Beta and near-beta titanium (Ti-5Al-2Sn-4Zr-4Mo-2C-1Fe_ Beta-CEZ)

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584 / Heat Treater’s Guide: Nonferrous Alloys

Ti-5Al=2Sn-4Zr-4Mo-2Cr-1 Common

Name. Beta-CEZ@

Chemical

Composition.

Fe

SeeTable for chemical composition.

Beta-CEZ@is a multifunctional near-p titanium alloy exhibiting high strength, high toughness, and intermediate-temperaturecreep resistance. Processingflexibility makesit suitable for a wide range of applications

Characteristics Ctystal Structure. In the solution treatedand agedcondition, the microstructure consists of a + p phases.The lattice parametersof the closepackedhexagonal a phasearea = 2.9287 A and c = 4.~ A, whereasthe lattice parameterof the body-centeredcubic p phase is a = 3.2040 A

Beta and Near-Beta Alloys / 585 Grain Structure. The microstructure is typical of p metastablealloys and may be p or a + p. eithherequiaxed or larnellar. Highest strength and ductility are achieved with an equiaxed primary a phase and a finely precipitated secondary a phase microstructure. Optimum toughness is obtained with IameUarprimary a microstructures Products. The continuous cooling (CCT) diagram for Beta-CEZ@is similar to that of Ti-17. Alpha precipitation occurs first at p grain boundaries and secondly inside the grains. For instance, the time difference betweengrain boundary and intragmnular precipitation is about I h when cooled at I Wmin (I .8 “F/min) tirn the p field. A temperature of >750 “C (I 380 “F) is recommendedfor solution treatmentsbelow the transus. whereasaging treatmentsare.performed below 700 “C (1290 “F) Transformstion

Beta Trsnsus.

890 “C (1635 OF)

Chemical Cowosion Resistsnce. Corrosionresistancein acid or seawater, as well as hydrogen uptake and embrittlement are currently being studied. Data are not available Product Forms. ‘I)lpical product forms consist of forged billets in diametersranging from I50 to 300 mm (6 to I2 in.) and forged or rolled bar in diameters ranging Tom 10 up to I10 mm (0.4 to 4.3 in.). Rolled plate and sheetare also available in thicknessesranging from 25 to 3 mm (I to 0.1 in.) and 500 mm (20 in.) wide. Products are supplied in the forged or solution treatedconditions. The microstructure is tine and equiaxed

Fabrication

Properties

Forming. Becausethe strain-rate sensitivity exponent of Beta-CEZ@is rather high comparedto conventional alloys (0.3 for [email protected] for Ti-6Al-4V), plastic flow is more stable and enhancesformabiity. The metastablenature of the alloy lowers its sensitivity to lemperature.

Hot working in the a + p range is recommendedat 800 to 860 “C (1470 to 1580 “F) to maintain a fine equiaxed microstructure. In the p range, a temperaturearound 920 “C (1690 “F) is suggestedto obtain a lamellar structure by fl processing “Through

the Transus”

Processing.

A patented technique that re-

suits in a “necklaced” microstructure. It is applied to a 100% /3metastable structtm below 890 “C (1635 OF).Lamelk in the core of the grains and fine equiaxed grains at the boundaries are thus obtained. which leads to an exceUentcombination of strength, ductility, and toughness Superplastic Forming. The alloy displays superplastic Propemesbetween 725 and 775 “C (1335 and 1425OF);1000%ductility can be reached at strain rates as high as 8 x lOA s-‘. Diffusion bonding is being studied.

Superplasticpropertiesof Beta CEZ@alloy are obtained at te.mperaturesas low as 725 “C (Scripra Mer. Vol29. No. 4, 1993,p 503-508)

Recommended

Heat Treating

Practice

Apical applications include heavy section forgings for medium-temperaturecompressordisks in which an optimum combination of strength. ductility, toughness, and creep resistance is required. BetaCEZ@is a structural alloy with very high strength and a good combination of strength, ductility. and toughness.Near-net shapeforgings are possible due to the excellent formability of the alloy. Component applications are as forged parts, springs, and fasteners

Solution treatment is at 750 to 860 “C ( I380 to I580 “F) for 6om I to 4 h.

Mechanical

Beta-CEZ@: Chemical composition

Applications.

Properties

Tensile propertiesdependstrongly on microstructure. Forgedor rolled bars exhibit an equiaxed microstructure, whereasp processedand “through the p transus” processedpancakesexhibit lamellar and necklacedmicrostructures. respectively. Beta-CEi!@can maintain a high strength level at high temperaturesfor both the equiaxed or lamellar microstructures. SeeTable for typical tensile properties

Aging is at 525 to 650 “C (970 to 1200 “F) for from 30 min to 8 h. As a function of aging time, hardnessevolves rapidly. Maximum hardnessis about 560 HV. SeeTable for hardnesskinetics for equiaxed microstructures

PLmcm

CWplldhWl%

Aluminum lin zirconium Molybdenum chmmium ‘run W8en Hydrogen

4.5-5.5 I z-2.5 3.545 3.54.5 1.5-2.5 05-1.5 800-13OOppm cl5Oppm

Beta-CEZ@: Typical tensile properties

15Omm(6in.)diamfcrgedbar

12.7mm(‘/zin)diammlledbar

25mm(lm.)rhickroUedpl;ue

3OOmm(l2in.)diamp-pmcessed pancake MOmm(l2in)dam”rhroughti uansus” ‘en-ocessed

&forged 830”C(1525°F). I hWQ+55O”C(IO2O”F).8h,AC 830°C(15250F).lh.WQ+600”C(ll100F).8h,AC ~“C~15~“~.l~WQ+5~oC(lo200~,~hAC 860°C(1580”R.lhWQ+6CUI”C(llIO”F).8h.AC Asmlkd 830°C(1525”F$lh.WQ+5500C(1020”F~.8hAC 83O”C(l525”F). I h.WQ+600°C(1110”F).8h,AC 86O”C(l5EO”F). Ih.WQ+550°C(1020”F).8hAC 860”C~1580”R.IhWQ+600°C(IIIOoR.8h.AC AsroueQL A.SmlM.T 8M)“C(1525”~.lh.WQ+600°C(IIIO”F).8h.AC.L 830”C(1525”F).lh.WQ+600°C(Il100F).8h.AC.T 86L”C(l58o”F). I hWQ+6OD”C(lll0”F).8h.AC.L 860”C~1580°F).lhWQ+600”C(II100F).8h.AC.T 6oo”C(llIO”F).8h.AC 830”C(1525°F). I hWQ+570”C(lO6O”Fj.8h.AC 83Q”C(1525°F).I hWQ+6OO”C(IIIO”F).8h.AC 6OO”C(lllO”F).8h,AC 830°C(15250F), lh,WQ+570”C(lO6O”F).8h,AC 830°C(1525”F). I hWQ+600°C(ll10”F).8h.AC

1040 1601 1283 1557 I370 I490 1506 1373 1723 1540 1222 I260 1334 1351 1405 1418 1608 I357 1326 I227 I314 I263

150 232 I86 226 I98 216 218 199 250 223 177 182 193 1% 203 205 233 I97 I92 I78 190 183

960 1518 1208 1478 1304 1345 1460 1349 I683 1485 1124 I I63 1287 1300 I338 1340 1472 1171 1188 II38

139 220 I75 214 I89 I95 211 195 244 215 I63 I68 I86 I88 I94 I94 213 170 172 I65 174 169

I8 2 II 2 5 II 13 I5 7 9 I5 II I3 I2 IO 6 2 5 6 IO IO II

588 / Heat Treater’s Guide: Nonferrous Alloys Beta-CEZ@: Hardness kinetics for equiaxed microstructures

15Omm(6in.) diamfargedbar

As forged 860”Cf1580°~.2h.WQ+550”C~1020”F).r.AC

0 I 3 IO 30 100 300 looo 3ooo

345 380 -MO 470 48.5 480 465 460 460