Srinivasulu P viva.pdf

7/30/2019 Srinivasulu P viva.pdf

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Title of the M. Tech Dissertation

Estimation of-transus temperature in an alloy

based on Ti-6Al-4V

Schoo

U

Dr. K

Schoo


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Introduction I think it is best to choose such a denomination as means nothus can give no rise to any erroneous ideas. In consequence ofcase of Uranium, I shall borrow the name for this metallmythology, and in particular from the Titans, the first so

therefore call this metallic genus TITANIUM.

- Martin Heinrich K

The transformation temperature from + or from to all-transus temperature (tr). Pure titanium undergotransformation (-HCP to -BCC) at 8822 oC.

The transus is an important parameter to be considered duthermo-mechanical processing schedules since a variety of mbe obtained depending upon whether the material is processe

this temperature.

Titanium and titanium alloys three major categories (predominant phases present in their microstructure) : , +

Co


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Int(con

Objectives of the present investigation

To estimate transus temperature, by performing heat treatment procedures for Ti-6Al-4V and Ti-6Al-1.5V-2.5Cu alloys at 900 oC, 950 oC, 1000 oC respectively.

Performing metallographic procedures to obtain microstructures in order to estimate the transus temperature. The microstructures are analyzed by stereographic techniques to quantify thetransformed phases for different sample conditions at different temperatures (Imageanalysis-Optical microscopy).

Study on X-ray diffraction results of alloy samples and correlate them with existing phasesduring heat treatments.

Remarks on the obtained measurements of micro-hardness.


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Literature Review

Titanium alloys and their classification Crystal structures of titanium alloys Phase transformations in titanium alloys Principles of alloying and alloying titanium Effect of alloying additions on -transus temperature in tit

Effect of alloying Al, V additions on -transus in Ti-6Al-4V Overview of high pure Ti, Ti-6Al-4V and Ti-6Al-1.5V-2.5C

(a)

Widm


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TiAlumIncrtemsubs TCoptran

(substrehard Tandin tr(Ne

Effect of Al, V alloying additions on transus temperature in Ti-6Al-4V alloy:* Due to the addition of Vanadium (V) content at constant Aluminum (Al) concentration,there is a rapid decrease in the (+)/ transformation temperature (i.e. transus) and it doesnot significantly influence the position of/ (+) transformation temperature (i.e. transus).

Lit


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Variatio

with sta

Literature Review(continued)

Heat treatments for titanium

alloys

Titanium alloys- effects of

stabilizing elements on transus

and phase stabilization

Heat treatments for titanium alloys

------------------------------------------------------------------

Stabilizer Type Approx. wt% needed toretain 100% upon quenching-------------------------------------------------------------------------------------Mo Isomorphous 10V Isomorphous 15W Isomorphous 22.5Nb Isomorphous 36.0Ta Isomorphous 45.0Fe Eutectoid 3.5Cr Eutectoid 6.5Cu Eutectoid 13.0Ni Eutectoid 9.0-------------------------------------------------------------------------------------

stabilizing effect of Mo/V/Nb/Ta--> 10/6.7/2.8/2.2 (wt%)


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Stability of a phase:HCP () and BCC () structures

The stability of a phase is determined by binding energy at ab

entropy of the system.

During heat treatment, the free energy of an imaginary bcc

more rapidly than those of the competing alternatives suchtemperature will be reached where at the lattice will trans

temperature stable closed packed structure to bcc.

For the relatively loose bcc packing and atoms within the lat

this may result in high amplitude of vibration in certain direction

contribution to -TS term of the free energy.

At high temperatures, F= H-TS is small.

Upon cooling from the phase field the most densely packe

phase {110} transform to the basal planes {0001} of the hexagonal

Titanium HCP phase is stable at lower temperatures, beca

binding energy, where entropy effects are unimportant.


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Experimental work

Metallographic preparations

Heat treatments

Image analysis- Optical

X-ray diffraction analysis

Vickers Micro hardness

Materials: Ti-6Al-4V Ti-6Al-1.5V-2.5Cu Nask(

Optical microscopy Heat treated specimen

Bruk

D il f i O i l O i


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Details of operation- Opticalmicroscope: for quantitative phaseanalysis Apparatus model: Olympus GX 51compact inverted metallurgicalmicroscope Mode of illumination: Halogen (optical

transmitted) illumination Mode of examination: Bright field andsimple polarization mode

Magnification range: 50X-1000X

Experimental details(continued..)

Heat treatments performed in thepresent work: As-cast Ti-6Al-4V HT at 900, 950

and 1000 oC and then furnace cooled,water-quenched. Soak time 2 hoursand cooling rate 15 oC/sec. As-cast Ti-6Al-1.5V-2.5Cu HT at900, 950 and 1000 oC and thenfurnace cooled, water-quenched. Soaktime 2 hours and cooling rate 15oC/sec.

Heating muffle furnace Operating temp. range Model name: Electro h

furnace Temp. measurements: Thyrister current range Operating atmosphereatmosphere

Operating parameters Incident radiation: Cu kSample type: Flat bulk t

etched Sample Dimensions: Pla

mm-7 mm-4 mm

Scan mode: Step mode

Step size: 0.1-0.2o

(depthe sample) Scan speed: 1 step/sec

Scan angle (vertical thet

Etchant:50 ml diluted s(2 ml HF-40% Con., 3 m

1.5 ml H2O2 and 45 ml H

Metallurgical specimen

preparation:

Mirror-like finish of thespecimen is needed Remove oxide layer withrough polishing

for X-ray diffraction:

Flat & thin samples couldbe used

Calibration of XRDInstrument is must beforedoing experiment


10/26Continued

Process flow-chart for Image analysis: Experime


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Results and Discussion

Phase disappearing method

Microstructural analysis-Optical microscopy

Quantitative phaseanalysis- XRD

Remarks on Vickers micro-hardness

Microstructures of as-cast Ti-6Al-4V alloy ( Coarse, heterogeneoudark phase- and bright phase- )

Phase disappearing method: A series of two phase (+) alloya given temperature or solutionized, quenched to room temparrest technique the retained phase measured through the heland as well as XRD. According to Lever rule at the / (+) solvus line, the amousolvus temperature determines the transus temperature acommercially pure titanium, and for Ti-6Al-4V and Ti-6Al-1.5Vbetween 970 oC to 1005 oC, from the sequential investigations et.al.


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Microstructures of Ti-6Al-4V Heat treated at 900 oC then furnace

Microstructure of Ti-6Al-4V alloy heat treated at 900 oC, and then

Lath-like Widmanstttenmorphology consists of plates

At intermediate cooling rates

or furnace cooling from phasefield the resultantWidmansttten structures areproduced.

Fine acicular martensite

structure.

Partial disordered array ofindividual platelets and phaseis parallel to {110} planes ofmatrix.


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Microstructure of Ti-6Al-4V alloy heat treated at 950 oC, and then

Theoretically predictedWidmansttten morphologywith recrystalized plateletssurrounded by prior

boundaries.

Basket-weave withinWidmansttten structure. Thebasket-weave structure resultsfrom nucleation and growthduring the transformation of to in a Widmanstttenpattern

The distribution of smallerand finer colonies is due to thecharacteristic nature of basket-weave structures


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Microstructure of Ti-6Al-4V alloy heat treated at 1000 oC, and the

The microstructure exhibitsthe fine lamellae delineatingby phase boundary.

The microstructure is needlelike lamellar HCP martensite

At higher cooling rates, Ti-6Al-4V can form Hexagonalclosed packed martensite ()which contains vanadiumsupersaturaion.


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For Ti-6A

maximum

fractions aobserved awater-que81.17%

For Ti-6Al

the maxim

fractions aobserved aquenched,


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Microstructures of as-cast Ti-6Al-1.5V-2.5Cu alloy

The commercial Ti-6Al-1.5V-2.5Cu alloy is also an + eutecto

Copper is one such -eutectoid stabilizing element and interm

former in titanium alloys

Just like silicon, Cu can also be added to titanium, by forming

exhibits precipitation-strengthening. As the temperature decreas

solubility of this system too decreases, precipitating Ti2Cu.

An intermetallic precipitation(Ti2Cu) in the vicinity of

dislocations acts toobstruct their movement,

improving the systems creepresistance.


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Microstructures of Ti-6Al-1.5V-2.5Cu Heat treated at 900 oC then

Microstructure of Ti-6Al-1.5V-2.5Cu alloy heat treated at 900 o

quenched

copper precipitates appeared inthe form of newly grown

crystalline morphology i.e.serrated or elongated

lamellae

Basket-weave Widmanstttenstructure and the lamellar

structure is indeed present amongthe lamellae

A mixture of and Cu diluted

phase representing the uniformedsurface without any phases into

the matrix of phase. There is alsoa secondary observed in the

micrographs


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Microstructure of Ti-6Al-1.5V-2.5Cu alloy heat treated at 950 o

quenched

In these microstructures thetransformation product is most

commonly recognized in the formof colonies of what appeared to

be alternating and almost parallelstrips of two-phase products

Martensitic transformed phaseas in the form of needle like

phase or fine acicular phase. The intergranular morphologyalso martensitic phase product in

the form of fine or acicularstructure. This is good for wear

resistance


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Microstructure of Ti-6Al-1.5V-2.5Cu alloy heat treated at 1000

quenched

Homogeneous microstructure isproduced by furnace cooling

from 1000 oC.There is a fine grain boundary

separating the and andinternal structures.It reveals that there is no

secondary phase product form

The structure is fully populatedwith the Widmansttten

arrangement of platelets


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XRD profiles

Ti-6Al-4V HT 1000 o C then water-quenched alloy XRD Braggs pattern

contain no reflections.


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XRD profilesalloy


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Vickers Micro hardness The maximum Vvalue (in no.) of Ti-at 900 oC, furnace

condition ( Surfaceduring slow coolinThe maximum Vivalue (in no.) of Ti-attain at 1000 oC, condition (Precipiteffect)


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Conclusion The objective was to estimate the transus temperatmetallographic techniques or procedures i.e. phase disappmicroscopic methods as well as X-ray diffraction phase analysis.

Through the subtransus or transus processing, varying micr

such as morphology and phase transformations can be reviewed

6Al-1.5V-2.5Cu alloys.

Ti-6Al-4v alloy specimens are heat treated at 900, 950 and

furnace cooled, the measurements of retained phase fracti

microstructural analysis, are as 65.72%, 59.08 % and 69.28% respe

Ti-6Al-4V alloy specimens are heat treated at 900, 950 and

water-quenched, the measurements of retained phase fract

microstructural analysis, are 64.68%, 62.20% and 81.17% respect

Processing

Metallographic Evaluation:

Phase analysis

Estimation of transus

temperature for Ti-6Al-4V and

Ti-6Al-1.5V-2.5Cu alloys

Mechanical behavior:

Vickers hardness of Ti-6Al-4V

and Ti-6Al-1.5V-2.5Cu alloys

C


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Ti-6Al-1.5V-2.5Cu alloy specimens are heat treated at 900,

then furnace cooled, from quantification of phase by microstr

retained phase is found to be 60.65%, 63.31% and 67.47% respec

Ti-6Al-1.5V-2.5Cu alloy specimens are heat treated at 900, 9

then water-quenched, from quantification of phase by microst

retained phase is found to be 60.95%, 75.35% and 55.53% resp

The estimated transus temperature in Ti-6Al-4V alloy is 1

greater than the transformation temperature of Pure titanium i.

The estimated transus temperature in Ti-6Al-4V alloy is

greater than the transformation temperature of Pure titanium i.


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Continued to acknowledgement


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Dr.

Prof

Prof

P

...

Pro

Dr

A

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