Materials Week '97: Tuesday PM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Tuesday afternoon, September 16.

MICROSTRUCTURE PROPERTY RELATIONSHIPS IN / TITANIUM ALLOYS: Session I: Developments in Ti-6-22-22 and Other Alloys

Session Chair: Patrick L. Martin, Rockwell Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360-2398

ALPHA/BETA TITANIUM ALLOY DEVELOPMENT FOR HIGH SPEED AIRCRAFT STRUCTURES: William D. Brewer, Terryl A. Wallace, R. Keith Bird, NASA Langley Research Center, Mail Stop 188A, Hampton, VA 23681-0001

Alpha/Beta titanium alloys are among those being considered for strength, stiffness and fracture critical applications on advanced high speed aircraft. However, to meet some projected mission requirements, alloy performance must be improved. This presentation will discuss on-going research on some conventional and emerging alloys, including Ti-6Al-2Mo-4Zr-2Sn-0.08Si (Ti-6242S), Ti-6Al-2Cr-2Mo-2Zr-2Sn (Ti-62222), Ti-4Al-4Mo-2Sn-0.5Si (IMI 550), and Ti-4.5Al-5.4Mo-2Cr-1Ni (Corona X), that show promise for application to high speed aircraft structures. Effects of heat treatment, cryo- and elevated-temperatures, and selected processing on alloy microstructure and mechanical properties will be discussed. The emphasis is on improving strength-toughness combinations in sheet product.

2:40 pm INVITED

THE EFFECTS OF MICROSTRUCTURE AND COMPOSITION ON THE PROPERTIES OF IMI-550: R.R. Boyer, Boeing Commercial Airplane Group, P.O. Box 3707, MS 6H-CJ, Seattle, WA 98124; R.J. Lederich, McDonnell Douglas Aerospace Co., P.O. Box 516, MC S111-1041, St. Louis, MO 63116: R.J. Tisler, McDonnell Douglas Aerospace Co., 2401 E. Wardlow Rd., MC C071-0034, Long Beach, CA 90807

The effects of heat treatment on the microstructure of IMI 550 (Ti-4Al-4Mo-2Sn-0.5Si) on the resultant properties will be discussed. Heat treatment parameters studied include solution treatment temperature, cooling rate from the solution treatment temperature, and aging temperature. The effects of these variables on tensile, fatigue, fracture toughness and crack-growth resistance will be discussed. Generally, as the solution treatment increases and the cooling rate decreases, fracture toughness and crack-growth resistance are improved - the trends for tensile and fatigue strengths are not as well defined. Chemistry modifications of this alloy, reduced O₂ and reduced O₂+Si were also investigated. These modifications provided a significant toughness increase with a moderate reduction in tensile strength. The fatigue properties of the reduced O₂+Si were somewhat better than the "standard" and low O₂ grades of the alloy, though the differences were not large. Rationale for the trends observed will be provided.

3:20 pm

KINETICS OF ORDERING IN Ti-6Al-2Mo-2Cr-2Sn-2Zr: X. Tang, H.J. Rack, Clemson University School of Chemical and Materials Engineering, 501 Rhodes Hall, Clemson, SC 29634-0922

A significant loss in fracture toughness may be observed in Ti-6Al-2Mo-2Cr-2Sn-2Zr containing 0.1 to 0.3 wt.% Si following thermal exposure to temperatures between 1000 and 1200°F. Prior explanations for this loss have centered upon either silicide formation and/or ordering of the alpha matrix. This investigation has considered the kinetics of the latter ordering reaction as determined by in-situ electrical resistivity measurements. It will examine the effects of alpha phase composition and Si content on the ordering kinetics, the former controlled by prior alpha-beta solution temperature, the latter by overall alloy composition. Finally, analysis and separation of these contributions to the fracture toughness loss in Ti-6Al-2Mo-2Cr-2Sn-2Zr will be presented.

3:40 pm

MICROSTRUCTURE-PROPERTY RELATIONSHIPS IN Ti-6-22-22: X.D. Zhang, H. Fraser, Department of Materials Science and Engineering, P. Bonniwell, W. Baeslack, Welding Engineering, The Ohio State University, 2041 College Road, Columbus, OH 43210; D.J. Evans, ML/Wright Laboratories, WPAFB, OH; T. Ginter, T. Bayha, Lockheed-Martin Co., Marietta, GA

A wide range of microstructures has been effected through heat-treatment of the alloy Ti-6Al-2Mo-2Cr-2Sn-2Zr with and without additions of 0.2Si, and these have been characterized in detail using optical metallography, scanning electron microscopy and high resolution and analytical transmission electron microscopy. It is shown that in conditions of heat-treatment which resemble those adopted commercially, the w phase and also (2 are found to be present. Silicides are also observed to form, but only after relatively high temperature anneals. The compositional variations that result from and / heat-treatments and following aging in the temperature range 480 to 600°C have been determined using EDS in the TEM. The tensile strengths and ductilities, and fracture toughnesses of samples in these various heat-treated conditions have been measured, and the relationship between these properties and the microstructures has been determined. This research has been supported by the U.S. Air Force.

4:00 pm

THE MICROSTRUCTURAL BASIS OF TOUGHNESS LOSS IN AGED Ti-6-22-22: Z.M. Wang, R. Crooks, Analytical Services & Materials, Inc., 107 Research Drive, Hampton, VA 23666

The aging temperature has a significant effect on the mechanical properties of the / titanium alloy Ti-6222. Two product forms of alloy Ti-62222, 2 in. (50 mm) plate and 0.060 in. (1.5 mm) sheet, have been studied in an attempt to explain a drop in toughness associated with aging above 1000°F. Samples of plate products aged 8 hours at 1000 and 1100°F, and sheet product aged 8 hours at 1000, 1100, and 1200°F were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Microstructures and fracture behavior were studied in both product forms, and the alpha phase deformation mode was examined in the sheet material. A monolithic, FCC interface phase was found in ion-milled foils of low-toughness plate, and the volume fraction of a ₂ (Ti₃Al) precipitates increased with higher aging temperatures. Dislocation analyses of deformed sheet samples revealed a slip mode transition and a decrease in the number of active slip systems after aging at higher temperatures. The changes in dislocation behavior are apparently related to the precipitation of ₂.

4:20 pm

PHASE TRANSFORMATIONS IN Corona-X (Ti-4.5Al-5Mo-2Cr-1Ni): P. Martin, Rockwell Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360-2398; H.J. Rack, Clemson University School of Chemical and Materials Engineering, 208 Rhodes Hall, Clemson, SC 29634-0922

This presentation will examine the phase transformations observed in - Corona-X titanium following rapid cooling from solution treatment at temperatures between 750 and 910°C. The types and extent of these transformations were found to be functions of the amount/compositions of the a and b phases, the latter having been determined by quantitative x-ray analysis. BSE, X-ray, and TEM have shown that as the phase stability increases the morphology of the resulting microstructures progressively changes from martensitic platelets to retained equiaxed . TEM analysis of retained further indicates that athermal w may also form on cooling from the solution treatment temperature. These results will be discussed by considering the observed transformations as competitive processes involving the formation of the martensitic and athermal w phases.

4:40 pm

THE EFFECT OF SOLUTION TREATMENTS ON THE MICROSTRUCTURE AND PROPERTIES OF THE + TITANIUM ALLOY Ti-4Al-4Mo-2Sn-05Si (wt %): L.J. Hunter, M. Strangwood, The University of Birmingham, School of Metallurgy and Materials, Elms Rd., Edgbaston, Birmingham, B15 2TT, UK

The room temperature tensile strength and fracture toughness have been determined for Ti-4Al-4Mo-2Sn-0.5Si (wt %) for solution treatment in the and fully phase fields followed by cooling at three rates prior to a standard aging treatment. The resulting microstructures have been characterized by transmission electron microscopy and related to the mechanical property behavior determined. Failure in the + solution treated specimens was controlled by interfacial regions between primary a and transformed ( and within the transformed , whilst ductile tearing also occurred in the fully solution treated material.

5:00 pm

QUANTIFYING THE AGEING RESPONSE OF MARTENSITE IN THE Ti-6Al-2Sn-4Zr-6Mo (wt.%) ALLOY: M. Strangwood, D.J. Meadows, The University of Birmingham, School of Metallurgy and Materials, Elms Road, Edgbaston, Birmingham, B15 2TT, UK

Samples of Ti-6246 have been quenched to a fully ('') microstructure prior to aging for up to 4 hours at temperatures of 650, 700, and 750(C. The resulting material was characterized microstructurally using transmission electron microscopy and by microhardness. In addition, ultrasonic methods were used to follow variations in Young's modulus and internal friction for in-situ aging over the same time and temperature regimes. The aging treatments produced microstructures consisting of mixtures of '', w and , which have been related to the variation in physical and mechanical properties recorded.