Sponsored by: SMD Titanium Committee, MDMD Shaping and Forming Committee
Program Organizers: Prof. Isaac Weiss, Prof. Raghavan Srinivasan, Mechanical and Materials Engineering Dept., Wright State University, Dayton, OH 45435; Dr. Paul Bania, Timet Corporation, Timet-Henderson Technical Laboratory, P.O. Box 2128, Henderson, NV 89009; Prof. Daniel Eylon, Graduate Materials Engineering, University of Dayton, Dayton, OH 45409
Wednesday, PM Room: B5-6
February 7, 1996 Location: Anaheim Convention Center
Session Chairperson: R.R. Boyer, Boeing Commercial Airplane Group, Seattle, WA 98124; H. Rack, Materials Science and Engineering Program, Clemson University, Clemson, SC 29634-0921
2:00 pm Invited
HEAT TREATMENT OF TITANIUM ALLOYS: J. R. Wood, P. A. Russo, RMI Titanium Company, 1000 Warren Avenue, Niles, OH 44446
Titanium and titanium alloys are heat treated for a variety of purposes. Examples are: stress relieving to relieve residual stresses during fabrication; process annealing to produce an acceptable combination of ductility, machinability, and dimensional stability; and solution heat treating and aging to optimize strength, ductility, fracture toughness, fatigue strength, creep resistance, etc. A review of these processes and a discussion on specialized heat treating processes are described in this paper for alpha-beta titanium alloys and metastable beta titanium alloys.
2:25 pm Invited
ROLE OF OXYGEN ON TRANSFORMATION KINETICS OF TIMETAL 21S TITANIUM ALLOY: M.A. Imam, C.R. Feng, Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375-5343
The Timetal 21S is one of the newest beta titanium alloy which has shown excellent resistance to corrosion and heat compared to other beta titanium alloys. Interstitial elements such as oxygen, nitrogen, carbon, and hydrogen affect the transformation characteristics of the Timetal 21S resulting in the variations of the mechanical properties. Although the stable phase at room temperature is alpha, the measureable beta is retained even after slow cooling from above the temperature. The transformation of beta phase is sluggish and can be controlled to produce desired properties. The structure of the transformed product and their distribution depend on the aging conditions and interstitial contents. The present investigation deals with the role of oxygen on the phase transformation kinetics and establish a time-temperature and transformation curves of timetal 21S, Ti-15Mo-3Al-2.8Nb-0.2Si, Oxygen contents in the alloy was systematically varied from 0.9wt% to 0.33wt%.
2:50 pm
PROCESSING - MICROSTRUCTURE- PROPERTY RELATIONSHIPS IN Ni MODIFIED CORONA 5: J. C. Fanning, Henderson Technical Laboratory, Timet, P.O. Box 2128, Henderson, NV 89015; P.L. Martin Rockwell Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360
Three Alloys were defined to modify the relative strength and volume fraction of the [[alpha]] and ß phases in Corona 5 (Ti-4.5Al-5Mo-1.5Cr). The Al, Mo, Cr, and oxygen levels were varied and Ni was added to increase the volume fraction of ß. Ingots weighing 36 kg of three compositions were double VAR melted then ß forged followed by [[alpha]]/ß forging to produce 50mm slab. Sections were cross-rolled to a thickness of 19mm using two starting temperatures; Tß +/-28deg.C. The microstructure at each stage of processing was documented using backscattered electron metalography on electropololished sections. Two step heat treatments, beginning both above and below the ß transus, were used to modify the primary and secondary morphology in order to maximize the tensile strength/toughness trade-off. Ambient temperature fracture toughness values as high as 70 MPa m1/2 were measured at a corresponding UTS of 1120 MPa. The variation of K1c with tensile strength as influenced by the microstructure will be shown and discussed in light of the probable mechanisms of fracture.
3:05 pm
PRODUCTION AND HEAT TREATMENT OF Ti-15-3 ALLOY TUBE: Hong Quan, Luo Guogzhen, Wu Yiqing, Northwest Institute for Nonferrous Metal Research, P.O. Box 51 Xian, China 710016
This paper described the process of Ti-15-3 alloy tube production and its processing behavior, as well as the effect of heat treatment on its mechanical properties are studied. The microstructure and texture type of the tube has been investigated by optical microscope and X-ray diffraction methods. The results show that Ti-15-3 tube has good processing properties: flattening is 4s, expanding > 25%, which is similar to pure Ti. Its mechanical properties can be easily controlled by adjusting heat treatment parameters. Cold rolling and ageing is suitable for Ti-15-3 tube because of its exellent properties and low cost. This tube can be applied to the field of sport material.
3:20 pm
DIRECT AGING OF Ti-6.8Mo-4.5Fe- 1.5AI: S. Azimzadeh, H. J. Rack, Materials, Science and Engineering Program, Clemson University, Clemson, SC 29634-0921
The kinetics of phase transformations occurring in TIMET LCB (Ti-6.8Mo-4.5Fe-1.5AI) upon ß solution treatment and direct aging were investigated over the temperature range 345-650deg.C utilizing hardness, x-ray diffraction, optical and electron microscopy. Aging below 400deg.C resulted in precipitation of ellipsoidal [[omega]]isothermal either through a nucleation and growth mechanism or by displacive controlled growth of [[omega]]thermal, depending upon the aging temperature relative to the [[omega]]start temperature. At higher temperatures Widmanstätten [[alpha]] precipitated directly from the ß matrix, extended aging times resulting in [[alpha]] platelet growth and spherodization. These observations will be discussed and contrasted with studies of solution treated, water quenched and aged TIMET LCB.
3:35 pm BREAK
3:45 pm
A STUDY OF GRAIN BOUNDARY NUCLEATED [[alpha]] PRECIPITATES IN AN ([[alpha]]+ß) TITANIUM ALLOY: Kei Ameyama, Dept. Sci. & Eng. Ritsumeikan University, Kusatsu, Shiga, Japan 525-77; Hiroshi Fujiwara, Hajime Kawakami Graduate School, Ritsumeikan University, Allec Mitchell, Dept. Metals & Mater. Eng., University of British Columbia, Vancouver, B.C., Canada V6T 1Z4
The Morphology and crystallography of a grain boundary [[alpha]] (HCP) precipitates formed on the ß (BCC) matrix grain boundaries have been studied with TEM and SEM-ECP inä a Ti-22V-4Al alloy. Most of [[alpha]] precipitates have a near-Burgers orientation relationship, i.e., (0001)[[alpha]]//{110}ß, [2-1-10][[alpha]]//<111>ß, with respect to, at least, one of the adjacent ß grains. Variant selections of precipitates are made so as to minimize the misorientation with respect to the "opposite" ß grain from the Burgers one. Such rules in variant selection frequently result in the formation of [[alpha]] precipitates with a single variant at a planar grain boundary and thus the precipitates appear as a film like morphology due to the coalescence of the single variant precipitates. Additionally, at triple points of the high-angle grain boundaries, very few precipitation is observed because of difficulties of the variant selection to three ß grains at once. On the other hand, the triple points of sub-boundaries are observed to be the preferred nucleation site for [[alpha]] precipitation.
4:00 pm
MECHANICAL BEHAVIOR AND TRANSFORMATIONS IN Ti-60wt%Ta: Robert W. Margevicius, James D. Cotton, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
Of the ß-stabilized Ti alloy systems, Ti-Ta has not been extensively investigated. In a broader research program, a range of Ti-Ta alloy compositions was investigated. The results for one alloy, Ti-60wt%Ta (Ti-28at%Ta), will be presented here. The alloy was plasma arc-melted and cross-rolled at 900deg.C in air to approximately 80% reduction. The rolled plate was subjected to heat treatment at 700deg.C, 800deg.C, or 900deg.C for one hour in argon followed by a water quench. Tensile tests on the heat-treated material showed a plateau in the stress-strain curve at a relatively low stress, indicative of a stress-assisted transformation of metastable ß->[[alpha]]", as confirmed with optical and electron microscopy and texture measurements. The stress required to trigger the transformation increased with increasing heat-treat temperature, suggesting that stored work removed by annealing processes stabilizes the metastable ß phase. Mechanisms for this phenomena are discussed.
4:15 pm
EFFECTS OF HEAT TREATMENT ON MICROSTRUCTURE, STRENGTH, AND TOUGHNESS OF TIMETAL 21S SHEET: R. Kieth Bird, Terry A. Wallace, William D. Brewer, NASA Langely Research Center, Hampton, VA
Because of their versatility, Beta titaium alloys are of interest for a variety of aerospace applications, including subsonic and supersonic airframe structures. Generally, they have high strength to density ratios, deep hardenability, can be heat treated to a wide range of properties, and have potential for lower cost because of being strip producible. In particular, Timetal 21S has been given considerable attention because of the additional benefits of improved oxidation, and corrosion resistance. In this study, the effects of heat treatment on the tensile properties and toughness of 0.022 inch thick, Timetal 21S sheet were studied over a range of temperatures, with the prupose of developing appropriate microstructures and phase distribution to maximize strength/toughness combinations. The heat treatments included beta and alpha-beta anneals with various quenches and ages, as well as direct aging. Optical, SEM., TEM, and x-ray analyses were used to define the microstructures. Toughness was measured by the J-integral method using compact tension specimens. Heat treatments, microstructure, tensile and fracture properties were correlated from -65deg.F to +350deg.F.
4:30 pm
ISOTHERMAL DECOMPOSITION OF TIMETAL-21S: Qiong Li, Roy Crooks Analytical Services and Materials, Inc., Metallic Materials Branch NASA Langley Research Center, Hampton, VA
The decomposition of the metastable ß-phase titanium alloy TIMETAL-21S was studied by transmission electron microscopy after ß-annealing, quenching and isothermal aging at temperatures ranging from 450-565deg.C. Uniformly distributed isothermal [[omega]]-phase was observed after short aging times at lower temperatures; while was the dominent phase after further aging. Several stages were observed in the precipiation and growth of [[alpha]]1 and these were characterized by their morphologic and crystallographic changes. Colonies of fine "sideplate" [[alpha]] were observed to extend from some grain boundaries, and much coarser was present in grain interiors. The intragranular [[alpha]] was associated with [[omega]]-phase in the early stages of aging. The sideplate [[alpha]] grew from a polycrystalline prism structure formed by the junction of three [[alpha]] variatiants. After prolonged aging times, [[alpha]] further decomposed into type II . Nucleation theories for these phases are discussed.
4:45 pm
EFFECTS OF MICROSTRUCTURE AND OXYGEN CONTENT ON THE FRACTURE BEHAVIOUR OF THE [[alpha]] + ß TITANIUM ALLOY Ti-4Al-4Mo-2Sn-0.5Si wt.% (IMI 550): L.J. Hunter, M. Strangwood, P. Bowen, School of Metallurgy and Materials / IRC in Materials for High Performance Applications, The University of Birmingham, Edgbaston, Birmingham, B 15 2TT, UK
It is well established that both fracture toughness and strength of [[alpha]] + ß titanium alloys are sensistive to variations in microstructure and alloy composition. Hence, in this and previous studies, the roles of microstructure and oxygen content on the balance of strength and fracture toughness for the Ti-4Al-4Mo-2Sn-0.5Si alloy have been investigated. A detailed investigation to elucidate the micromechanism of ductile failure has also been undertaken. Both fracture toughness and tensile strength levels revealed a strong dependence on microstructure and oxygen content. In all fracture toughness specimens, the ductile micromechanism of failure is dominated by interfacial decohesion. TEM characterization of interfacial regions has been undertaken and related to variations in the microstructure and the amount of oxygen present.
5:00 pm
PHASE STABILITY IN A Ti-45.5Al-2Nb-2Cr ALLOY: V.Seetharaman, Materials and Processes Division, UES Inc., Dayton, OH 45432-1894; C.M.Lombard, S.L.Semiatin, Wright Laboratory, Materials Directorate, WL/MLLN, Wright-Patterson AFB, OH 45433-7817
High temperature phase equilibria in a Ti-45.5Al-2Nb-2Cr alloy were investigated via X-ray diffraction and metallographic techniques. The alloy was hot worked through a sequence of isothermal forging and pack rolling operations coupled with intermediate, recrystallization heat treatments. Specimens from the rolled sheets were subjected to isothermal heat treatments in the temperature range 900-1320deg.C for durations ranging up to 100 hours, followed by water quenching as well as slow cooling. The results obtained indicate that a three phase equilibrium involving [[gamma]], [[alpha]]/[[alpha]]2, and ß2 phases exists in the temperature range 1100-1300deg.C. While the volume fraction of ß2 appears to reach a maximum at ~1200deg.C, that of [[gamma]] decreases progressively with an increase in temperature in the range 1100-1300deg.C. The influence of temperature and time of annealing and cooling rate on microstructure of this alloy will be discussed in the light of available information on phase stability in TiAl-X systems, where X is a beta stabilizing element.
5:15 pm
MICROSTRUCTURE EVOLUTION IN AN ORTHORHOMBIC TITANIUM ALUMINIDE AS A FUNCTION OF TEMPERATURE-STRAIN -TIME: R.W. Hayes, Metals Technology Inc.; 19801 Nordhoff St., Northridge, CA 91324; C. G. Rhodes, Rockwell International Corp., 1049 Camino Dos Rios, Thousand Oaks, CA 91360
Uniaxial tension creep tests have been performed on the orthothrombic titanium aluminide alloy Ti-22Al-23Nb (a/o) over the temperature range 650deg.C-760deg.C at constant initial applied stress levels ranging from 69 MPa up to 172 MPa. During the course of creep testing within this temperature-stress regime, the development of a phase at the primary alpha-2-orthorhombic + ordered beta phase matrix interface appears to occur. This phase appears in the grip section of creep specimans as well as in the gage section. The formation of this phase appears to be driven by temperature, strain and time. This paper will address through detailed microstructural characterization, the nature of this phase and the parameters which are primarily responsible for its formation.
5:30 pm
HYDROGEN TECHNOLOGY AS NEW PERSPECTIVE TYPE OF TITANIUM ALLOY PROCESSING: B.A. Kolachev, A.A. Ilyin, V.K. Nosov, Moscow State University of Aviation Technology after K. Tsilkovsky, Metals Science Dep. Petrovka St. 27, K-31, Moscow, Russia, 103767
In studying the "metal-hydrogen" problem it was found that though hydrogen
caused embrittlement, it also had some effects which might be used for
improvement of the processing technology of metals, for example titanium
alloys. These effects include hydrogen induced decrease in flow stresses,
increase of maximum deformation prior to the occurence of the first crack,
structural and phase transformation, hydrogen enhanced adhesion phenomena, and
hydrogen influence on thermo-physical properties. The above mentioned effects
have formed the basis of hydrogen technology of titanium alloys which includes
the following processing: a) hydrogen plasticization; b) thermohydrogen
treatment; c) mechanical-hydrogen treatment; d) processes based on hydrogen
strengthening of adhesion phenomena; e) hydrogen technology of casting. In
the paper there are given the examples of successful using of hydrogen
technology for solving the following problems: a) refinement of micro- and
macrograins of castings; b) improvement of quality welded bonds; c) increasing
of heat treatment effects in pseudo [[alpha]]-alloys; d) producing of high
quality active semiproducts from difficult to deform alloys; e) improvement of
fasteners technology production; f) easier PM processing and diffusion bonding
of half-finished pressings from titanium chip without its remelting; h)
improvement machining of titanium alloys; i) enhanced of quality of castings;
j) utilization of cast scrap. Hydrogen technology allows the increase in
part-to-scrap ratio, to raise labor productivity, to reduce energy and metal
consumption.
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