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Mo'az Galbat

on 25 December 2014

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Transcript of Ti6Al4V

TI Alloys (Ti 6Al 4V as an example)

Classification of titanium alloys

Specification and code
Chemical composition of Ti-6Al-4V
Alloying system of titanium alloys
Physical and Mechanical properties of titanium

Typical properties for Ti6Al4V.
Microstructure of Ti-6Al-4v

Commercially pure (CP) titanium alpha and near alpha titanium alloys:
- Generally non-heat treatable and weldable
- Medium strength, good creep strength, good corrosion resistance.

• Alpha-beta titanium alloys:
- Heat treatable, good forming properties
- Medium to high strength, good creep strength

• Beta titanium alloys:
- Heat treatable and readily formable
- Very high strength, low ductility
Alpha stabilizers.
Al, O, N
Beta stabilizers:
Isomorphous: Mo, V, W, Nb, Ta.
Eutectoid: Fe, Cr, Cu, Ni, Co, Mn.

Zr, Si, Sn

Physical properties of titanium:

Experiences allotropic transformation (α β) at 882.5oC.
• Highly react with oxygen, nitrogen, carbon and hydrogen.
• High strength and toughness.

Mechanical properties:

Material strength,
creep resistance
fatigue properties
are the main properties usually required for applications of titanium alloys.

Titanium alloys provide
superior specific yield strength (high strength to weight ratio)
than other alloys.

Deformation of titanium alloys
Forging of titanium alloys:
Ti alloys have much higher flow stress than Al alloys or steels.
requiring high forging pressure, capacity.
Rolling of titanium alloys:
Titanium alloy sheet is normally packrolled to avoid surface oxidation.

Machining of Titanium alloys
Titanium and titanium alloys are relatively more difficult to machine (especially α Ti alloys) in comparison to steels and aluminum alloys for all conventional methods such as milling, turning, drilling etc.

ASTM B265 / B348 Grade 5
Type Analysis
Titanium Balance
Aluminum 5.50 to 6.75 %
Vanadium 3.50 to 4.50 %
Carbon (Maximum) 0.10 %
Nitrogen 0.05 %
Iron (Maximum) 0.40 %
Oxygen (Maximum) 0.020 %
Hydrogen (Maximum) 0.015 %
Other, Total (Maximum) 0.40 %

Where Al work as alpha stabilizer .i.e. it rises the temperature at which alpha transforms to beta.
And vanadium works as beta stabilizer, it lower the temperature at which beta transforms to alpha.

The three main Alloying elements:

Corrosion of Titanium alloys
When fresh titanium is exposed to environment containing oxygen, it will develop oxide films.
Good corrosive resistance to salt water and marine, acids, alkalis, natural waters and chemicals

Welding of titanium alloys
α and α+β titanium alloys are readily weldable.
β titanium alloys are not readily weldable due to high amounts of alloying element
Grades 1-4 are unalloyed and considered commercially pure or "CP". Generally the tensile and yield strength goes up with grade number for these "pure" grades.

Grade 5, also known as Ti6Al4V, Ti-6Al-4V or Ti 6-4, It is significantly stronger than commercially pure titanium while having the same stiffness and thermal properties. 

Alpha alloys have relatively low density but have low strength and can’t be heat treatable .

Alpha – beta alloys have medium strength values but the presence of alpha phase increases the ductility and they are heat treatable .

Beta alloys are very strong but at the expense of ductility, and they are fully heat treatment

High reactivity with oxygen and hydrogen from beta can cause the alloy to be brittle. Therefore, welding of titanium alloys has to be performed either in vacuum or an inert gas atmosphere.

alpha and alpha –beta alloys are easier to weld than beta alloys.

The more limited deformation capability and the stronger work hardening ability of the beta phase implies that alpha and alpha-beta alloys can only be deformed at high temperatures.

The deformation temperature decreases with increasing _ beta volume fraction.

The microstructure of conventional titanium alloys is primarily described by the size and arrangement of the two phases α and β.

The two extreme cases of phase arrangements are the lamellar microstructure , which is generated upon cooling from the β phase field, and the equiaxed microstructure , which is a result of a recrystallization process.

Both types of microstructure can have a fine as well as a coarse arrangement of their two phases.

lamellar microstructure

Lamellar microstructures are a result of simple cooling from temperatures above the β-transus temperature. Once the temperature falls below the transus temperature α nucleates at grain boundaries and then grows as lamellae into the (prior) β grain. (Fig. 1.11).

Depending on the cooling rate, the lamellae are either fine or coarse.

Slow cooling from the phase field results in pure lamellar microstructures (Fig.1.12 a) .

Rapid quenching leads to a martensitic transformation of β , resulting in a very fine needle-like microstructure(Fig. 1.12 b).

the hardening effect observed for titanium alloys on martensitic transformation is moderate (unlike steel).

Equiaxed Microstructures
equiaxed microstructures are the result of a recrystallization process. Therefore, the alloy first has to be highly deformed in the α+β field to introduce enough cold work into the material.

Upon subsequent solution heat treatment at temperatures in the two-phase field, a recrystallized and equiaxed microstructure is generated (Fig. 1.13 a).

Extended annealing coarsens the equiaxed microstructure (Fig. 1.13 b).

The solution heat treatment temperature itself determines the volume fraction of the primary .

Solution heat treatment just below the β-transus temperature results in bimodal microstructures that consist partly of equiaxed (primary) α in a lamellar α+β matrix (Fig. 1.13 c, d).
bimodal microstructures can be considered to be a combination of lamellar and equiaxed microstructure.

The various microstructures have a strong influence on the mechanical behavior of the titanium alloys.

Fine-scale microstructures increase the strength as well as the ductility. Furthermore, they retard crack nucleation and are a prerequisite for superplastic deformation.

Coarse microstructures, on the other hand, are more resistant to creep and fatigue crack growth.

Equiaxed microstructures often have high ductility as well as fatigue strength and are preferred for superplastic deformation.

while lamellar structures have high fracture toughness and show superior resistance to creep and fatigue crack growth.

Since bimodal microstructures combine the advantages of lamellar and equiaxed structures, they exhibit a well-balanced property profile.

Heat treatment
Titanium Alloys are heat treated in order to:

Reduce residual stresses developed during fabrication (stress relieving)

Produce an optimum combination of ductility, machinability, and dimensional and structural stability (annealing)

Increase strength (solution treating and aging)

1- Anneal: 1,275 -1,400°F; (691 - 760°C), ½ to 2 hours, air or furnace cool.

Annealing is a heat treatment procedure involving heating the alloy and holding it at a certain temperature (annealing temperature), followed by controlled cooling.
Annealing results in relief of internal stresses, softening, chemical homogenizing and transformation of the grain structure into more stable state.
Annealing increases an extent of equilibrium of the metal structure resulting in softening and high ductility.

2. Stress Relief Anneal: 1,000 -1,200°F; (538 - 649°C), 1 to 8 hours, air or furnace cool.

Stress-relieving treatments decrease the undesirable residual stresses  of previous treatingins.
The removal of such stresses helps maintain shape stability and eliminates unfavorable conditions, such as the loss of compressive yield strength.

3. Solution Heat Treatment: 1,675 -1,750°F; (913 - 954°C), 1 hour, water quench.

A process in which an alloy or metal is heated to a suitable temperature, is held at that temperature long enough to allow a certain constituent to enter into solid solution, and is then cooled rapidly to hold that constituent in solution

4. Aging Treatment: 975 -1,025°F; (524 - 552°C), 4 to 8 hours - air cool.

is a technique where heat is applied to a malleable material, such as a metal alloy, in order to strengthen it. The technique hardens the alloy by creating solid impurities, called precipitates, which stop the movement of dislocations in the crystal lattice structure. Dislocations are the primary cause of plasticity in a material; thus, the absence of dislocations increases the material's yield strengt

Direct Manufacturing of parts and prototypes for racing and aerospace industry
Biomechanical applications, such as implants and prosthesis
Marine applications
Chemical industry
Gas turbines

Titanium alloys were developed in the early 1950s for defense and aeronautical applications because of their
high strength-to-weight ratio
. Through innovation in very diverse markets, production of titanium significantly increased making the material much more readily available. This increase in production has lowered costs allowing even more industries to utilize its unique combination of strength, weight, and corrosion resistance.

General information about Ti alloys
Specification and codes
Chemical composition
Phase diagram and Microstructure
Heat treatment
Full transcript