phase field giving transformed β phase (acicular) Air-cooled from 𝛼 + 𝛽 phase field, showing primary 𝛼 grains in a matrix of transformed 𝛽(acicular).
- 26. Heat treatment of alpha-beta titanium alloy Annealing from the β and α+β phase field. Air cooling from the β and α+β phase field. Quenching from β and α+β phase fields. Tempering of titanium martensite. Decomposition of metastable β
- 27. Composition and application of Ti alloys Alloy composition • 6% Al, 4% V • 6% Al, 4% V(low O2) • 6% Al, 6%V, 2% Sn • 8% Mn • 3% Al, 2.5% V Condition • Annealed(solution + age) • Annealed • Annealed (solution + age) • Annealed • Annealed Application • Rocket motor cases, blades and disk, turbines and compressors, pressure vessels • High pressure cryogenic vessels • Rocket motor cases, aircraft parts, landing gears, good hardenability. • Aircraft sheet components, structural sections, good formability and moderate strength. • Aircraft hydraulic tubing, foil; combines strength, weld- ability and formability .
- 28. Quenching from 𝛽 phase field • Martensite of different crystal structure. • Increasing solute, 𝛼′ to 𝛼“. 𝛽 𝛼′(martensite) Lath martensite colonies Lenticular or twinned martensite 𝛼”(𝑚𝑎𝑟𝑡𝑒𝑛𝑠𝑖𝑡𝑒) 𝛼”′(martensite) 𝑚𝑒𝑡𝑎𝑠𝑡𝑎𝑏𝑙𝑒 𝛽 Possible reaction due to quenching from the 𝛽 phase field. Increasing solute content Hexagonal 𝛼’ lath, (b) hexagonal lenticular 𝛼’, (c) orthorhombic 𝛽’’
- 29. Tempering of Ti martensite Decomposition of martensitic structure occurs when a quenched alloy is subjected to elevated temperature treatment. Decomposition reaction depends on martensite crystal structure and alloy composition. 𝛼′ martensite 𝛽-isomorphous alloys 𝛽 eutectoid alloys Alloys with slow eutectoid reaction 𝛼′ → 𝛼 + 𝛽 → 𝛼 + 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 Alloys with fast eutectoid reaction 𝛼′ → 𝛼 + 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑
- 30. Decomposition of metastable 𝛽 Retained 𝛽 obtained after quenching decomposes when subjected to aging at elevated temperature→developing high tensile strength. The metastable 𝛽 is transformed into equilibrium 𝛼 phase at high aging temperature due to difficulty in nucleating HCP 𝛼 phase on BCC 𝛽 matrix. 𝛽 isomorphous alloy phase diagram Medium alloy content 100-500°C 𝛽 → 𝛽 + 𝜔 → 𝛽 + 𝛼 Concentrated alloys 200-500°C 𝛽 → 𝛽 + 𝛽1 → 𝛽 + 𝛼
- 32. Microstructure vs Heat treatment
- 33. Beta Titanium Alloys Beta stabilizers are sufficiently added to retain a fully β structure when quenched from β phase field. Moeqiv%= 1.0Mo+ 0.67V +0.44W -0.28Nb +0.22Ta +1.6Cr+…-1.0Al Metastable β alloys : Mo eq. <25 Stable 𝛽 alloys : Mo eq. 25-40
- 34. 𝛽 titanium alloys It posses BCC crystal structure which is cold worked in beta phase field. Microstructure after quenching contains equi-axed 𝛽 phase. After solution heat treating and quenching, it gives very high strength. Metastable 𝛽 titanium alloys are hardenable while stable 𝛽Ti alloys are non-hardenable. Flow stress of Ti alloys hot workedTi alloy heat treated and water quenched
- 35. • Most β titanium alloys are metastable and transform into:- 1. Coarse 𝛼 platets after heat treated in the 𝛼 + 𝛽 phase field 2. 𝛼 phase precipitation after long term aging at elevated temperature. High strength causes embrittlement that is not required
- 36. Advantages • High strength to density ratio • Low modulus • High strength/toughness • High fatigue strength • Good deep hardenability • Low forging temperature • Easy to heat treat • Excellent corrosion resistance • Excellent combustion resistance Disadvantages • High density • Low modulus • Poor low and high temperature properties • Small processing window • High formulation cost • Segregation problems • High spring-back • Poor corrosion resistance • Interstitial pick-up • Microstructural instabilities
- 37. TMP of β titanium 𝛽 annealing 𝛽 −annealed microstructure Ti-6246 TMP for β annealing Step 1 • Homogenization treatment above β transus temperature. • Depending on the cooling rate from homogenization temperature the grain boundary 𝛼 layer form Step 2 • Aging at high temperature • High temperature aging will produce coarse alpha precipitate throughout the matrix. Step 3 • Aging at low temperature • Low temperature aging will produce dine alpha precipitate in the matrix.
- 38. Processing bi-modal microstructure Bi-modal processing route Bimodal microstructure 𝛼 + 𝛽 microstructure • The processing consists of homogenization in the β phase field, deformation in the 𝛼 + 𝛽 phase field. • After cooling from homogenization temperature and heating to deformation temperature, large equiaxed β grains with grain boundary 𝛼 and 𝛼-plates within the grain. • The next step is deformation in the 𝛼 + 𝛽 phase field, the structure is deformed to higher degree. • Then it is deformed so that complete recrystallization of the phase occurs. • Aging is done to precipitate the particles of different sizes according to temperature decrease.
- 39. 𝛽 processing Ingot breakdown Hot working is done in β phase field After finishing the deformation, fast cooling is applied so that no recrystallization happens 𝛽 processed microstructure (a)LM (b)TEM
- 40. Through transus processing Necklace microstructure • Time temperature control of the deformation process is presented. When temperature drops under 𝛽 transus, 𝛼 phase start to precipitate at 𝛽 grain boundaries. • Due to high dislocation density the 𝛼 phase precipitate in the form of round particles at 𝛽 grain boundaries. That is why it called necklace. • Deformation is two step. High temperature aging leads to precipitation of 𝛼 − plates within 𝛽 grains. The dislocation density is so high that plates are small. • Low temperature aging leads to precipitation of small secondary 𝛼 platelates to harden the alloy
- 41. Fatigue Properties S-N curve β-Cez S-N curve Ti -6246 • The high cycle fatigue properties of different microstructure is compared by anisotropy characteristics of β- grains. • The crack plane and β grain boundary for ST orientation and 45° orientation. • The S-N curve of β processed condition of β- Cez and Ti-6246. • The 45° orientation exhibit the lowest HCF strength for both alloys. • For 𝛽-cez, the ST direction shows highest HCF strength and vice versa of Ti-6246. • Also the bi-modal microstructure shows highest HCF strength. Fatigue cracks in the microstructure nucleates at coarse 𝛼-plates in the matrix. The small dimension of plates lead to small maximum slip length and high HCF strength.
- 42. Deformation of titanium alloys HCP 𝛼 Ti alloys Deformation is limited on available slip planes and relies on twinning. BCC β Ti alloys Deformation relies on more slip system with limited twinning deformation.
- 43. Forging of Ti alloys Ti alloys have much higher flow stress than Al alloys or steels requiring high forging pressure, capacity. Near net shape is obtained using precision die forging. Initial working is done about 150°C above the beta transient temperature to about 28-38% strain, depending on alloy types and prior heat treatments. Subsequent deformation processes can be done in the α+β region
- 44. Rolling of Ti alloys Packed to avoid surface oxidation. group of titanium sheet blanks are sealed with steel retort and rolled as a group. Parting agent is filled between individual blanks to prevent sheet bonding. After hot rolling, the sheets are extracted, pickled and flattened for finishing process Hot-rolled Ti clad steel plates used in condenser in power station Titanium ring rolling
- 45. Machining of Ti alloys These alloys are more difficult to machine compared to steel and conventional alloys for milling, drilling, turning, etc. Titanium’s low thermal conductivity reduces heat dissipation at metal-workpiece interface decreased tool life, welding or galling at tool- workpiece interface. Machining tools are critical carbide or ceramic toolings. Avoid loss of surface integrity due to tool damage dramatically reduce properties especially fatigue.
- 46. Powder metallurgy of Ti alloys Titanium PM parts are made from pressing and sintering, giving near-net shape products. Production of titanium powder is quite difficult due to high reactivity of titanium with oxygen. The whole process (atomisation, pressing and sintering) requires prevention from atmospheric contamination. a)Ti-6Al-4V alloy produced from CIPing and sintering of blended CP sponge and ALV master alloy b)Same material after HIPing, showing no porosity
- 47. Properties of Ti alloys Alloying (chemistry) • density • Precipitation hardening • Solid solution hardening • Ordered structure • Stiffness • Thermal expansion • Corrosion behavior • Oxidation behavior Processing (microstructure) • Hardening • Thermo-mechanical treatment • Stress corrosion cracking • SPF(grain size) • Rapid solidification • Mechanical alloying • HIP(PM, casting) • consolidation Composites (MMC) • density • Stiffness • Strength • Wear • Fatigue • Thermal expansion • Oxidation resistance • Corrosion protection Specific proof stress of various materials
- 48. Strength and toughness of Ti alloys Tensile strength of different Ti alloys at a range of temperatures
- 49. Microstructural and tensile properties of Ti alloys • Bimodal microstructure is more resistant to fracture due to equaixed α phase giving higher strength. • Equiaxed α phase is also more resistant to nucleation of voids higher ductility.
- 50. Microstructure and fracture toughness properties of Ti alloy Coarse lamellar and fine lamellar • More torturous path in coarse lamellar microstructure leads to higher energy dissipation during fracture higher toughness.
- 51. Fatigue properties of Ti alloys Smaller equiaxed α grains are more beneficial to fatigue strength. Crack nucleates within the lamellar region more easily than in the equiaxed α phase region. But crack propagation is more difficult in the lamellar structure Crack initiation at lamellar region in bi-modal microstructure Crack propagation paths in (a) lamellar and (b) bi-modal structures
- 52. GUM TITANIUM • It is a beta titanium based alloys having excellent mechanical behavior at room temperature. • It exhibit high yield stress(1Gpa) and very good elongation before failure (upto 35%) • The governing mechanism is still unclear. • Observation revealed that there is existence of micro-meter size 2-D band like feature that shows local shear.
- 53. Titanium alloy for biomedical applications • Hip and knee prostheses • Good corrosion stability in human body • High fatigue resistance • High strength to weight ratio • Good ductility • Low elastic modulus • Excellent wear resistance • Low cyto-toxicity • Less tendency for allergic reactions
- 54. Deformation behavior of alpha and near alpha Ti alloys Flow stress of CP Ti at various temperature. Flow stress of Ti-5Al-2.5Sn at 800°C and various strain rate. Flow stress of IMI 834 at 1000°C at various strain rate
- 55. Observation from deformation curve • Stress-strain curve show initial work hardening. • Higher peak stress are observed at higher strain and low temperatures. • Flow stress increases with increase in strain at given temperature. • Increase in flow stress with increase in substitutional solute strengthening. • Below beta transus temperature, material is undergoing dynamic recovery in which rate of hardening is balanced by rate of softening by dislocation anhilation.
- 56. Stress temperature map of Ti
- 57. TMP of 𝛽-Ti TMP process Step1- Heating at 10Ks-1 at 1223K and hold on for 12 Step2- Step1+ cooling at 35Ks-1 from 1223K to 1173K where 25% deformation occurs. Step3- Step2 + Cooling at 35Ks-1 from 1173K to 1023K, 1800s soaking Step4- Step3 + 40% Deformation at 1023K
- 58. Grain boundary variation width Variation of width of the grain boundary α-phase with TMP
- 59. Distribution of alloying elements between the phases after TMP Elemental map of Ti-55511 after TMP (a)Ti (b)Al (c)Mo (d)V (e)Cr (f)Fe Elemental map of Ti-55521 after TMP (a)Ti (b)Al (c)Mo (d)V (e)Cr (f)Fe
- 60. TMP for tri-modal properties (strength, ductility and rupture) of Ti Step 1 • Homogenization and primary hot rolling Step 2 • Secondary hot rolling Step 3 • Solution annealing Step 4 • aging
- 61. Microstructure after TMP Optical micrographs of Ti-6242S alloy with (a) widmanstätten, (b) bimodal and (c) trimodal microstructures
- 62. Effect of microstructure on strength Parameter for mechanical properties • Volume fraction of alpha and beta transformed phase • Colony size • Alloying element partitioning effect Volume fraction of alpha and beta transformed phase • Volume fraction of alpha phase has limited slip system compared to that of beta phase • The ratio of alpha to beta is used to determine strength of alloy.
- 63. Colony size • Several colonies with alpha/beta layers. • Alpha/beta interfaces are not effective barrier to slip and slip expand rapidly. • Every colony has distinct orientation that act barrier for slip. These colony size is important for mechanical properties. • Beta grain size is important factor since beta grain size acts as barrier to slip and limits the colony size.beta grain size in the widmanstätten microstructure was about • 600 μm, while the similar value for bimodal microstructure is about 16 μm. There is a significant difference in beta grain size in widmanstätten and bimodal microstructure. Based on hall-petch relation, reduction in grain size improves the yield and ultimate strength Alloying element partitioning effect • Cooling from solution annealing temperature and formation of alpha phase, alloying element partitioning take place. • By an increase in alloying element partitioning, the transformed beta regions will be poor in • alpha stabilizer elements • The element which are strong alpha stabilizers will partition into two phases. • precipitation of these particles is related to the concentration of alpha stabilizer elements. This led to decrease in strength. • A significant part of alpha stabilizer elements in the trimodal microstructure is consumed to stabilize the globular and lamellar alpha phases. Hence, concentration of these elements in the transformed beta regions of trimodal microstructure is certainly lower than the bimodal microstructure
- 64. Mechanism of globularization of widmanstatten 𝛼 in 𝛼/𝛽 Ti alloys The globularization of both the lamellar plates within the prior-beta grains as well as grain- boundary alpha. Initially, recrystallized alpha grains are formed within the alpha plate. Surface tension requirements do not permit a 180 ~ dihedral angle to exist between the alpha/alpha boundary and the beta plate boundary. Driving force is provided for the movement of some beta phase into the alpha/beta boundaries and a simultaneous to rotation of the alpha/beta boundaries toward one another. Rotation enlarges the recrystallized alpha grain to a size larger than the original plate thickness, bringing it into contact with the adjacent alpha plate, which may or may not have recrystallize
- 65. Effect of deformation on volume fraction of 𝛼-phase • The volume fraction of globular 𝛼-phase increases from zero in un-deformed sample to about 10% in deformed sample at strain of 1. • Under deformation condition, the kinetics of 𝛽 𝑡𝑜 𝛼 phase transformation increases due to deformation strain induced transformation. • The fraction of globular 𝛼-phase, which result from deformation is high enough to provide 𝛼 + 𝛽 grain microstructure. • Under TMP condition, the high critical strain initiate transformation to very large 𝛽 grain size. • By increasing the strain beyond critical point, the serration of 𝛽 grain boundary increase, increases the nucleation opportunities around 𝛼 phase.
- 66. Effect of slow cooling on volume fraction and morphology of deformed and un-deformed sample
- 67. Microstructure development during slow cooling of deformed and un-deformed sample Initial microstructure before deformation consists of large and equi-axed grains of β-phase. Deformation causes elongation of β grains and serration of their boundaries. Transformation initiates by nucleation of 𝛼 grains and plates along the serrated boundaries of β grains The volume fraction of acicular and globular 𝛼 increases in the course of deformation. On the deformation completion there is some 𝛼 grains with β grains.
- 68. Application of titanium alloys Aero-engine Automotive and road transport Dental alloys Nuclear and environmental safety Geothermal plant condensers Heat exchangers Offshore production tubulars Pulp and paper Metal extraction equipment Jewelry manufacture Cryogenic logging tool Medical implants Military hardware Electrochemical anode
- 69. Summary 1. Titanium is the most rarest element and fourth most abundant structural metal. 2. The type and quantity of alloying element make the alloy specific. 3. Because of its physical and mechanical properties titanium has high melting temperature and lightweight compared to steel. 4. Some Ti alloys used in cryogenic applications because they do not have ductile to brittle transition. 5. Titanium alloys have high fatigue strength.
- 70. Doubt Grain boundary width variation How deformation introduces phase transformation? Did not understood Grain boundary width variation with TMP concept.