Effects of Cryogenic Treatment after Annealing of Ti-6Al-4V Alloy Sheet on Its Formability at Room

16 Pages·2017·6.2 MB·English

metals
Article
Effects of Cryogenic Treatment after Annealing of
Ti-6Al-4V Alloy Sheet on Its Formability at
Room Temperature
ZhiqingHu1,2,*,HuihuiZheng3,GuojunLiu3andHongweiWu4
1 RollingForgingResearchInstitute,JilinUniversity,Changchun130025,China
2 KeyLaboratoryofAutomobileMaterials,MinistryofEducation,JilinUniversity,Changchun130025,China
3 CollegeofMaterialScienceandEngineering,JilinUniversity,Changchun130025,China;
[email protected](H.Z.);[email protected](G.L.)
4 SchoolofEngineeringTechnology,UniversityofHertfordshire,HatfieldAL109AB,UK;[email protected]
* Correspondence:[email protected];Tel.:[phone]
(cid:1)(cid:2)(cid:3)(cid:1)(cid:4)(cid:5)(cid:6)(cid:7)(cid:8)(cid:1)
(cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:7)
Received:24February2018;Accepted:22April2018;Published:24April2018
Abstract: In this article, the effects of cryogenic treatment after annealing on the formability of
Ti-6Al-4V alloy sheet were experimentally studied. The Ti-6Al-4V titanium alloy was treated by
cryogenictreatmentafterannealing(ACT).Tensiletestswerecarriedoutusingauniversalmachineat
roomtemperature. ThemicrostructureevolutionofTi-6Al-4VsubjectedtoACTwasalsoinvestigated
usinganopticalmicroscope(OM).Boththeshearingperformanceanddrawingformabilitywere
analyzedbypunchshearingtestsanddeepdrawingtests,respectively. Resultsshowedthatafter
ACT,thetendencyoftheβphasecanbeapparentlychangingintostableβ’andα’phases. Theelastic
modulus is lower than that of the untreated material. It was found that both the yield strength
andtensilestrengtharedeclinedslightly,whereastheductilityisincreasedsignificantly. Theshear
strengthinpunchshearingisdecreasedatroomtemperatureandcryogenictemperature. Theratioof
smoothzoneonthesectionafterACT3ismuchlargerthantheothers. Therolloverdiametersarenot
obviouslygreaterthanthoseoftheuntreated. Additionally,theheightoftheburrshowsadecreasing
trendafterACT.Duringdeepdrawing,drawingdepthisdeeperthanthatoftheuntreatedmaterial,
thedrawingloadafterACTisreduced,andthedecreasingtendencyofthedrawingloadslowsdown.
Itisnotedthatthemicro-cracksoccuratthebottomofthesample.
Keywords: Ti-6Al-4Vtitaniumalloys;cryogenictreatment;mechanicalproperties;punchshearing;
deepdrawing
1. Introduction
Ti-6Al-4Vtitaniumalloyisbeingincreasinglyusedinautomation,energy,aerospaceindustries,
healthcareandautomobileduetotheirexcellentcharacteristicssuchaslowdensity, highspecific
intensity, strongcorrosionresistance, excellentheatresistance, goodperformanceathighandlow
temperature, no magnetism, and good damping performance, as well as it has a special shape
memory [1] and outstanding biocompatibility. Ti-6Al-4V is a type of titanium alloy of α + β with
excellentcomprehensiveproperties. NowadaysTi-6Al-4Valloyiswidelyappliedanditaccountsfor
approximately50%ofthetotalworldproductionoftitaniumalloys[2].
The cryogenic treatment (CT) is a treatment method that can change material properties by
thesamplesbeingimmersedinliquidnitrogen. CTisasupplementaryprocessoftraditionalheat
treatmentwhichhasbeenacknowledgedfordecades[3]. CTonmaterialscouldbefirstlyreported
by Gulyaev in 1937, and CT could improve the cutting properties of tool steels [4]. Afterwards,
Kamranetal.[5,6]investigatedtheeffectsofCTonthemechanicalpropertiesofsomeselectedtool
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Metals2018,8,295 2of16
steels,i.e.,D2and80CrMo125,anditwasfoundthatCTcaneliminatetheretainedaustenite,whichcan
makeabettercarbidedistributionandahighercarbideamount. Anobviousimprovementinwear
resistanceofcryogenically-treatedsampleswasindicated. Gaoetal.[7]studiedtheeffectsofCTonthe
microstructureandpropertiesofWC-Fe-Nicementedcarbides.ItwasstatedthatCTcouldpromotelath
martensiteformation,afterCT,thehardnessandtransverserupturestrengthofWC-Fe-Nicemented
carbideswerehigherthanthatoftheuntreated,whilefracturetoughnesswasdecreased. Inaddition,
thewearresistancewasimprovedobviously.Lateron,Baldisserietal.[8]reportedthatCTcanproduce
amorehomogeneousstructurewhichdelayedthenucleationofcracksandincreasedthefatiguelifeof
thetool. Duringrecentyears,manyeffortshavebeendevotedtotheeffectsofcryogenictreatment
onmagnesiumalloy. Severalresearchers[9–11]investigatedtheeffectsofCTonthemicrostructure
andmechanicalpropertiesofAZ31magnesiumalloy. Theirresultsshowedthatthetensilestressand
hardnessofthesamplestreatedincryogenicenvironmentwerehigherthanthoseoftheuntreated
samples. TheCTofothermagnesiumalloys,suchasMg-1.5Zn-0.15GdandAZ91,wereinvestigated,
and it was found that CT could improve the microstructure and mechanical properties of the
alloys [12,13]. Studies also revealed that CT improved the mechanical properties, dimensional
stability,wearresistanceandthermalconductivityofaluminumalloys,magnesiumalloys,andcopper
alloys[14].Zhouetal.[15]experimentallyinvestigatedthetensilepropertiesandmicrostructuresofthe
2024-T351aluminumalloysubjectedtoCT.Theyrevealedthattheresidualtensilestressin2024-T351
wasremoved,andslightcompressiveresidualstresswasgeneratedafterCT,thiscouldcontributeto
theimprovementofthetensilepropertiesofthealloy.Intermsoftheresidualstress,similarconclusions
have been obtained for 2024 aluminum alloy. Zhangetal.[16]investigated the tensile behavior of
3104aluminumalloywithCT.Theirresultsshowedthatthesampleexhibitedsuperiorcomprehensive
mechanicalproperties,includingtensilestrength,yieldstrength,andelongation. Thestress-strain
curveofthesampleexhibitedthePortevin-LeChateliereffect. InthiscasetheCTcouldaccelerateboth
theprecipitationanddispersionofsecondaryphaseparticles,whichcouldenhancethedislocation
pinningeffectofsolventatoms. Moreover,theyalsoconductedscanningelectronmicroscope(SEM)
analysesofthefracturesurfacesandagoodplasticitywasachieved. Araghchietal.[17]carriedout
microstructureobservation,mechanicalpropertiesmeasurement,andresidualstressesdetermination
on 2024 aluminum alloy. It was found that CT not only resulted in reduction of residual stresses,
butalsoimprovedthemechanicalproperties. Vidyarthietal.[18]experimentallystudiedtheeffectsof
CTonthemicrostructureandwearperformanceofCr-Mn-Cuwhitecastirongrindingmediacopper
alloys. Theirresultsshowedthatthehardnessandwearpropertieswereimprovedsignificantly.
Most recently, Kim et al. [19] investigated the effects of CT on nickel-titanium endodontic
instruments,andfoundthattherewasaslightincreaseinmicrohardnessafterCT.Gu[20]foundthat,
afterCT,wearresistancewasincreasedduetothereductionofβphase. Yumark[21]alsofoundthat
thecontentofβphasewasdecreasedafterCT,andtheenergyabsorptionincreasedanddamaged
areasweredecreased. Moreover,Guetal.[14]alsoinvestigatedtheeffectofCTonthemechanical
propertiesofTi-6Al-4Valloy. TheyfoundthatthemicrostructureofTi-6Al-4Valloyconsistedofα
phaseandβphase,withβphasesdispersedintheboundariesofequiaxedαgrains. Theyreported
that CT reduced the quantities of β phases by transforming the metastable β phases into stable β
phasesandαphase. Thisreductionofβphaseparticleswasbeneficialtotheimprovementinplasticity
ofTi-6Al-4Valloy. CTincreasedtheductilityandstrengthofTi-6Al-4Valloy. AlthoughCTisbeneficial
toTi-6Al-4Valloy,theresearchabouttheeffectofCTonthemechanicalpropertiesofTi-6Al-4Valloy
isscarce.
Therearemuchliteratureontheformabilityofmaterialdescribedbytheforminglimitdiagram
(FLD). Veenaas et al. [22] carried out scaled Nakajima tests to determine the FLD for describing
the limit of formability under deep drawing stress state conditions. Zhang et al. [23] carried out
uniaxialtensiletests,cuppingtestsandrigidbulgingexperimenttoobtaintheforminglimitdiagram
(FLSD),takingthecold-rollingdeepdrawingsheetSPCEN-SDandDC04asresearchobject. TheFLSD
can provide reference for practical production according to the values of hardening exponent (n),
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Metals 2018, 8, x FOR PEER REVIEW 3 of 16
sptrlaasinti crasttrioai n(rr) aatinod( rs)tarenndgstthr ecnogetfhficcoieenffit c(iKe)n. tH(Ko)w.Hevoewr,e vite rs,hiotushldo ubled nbeotneodt etdhatth aitt iits isnonto teennoouugghh ttoo
eevvaalluuaattee tthhee ffoorrmmaabbiilliittyy oofft htheet ittiatnaniuiumma lalollyoysh seheeteotn olynlbyy bteyn tseilnestieles ttse.sPtsu.n Pcuhnschhe asrhinegartiensgts taenstds daenedp
ddereapw dinrgawteisntgs aterestesm arpel oeymedpltooysetdu dtoy sthtuedfoyr tmhea bfiolirtmy.aIbnilaidtyd. iItnio nad,tdhietiopnu,n tchhein pgudnecphtihngin ddeepetph dinr adweienpg
disraawlsionga mis aatlesroi aal mchaatrearciatel rcihstaircavcateluriestfioc rveavlualeu faotrio env.aTluhaetrieofno.r eT,hpeurenfcohres,h peuarnicnhg sthesetasr,indgee tpesdtsr,a dweienpg ,
darnadwtienngs, ialendte stetsnswileer eteesmts pwloeryee deminptlohyisedp aipne trhtios pinavpeesrt itgoa itnevtehsetiegfafteec ttsheo feCffTecotsf oTfi -C6AT lo-4f VTit-i6taAnli-u4Vm
taitlalonyiusmon ailtlsoyfosr omna ibtsil iftoyrmatarboiolimty taetm ropoemra ttuerme.perature.
22.. EExxppeerriimmeennttaall PPrroocceedduurree
2.1. Material
2.1. Material
Incurrentwork,thecommercialTi-6Al-4ValloysheetwasselectedandTable1listischemical
In current work, the commercial Ti-6Al-4V alloy sheet was selected and Table 1 list is chemical
ccoommppoossititioionnss. .ThTeh teentesnilsei lsetrsetnrgetnhg, tyhi,elydie sltdresntgrethn g(th0(.2σ)0,. 2a)n,da ndducdtiulicttyil wityerwe 1e0re701 M07P0aM, 9P3a0, M93P0a,M anPda ,
and11%respectively.
11% respectively.
Table1.ChemicalcompositionsofTi-6Al-4Vtitaniumalloy(wt%).
Table 1. Chemical compositions of Ti-6Al-4V titanium alloy (wt%).
Ti TiA l Al V V FFee CC N N H H O OtOhers Others
89.1755 89.167.1545 6.144 .074.07 00.0.07575 0.00.01166 0.0202.0 220.00105.0 0105.1 00.1.4 0.4
2.2. Samples
2.2. Samples
TThhee ssaammpplleess wweerree aannnneeaaleledd aatt 776600 °◦CC ffoorr 9900 mmiinn [[2244]], ,tthheenn tthheeyy wweerree ccoooolleedd iinn tthhee QQTTFF--11220000XX
vvaaccuuuumm tutubbee fufurnrnacaec ewwithit hthteh teemtempepreartuatrue rceocnotrnotlrloinllgin agccaucrcaucrya cisy ±i1s °±C1, a◦sC s,haoswsnh oinw FniginurFei g1ua.r eTh1ea .
mThaxeimmuaxmim huematihnega triantge raanted acnodolcinoogl irnagter aatree a2re0 2°0C◦ C/m/imn.i nD.uDruinrgin ganannenaelianlign gthteh eAArgrgoonn ggaass wwaass
continuously injected into the tube. After annealing the samples (see Figure 1b) with different CT
continuouslyinjectedintothetube. Afterannealingthesamples(seeFigure1b)withdifferentCTtime
time were stored in a liquid nitrogen. All the samples were divided into seven groups according to
werestoredinaliquidnitrogen. AllthesamplesweredividedintosevengroupsaccordingtoCTtime.
CT time. The details of groups are shown in Table 2.
ThedetailsofgroupsareshowninTable2.
(a) (b)

FFiigguurree 11.. ((aa)) QQTTFF--11220000XX vvaaccuuuumm ttuubbee ffuurrnnaaccee;; aanndd ((bb)) tthhee aannnneeaalleedd ssaammpplleess ffoorr ppuunncchh sshheeaarriningg tetesststs. .
TTaabbllee 22.. TTrreeaattmmeenntt ggrroouuppss..
Group Index Treatment Method CT Time
GroupIndex TreatmentMethod CTTime
AT Annealed -
AT Annealed -
ACT1 Annealed −196 × 4 h
ACT1 Annealed −196×4h
ACT2 Annealed −196 × 8 h
ACT2 Annealed −196×8h
AACCTT33 AAnnnneeaaleledd −−119966 ×× 1122 hh
AACCTT44 AAnnnneeaaleledd −−119966 ×× 1166 hh
AACCTT55 AAnnnneeaaleledd −−119966 ×× 2200 hh
ACT6 Annealed −196×24h
ACT6 Annealed −196 × 24 h
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2.3. Metallographic Observation
2.3. MAefttaelrlo tgrreaapthmiceOntbss,e trhvaet isounrface of the samples was initially grinded by abrasive paper and then
polisAheftde.r Atrfeteartmwaerndtss,, tthhee ssuamrfapclee osufrtfhaeces awmaps lecosrwroadseidn ibtiya lclyhegmriincdale drebagyeanbtsra wsiivthe p88a pveorl%an dH2tOhe, n2
pvoolli%sh HedF., aAnfdte 1r0w vaordl%s, HthNeOsa3.m Fpinleallsyu,r tfhaec esawmapslceo orfr oedacehd gbryoucph ewmaisc adlerteecatgeedn btsy wopitthic8a8l mvoiclr%osHcopOy,
2
(ZEISS microscope; Axio.Imager.A2m, manufactured by Carl Zeiss Microlmaging GmbH,Gottingen,
2vol%HF,and10vol%HNO . Finally,thesampleofeachgroupwasdetectedbyopticalmicroscopy
3
Germany).
(ZEISSmicroscope;Axio.Imager.A2m,manufacturedbyCarlZeissMicrolmagingGmbH,Gottingen,
Germany).
2.4. Vickers Hardness
2.4. VickersHardness
Vickers hardness values of the samples were obtained using Vickers hardness tester under
different treatment process. During the tests, the load is 100 N and the duration is 5 s with the
Vickers hardness values of the samples were obtained using Vickers hardness tester under
magnification is 400 times. In the current study, the sample surface o roughness is Ra0.2. For each
different treatment process. During the tests, the load is 100 N and the duration is 5 s with the
group sample, five points were tested for hardness, and the average values were calculated
magnificationis400times. Inthecurrentstudy,thesamplesurfaceoroughnessisRa0.2. Foreach
accordingly.
groupsample,fivepointsweretestedforhardness,andtheaveragevalueswerecalculatedaccordingly.
22..55.. TTeennssiillee TTeessttss
TThhee ddeettaaiillss ooff tthhee ssaammppllee ddiimmeennssiioonnss aarree sshhoowwnn iinn FFiigguurree 22,, tthhee tteennssiillee tteessttss wweerree ccaarrrriieedd oouutt aatt
rroooomm tteemmppeerraattuurree uussiinngg aa uunniivveerrssaall tteessttiinngg mmaacchhiinnee aatta at teennssiilleer raatteeo off2 2m mmm//mmiinn.. TThhrreeee ssaammpplleess iinn
eeaacchh ggrorouuppw wereersee lseeclteecdtefdor ftohre ttehset .tTehste. mTahxei mmuamximfourcme (Ffobr)coef t(hFebsa)m opfl ethaen dsathmeptloet aalnddef othrme attoiotanl
odfetfhoermgaautigoen leonf gtthhes egcatiuognea fletenrgttehn ssielectfiroanc tuafrteeor fttehnesislaem fpralectcuarne boef otbhtea inseadm.pElne gcinanee rbien gosbttraeisnseσd.
b
aEnndgisntreaeirninδgc satnrebses calbcu alantded stbryaitnh ee ncgainn ebeer icnaglcsutlraetsesd-s btrya itnhef oernmguinlaee.ring stress-strain formula.
(b)
1200
1100
1000
(a) aP900 AT
M/sse780000 AACCTT12
rts gn600 AACCTT34
ire500 ACT5
e
nig400 ACT6
nE 300
200
100
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Engineering strain/%
FFiigguurree 22.. TTeennssiillee ssaammppllee aanndd ssttrreessss aanndd ssttrraaiinn ccuurrvveess uunnddeerr ddiiffffeerreenntt ttrreeaattmmeenntt ((aa)) tthhee tteennssiillee ssaammppllee;
(aunndit (:bm) mstr)e;sasn-dstr(bai)ns tcruersvs-esst ruanindecru drvifefseruenndt etrredaitfmfeerennt.t treatment.
Figure 2b plots the stress and strain curves of the samples. From Figure 2b, in the process of
Figure 2b plots the stress and strain curves of the samples. From Figure 2b, in the process of
deformation, elastic deformation occurs firstly, and the stress is proportional to strain. When the
deformation, elastic deformation occurs firstly, and the stress is proportional to strain. When the
stress exceeds e (e is the elastic limit), and the material starts to yield, it can also be noted that
stressexceedsσ (σ istheelasticlimit),andthematerialstartstoyield,itcanalsobenotedthatthere
e e
there is not apparent yield platform in the curves. Under the condition, the stress value that produces
is not apparent yield platform in the curves. Under the condition, the stress value that produces
0.2% residual deformation is defined as its yield limit (s). When the stress exceeds the yield limit,
0.2%residualdeformationisdefinedasitsyieldlimit(σ ). Whenthestressexceedstheyieldlimit,
plastic deformation occurs. As the cross-sectional area shsrinks, the maximum force (Fb) when the
plastic deformation occurs. As the cross-sectional area shrinks, the maximum force (F ) when the
sample is broken is divided by the original cross-sectional area (S0), the result is cablled tensile
sampleisbrokenisdividedbytheoriginalcross-sectionalarea(S ),theresultiscalledtensilestrength
strength (b). When the stress reachesb, the stage of uniform0 plastic deformation has ended. The
(σ ). Whenthestressreachesσ ,thestageofuniformplasticdeformationhasended. Thesamplestarts
b b
sample starts to produce uneven plastic deformation and form necking, followed by the stress
toproduceunevenplasticdeformationandformnecking,followedbythestressdecreases. Whenthe
decreases. When the final stress reaches K (Fracture strength), the specimen is found to be broken.
finalstressreachesσ (Fracturestrength),thespecimenisfoundtobebroken.
K
22..66.. PPuunncchh SShheeaarriinngg TTeessttss
In the current study, punch shearing was employed to investigate the effects of ACT on the
In the current study, punch shearing was employed to investigate the effects of ACT on the
properties of Ti-6Al-4V titanium alloy. The principle of punch shearing and the die are shown in
properties of Ti-6Al-4V titanium alloy. The principle of punch shearing and the die are shown in
Figure 3a,b,d, respectively. The diameter of the punch is 3 mm and the die is 3.07 mm. A slot is
Metals2018,8,295 5of16
Metals 2018, 8, x FOR PEER REVIEW 5 of 16
Figure 3a,b,d, respectively. The diameter of the punch is 3 mm and the die is 3.07 mm. A slot is
machined in the die to clamp the sample. In order to obtain better section quality, the punching speed
machinedinthedietoclampthesample. Inordertoobtainbettersectionquality,thepunchingspeed
is set to be 5 mm/s 24. After ACT, the samples with the length of 30 mm, the width of 19 mm and the
issettobe5mm/s24. AfterACT,thesampleswiththelengthof30mm,thewidthof19mmand
height of 0.2 mm will be punched and divided into two groups. A group of the samples will be
the height of 0.2 mm will be punched and divided into two groups. A group of the samples will
immersed into the liquid nitrogen and punched as shown in Figure 3c. Another group of the samples
be immersed into the liquid nitrogen and punched as shown in Figure 3c. Another group of the
will be punched at room temperature. Fracture surface was detected by optical microscopy (ZEISS
sampleswillbepunchedatroomtemperature. Fracturesurfacewasdetectedbyopticalmicroscopy
microscope; Axio.Imager.A2m). Table 3 lists the test numbers of the samples under different
(ZEISSmicroscope;Axio.Imager.A2m). Table3liststhetestnumbersofthesamplesunderdifferent
conditions. During punch shearing, the relationship between the maximum deformation resistance
conditions. Duringpunchshearing,therelationshipbetweenthemaximumdeformationresistance
Pmax and shear strength  is calculated by the following formula:
P andshearstrengthτiscalculatedbythefollowingformula:
max
= Pmax (cid:0)2πravgt(cid:1) (1)
τ = P / 2πr t (1)
max avg
where t is the thickness of the plate, ravg (cid:0)rprd(cid:1) 2, rp is the radius of the punch, and rd is
wheretisthethicknessoftheplate,r = r +r /2,r istheradiusofthepunch,andr isthe
avg p d p d
trhaed iruasdoiufst hoef tdhiee .die.
Servo press
(a) (b)
Punch
Guide sleeve and claming
Liquid nitrogen
Liquid nitrogen Die Sheet
container

R=1.515mm R=1.535mm
(c) (d)
m Punching
Die
m
8
=
h
h=3.5mm
Punch
Slot
liquid nitrogen
tank R=8.95mm
Guide sleeve and
clamping

FFiigguurree 33.. ((aa)) PPrriinncciippllee ooff ppuunncchh sshheeaarriinngg;; ((bb)) tthhee ppuunncchhiinngg pprroocceessss;; ((cc)) aatt ccrryyooggeenniicc tteemmppeerraattuurree
ppuunncchhiinngg;; aanndd ((dd)) tthhee ppuunncchh aanndd ddiiee..
TTaabbllee 33.. TTeesstt ssaammpplleess ffoorr ppuunncchh sshheeaarriinngg tteessttss..
Group Index
GroupIndex
Number at the Untreated AT ACT1 ACT2 ACT3 ACT4 ACT5 ACT6
theUntreated AT ACT1 ACT2 ACT3 ACT4 ACT5 ACT6
Diff. Temp.
NumberatDiff.Temp.
Number at room temp. 3 3 3 3 3 3 3 3
Numberatroomtemp. 3 3 3 3 3 3 3 3
NNuummbbeerr oonnlilnineec rcyroygoegneicnic 3 3 33 33 33 33 33 33 33
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2.7. DeepDrawing
2.7. Deep Drawing
Inthecurrentwork,deepdrawingtestswerealsoconductedusingaservopresstostudythe
In the current work, deep drawing tests were also conducted using a servo press to study the
effect of ACT on the formability of Ti-6Al-4V titanium alloy. The size of the sample for the deep
effect of ACT on the formability of Ti-6Al-4V titanium alloy. The size of the sample for the deep
drawingtestis29mm×29mm×0.2mm. Table4listedthetestcases. Theprincipleofdeepdrawing,
drawing test is 29 × 29 × 0.2 mm. Table 4 listed the test cases. The principle of deep drawing, the
theschematicdiagramofthedieandpunchareshowninFigure4. Additionally,thediameterofthe
schematic diagram of the die and punch are shown in Figure 4. Additionally, the diameter of the
punchwithsphereis4mm,andthedieis5.4mm. Duringdeepdrawing,thepunchcontinuously
punch with sphere is 4 mm, and the die is 5.4 mm. During deep drawing, the punch continuously
descendsdownuntilthesamplehappenstocrack. Atthistime,thedisplacementvalueofthepunchis
descends down until the sample happens to crack. At this time, the displacement value of the punch
thelimitdepthofdeepdrawing.
is the limit depth of deep drawing.
Table4.Testsamplesfordeepdrawingtests.
Table 4. Test samples for deep drawing tests.
GGroruopup InInddeexx ththe eUUnnttrreeaatteedd AATT ACACTT1 1 AACCTT22 AACCTT33 AACCTT44 AACCTT55 AACTC6T6
NNuummbbeerr 33 33 3 3 33 33 33 33 3 3

(a) Servo press (b) R=2mm
Punch m R=2.7mm
Guide sleeve and claming m Punching Die
0
1
=
h
Liquid nitrogen
Liquid nitrogen
Die Sheet
container R=8.95mm

FFiigguurree 44.. ((aa)) TThhee pprriinncciippllee ooff ddeeeepp ddrraawwiinngg;; aanndd( (bb))t thheep puunncchha annddd diiee..
33.. RReessuullttss aanndd DDiissccuussssiioonn
33..11.. MMiiccrroossttrruuccttuurraall CChhaarraacctteerriissttiiccss
FFiigguurree 55 sshhoowwss tthhee mmiiccrroossttrruuccttuurreess ooff tthhee ssaammpplleess aafftteerr AATT aanndd AACCTT.. AAfftteerr rreeccrryyssttaalllliizzaattiioonn
aannnneeaalliinngg,, tthhee mmiiccrroossttrruuccttuurree iiss ccoommppoosseedd ooff αα aanndd ββ pphhaasseess,, aanndd tthhee ββ pphhaassee iiss ddiissppeerrsseedd iinn tthhee
bboouunnddaarryyo offe eqquuiaiaxxeeddα αg grarainins.s.I nInF Figiguurere5 5t htheeb rbirgihgthrte rgeigoinosnas raerαe αp hpahsaesse,sa,n adntdh ethbel abclkacgkr agirnasinasr earβe
pβh pahseass.eTs.h Tehdei dstirsitbruibtuiotnioonf oβf βp hpahsaesseiss issh sohwownnin inF iFgiugurere5 a5,ab,,ba, nanddit itc acannb bees seeeennc cleleaarrlylyt hthaattβ βp phhaasseess
ddiissppeerrssee iinn tthhee bboouunnddaarriieess ooff αα ggrraaiinn aaftfeterr AATT. .HHoowweevveerr, ,aaftfeter rAACCTT11, n,newew phpahsaesse isnicnlculduidnign gα’α a’nadn βd’
βa’rea rperepcriepciitpaitteadt e[d26[]2. 6T].heT hαe’, αβ’’, aβn’da nudntruanntsrfaonrsmfoerdm βe dphβaspeh adsisepdeirsspee ursneifuornmifolyr minl yboinunbdoaurniedsa orife sα
opfhαaspehs,a asse ss,haoswsnh oinw FnigiunrFe i5gcu,dre. F5rco,dm. AFrCoTm1 AtoC ATC1Tt2o, AthCe Tc2h,atnhgee cihna mngiceroinstrmuicctruorset rwuictthu trheew initchretahsee
ionfc rtheaes CeTo ftitmhee,C isT sthimowe,ni sins hFoigwunrei n5eF,ifg. uItr seh5oeu,fl.dI tbseh nooutledd btheanto ttheed ptrheactipthiteatperse icnipcliutadteinsgi nαc’l,u βd’,i nagndα ’β,
βin’,carneadsβe rienmcraerakseabrelym aanrkda dbilsypaenrdsed uisnpifeorrsmeulyn.i fWorhmelny .thWe hCeTn tthimeeC aTrtriimvees aartr i1v2e sha, tth1e2 qhu,tahnetiqtiueasn otfit tiehse
opfrtehceippitraetceips iatartee sinacrreeianscerde,a saendd, athned tshizeessi zbeescboemcoe mlaerglaerrg, ear,s asshsohwown nini nFFigiguurere 55gg,,hh.. WWhheenn tthhee ttiimmee
iinnccrreeaasseessf frroommA ACCTT44t otoA ACCTT6,6t, htehec hcahnagnegein inth tehme micriocrsotrsutrcutuctrueries eisx hexibhiitbeidteidn iFnig Fuirgeu5rei– 5ni.–Int.n Iet endesetdos
btoe obbes eorbvseedrvtheadt tthheatb tohthe qbuoathn tiqtuieasnatnitdiessi zaensdi nscirzeeass einfucrrethaseer, wfuhrtihcheri,n dwihcaictehs itnhdaticAatCeTs cthanatt rAanCsTfo cramn
tthreanmsfeotramst atbhlee mβepthasatsaebilne tβo spthaabslee βin’tpoh sataseblaen βd’ αp’hpahsea saen,da nαd’ pthhearseei, sannod othbevrioe uiss nchoa onbgveioinusα cphhaansgee.
Tinh eαr peshualstes. aTchheie rveesdulatss aabchoiveeveadre aisn acboonvseis aterne cien wcoitnhsitshtoenseceo bwtaitihn ethdoisne tohbetlaiitnereadt uinre th2e4 .literature 24.
IItt ccaann bbee sseeeenn ffrroomm aallll tthhee fifigguurreess tthhaatt bbootthh tthhee qquuaannttiittiieess aanndd ssiizzeess ooff tthhee pprreecciippiittaatteess aarree
aappppaarreennttllyy iinnccrreeaasseedd aafftteerr AACCTT.. TThhee rreeaassoonn ccoouulldd bbee tthhaatt,, tthhee αα--TTii iiss aa hheexxaaggoonnaall cclolossee--ppaacckkeedd
ssttrruuccttuurree,,w whheerreeaasst thheeβ β--TTiii iss tthhee bbooddyy cceenntteerreedd ccuubbiicc ssttrruuccttuurree,, aanndd tthhee ddiiffffuussiioonn aabbiilliittyy ooff hheexxaaggoonnaall
cclloossee--ppaacckkeedds tsrtuructcuturereis ifsa rfabre lboewlotwhe tbhoed byocdeyn tceerendtecruebdi ccustbruicc tsutrreucotwurine gotwoihnegx atog ohneaxlacgloosnea-pl acclokesed-
sptrauckcteudr estirsuicntucrleo sies ianr rcalyo.seG aurreatya. lG.[u2 6e]t satla. t[e2d6]t hstaattethde thcoant ttrhaec tcioonntrvaecltoiocnit yveolfotchitey βofp thhaes eβ ipshfaassete irs
faster than that of α phase at low temperature, which can produce enough driving force to promote
the precipitate of the α titanium particle s depending on the matrix. Moreover, at low temperature,
Metals2018,8,295 7of16
thanthatofαphaseatlowtemperature, whichcanproduceenoughdrivingforcetopromotethe
pMreectailps i2t0a1t8e, 8o, fx tFhOeR αPEtEitRa RnEiuVmIEWp a rticlesdependingonthematrix. Moreover,atlowtemperatu7r eo,f t1h6e
solubilityofvanadiumdropssignificantly,resultinginβphaseisinmetastablestateandtransformed
the solubility of vanadium drops significantly, resulting in β phase is in metastable state and
tostableβ’phase. ACTcantransformthemetastableβphaseintostableβ’phaseandα’phase. Due
transformed to stable β’ phase. ACT can transform the metastable β phase into stable β’ phase and α’
totheprecipitationofprecipitates,thebondingforcebetweengrainboundaryandgrainboundaryis
phase. Due to the precipitation of precipitates, the bonding force between grain boundary and grain
small,thiswilllowerthebondstrengthatthecrystalboundary,resultinginthedecreaseoftensile
boundary is small, this will lower the bond strength at the crystal boundary, resulting in the decrease
strength. Ontheotherhand,theeffectofthecoldcompressioninACTprocesscouldmakethegaps
of tensile strength. On the other hand, the effect of the cold compression in ACT process could make
in the material larger. Especially at the grain boundary, the number of the pores increases due to
the gaps in the material larger. Especially at the grain boundary, the number of the pores increases
weakbondingforcebetweentheprecipitatesandthegrainboundary. Thus,theunrecoverableplastic
due to weak bonding force between the precipitates and the grain boundary. Thus, the unrecoverable
deformationiseasiertooccur,theelasticmodulusandtensilestrengthdecrease.
plastic deformation is easier to occur, the elastic modulus and tensile strength decrease.

Figure5.Cont.
Metals2018,8,295 8of16
Metals 2018, 8, x FOR PEER REVIEW 8 of 16

Figure 5. Microstructure of Ti-6Al-4V with different the treatment: (a) AT, 500×; (b) AT, 1000×; (c)
Figure 5. Microstructure of Ti-6Al-4V with different the treatment: (a) AT, 500×; (b) AT, 1000×;
ACT1, 500×; (d) ACT1, 1000×; (e) ACT2, 500×; (f) ACT2, 1000×; (g) ACT3, 500×; (h) ACT3, 1000×; (i)
(c)ACT1,500×;(d)ACT1,1000×;(e)ACT2,500×;(f)ACT2,1000×;(g)ACT3,500×;(h)ACT3,1000×;
ACT4, 500×; (j) ACT4, 1000×; (k) ACT5, 500×; (l) ACT5, 1000×; (m) ACT6, 500×; (n) ACT6, 1000×.
(i)ACT4,500×;(j)ACT4,1000×;(k)ACT5,500×;(l)ACT5,1000×;(m)ACT6,500×;(n)ACT6,1000×.
MMeteatlasls2 2001188,,8 8,,2 x9 5FOR PEER REVIEW 9 9ofo f161 6
3.2. Tensile and Hardness Properties
3.2. TensileandHardnessProperties
Figure 6 plots the average values of elastic modulus, tensile strength, yield strength, and the
ductFiliigtuy.r eIt 6capnl obtes steheen afrvoemra gFeigvuarelu 6eas tohfate, laafstteirc AmTo, dthuelu esla,stteinc smiloedsutrleuns gisth 1,2y1.i6e lMdPstar,e wnghtehre,aasn adfttehre
dAuCctTil1it, yt.heI tacvaenrabgee vseaelunef orof mtheF ieglausrteic6 maothdautl,uas fitse rdeAcTre,atsheede tloa s1t1ic9.2m ModPual.u Fsroism1 F2i1g.6urMe 6Paa,, iwt ihs earlesoa s
aoftbesreArvCeTd 1t,htaht ethaev oevraegraellv aavluereaogfet vhaelueelass otifc thmeo edlausltuics misoddeuclruesa asered dtoec1r1ea9s.2edM sPloaw. Flyr owmithF itghue rienc6rae,aistei s
aolsfo CoTb tsiemrve,e rdeathchatintgh ea omvienriamlluamv evraalguee voaf l1u1e5s.8o fMtPhae aefltaesrt iAcCmTo4d. uWluitsha trhee dineccrreeaassee dofs CloTw tliymwe,i ftrhotmhe
inAcCreTa5s etoo fACCTTt6im, teh,er eaavcehraingge avamluinei mofu tmhev eallausetioc fm11o5d.8ulMusP saliagfhtetrlyA iCncTr4e.aWsei tfhrotmhe 1i1n7c.r5e aMsePoaf tCo T11ti8m.7e ,
frMomPa.A TChTe 5cotorrAelCatTio6n, tehqeuaatvieorna gise evstaalbuleisohfedth aenedla ist tcicanm boed cuolnucslusldigedh ttlhyaitn tchree aesleasftrioc mmo1d1u7.l5usM oPf aaltlo
1t1h8e.7 sMamPpal.eTs hweictho rAreTla otiro AnCeqTu ias tdioencriesaessetda,b wlishheerdeaasn tdheit eclaanstibce mcoondculluudse ids itnhcartetahseedel aafstteicr mACodTu4,l ubsuot f
atlhleth oevsearamllp vlaelsuwesi tohf AthTe eolraAstiCc Tmiosdduelcurse iass leodw,ewr hthearena tshtaht eofe tlahset iucnmtreoadtuedlu ssaimspinlecsr.e Faisgeudrea f6tber shAoCwTs4 ,
btuetntshilee ostvreernagltlhv, aalnude sito cfatnh ebee lsaesetinc tmhaotd tuhleu vsailsuleosw oebrtatihnaend tbhya tthorfeteh teeustns tarepaptreodacsha meapclhe so.tFhiegru broet6hb
shafotwers AteTn sainled sAtrCenTg. tMh,oarnedovietrc,a wnibthe stheeen inthcraetatshee ovfa CluTe stiombeta, itnheed tebnystilher esetrteensgtstha pdpercoreaacshees aacnhdo tthhee r
bdoethcraefatseirnAg Ttraenndd AfoCllTo.wMso arecocovredr,awncieth wthitehi nthcree aesqeuoaftiConT taism feo,ltlhoewtse: nsilestrekntgthdec, rweahseersea nkd tihse
b ADCT
dceocnresatasnint,g atnrden cdalfcoulllaotweds aasc c1o1r4d4a.3n8c MewPait,h anthde equ iast cioonnsatsanfot,l laonwds c:aσlcbu=latketdA DasC T−0β.,0w3.h Feirgeukrei s6cc osnhsotwans t,
andcalculatedas1144.38MPa,andβisconstant,andcalculatedas−0.03. Figure6cshowstheyield
the yield strength it is clearly observed that with the increase of the CT time, the values of the yield
strengthitisclearlyobservedthatwiththeincreaseoftheCTtime,thevaluesoftheyieldstrength
strength decreases, and the equation of declining trend is in accordance with that of the tensile
decreases, andtheequationofdecliningtrendisinaccordancewiththatofthetensilestrengthas
strength as mentioned above, where k is calculated as 1028.74 MPa, and  is calculated as −0.027.
mentioned above, where k is calculated as 1028.74 MPa, and β is calculated as −0.027. Figure 6d
Figure 6d demonstrates the ductility, and it can be seen that the ductility is increased gradually with
demonstratestheductility,anditcanbeseenthattheductilityisincreasedgraduallywithtreatment
treatment methods from AT to ACT. Furthermore, with the increase of the CT time, the ductility is
methodsfromATtoACT.Furthermore,withtheincreaseoftheCTtime,theductilityisincreased
increased remarkably until, the peak value is achieved after ACT3, which is increased by 17.5%
remarkablyuntil,thepeakvalueisachievedafterACT3,whichisincreasedby17.5%comparedtothe
compared to the values after AT. Afterwards, the values decrease from ACT4 to ACT6. The
valuesafterAT.Afterwards,thevaluesdecreasefromACT4toACT6. Thecorrelationequationcan,
thcoursr,ebleatδio=n 1e5q.u9a3t+ion1 .6c7aen−, (0th.1u8ts−, 2)b2e. Thδe=i1m5.p9r3o+v1e.6m7eent-(o0f.1m8t-e2c)2han.i cTahlpe roimpeprrtoievsemhaesnot bovfi omusecinhflanuiecnacle
opnrtohpeefrotirems ahbailsit yoobfvTioi-u6sA li-n4fVlusehneceet .oAnf tetrhAe CfTo,rmplaabstiilcityd efoofr mTai-t6ioAnl-i4sVm osrheeelitk. elAyfttoero cAcuCrTd, upeltaosttihce
ddeecfroeramseaotifoyni eisld msotrreen lgikthelayn tdo eolcacsutirc dmuoed tuol uthse. Tdheecrdeauscet iloift yyiiselcdl esatrrleynginthcr eaansde del,awsthicic mhoredsuullutss.i nThthe e
ladtuecoticlcituyr ries nccleeaorlfyc rinacckresadseudri, nwghdicehfo rremsualttiso nin. Tthhee lpatreo pooccrutirornenocfes mof ocortahckzso dnueriinngp udnecfohrsmhaetairoinn.g Tahned
thperodpeoprtthioinn odfe sempodortahw zionngei ninc rpeuansec.h shearing and the depth in deep drawing increase.
(a) 1200
123 1160 (b)
122 121.6
a
121 P1120
M
us/GPa111112890 119.2 118.3 118.1 117.5 118.7 gth σ/b11004800
modul111167 115.8 stren1000 σb=1144.38t-0.030
Elastic 111111345 Tensile 992600
112 AT ADCT1 ADCT2 ADCT3 ADCT4 ADCT5 ADCT6 880 AT ACT1 ACT2 ACT3 ACT4 ACT5 ACT6
Different treatment Different treatment
1080 18.0
1060 17.7 (d)
(c)
Pa1040 17.4
M
σ/s1020 17.1
gth 1000 %16.8
eld stren996800 ctility δ/1166..25
Yi940 Du15.9 δ=15.93+1.67e-(0.18t-2)2
920 σs=1028.74t-0.027 15.6
900 15.3
880 15.0
AT ACT1 ACT2 ACT3 ACT4 ACT5 ACT6 AT ACT1 ACT2 ACT3 ACT4 ACT5 ACT6
Different treatment
Different treatment
FFigiguurere6 .6C. hCahnagnegseosf otef ntseinlesitlees tt:e(sat): e(laa)s teilcamstiocd mulouds;u(lbu)st; e(nbs)i letesntrseilneg sthtr;e(nc)gythie; ld(c)s tyreienlgdt hs;t(rden)gdtuhc;t i(ldit)y .
ductility.
Metals 2018, 8, x FOR PEER REVIEW 10 of 16
Metals2018,8,295 10of16
Five points distributed uniformly on each sample were marked by the Vickers hardness tester.
VariatFiiovne opfo Vinitcskderiss thriabrudtneedssu nwiiftohr mdilfyfeorneneta tcrheastammepnlte iws sehreowmna rikne Fdigbuyrteh 7e. VTihcke earvsehraagrden veaslsuteess toefr .
fVivaer ivaatilouneso ifnV eiacckhe rgsrohuaprd wneesrse wcailtchudlaitfefedr eanntdt trheea tcmuervnet iosf sthhoe wvanriiantiFoing uisr eas7 .foTllhoewasv: erHaVgevavltu0e.0s05o8f
wfihveerve alvu eiss itnhee accohnsgtraonut panwde craelccuallcauteldat aesd 3a8n8d.4t HheVc, uarnvde ot fitsh veavriaarbialeti oofn CisTa tsimfoel.l oItw casn: HbeV se=env tf0r.o00m58
Fwighuerree 7v tihsatht ethceo nhsatradnnteasns dvaclaulceus ldatiestdriabsu3te8 8o.n4 HboVt,ha sniddetsi sofv athriea bculervoef.C ItT atlismo ec.aInt cbaen sbeeens etehnatf rtohme
hFairgnuerses 7vtahluaetst haereh ainrcdrneeasssedv awluitehs tdhiest rinibcureteasoen obf oCtTh stiimdees, oafndth tehceu irnvcer.eaItsianlgso trceanndb oef sveaelnueths aits tihne
ahcacronreds swviathlu tehsea reeqiunactrieoans.e Adlwthitohutghhe itnhcer ehaasredonfeCssT otfim thee, asnadmtphleei nacftreera sAinCgTt riesn odvoefravlall uinecsriesaisneadc, ctohred
cwhaitnhgtehse ineq tuhaet ihoanr.dAnletshso aurgeh ntohte ohbavridonuess sbeocfatuhsees athme pmleaaxfitmeruAmC dTififseroevnecrea lbleintwcreeeans etdh,et hmeacxhimanugmes
ainndt htheeh maridnnimesusma ries 4n.o5t HoVbv. iIot ucasnb beeca cuosnecltuhdeemd athxiamt AumCTd hifafse riennsicgenbifeitcwanete enfftehcet omna txhime huamrdannedss tohfe
tmhei nailmlouym. is4.5HV.ItcanbeconcludedthatACThasinsignificanteffectonthehardnessofthealloy.
397 The plots of hardness values
Fitting cu rve
396
V
H 395
s/
s
e
n 394
d
r
a
h
s 393
r
e
k
c HV=388.4t0.0058
Vi 392
391
AT ACT1 ACT2 ACT3 ACT4 ACT5 ACT6
Different treatment
FFigiguurere 77. .VVaarriaiatitoionn oof fVVicickkeerrss hhaarrddnneessss wwiitthh ddiiffffeerreenntt ttrreeaattmmeenntt..
33.3.3. .EEfffefecctt oonn PPuunncchh SShheeaarriningg PPrrooppeerrttiieess
33.3.3.1.1. .SShheeaarr SSttrreennggtthh
FFiigguurree 88aa,b,b sshhooww tthhee sshheeaarr ssttrreennggtthh ooff tthhee ssaammpplleess wwiitthh ddiiffffeerreenntt ttrreeaattmmeennttss aatt bbootthh rroooomm aanndd
ccrryyooggeennicic tetemmppeeraratuturer,e r,ersepsepcetcivtievleyl.y I.t Ictanca bne bseeesne efrnomfro FmigFuirgeu 8rae t8haatt hwahtewthheert ahfetrera AfteTr oAr TACorTA, tCheT ,
sthheeasrh setarernstgrtehn gdtehcrdeeacsreesa sines cionmcopmarpisaornis oton tthoet huenutrnetarteeadte mdamteartiearli.a Il.t Isthsohuoludl dbeb enontoetded ththaat,t ,aaftfeterr tthhee
ttrreeaattmmeennttss ffrroomm AATT ttoo AACCTT22,, tthhee sshheeaarr ssttrreennggtthh ggrraadduuaallllyy ddeeccrreeaasseessf frroomm7 76688M MPPaat oto7 74499M MPPaa,,t htheenna
aq quuicikckin icnrceraesaesaet aAt CATC3T,3w, hwichhicihs 7i5s 47M54P Ma,Paan,d aanfdte arwftearrwdsairtddse ictr deaescerseatose7s4 t4oM 74P4a MatPAaC aTt4 A.FCrTo4m. FArComT4
AtoCAT4C tTo6 A,tCheT6sh, tehaer sshtreeanrg stthreinsginthcr iesa isnecdrefarosemd 7fr4o4mM 7P4a4t Mo7P5a8 toM 7P5a8. MInPoar.d Ienr otrodsetru tdoy stthuedyef tfhecet esfofefcCtsT
oofn CtTh eonp uthnec hpsuhnecahr isnhge,atrhinegp, uthnec hpushnecahr isnhgeawriansgp werafso rpmerefdoramtecdry aotg cernyiocgteenmicp etermatupreer,aatunrde,t haneds htehaer
sshtereanr gstthreinsgsthho iws nshinowFing uinre F8igbu. rIte c8abn. bIte csaene nbec leseaerlny cflreoamrlyF ifgruorme 8Fbigtuhraet t8hbe tchhaat nthgee icnhashnegaer isnt rsehnegatrh
sotrfesnagmthp loefs saafmterplAeTs aisftsemr AalTle rist hsmanalulenrt rtehaatne dunontreesa.tFedro omneAsC. FTr1otmo AACCTT41, ttoh eAsChTe4a,r tshtere snhgetahr dsetrcerneagstehs
dfreocmrea8s3e1s MfrPoamt o83810 7MMPPaa ,tob u8t0d7e McrePaas,i nbgutt ednedcernecaiseisnagr etesnlodwenecdi.eAs taAreC sTlo5,wthede.s hAeta rAsCtrTe5n,g tthher esahcehaers
stthreenmgtihn imreuacmhevsa ltuhee omfi8n0i1mMumPa v,aanlude thofe n80it1 inMcPreaa, saensdto th82e3n Mit PinacarteAasCesT 6to. T8h2e3 cMomPap aarti sAoCnTo6f.s Thehaer
csotmrepnagrtihsoant roofo smhetaerm stpreenragttuhr eata rnodomcr yteomgepneircatteumrep aenrdat curryeoigsesnhioc wtenmipneFraigtuurree i8sc s.hIotwcann ibne Foigbusreer v8ecd.
Iftr ocamn Fbieg uorbes8ecrvtehda tfsrhoema rFsitgruenreg t8hc atthraoto smhetaerm sptreernatguthre aist lroowomer tthemanptehraattuartec risy ologweneirc tthemanp ethraattu arte .
cMryeoagnewnihci ltee,mthpeecrhataunrgee. oMfethanewshheialer, stthreen cghthanagtec royfo gtheen ischteeamr psetrraetnugrtehi samt curcyhoggeennitcle rtetmhapnertahteusrhe eiasr
msturecnhg gtehnattlerro tohmant etmhep sehraetaur rset.rength at room temperature.