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
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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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Microstructures of Ti-6Al-4V Heat treated at 950 oC then furnace
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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Microstructures of Ti-6Al-4V Heat treated at 1000 oC then furnace
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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Microstructures of Ti-6Al-1.5V-2.5Cu Heat treated at 950 oC then
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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Microstructures of Ti-6Al-1.5V-2.5Cu Heat treated at 1000 oC then
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
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