Phase Evolution in Hot Forging of Dual Phase Titanium Alloys

Please citeanalysis. J

ARTICLE IN PRESSG ModelJMP-286; No. of Pages 7Journal of Manufacturing Processes xxx (2015) xxxxxx

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Journal of Manufacturing Processes

j ourna l h o me page: www.elsev ier .com/ locate /manpro

Technical Paper

Phase e tanExperim

Stefania an Fa Department o f Palerb Department o

a r t i c l

Article history:Received 9 JunReceived in re12 December 2Accepted 22 DAvailable onlin

Keywords:ForgingTitanium alloysPhase transformationFE model

indussts c

increan bei-nctionnforterly erim

for aeronautical engines, is carried out. The aim of this research is to investigate the process mechanicsand the causes for the nal microstructure observed through micrographic analysis. Once set-up andtested against experimental loads, the model was used to predict phases distributions after both forgingand cool down.

2015 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.

1. Introdu

Forging cation of cocreate a desthe forged the materiaGrain strucing the procfavorable grduced partsover other pproperties o

Differenfrom low-capplicationalloys. In ththe efcienical analysi

CorresponE-mail add

http://dx.doi.o1526-6125/ this article in press as: Bruschi S, et al. Phase evolution in hot forging of dual phase titanium alloys: Experiments and numerical Manuf Process (2015), http://dx.doi.org/10.1016/j.jmapro.2014.12.001

ction

is a manufacturing forming process involving the appli-mpressive forces in order to deform a workpiece andired geometric change. Forging affects the properties ofproduct material. In particular, forging can strengthenl by eliminating cracks and voids within the metal.ture can also be altered due to the material ow dur-ess. Thus, forging represents an optimum way to createain structure greatly increasing the strength of the pro-. For these reasons, forging gives distinct advantagesrocesses as casting or machining in terms of mechanicalf nal products.t materials can be successfully used in forging, rangingarbon steels, used in the automotive eld, to specials materials like aluminum, titanium, and nickel-basee last two decades, the quality of formed products andcy of production lines increased by means of numer-s. This approach was made possible thanks to the

ding author. Tel.: +39 3293517915; fax: +39 091 23861869.ress: [email protected] (G. Buffa).

evolution of the electronics and computer science, which allowedthe decrease of both the hardware costs and computational times.

In this competitive eld, in the last years, aeronautical andaerospace industry attention was strongly focused on the devel-opment of the forging process of materials characterized by highspecic resistance and used for high added value applications.

Titanium alloys often contain a signicant amount of other ele-ments, which are added for a variety of metallurgical reasons [1].The strength of titanium alloys can often be comparable to steel, butthey have only about 60% of the weight. Their lower density allowsthese alloys to be used in applications for which lower weightis advantageous. Other important properties include high corro-sion resistance and tolerance to high temperatures. In the last fewyears, titanium alloys have been extensively used in automotiveapplications including crankshafts, connecting rods and a varietyof drivetrain components [2].

Titanium has two solid crystalline forms: at low temperature,the crystalline phase is called alpha, having a hexagonal closedpacked (HCP) structure; at high temperature, the crystalline phaseis called beta and shows a body centered cubic (BCC) structure(Fig. 1). The temperature at which the solid becomes fully betais called -transus temperature and changes as a function of thealloying elements, ranging from 670 to 1050 C [3].

rg/10.1016/j.jmapro.2014.12.0012015 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.volution in hot forging of dual phase tients and numerical analysis

Bruschib, Gianluca Buffaa,, Antonino Ducatoa, Livf Chemical, Management, Computer Science and Mechanical Engineering, University of Industrial Engineering DII University of Padua, Italy

e i n f o

e 2014vised form014ecember 2014e xxx

a b s t r a c t

Modern aeronautical and aerospace tional consumption and production cois oriented to meet both requirementstance as titanium alloys. Hot forging cforging in closed dies of billets or semtransus temperature, allows the produand machining rework after forging. Umaterial peculiarities have to be propalloy components. In the paper, an expium alloys:

ratinia, Andrea Ghiottib

mo, Italy

tries must face the demanding challenge of reducing opera-oming from materials and labor. Current trend of engineeringasing the use of materials characterized by high specic resis-

used to reduce the production costs of titanium components:ished forms, at different temperatures above or below the -

of complex shapes with limited amount of edge trim removalunately, as far as Ti6Al4V titanium alloy is regarded, severaltaken into account in order to produce defect free Ti6Al4Vental and numerical campaign, focused on a typical case study


ARTICLE IN PRESSG ModelJMP-286; No. of Pages 72 S. Bruschi et al. / Journal of Manufacturing Processes xxx (2015) xxxxxx

Fig. 1. (

The usuaprocesses cying eleme-phase staature. Vana(011%), wtransus temwith an adalloying eletent of the into ve mbeta and bforging temthe forginga strong inthe microstachieve gooture [6] resucomponent

Due to throsion resisindustry [7]drawbacks trial needs address thrsafety, reduHowever, tirespect to sformed.

The heatfactors are thydrogen aalloy billetsing equipmfurnaces, inthe specicnium alloysin most heaboth oxygestructure wcracking proof Alpha miby pre-coatInduction hfrequently processes. Salloys oftentime varyinheating equ

Nowadamodels, whing processtime reduc

utilized numerical models have to be properly tuned in orderto become effective devices for forging process design. Correctthermo-mechanical data, within the temperature ranges of the pro-

s well as proper data and algorithms are needed to correctlyte the phase transformation phenomena. In literature, a fewical models concerning phase transformation and formingses of titanium can be found.zarov et al. [11] proposed a model for the analysis of theansformation for a Ti6Al4V alloy based on an implicit time-g technique that resolves a diffusion equation as functionvolume occupied by the -phase in a space-time domain.

[12]he hoessios woentiulta

urgic stat

inclue claf thebilityility

hot htrong

kinehis p

nume bladsing

takephase mestart

doeson to-me

the pmenauent

teria

ateri

matm al

titanonau17,18. Eve

bilitythe wappred bya) HCP and (b) BCC crystalline structure of titanium alloys [4].

l composition of all common titanium alloys for forgingomprises 70100% of pure titanium. The main allo-nts are: aluminum (06%), tin (06%), which work asbilizers and cause an increase of -transus temper-dium (013%), molybdenum (011%), and chromiumhich are -phase stabilizers, causing a decrease of -perature. The use of aluminum allows for lower densityvantage in the nal part weight, while all the otherments cause the increase of density. Based on the con-alloying elements, titanium alloys are often classiedajor categories: alpha, near alpha, mixed , near-eta alloys. Each of these categories requires specialperatures and operative considerations because both

temperature and the cooling rate after forging haveuence on the morphology of the two phases withinructure [5]. In fact, temperature control is essential tod forgeability and to produce the required microstruc-lting in the desired mechanical properties of the forged.eir high strength-weight ratio as well as their good cor-tance, titanium alloys are widely applied in aerospace. These materials present several advantages and a fewthat must be overcome. In particular, as far as indus-are regarded, through a proper design it is possible toee of the main issues: increase in the active and passivection of fuel consumption and environmental impact.tanium alloys are characterized by lower ductility withteels, anisotropy and are often considered difcult to be

ing stage of the billet is a critical part of the process. Keyhe limitation of contamination by oxygen, nitrogen, andnd temperature control within proper ranges. Titanium

are heated before forging with various types of heat-ent, including electric furnaces, open gas furnaces, oilduction and resistance heating. The choice depends on

alloy used and the temperature level needed as tita- have a strong afnity with gaseous elements presentting techniques. Above 600 C titanium alloys react withn and nitrogen to form scale having an Alpha stabilizedhich is very hard and brittle. If deep enough, it can causeblems and strong tooling wear. In this case the increase

crostructure and relative scale formation may be limiteding or by proper choice of heating parameters [810].eating, resistance heating, and uidized-bed heating are

cess, asimulanumerproces

Kat-trsteppinof the In Ref.study tcompr

It ithe sciels simmetall

Thecessesboth thMost oworkaavailabsis to awork smation

In ttal andturbinoped uable toas the and thtuned modeltributithermotive ofphenosubseq

2. Ma

2.1. M

Thetitaniuwholethe aermass [Table 1forgeaselect ferent follow this article in press as: Bruschi S, et al. Phase evolution in hot forging of d Manuf Process (2015), http://dx.doi.org/10.1016/j.jmapro.2014.12.001

used in forging titanium alloys by automated forgingtate-of-the-art gas and electric furnaces for titanium

have fully automated handling systems with heatingg as a function of thickness of the stock to be heated andipment.ys process designers are strongly aided by numericalich provide the possibility to simulate complex form-es. Considering proper settings and assumptions, designtion and process optimization can be achieved. The

peratures babout 995

Table 1Chemical com

Weight % ual phase titanium alloys: Experiments and numerical

the authors proposed a 2D thermo-plastic model tot die forging of titanium alloy aerofoil sections based onn tests and analysis of microstructure of forged pieces.rth noticing that a growing interest is developing inc community regarding the set-up of numerical mod-neously taking into account mechanical, thermal andal effects [1316].e of art of numerical models applied in hot forming pro-des the constitutive approach, which take into accountssical thermo-mechanical aspect and metallurgical one.m provide good prediction accuracy within a narrow

window. The authors of this paper want to extend the of a coupled thermo-mechanicalmetallurgical analy-igh dynamic forming process in which the deformationly inuences the thermal evolution and phase transfor-tics.aper, the authors present the results of an experimen-erical campaign on the forging process of a Ti6Al4Ve using a screw press. The numerical model was devel-

the Lagrangian implicit commercial code DEFORMTM, into account the thermo-mechanical behavior as welle transformations As far as both the thermo-mechanicaltallurgical problems are regarded, the model was ne-ing from literature data. It is worth noticing that the

not consider the diffusional phenomenon and its con- microstructural evolution of material but only thechanical aspect of the transformation. The nal objec-resent work is to analyze and explain the metallurgical

taking place during both the forging process and the cool down.

ls and methods

al

erial utilized in the present investigation is the loy Ti6Al4V that accounts for more than 50% of theium alloy industrial production and is widely utilized intic industry for its high ratio between the strength and]. The Ti6Al4V chemical composition is reported inn at high temperature, this material presents a limited

window [19,20], which makes necessary to carefullyorking parameters utilized in its hot forging. Two dif-oaches to dening the forging process parameters are

the industries. (i) the forging, which implies tem-elow the Ti6Al4V -transus temperature (equal toC) and produces components of equiaxed primary in

position of the Ti6Al4V alloy.

Element

Ti Al V Fe O Others

Balance 6 4 Max 0.14 Max 0.13


ARTICLE IN PRESSG ModelJMP-286; No. of Pages 7S. Bruschi et al. / Journal of Manufacturing Processes xxx (2015) xxxxxx 3

Fig. 2. The 230of the plane st

a transformand fatiguecarried outin a transfofracture-relcomponentis followed approach, nused.

In the a + micromatrix. If thture, the mto room temtransformeponents chathe temperheating mu

2.2. Experim

The testleft). The horder to appthe sketch ocing nearly geometry wtion, the covelocity at are typical owere 30 mm

The diesand are closmetal ow stand the hthe plates tthrough resthe experimFig. 3.

The heaout by meaelectrical poually positimeasured ojust before die temper

odel of the dies with the spring elements (on the right), and detail of theouples embedded in the dies to monitor the interface temperature (on the

thermocouples embedded inside both the dies. The wiresositioned inside the grooves machined in one of the two

and the hot junctions were made by electro-discharge weld- twor anre p

exp closraturarriestrokt 55

ocessr coowereur psh re

by iom 3

ansfo

num im-metransal libh, th

curvenge valuellect0 kN screw press used in the experiments (left) and, and the schemerain case study derived from a blade forging (right).

ed matrix, having an optimal combination of strength properties. (ii) the forging, for which the process is

above the -transus, resulting in acicular primary rmed matrix, with consequent enhancement of theated properties. Depending on the service-life of the

to be produced, either the rst or the second approachin the industrial practice. In the present study, the rstamely forging at temperatures below the -transus, is

s-received condition, the Ti6Al4V presents a mixedstructure, with equiaxed primary in a transformed e alloy temperature exceeds the -transus tempera-

icrostructure transforms in and, when cooling downperature, it is characterized by acicular primary in a

d matrix, typical of a -forging. In order to obtain com-racterized by properties typical of -forging processes,

ature increase in the workpiece due to the deformationst not exceed the -transus temperature.

ents

s were carried out on a 2300 kN screw press (see Fig. 2,ot forging laboratory experiments were designed inroximate the forging of turbine aerofoil type sections:f the case study used in the experimentation, reprodu-plane-strain conditions, is reported in Fig. 2 (right). Thisas chosen as the thickness variations in the nal sec-nsequent distributions of contact pressure and slidingthe interface, and the high surface extension involvedf actual industrial processes [21]. The Ti6Al4V billets

Fig. 3. Mthermocleft).

k-typewere phalvesing theNumbeto ensu

Thecate, astempewere ca ram of abouand pr

Aftebillets into fothe aetchedging fr

2.3. Tr

Thecial FEMthermophase materiresearcstress rate rastress data co this article in press as: Bruschi S, et al. Phase evolution in hot forging of d Manuf Process (2015), http://dx.doi.org/10.1016/j.jmapro.2014.12.001

diameter and 50 mm long cylinders. utilized for the forging tests present a convex proleed by thick plates in order to assure nearly plane strainduring deformation. An external frame able to with-igh separating forces due to hydrostatic pressure keepsogether. Both the lower and the upper dies are heatedistance cartridge heaters up to 180 C. The scheme ofental set-up and a photo of the lower die are shown in

ting of the Ti6Al4V billets up to 980 C was carriedns of an induction furnace (heating time of 80 s with anwer of 8 kW). At the furnace exit, the billets were man-

oned on the press lower die: the average temperaturen the billet surface through an infrared thermo-camerathe forging hit was approximately equal to 890 C. Theature during the deformation phase was measured by

Fig. 4. Ti6Alvalues. wires to the die material at the end of the grooves.d location of the thermocouples were designed in orderroper accuracy in surface temperature monitoring [22].erimental conditions were designed in order to repli-ely as possible, the industrial process in terms of forginge, die temperature and ram velocity. The experimentsd out using the 100% of the press ywheel energy ande of 200 mm, capable to assure a ram impact velocity0 mm/s. The experimental data were acquired at 10 kHzed by a dedicated LabviewTM application.ling down to room temperature, the Ti6Al4V forged

cut along their longitudinal symmetry plane, dividedarts in order to examine the whole section includinggion, and nely polished. Finally, they were chemicallymmersion in Krolls reagent, with an etching time ran-0 s to 45 s, and observed through an optical microscope.

rmation model set-up and tuning

erical simulations were carried out using the commer-plicit Lagrangian code DeformTM [23], allowing coupledchanical analyses [2426] of forming processes withformation. Although the software pack has a built-inrary that includes Ti6Al4V titanium alloy, for thise authors collected literature data regarding the ows in a temperature range from 25 to 1200 C and strainfrom 0.001 to 1000 s1 [27,19,2830], with a range ofs from 1400 to 25 MPa. An example of the mechanicaled by the authors is shown in Fig. 4.ual phase titanium alloys: Experiments and numerical

4V ow stress curves at 0.1 s1 strain rate and different temperature



Fig. 5. -ptransformatio

The litertion to thetitanium allof the materesearch accoming botand researcplastic behaa given temtion was siggiven in thalgorithm wface for couevolution b

The rstform of the

v = 1 e

{

where:

v is the T is the te Ts = 600 C Te = 980 A = 1.86 D = 4.35.

This moformations of the transto the provand -phacoefcientswere calculation betweand the numare shown iheating stag

The apprvides a goocomplete ph50 C higheresults in a

The tranphase chan

TT staV tita

use teria

shoure apringempan be. A md to

TTTrami ient re [3

ex:

.35 is coe

modl stud

3 mraturto

rateraturwas s

expeodeling a

esignhase transformation model curve compared with the experimentaln curve.

ature research was conducted paying particular atten- phase transformation phenomena of the Ti6Al4Voy in order to investigate the microstructural evolutionrial as a function of the thermal history. At the end of thetivity the authors collected over 200 ow stress curves,h from the database of the JMatproTM Demo softwareh papers. Tabular format was used to model the materialvior. Using the collected data, the interpolation error forperature and strain rate condition during the simula-nicantly reduced with respect to the material modele default software library. The phase transformationas implemented using the dedicated DEFORMTM inter-pled thermo-mechanical analysis with microstructuralased on diffusive and diffusionless models.

transformation was modeled by means of the simplied Avrami model embedded in the code [23].

A(

TTsTeTs

)D}(1)

percentage of -phase that transforms into ;mperature;

is the transformation starting temperature;C is the end of transformation temperature;;

del was demonstrated effective for prediction of trans-in titanium alloys [31]. Eq. (1) provides the percentage

Fig. 6. TTi6Al4

was tothe ma[32]. Itthe mothat dusmall ttions cis usedcouple

Thethe Avcoefcliteratu

v = 1where

n = 1 b is a

Thementa60 mmtempephase coolingtempephase

Thecally msatisfy

2.4. D this article in press as: Bruschi S, et al. Phase evolution in hot forging of d Manuf Process (2015), http://dx.doi.org/10.1016/j.jmapro.2014.12.001

formed phase. A starting distribution correspondingided Ti6Al4V at room temperature (-phase = 91%se = 9%) was given as initial phase distribution. The

of the Avrami model for this rst phase transformationated by performing a minimization of the standard devi-en the experimental curve of the phase transformationerical model curve [23]. The results of the optimization

n Fig. 5, representing the -phase change during thee.oximation given by the Avrami generalized model pro-d overlapping of experimental curve (Fig. 5) but thease change takes place at a temperature which is about

r than the real -transus temperature. This differenceresidual -phase of about 6% at 980 C.sformation model was completed with the beta to + ge during cool down. The rst approach to this model

The aboprocess of apress in dryproperly seshows the irt curve and transition zone for beta to + -phase transformation ofnium alloy.

the Time Temperature Transformation (TTT) curves ofl to calculate the transformed phase volume fractionld be observed that TTT curves can be used instead ofpropriate Continuous Cooling Curves (CCC) considering

the extremely small time steps used for the simulationerature changes take place and almost isothermal condi-

considered. In this research, an evolution of the modelixed approach, in which the TTT start curve (Fig. 6) is

the general Avrami model, is adopted. curve provides the starting line of phase change whileequation controls the amount of transformed phase. The(Avrami number) of the Avrami equation was found in1]:

p(btn) (2)

the Avrami number;fcient calculated by the TTT start curve of the alloy.

el was tuned on the basis of the results of an experi-y by Malinov and Sha [33] focused on the analysis of am 1.5 mm Ti6Al4V sheet metal, heated from room

e to beta zone till a complete transformation of the --phase. The workpiece was then cooled with differents and it was nally quenched by water back to roome. During the process the evolution of the mixed + tudied.rimental procedure followed in the paper was numeri-ed by the authors in [32] and the results compared withgreement.

of the forging simulation

ve described model was used to simulate the forging Ti6Al4V turbine blade formed by means of a screwual phase titanium alloys: Experiments and numerical

conditions. Process parameters and geometries weret in order to reproduce the experimental methods. Fig. 7nitial billet and the forged one.

Fig. 7. Billet (a) and forged workpiece (b) geometries.



Fig. 8. 2D simulation objects.

A 2D model with plane strain conditions was used to simulatethe process (Fig. 8).

The experimental screw press was modeled using the followingparameters:

Max force: 2300 kN; Stiffness: 61500 (100%), 19200 (56%), 6500 (40%) kN/mm; Initial ram

The lubrtor equal toexchange cbetween th[34] showecoefcient wshows the h

In each sdown to 89

3. Results

Fig. 10 sthe experim

As it caneffectivenestion of the and with pheight of thwere utilizefoil section presult implifairly exceemicrostructif the procetemperaturrent factorsincrease in contact-tim

Fig. 9. Heat tr

Fig. 10. Experimental and numerical load curves results for the tested conditions.

due to the dry conditions used. Smaller dimension of the matrixcan be observed just on observation point (c), which experienced

r contact time with the die thus reducing its temperatureith respect to the other parts of the aerofoil.

t, the temperature eld was analyzed. In Fig. 11 the micro- of the transverse section are reported for the pointshted. It is seen a symmetric microstructure, i.e. (a) is sim-

(e), (b) to (d), etc. The numerical prediction was used togate the reasons for the observed experimental evidence andve the assumptions made. In Fig. 12 both the temperature stroke: 200 mm

ication conditions were modeled using a shear fac- 0.7. The authors focused their attention on the heatoefcient and its distribution along the contact areae workpiece and the dies. Bruschi, Ghiotti and Croind the inuence and variation of the thermal exchangeith respect to normal pressure and sliding speed. Fig. 9eat transfer coefcient as function of normal pressure.imulation, the billet was heated at 980 C, then cooled0 C and forged with initial die temperature of 180 C.

hows the forging load vs. time curves, as measured inents for the dry conditions and numerically calculated.

be seen, a good overlapping is obtained proving thes of the tuned model. Fig. 11 shows the transverse sec-actual forged aerofoil in case of dry forging conditionsress stiffness of 100%. Ten different points, ve at mide section and ve close to the edge surface of the part,d for the microstructural observations. The whole aero-resents acicular phase in a transformed matrix: this

es that, during the forging process, the temperature hasded the Ti6Al4V -transus temperature. The obtainedure is therefore typical of the forging process, evenss was conducted under forging conditions. Thee increase during the process is due to two concur-: (i) the deformation heating resulting in a temperaturethe billet, which cannot be dissipated due to the lowe. (ii) the heat coming from the friction forces work

a longemore w

Firsgraphshighligilar toinvestito pro this article in press as: Bruschi S, et al. Phase evolution in hot forging of d Manuf Process (2015), http://dx.doi.org/10.1016/j.jmapro.2014.12.001

ansfer coefcient vs. normal pressure at die/workpiece interface [34]. Fig. 11.ual phase titanium alloys: Experiments and numerical

Microstructure obtained when forging under dry conditions.



Fig. 12. (a) Temal histories f

distributiontories of the

The threi.e. (a), (b), the combinof the utilizparticular, aobserved fothe processsurface of tthe larger into small dimobtained fothe end of tundergoes.

The evolthe developat the end o

Due to thtion work d15% is obserarea. It is wsignicant pin a microssee Fig. 5). Texperiencedinto + ppercentagehand, in thdue to the transformaincreased p

After thforms into lmostly charuntransformlarger volum

Fig. 13. Phase distributions at the end of the forging process.mperature distribution at the end of the forging process and (b) ther-or the points (a), (b), (c), (a), (b) and (c).

at the end of the forging process and the thermal his- points (a), (b), (c), (a), (b) and (c) are reported.e points laying at mid height of the transverse section,and (c), experience an increase in temperature due toation of short process time, low thermal conductivityed titanium alloy and distance from the die surface. Inn almost identical temperature evolution with time isr points (b) and (c), reaching about 1000 C at the end of

(Fig. 12). In turn, looking at the points close to the tophe aerofoil, a decrease in temperature is found, due touence of the heat exchange with the dies. Finally, dueension of the ash area, similar temperature curves are this article in press as: Bruschi S, et al. Phase evolution in hot forging of d Manuf Process (2015), http://dx.doi.org/10.1016/j.jmapro.2014.12.001

r points (a) and (a), with an increase in temperature athe process because of the large deformation that area

ution of the phase transformation has been studied byed numerical tool. Fig. 13 shows the volume fractionsf the forging process.e increase in temperature determined by the deforma-

ecaying into heat, a percentage of phase equal to aboutved at the core of the forged component and in the ashorth noticing that, during the pre-heating of the billet, aercentage of the phase transformed into resultingtructure characterized by predominant (about 90%,hen, during the forging process, in the airfoil areas that

a decrease in temperature, the phase transformedhase with acicular grains, while the untransformed

of volume fraction remained constant. On the othere areas that experienced an increase in temperaturedeformation work and reduced heat exchange, furthertion of the residual phase occurred, resulting in anercentage of the lamellar + phase (Fig. 13).e cool down of the part, the residual phase trans-amellar + phase, resulting in a nal microstructureacterized by + phase with small volume fractions ofed phase. As expected, the latter phase is present ine fractions closed to the central area of the top surface

of the part, shows the nthe produce

4. Conclus

In the pdeveloped

A numeeld variabrial microspre-heatinga prevalentobservationual phase titanium alloys: Experiments and numerical

Fig. 14. Phase distributions after cool down.

where longer contact time with the die occurred. Fig. 14umerical prediction of the nal phase distributions ind part.

ions

aper, an experimental and numerical campaign wason hot forging of Ti6Al4V titanium alloy.rical model, able to predict the distribution of the mainles, the forging load and the evolution of the mate-tructure was set up. Experiments were conducted by

the billed below the -transus temperature. However, fully lamellar structure was found by experimentals.

Please cite g of danalysis. J .001


The numerical model was used in order to explain this behavior.On the base of the obtained results the following main conclusionscan be drawn:

During the forging process temperature increases in the areaslocated at mid height of the transverse section. This is due to theextremely reduced process times and contact times between thedies and the workpiece because of the elevated press stiffnessadopted;

Consequently, a further increase in the phase occurred dur-ing the process. The grain transformed both during the forgingand during the cool down into a + structure characterized byacicular grains (lamellae);

Larger phase volume fraction is observed close to the centerof the top and bottom surface of the produced part, due to thecooling this area experiences even during the process. For thesame reason smaller grains are observed in the same area.

Future work includes the implementation of a homemade soft-ware for quantitative experimental measurement of the phasevolume fraction.

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Phase evolution in hot forging of dual phase titanium alloys: Experiments and numerical analysis1 Introduction2 Materials and methods2.1 Material2.2 Experiments2.3 Transformation model set-up and tuning2.4 Design of the forging simulation

3 Results4 ConclusionsReferences

Phase Evolution in Hot Forging of Dual Phase Titanium Alloys

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