Heat treatment of Ti and its alloys.pptx.pdf

Heat treatment

1. TITANIUM AND ITS ALLOYS
Titanium alloys are high strength to weigh ratio materials with excellent fatigue
and corrosion resistance due to thin, impermeable oxide film formed on the
surface.
Because of its high melting point (1720º C), its alloys have potentials for high
temperature applications, but is a bit expensive to produce them from ores even
though they are present abundantly in earth’s crush.
It goes allotropic transformation from the low temperature HCP to BCC at
822º C to be stable up to melting point.
The titanium alloys are classified as:
α Alloys
β Alloys
(α + β) Alloys

2. CONSTITUTION DIAGRAM FOR
TI - ALLOYS

3. WHY HEAT TREATMENT IS IMPORTANT FOR
TI – ALLOYS ?
Improving Mechanical Properties
Ductility
Strength and hardness
Controlling Microstructure
Phase Transformations
Stress relieving
Improving machinability
Softening
Controlling Oxidation and Corrosion
Protective layers

4. TYPES OF HEAT TREATMENT FOR TI -
ALLOYS
Stress Relieving
Annealing
Solution heat treatment and precipitation hardening
Stress Relieving
Relieve residual stress caused during fabrications.
Stress relieving does not cause adverse effect on strength or ductility.
Separate relieving treatment may be omitted (For: Sequence -
production employes annealing or hardening treatments.

5. STRESS RELIEVING TEMPERATURE RANGE
& TIME RANGE

6. ANNEALING
To induce maximum ductility at room temperature
To improve machinability
To induce adequate toughness
To induce dimensional and microstructural stability at high temperatures
(i.e, to induce maximum)

7. ANNEALING TREATMENT

8. PRECIPITATION HARDENING
To Improve strength
To hardness
1.SOLUTION TREATMENT
All the three types of titanium alloys are given precipitation
hardening.
Changing the solution temperature alters the amount of ẞ-phase.
Solutionising -100%, B-phase region, the resulting ductility is
impaired.
2.QUENCHING
ẞ-alloys are air-quenched from solution temperature
(alpha + beta) alloys are water-quenched, or 5% brine-quenched.
Cooling rate from solution temperature - strengthening the alloys.

9. A slower cooling allows - diffusion - the changed ẞ phase not
effective strengthening - ageing.
Rapid rates of quenching is less critical in many alloys (Except Ti-6
Al-4V).
Section size directly affects the effectiveness of quenching.
In (alpha + beta) alloys, quenching - metastable & brittle phase(omega).
Severe quenching and rapid heating to high ageing temperature can avoid
it.
Ageing above 430°C, can change omega (to ẞ).
100% beta alloy Ti-13V-11 Cr-3Al - forged & rolled in beta range & air
cooled after hot working yields solution treated condition.
This alloy aged at 500°C for 8 to 100 hrs. yields a UTS of 1100-1380
MN/m^2
3. AGEING

10. In (alpha + beta) alloys, quenching - metastable & brittle phase(omega).
Severe quenching and rapid heating to high ageing temperature can avoid it.
Ageing above 430°C, can change omega (to ẞ).
100% beta alloy Ti-13V-11 Cr-3Al - forged & rolled in beta range & air cooled
after hot working yields solution treated condition.
This alloy aged at 500°C for 8 to 100 hrs. yields a UTS of 1100-1380 MN/m^2

11. EFFECT OF HEAT TREATMENT ON MICROSTRUCTURE:

14. EFFECT OF HEAT TREATMENT ON MECHANICAL PROPERTY

16. REFERENCES
Heat Treatment of Metals By Vijendra Singh.
Effect of heat-treatment on microstructure and mechanical
properties of Ti alloys: An overview By Puja Yadav, Kuldeep K.
Saxena