Materials Properties Handbook - Titanium Alloys

788 Pages·1994·87.03 MB·English

by  Boyer, Rodney, Welsch, Gerhard, Collings, E.W. (Eds.)

Materials Properties Handbook:
Titanium Alloys
Rodney Boyer
Boeing Commercial Airplane Company
Gerhard Welsch
Case Western Reserve University
E.W. Codings
Battelle Memorial Institute (Columbus)
Dr. William W. Scott, Jr., Director of Technical Publications
Scott D. Henry, Manager of Handbook Development
Steve Lampman, Handbook Editor
Veronica Flint, Acquisitions and Review
Production Assistance
Nancy M. Sobie
Ann-Marie O'Loughlin
Randall L. Boring
Patricia Eland
William J. O'Brien
Jeff Fenstermaker
Editorial Assistance
Nikki D. Wheaton
Judith Woodruff
Terri Weintraub
The Materials
Information Society
Copyright © 1994
by
ASM International
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Library of Congress Cataloging-in-Publication Data
Materials properties handbook: titanium alloys /
editors, Rodney Boyer, Gerhard Welsch, E.W. Collings
p. cm.
ISBN-10: 0-87170-481-1
ISBN-13: 978-0-87170-481-8
1. Titanium alloys.
I. Welsch, Gerhard.
II. Boyer, Rodney
III. Collings, E.W
TA480.T54M37 1994
620.1 '89322—dc20 94-15791
CIP
SAN No. 204-7586
ASM International
Materials Park, OH 44073-0002
Printed in the United States of America
Preface
Titanium Alloys is the result of an ambitious effort to pro- This handbook will be a valuable addition to the library of
vide comprehensive property data in electronic form for not anyone with more than a superficial involvement or interest in
only databases but also print products such as the Materials titanium in that in this single volume, the physical, thermal,
Properties Handbooks series. In this endeavor, Titanium Alloys mechanical, corrosion, fatigue, and fracture properties of al-
represents a "book-first" approach devoted to comprehensive, most all titanium alloys (except for alloys of the former Soviet
alloy-specific compilations of properties and processing infor- Union), along with chapters on the basic metallurgy of tita-
mation on engineering materials. This work has produced a nium are compiled. This greatly facilitates comparison of alloy
substantial amount of titanium property data in electronic properties; thermomechanical and heat treatment effects on
form, and follow-up efforts will determine which of the infor- the properties of these alloys are also provided. This book will
mation is suitable for more structured and searchable elec- furnish a quick, state-of-the-art overview, which will provide
tronic formats such as MatDB. the starting point from which a more detailed search of the
literature can be initiated, leading to an intelligent assess-
Titanium was chosen as the first topic in this "book-then-da-
ment of the proper alloy for a specific application. It is truly
tabase" effort because the small number of major titanium
unique to have a database this comprehensive for basically all
alloys was a factor considered by the initial project managers.
alloys in a given alloy system contained in one volume. This
However, the scope was expanded and a substantial effort was
one book will either provide the data you need, or provide
expended in collecting a wide variety of information on differ-
references on where to find it, for any titanium alloy.
ent alloys and properties (with particular emphasis on the
In addition, this volume also contains processing informa-
work horse alloy, Ti-6A1-4V). The amount of information was
tion such as forging, forming, casting, powder metallurgy, and
monumental, and the task of selecting and editing the data for
welding. Recommended procedures/hmits in these areas are
subsequent production was pursued with the goal of providing
provided, and where appropriate, the affects of some of these
comprehensive coverage on an alloy-specific basis. Whether
processing variables on the final properties are discussed.
this approach was prudent may be questionable in hindsight.
This has been an international effort, with contributors
However, this handbook provides a compilation of properties
from North America, Europe, and Asia. These contributors are
and fabrication procedures for virtually all of the alloys which
leaders in the field, and represent all sectors of the industry
have been developed over the 45-year time span of the tita-
including titanium producers, titanium fabricators, end users,
nium industry up to early 1993. The data is quite comprehen-
governments, and academia. An effort of this magnitude rep-
sive for the more important alloys and not as complete for some
resents a substantial commitment by ASM International and
of the lesser alloys, particularly those that never went into
the efforts of hundreds of individuals in collection of the data,
production. It is not intended to provide all the data in the compilation into coherent chapters and sections, review of the
literature, but to provide a quick, up-to-date assessment of the assembled sections, and the painstaking efforts of producing
key information that is available. However, for those alloys and proofing graphics and page layouts. We would like to give
and/or properties where more detail is required, references are them our heartfelt thanks, for without them this book would
cited to enable the reader to obtain further information. not have been possible.
R. Boyer and S. Lampman
iii
Table of Contents
Preface "i Ti-5Al-6Sn-2Zr-lMo-0.1Si 445
Contributors and Reviewers ν
Summary Table of Titanium Section IV: Alpha-Beta Alloys
Alloys vii
Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) 453
Alloy Data Sheet Contents xiii
Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) 465
Technical Note Contents xix
Ti-6A1-4V 483
Abbreviations and Symbols xxi
Ti-6Al-6V-2Sn 637
Ti-7Al-4Mo 667
Section I: Physical Metallurgy of Titanium Alloys
TIMETAL® 62S 679
Introduction 3 Ti-4.5Al-3V-2Mo-2Fe (SP-700) 685
Classification of Titanium Alloys 5 IMI 367 693
Physical Properties 12 IMI 550 695
Equilibrium Phases 23 IMI 551 701
Nonequilibrium Pfiases 34 Corona 5 705
Deformation 49 Ti-6-22-22-S . 713
Aging 56 Ti-4Al-3Mo-lV 733
Titanium Alloys for Low-Temperature Service 68 Ti-5Al-1.5Fe-1.4Cr-1.2Mo 735
Evolution of Conventional (Ingot Metallurgy) Ti-5Al-2.5Fe 737
High-Temperature Titanium Alloys 76 Ti-5Al-5Sn-2Zr-2Mo-0.25Si 747
Powder Metallurgy and Rapid-Solidification Ti-6.4Al-1.2Fe(RMI Low-Cost Alloy) 751
Processing 81 Ti-2Fe-2Cr-2Mo 753
Rapid-Solidification Processing of Precipitate and Ti-8Mn 755
Dispersion-Strengthened Titanium Alloys 87
Mechanical Properties 94 Section V: Beta and Near-Beta Alloys
References 112
Ti-11.5Mo-6Zr-4.5Sn (Beta III) 767
Ti-8V-3Al-6Cr-4Mo-4Zr (Beta C) 797
Section ILTitanium Data Sheets
Ti-10V-2Fe-3Al (Ti-10-2-3) 829
High-Purity Ti 125 Ti-13V-llCr-3Al 867
Commercially Pure and Modified Ti 165 Ti-15V-3Al-3Cr-3Sn(Ti-15-3) 899
TIMETAL 21S 921
Section IILAlpha and Near-Alpha Alloys BetaCEZ® 931
Ti-8Mo-8V-2Fe-3Al 935
Ti-3A1-2.5V 263
Ti-15Mo-5Zr 943
Ti-5Al-2.5Sn 287 Ti-15Mo-5Zr-3Al 949
Ti-6Al-2Nb-lTa-0.8Mo(Ti-6211) 321 Ti-11.5V-2Al-2Sn-l lZr (Transage 129) 957
Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242) Si 337 Ti-12V-2.5Al-2Sn-6Zr (Transage 134) 971
Ti-8Al-lMo-lV 377 Ti-13V-2.7Al-7Sn-2Zr (Transage 175) 979
Ti-11 409 Ti-8V-5Fe-lAl 993
TIMETAL® 1100 411 Ti-16V-2.5Al 999
IMI 230 415
IMI 417 419
Section VI: Advanced Materials
IMI 679 421
IMI 685 431 Titanium Aluminides 1009
IMI 829 435 T13AI Alloys 1019
IMI 834 439 Gamma (Ti-Al) Alloys 1029
Ti-Ni Shape Memory Alloys 1035 Technical Note 5: Forming 1093
Technical Note 5a: Superplastic Forming 1101
Technical note 6: Heat Treating 1111
Section VII: Technical Notes
Technical Note 7: Machining 1119
Technical Note 1: Metallography and Technical Note 8: Powder Metallurgy 1137
Microstructure 1051 Technical Note 9: Surface Treatments 1145
Technical Note 1 Appendix: Example of CDiso Technical Note 10: Welding and Brazing 1159
formation 1065 Rolling 1167
Technical Note 2: Corrosion 1065 Friction and Wear of Titanium Alloys 1169
Technical Note 3: Casting 1079
Technical Note 4: Forging 1083
Physical Metallurgy of Titanium
Alloys*
E.W. Collings, Battelle Memorial Institute, Columbus, Ohio, U.S.A.
*Revised from The Physical Metallurgy of Titanium Alloys (ASM International, 1984) and "Introduction to Titanium Alloy Design"
in Alloying (ASM International, 1988)
1. Introduction
1.1 Origin and Uses of 1960s has served to somewhat offset the in each of the alloys Ti-6Al-2Sn-4Zr-2Mo
decline in mihtary demand during the (i.e., "Ti-6242"), Ti-6Al-2Sn-4Zr-6Mo (i.e.,
Titanium
same period, thereby yielding not only a "Ti-6246"), and Ti-ll.5Mo-6Zr-4.5Sn (i.e.,
net growth but a relatively steady one. "β-ΙΠ") was on the increase. Today the al-
Titanium is widely distributed
loy Ti-6242 to which about 0.1% Si has
throughout the universe. It has been dis- Titanium (meaning titanium and its
been added is being used in titanium alloy
covered in the stars, in interstellar dust, alloys) has two principal virtues: (1) a
forgings and has received extensive study
in meteorites, and on the surface of the high strength/weight ratio and (2) good
and use in its role as a gas-turbine com-
earth. Its concentration within the earth's corrosion resistance. At one time or an-
pressor-disc material. Finally it should be
crust of about 0.6% makes it the fourth other practically all aerospace structures
noted that Ti-10V-2Fe-3Al has been the
most abundant of the structural metals —airframes, skin, and engine compo-
beneficiary of the renewed interest being
(after aluminum, iron, and magnesium). nents—have benefited from the introduc-
shown in so-called "near-β" titanium al-
It is 20 times more prevalent than chro- tion of titanium. Nonaerospace applica-
loys [DuE80a] [TER80] [TOR80], while it is
mium, 30 times more than nickel, 60 tions include steam-turbine blades,
at last becoming recognized that Ti-50Nb,
times more than copper, 100 times more hydrogen-storage media, high-current/
one of the most important of today's tech-
than tungsten, and 600 times more than high-field superconductors, condenser
nical superconductors, is in fact a β-Ti al-
molybdenum. This abundance is to some tubing for nuclear and fossil-fuel power
loy [COL81].
extent illusory, however, in that titanium generation, and other corrosion-resistant
is not so frequently found in economically applications such as components for
extractable concentrations. Concentrated ocean thermal-energy conversion, off-
1.2 Extraction of Titanium
sources of the metal are the minerals il- shore oil drilling, marine-submersible
menite, titanomagnetite, rutile, anatase, vessels, desalination plants, waste-treat-
In order to cope with unexpected in-
and brookite. ment plants, the pulp-and-paper indus-
creases in the demand for a metal, it is
try, and the chemical and petrochemical
Ilmenite is haematite (Fe 03) in helpful to be able to rely on a copious and
2 industries.
which half of the iron has been replaced by stable supply of the basic ore. The tita-
titanium; titanomagnetite is magnetite Interest in the properties of titanium nium industry is fortunate in this regard.
(Fe3(>4) in which one-third of the iron has and its alloys began to accelerate in the Titanium dioxide is produced in large
been replaced by titanium. Rutile is TiC>2 late 1940s [CRA49] and early 1950s as quantities for many applications, so much
(as are anatase and brookite). Naturally their potential as high-temperature, so that in 1977, for example, only a few
occurring (and titanium-deficient) il- high-strength/weight materials with percent of the world's production of tita-
menite consists of haematite particles in a aeronautical applications became more nium ore was tapped for metallic sponge
matrix of ilmenite; naturally occurring and more widely recognized. The history refinement (most of the mined ore being
(and, again, titanium-deficient) ti- of titanium and its development in alloyed used to make paint pigment). Thus, since
tanomagnetite is magnetite containing form has been described in detail in the in- the overall demand for raw material is not
laths of ilmenite. In short, the most impor- troduction to the first International Con- subject to the same fluctuations as the de-
tant titanium minerals are ilmenite and
ference on the subject [JAF70] and in the mand for the metal, should the latter un-
rutile.
introduction to ZwiCKER's comprehensive dergo a significant increase at any time,
^anium was first discovered in min- metallurgical treatise Titan und Titanle- there is at least a strong raw-material
erals now known as rutile by W. Gregor gierungen [Zwi74]. As evidenced by the base from which to draw.
(England) and M.H. Klaproth (Germany) papers presented at the subsequent Inter- Industry's growing awareness of the
in about 1790. The first commercial mill national Conferences, titanium and its al- need for energy conservation has served
products were produced by the Titanium loys have by now found widespread use in to emphasize an unfortunate charac-
Metals Company of America (TMCA) the aerospace industry (for both frame teristic of the current methods of tita-
around 1950. From that time to the pres- and engine components) and in the chemi- nium metal refinement: their energy in-
ent, production of the metal has grown at cal and related industries, where advan- tensiveness. The energy required to
an average annual rate of about 8%. Su- tage can be taken of their corrosion resis- produce a ton of sponge-titanium from its
perimposed upon part of this temporal tance. According to WOOD [Woo72], by ore is 16 times that needed to produce a
growth curve is a large fluctuating compo- 1972 about 30 commercial alloys were al- ton of steel, 3.7 times that needed for fer-
nent, a reminder of the capriciousness of ready on the market in mill-product form. rochrome, 1.7 times that needed for alu-
the materials demands of the aerospace Of these, the eight most favored composi- minum production, and a little more than
industry, titanium's principal market dur- tions, accounting for some 90% of the that needed for a 1-ton ingot of magne-
ing the early years. Fortunately for the ti- sales, were three grades of unalloyed tita- sium. Since, however, the heats of forma-
tanium-production industry, the 13% an- nium and the alloys Ti-5Al-2.5Sn, Ή-6Α1- tion of rutile (—228 kcal/mol), haematite
nual growth rate exhibited by the civilian 4V, Ti-8Al-lMo-lV, Ti-6Al-6V-2Sn, and Ti- (~ -200 kcal/mol), and magnetite (~ -268
sector of the total market since the early 13V-llCr-3Al. At that time also, interest kcal/ mol) are in the ratio of 1:0.88:1.18,
4 / Physical Metallurgy of Titanium Alloys E-W. Collings
Table 1.1 Total Impurity Contents of Io- Table 1.2 Typical Interstitial Impurity Contents of Several Grades of Titanium
dide- and Kroll-Process Titaniums (in wt%)
[RAS72] Interstitial content, ppm Data
Grade of titanium C Ν Ο source
Element Iodide Ti KrollTi
MRC (MARZ-grade) 78 6 63 1
Mg 0.01 0.13 MRC (VP-grade) 150 40 350 2
Si 0.01 0.05 TMC electrorefined sponge (grade ELXX) 40 370 3
Al 0.02 Kroll-process (Toho sponge) 110 860 4
Fe 0.01 0.20 Kroll-process 800 400 1100 5
Ni 0.01 Iodide-process 100 200 200 5
Co 0.02
Cr 0.01 (1) Materials Research Corp.: Zone-refined; supplied typical analysis. (2) Materials Research Corp.: Vacuum
Mn 0.005 0.02 melted; supplied typical analysis. (3) Titanium Metals Corp.: See also fCoL701. (4) See [COLTOI. (5) See Table 1.1.
C 0.01 0.08
Ν 0.02 0.04
0 0.02 0.11
there seems to be some scope for increas- ucts are commercially pure sponge-tita- wire, which acts as nucleus for the growth
ing the energy efficiency of the titanium- nium (in the form of a porous, gray, coke- of a long cylindrical bar of high-purity ti-
refinement process. like mass) and MgCl2, most of which can tanium crystals. Typical impurity con-
be drained out of the reaction chamber as
The most well-known method of tita- tents of several grades of titanium are
a liquid. The MgCl2 is electrolytically
nium production is the Rroll process, listed in Tables 1.1 and 1.2.
recycled. The titanium sponge is conso-
which involves the reduction of T1CI4 °y
lidated by arc melting in a water-cooled These and other standard commer-
magnesium. The first step in the process
copper crucible: this process involves cial methods of titanium production, such
is the preparation of the tetrachloride it-
several iterations of a procedure in which as the sodium-reduction (or Hunter) proc-
self, which is carried out by the cMorina-
an arc is maintained between a consu- ess, the direct-oxide-reduction process,
tion of a mixture of carbon with rutile or il-
mable compacted-sponge-titanium elec-
and the electrolytic process, have been de-
menite. The Kroll magnesium-reduction trode and a pool of molten sponge.
scribed in detail by MCQUILLAN [MCQ56,
reaction takes place in a closed heated re-
The highest purity titanium is pre-
actor vessel under an inert atmosphere. Chap. 2], HOCH [Hoc73b], and ZwiCKER
pared for research purposes by the iodide
Liquid TiCl4 is introduced to the liquid process. Crude titanium is first reacted [Zwi74, pp. 21-27], while some new ap-
magnesium already present in the vessel, with iodine in an inert atmosphere to form proaches developed in the Soviet Union
thereby initiating the reaction 2Mg + titanium iodide. This can then be decom- have been outlined by REZNICHENKO and
TiCl 2MgCI + Ti. The reaction prod- posed at the surface of a heated titanium coworkers [REZ82, REZ823].
4 2
2. Classification of Titanium Alloys
2.1 Systematics of Phase loys. Solute atoms which lower the tem- rule was exemplified using data for the
perature of the allotropic α + β transfor- following pairs of competing phases: Ct2*
Stability
mation, with respect to that of pure tita- and a; a and β; ω and β [COL73].
Pure titanium undergoes an allotropic nium, are referred to as β stabilizers. With transition metals, the elec-
transformation from hep (a) to bec (β) as Conversely, α stabilizers raise that tem- tron/atom ratio, e/a, is the same as the av-
its temperature is raised through 882.5 °C perature. As pointed out by MCQUILLAN erage "group number"—referring to the
[MOL65][ZWI74]. Elements that when dis- [MCQ63], the relatively more open bec numbers assigned to the groups of the pe-
solved in titanium produce little change in structure has a higher vibrational en- riodic table. Thus, e/a takes on the values
the transformation temperature (e.g., tin) tropy than do the close-packed structures 4 through 10 when applied to the mem-
or cause it to increase (e.g., aluminum, hep and fee. Consequently, during heat- bers of the seven columns of the TM block
oxygen) are known as "a stabilizers"; they ing, the free energy of an imaginary bec of the periodic table headed by the ele-
are simple metals (SM) or interstitial ele- lattice will decrease more rapidly than ments Ti through Ni. The el a is a parame-
ments [MOL65, p. 154]—generally non- those of the competing alternatives such ter in terms of which numerous physical
transition elements. Alloying additions that eventually a temperature will be and mechanical properties of binary TM
that decrease the phase-transformation reached whereat the lattice (if it does not alloys, particularly Ti-TM, can be con-
temperature are referred to as "β stabi- melt) will transform from the low-tem- veniently displayed. Several important
lizers"; they are generally the transition perature-stable close-packed structure physical (mcluding superconductive) pro-
metals (TM) (e.g., Mo and V) and noble (generally hep, a) to bec. Underlying this perties may also be indexed in terms of
metals—i.e., metals that, like titanium, thermodynamic picture is an atomistic quantities related to the above-mentioned
have unfilled or just-filled cf-electron model involving electronic cohesive forces conventional el a, viz.: the atomic-volume-
bands. In the alloys, of course, the single- (directional or otherwise) and atomic-size corrected "electron concentration" of JEN-
phase-oc and single-phase-β regions are effects. JAFFEE, in an early analysis of the SEN etal. [JEN65] or the "effective electron/
not in contact as they are in pure tita- situation [JAF58], suggested that atomic- atom ratio," Νφ of DESORBO [DES65]. An-
nium; they are instead separated by a size effect was the dominant factor; sub- other quantity advocated by LUKE et al.
two-phase α + β region whose width in- sequently, he was able to conclude that, [LUK64] as being appropriate for the in-
creases with increasing solute concentra- although size effect needed to be taken dexing of the compositional threshold for
tion. Based on these considerations, tech- into consideration, the dominant phase- martensitic transformation in Ti-TM al-
nical alloys of titanium are classified as stabilizing mechanism was electronic in loys is an average Pauling valence which,
"α," "β," and "a + β." nature. MCQUILLAN also took this latter although equal to conventional e/a for the
view [MCQ63], but pointed out that excep-
groups IV through VI transition ele-
The question of lattice stability plays tions did of course exist—for example, the
ments, never exceeds the value 6 for ele-
an important role in any discussion of the β-stabilizing tendencies of the solutes
ments of later groups. The crystal struc-
physics of pure metal or alloy systems. bismuth and lead were thought to be
tures, particularly those of simple metals,
This is particularly true of titanium al- due to their relatively large atomic sizes
have been justified from several funda-
loys, whose lattice stability (i.e., struc- [MCQ63].
mental standpoints. BREWER [BRE67] has
tural phase stability) has technical as well
Factors controlling the stabilization of related structure to the spectroscopic
as fundamental significance. The crystal
the α and β phases in titanium alloys have states of the individual participating at-
structures of the three long periods of
also been discussed in several publica- oms. PAULING [PAU67], in considering the
transition elements change more or less
tions by COLLINGS and GEGEL [COL73a, metallic bond, has also utilized this as a
systematically from hep through fee as the
COL73b, COL75a], with particular refer- basis for discussion. The OPW type of ap-
group number increases from IV to VIII.
ence to the Ti-Al and Ti-Mo systems. Sta- proach also utilized atomic spectroscopic
Whether or not there is an underlying
bility was qualitatively discussed from states, but in a more satisfactory manner
physical significance to this, in the case of
both electronic [COL73, COL82a] and ther- by starting with an array of bare ions and
transition metals a useful correlation cer-
modynamic (phenomenological) [COL75a] then replacing the electrons in such a way
tainly exists between crystal structure
standpoints. that their wavefunctions represent
and group number (in the case of ele-
tightly bound electrons near the cores,
ments) or crystal structure and average
and nearly free electrons in the spaces be-
group number or electron/atom ratio (in
2.1.1 Electronic Considerations in tween. Although attempts to deal elec-
the case of alloys). The existence of such
Phase Stability tronically with phase stability in transi-
correlations suggests that electronic
tion metals have been made by
structure plays an important role in the As a result of low-temperature specific
INGLESFIELD [ING69] and PETTIFOR
control of phase stability. heat measurements, it was noted that the
Numerous workers have attempted to more stable of a pair of allotropes was as-
define the factors that govern the exis- sociated with the lower electronic density- *A hexagonal DO19 structure found in the
Ti-Al system.
tence of the α and β phases of titanium al- of-states at the Fermi level, n{Ep). This
6 / Physical Metallurgy of Titanium Alloys E.W. Collings
[PET72], the situation with regard to al- the technique employed coupled a KKR Alpha-stabilizing solutes are those
loys is much more difficult. band-structure and Fermi-surface calcu- which, as a function of concentration, ele-
Very successful calculations of the lation for bec zirconium with the effects of vate the temperature of the (α + β)/α tran-
electronic structures of alloys, and in par- "rigid-band" modifications of it brought sus. Such solutes are generally nontransi-
ticular the manner in which the band den- about by the addition of niobium, in order tion metals (i.e., "simple metals", SM). An
sity of states, n(E), varies with energy, E, to demonstrate that electronically insti- explanation of α stability based on elec-
have been made using the coherent poten- gated enhancement of the natural dip in tron-screening arguments proceeds as fol-
tial approximation (CPA) first applied by the bcc-lattice phonon spectrum at 2/3<111) lows: When simple metals (e.g., alumi-
EHRENREICH and colleagues [Km70] to the could lead, in a manner to be discussed be- num) are dissolved in titanium, very few
Cu-Ni system. The particular method low, to the ω-phase transformation. electrons appear at the Fermi level, most
used, since it took a tight-bmding (TB) ap- of them going to states within the lower
proach to the c?-electrons and a nearly- part of the band. The titanium c?-electrons
free-electron (NFE) one to the other elec- 2.1.2 Thermodynamic tend to avoid the aluminum atoms, which
trons in the band, has been referred to as Considerations in Phase Stability thereby have the effect of diluting the tita-
the NFE-TB-CPA. Although it was espe- nium sublattice. The consequence of this
Purely electronic descriptions of equi-
cially applicable to Cu-Ni, it was the fore- is to emphasize any preexisting Ti-Ti bond
librium-phase stability have been
runner of more sophisticated methods, directionality and thus to preserve the
strongly criticized from two standpoints
developed by others, of dealing with the hep structure characteristic of the tita-
by KAUFMAN and NESOR [KAU73]. They
energy-band structures of disordered al- nium crystal. In general, when simple
noted that: (1) in many treatments, com-
loys [FAU82]. In overcoming the limita- metals are added to titanium, the fields of
petition between phases was completely
tions of the NFE-TB-CPA, a CPA method titanium-like α stability are eventually
ignored; and (2) when electronic property
was developed which had some features terminated by intermetalhc compounds,
data acquired at low temperatures were
in common with the old Korringa-Kohn- of compositions such as Ti SM, which are
used to justify high-temperature phase 3
Rostocker (KKR) method. The first pub- also hexagonal in structure. The bond ar-
transformations, no account was taken of
lication of a full KKR-CPA calculation, gument is consistent with the observa-
the entropy differences. KAUFMAN and
again as it applied to Cu-Ni alloys, was by tion that α stabilizers are quite rapid so-
NESOR recommended the use of a thermo-
STOCKS et al. [STO78]. The number of alloy lution strengthened either in hep solid
dynamic procedure, in which the ener-
systems to which such calculations have solution or when added to bec alloys
getic competition between candidate
been applied, and for which the results [GEG73a]. The classification of α-phase al-
phases was fully taken into account, when
have been compared with experiment (an- loys into systems whose phase diagrams
attempting to define the lattice stabilities
gular resolved photoemission is a favored exhibit (1) peritectic transformations or
of metallic elements as well as alloy sys-
method), has been quite limited. (2) peritectoid transformations, according
tems. Full discussion of a quantitative
to Molchanova's simplified scheme, is con-
However, it is still a large step from thermodynamic approach, leading to the
sidered in Section 2.5.
calculations of this kind to calculations of computer-assisted calculation of binary
lattice-phase (crystal-structure) stability. and multicomponent phase diagrams, is
PETTIFOR [PET79] has made considerable to be found in the work of KAUFMAN
progress toward the calculations of the [KAU70].
heats of formation of binary alloys by us- 2.3 Beta Alloys
Pair-interaction-potential calculations
ing a simple formalism, based on a Friedel
based on the relative-vapor-pressure meas-
expression for the binding energy per Transition-metal (TM) solutes are sta-
urements of HOCH et al. [ROL71, ROL72],
atom, in which the CPA played a funda- bilizers of the bec phase. Thus all-β alloys
have divided the field of titanium-base al-
mental role. As indicated above, it is a re- generally contain large amounts of one or
loys into two regimes: (1) β-stabilized Ti-
markable experimental fact that the more of the so-called "β-isomorphous"-
TM alloys whose regular-solution thermo-
crystal structures of 3d, 4d, and od tran- forming additions—vanadium, niobium,
dynamic interaction parameter, Q , is
sition metals, and their "adjacent" binary y tantalum (group-V TM's), and molybde-
positive (indicative of clustering systems),
alloys, vary in a regular manner from hep num (a group-VI TM). The systematics of
and (2) α-stabilized Ti-SM alloys for
through bec to fee as a function of the el a β stabilization in binary and multicompo-
which Q is negative (short-range-order-
or average group number. MOTT and y nent titanium-base alloys has been dis-
ing systems) [COL753].
JONES' interpretation of one of the Hume- cussed in detail by AGEEV and PETROVA
Rothery rules was an unsuccessful at- [AGE70]. The archetypal binary β-stabi-
tempt to provide a crystal-structure/ lized titanium-base alloy, about which a
2.2 Alpha Alloys
electron-concentration relationship for great deal of physical and metallurgical
nontransition metals; other approaches Unalloyed titanium and alloys of tita- information has been garnered over the
have been more successful [BLA67]. SO far nium with α stabilizers such as alumi- years, is Ti-Mo. For a useful overview of
the empirical crystal structure ("phase num, gallium, and tin, either singly or in the mechanical properties and aging
stability") versus ela relationships as they combination, as in the commercial alloy characteristics of a pair of typical β alloys,
apply to transition metals seem to exist Ti-5Al-2.5Sn or the experimental Ti-Al- Ti-15Mo-5Zr and Ti-15Mo-5Zr-3Al, the
without a general theoretical interpreta- Ga alloys [HOC73][GEG73], are hep at or- work of NlSfflMURAei al. [Nis82] is recom-
tion [FAU82, p. 186]. dinary temperatures and as such are clas- mended. There are several important
The closest approach to an exact calcu- sified as α alloys. These alloys, according commercial β alloys; three that have been
lation of phase stability in a transition- to WOOD [WOO72], are characterized by attracting considerable attention re-
metal alloy system, in particular Zr-Nb, satisfactory strength, toughness, creep cently are Ti-10V-2Fe-3Al, Ti-15V-3Cr-
has been made by MYRONei al. [MYR75], resistance, and weldability. Furthermore, 3Al-3Sn, and Ti-3Al-8V-6Cr-4Mo-4Zr
who dealt not with equilibrium phases the absence of a ductile-brittle transfor- [FR073] [PET73] [VIG82] [WlL82a]. Beta al-
but with an electronic mechanism leading mation, a property of the bec structure, loys, according to WOOD [Woo72], are ex-
to the appearance of the metastable ω renders α alloys (typified by Ti-5Al-2.5Sn) tremely formable. They are, however,
phase. Adequately discussed in their pa- suitable for cryogenic applications prone to ductile-brittle transformation
per (see also SmHAand HARMON [SIN76]), [SAL79]. [G-OR73] and, along with other bec-phase