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, AM Room: B5-6
February 7, 1996 Location: Anaheim Convention Center
Session Chairpersons: T. Broderick, Processing Science Group, Wright Laboratory, Materials Directorate, Wright Patterson AFB, OH 45433; J.R. Wood, RMI Titanium Company, 1000 Warren Avenue, Niles, OH 44446
8:30 am Invited
HEAT TREATMENT OF TITANIUM ALLOYS: OVERVIEW: Rodney R. Boyer, Boeing Commercial Airplane Group, Seattle, WA 98124
There are several types of heat treatments used for titanium alloys, depending on the alloy type and specific application. Heat treatments include stress relief, annealing, duplex-, triplex-, recrystallization-, and beta-annealing, solution treat and aging, duplex aging etc. Each of these heat treatments, in conjunction with the prior processing history, provides a unique microstructure and properties combination. The heat treatments for the various alloy types and their rationale-effect on the microstructure and properties - will be discussed. Different heat treatments are utilized to optimize certain properties, such as fatigue, toughness, strength, etc.
8:55 am Invited
HEAT TREATMENT CHALLENGES FOR TITANIUM IN GAS TURBINE ENGINE APPLICATIONS: James Hall, Allied Signal Engines, Phoenix, AZ 85072
In modern gas turbine, aero propulsion, engines, the concurrent needs for increased performance, improved efficiency and greater reliability have placed heavy demands on titanium rotating components. These demands push titanium alloys closer to their capacity and thus, in turn, creates the need for better and tighter property control. It is the purpose of this paper to review these challenges with respect to microstructure control and the role that heat treatment and related processing play in affecting improved performance and reliability related properties.
SELECTION OF OPTIMUM TECHNOLOGIES OF HEAT TREATMENT OF INTRICATELY SHAPED TITANIUM ALLOY ARTICLES: A.N. Lozhko, G.Z. Malkin, State Metallurgical Academy of Ukraine, Dnepropetrovsk, Ukraine
Reheating of intricately shaped titanium alloy blanks was studied. Optimum heating schedules have been determined which provide for minimum oxidation, gas saturation, and the required final blank temperatures. Cooling of intricately shaped titanium alloy blanks during the thermal treatment procedure will be described. The optimum cooling schedules necessary to provide the required microstructure of the articles due to controlled and variable cooling of the sections of the articles with different mass was determined. Oxidation and gas saturation of titanium alloys in air and in combustion products of coke and natural gases have been studied experimentally at different composition of the fuel mix, within the temperature range of 900-1200deg.C. A search of the scientific technology of cooling (or heating) of an intricately shaped article has been carried out on a computer model which visualized the distribution of temperatures, distribution of heating (cooling) rates, gas saturation layer and scale layer during all the heat treatment stages. An original mathematical apparatus based on orthogonal conformal transformations has been used for the simulation of the non-stationary temperature field. This enabled to solve the problem with higher speed and accuracy in comparison with such methods as finite or bottleneck elements.
EFFECT OF COOLING RATE ON PHASE TRANSFORMATIONS IN Ti-6Al-4V: T. Ahmed, H.J. Rack, Materials Science and Engineering Program, Clemson University, Clemson, SC 29634-0921
The effect of cooling rate on the microstructure of Ti-6Al-4V has been examined. At the highest cooling rate examined, 523deg.C/s, ß transformed to acicular hexagonal martensite, [[alpha]]'. Decreasing the cooling rate to 410deg.C/s resulted in the introduction of a competitive massive transformation reaction, ß ->[[alpha]]m1 whose volume fraction increased with decreasing cooling rate. Finally, at slow cooling rates (~2deg.C/s) the microstructure was comprised of Widmanstättan [[alpha]]w. These results will be discussed with relation to the thermodynamic stability of [[alpha]]', [[alpha]]m and [[alpha]]w as represented in the form of a CCT diagram.
TITANIUM PRODUCTION TECHNOLOGIES AND THE AUTOMOTIVE MARKET: Christopher Sommer, Timet, 8615 Richardson Road, Suite 100, Walled Lake MI 48390
Due to the downsizing of the military aerospace industry and the fixed production overcapacity in the titanium industry, many new markets need to be pursued. One outstanding case in point is the O.E.M. automotive world. This industry is faced with a daunting task. That is to design and build, on a consumer affordable basis, a lightweight, energy efficient automobile. The recent approval of stricter C.A.F.E. requirements and the coming push for further clean air legislation ie; the electric car, has certainly sparked new intrest in titianium as a material of choice for automotive components. With this new interest increased focus has been placed on finished part costs, bypassing to a degree, the age old stigma of high input material cost. The focus of the titanium industry today should be placed on these finished component opportunities and the problems presented with their manufacture. This paper will present some of these components and so far successful methods of manufacture used to overcome these obstacles.
PROCESSING, MICROSTRUCTURE, AND PROPERTIES of ß-CEZ: G. Lutjering, J.O. Peters, TU Hamburg-Harburg, 21071 Hamburg, Germany
The influence of different processing routes ([[alpha]]+ß forging, "trough-transus" forging) and different heat treatments on the microstructure and mechanical properties of ß-CEZ will be discussed. The advantages and disadvantages of the so-called "necklace" microstructure achieved by "trough-transus" deformation will be outlined in comparison to the bi-modal microstructure resulting from conventional [[alpha]]+ß deformation. The discussion of the mechanical properties is based on tensile tests, fracture toughness tests, and fatigue tests (S-N curves, da/dN-K curves of micro-and macro- cracks).
PRINCIPLES OF TITANIUM ALLOYS' STRUCTURE CONTROL WITH A PURPOSE OF INCREASING THEIR MECHANICAL PROPERTIES: M. Brun, G. Shachanova, All-Russia Institure of Light Alloys, VILS, Moscow, Russia
Titanium alloys typical have diverse microstructures due to the presence of several phases, differences in their morphology, wide range of volume fractions and sizes of various structural constituents. The diversity of these alloys (especially of [[alpha]]+ß alloys) has a significant effect on their mechanical properties. The following "structural contribution to the properties" in annealed condition was obtained from the experimental data: strength -150-200 MPa, elongation -10-15%, reduction of area -40-40%, fracture toughness -50 -60 MPa Vm, high- cycle fatigue strength 120-150 MPa, creep resistance - 80-120 MPa, etc. These values are extremely high and exceed the so called "superiority's quota" which is used as one of the conditions for the development of new alloys. Another important aspect of the "structure-properties" problem for titanium alloys is that mechanical properties (ductility, fatigue resistance, etc.) are influenced by many structural parameters. The task of selecting the preferable structure selectionfor a specific component develops in 3 directions: 1. revealing of the mechanical properties which determine serviceability of various components; 2. determination of the correlation between structure and properties; 3. establishment of the conditions necessary to obtain required structures. This presentation is devoted to the consideration of titanium alloy structure formation's generality at deformation and heat treatment, as a scientifical base for the regulation of semiproducts structure. It will consider the general conceptions and quantitutive data for the influence of deformation and heat treatment regimes to various parameters of [[alpha]]+ß- alloys' structure.
EFFECTS OF HEAT TREATMENT ON MATRIX MICROSTRUCTURE, INTERFACIAL REACTIONS AND FATIGUE CRACK GROWTH RESISTANCE OF TITANIUM METAL MATRIX COMPOSITES: S.V.Sweby, A.Dowson, and P.Bowen, School of Metallurgy and Materials IRC in Materials for High Performance Applications, The University of Birmingham, Edgbaston, B15 2TT UK
A study has been undertaken to assess the effects of heat treatment on two titanium alloy metal matrix composites (MMC). Ti-6Al-4V (IMI 318) and Ti-5.8Al-4Sn-3.5Zr-0.Nb-0.5Mo-0.3Si (IMI 834) were chosen for this study, reinforced with SiC fibres. Beta transus approach curves were generated for the composite matrices. Shifts in beta transus temperature of up to 55deg.C have been recorded for the matrix regions of the composite over the monolithic alloys. Two fibre coating systems have also been evaluated: SM1240, which consists of a 1um carbon and a 1um titanium boride layer and SM1140+, which consists of a 4.5um carbon layer. Considerable differences in the morphology of the fibre/matrix interfacial regions and their effects on the fatigue crack growth resistance have also been recorded. The effects of matrix microstructure and interfacial reactions on the fatigue crack growth resistance of the two alloys will be discussed.
10:50 am BREAK
MICROSTRUCTURE/FATIGUE CRACK PROPAGATION RELATIONSHIPS FOR SP700 TITANIUM SHEET: C. N. Kimura, Boeing Defense & Space Group, Materials & Processes Technology, P.O. Box 3999, MS 3E-JE, Seattle, WA 98124; T. F. Archbold, University of Washington, Department of Materials Science & Engineering, FB-10, Seattle, WA 98195
SP700 is a beta-rich, alpha-beta titanium alloy (Ti-4.5Al-3V-2Mo-2Fe) specially developed by NKK (Japan) for superplastic forming (SPF). The alloy has a fine grain microstructure well-suited for SPF, exhibiting lower flow stresses and processing temperatures than Ti-6Al-4V. These characteristics provide the potential for less tooling wear, less accumulation of oxidation contamination (alpha case) on surfaces of SPF parts, and ultimately, reduced cost of SPF titanium parts. In addition, NKK has reported SP700's improved hot and cold formability, fatigue strength, and toughness. The alloy's heat treat response and age hardenability result in a wide range of micro-structures which includes elongated primary alpha. The microstructure/properties relationship of similar microstructures in Ti-6Al-4V is well-documented. This investigation seeks to identify microstructure vs. fatigue crack propagation relationships for SP700 sheet material. The microstructures described above will be evaluated for this study. A quantitative assessment of each microstructure in terms of primary alpha grain morphology and other factors will be related to tensile properties, da/dN vs. delta K, and fracture surface morphology. These relationships will be compared with those for Ti-6Al-4V.
EFFECT OF THE COOLING RATE FROM MILL ANNEALING TEMPERATURE ON STRESS CORROSION THRESHOLD OF Ti-6Al-4V ELI BETA ANNEALED: Bob Briggs, Boeing Company, PO Box 3707, M/S 73-44, Seattle, WA 99124
The cooling rate from the mill anneal heat treatment following the beta anneal was shown to have a dramatic effect on the stress corrosion threshold of Ti 6Al-4V ELI beta annealed. The stress corrosion threshold was reduced by more than half when slow cooling was performed. The stress corrosion threshold versus seven different cooling rates (from air cool to furnace cool) was measured and a correlation between stress corrosion threshold and cooling rate obtained. Additional stress corrosion specimens were exposed to various times and temperatures, and the resulting change in stress corrosion threshold used to create a Time-Temperature-Transformation (TTT) diagram to indicate the range in which the stress corrosion susceptibility was most acute, attributed to the formation of Ti3Al. The fracture surface of the stress corrosion specimens were examined metallographically and with SEM and TEM. Microstructural features such as colony size of transformed beta and the width of lamellar alpha were correlated to details observed on the fracture surface. TEM was used to examine specimens for the presence of Ti3Al. The formation of Ti3Al was explained using the Ti-Al phase diagram and the measuring aluminum content of the alpha phase due to partitioning.
ENHANCEMENT OF STRENGTH AND CREEP PROPERTIES OF TITANIUM ALLOYS BY SPECIAL [[alpha]]2-PHASE PRECIPITATION: P.E. Markovsky, Institute for Metal Physics National Academy of Sciences of the Ukraine, 36 Vernadsky str., 252142, Ukraine
An additional way of mechanical and creep property enhancement for titanium alloys with 6 wt.% aluminum and more the hardening by precipitation of very fine particles of [[alpha]]2 (Ti3Al)-phase is shown. The process of [[alpha]]2-phase precipitation is quickened by special deformation before the ageing, that allows to shorten ageing time from 24 hours and more to 2-3 hours. Since [[alpha]]2-phase precipitation leads to decreasing of titanium alloys' ductility this effect may be reduced by alloys' structure refinement. The best balance of tensile and creep properties have alloys with average grain size less than 2 um reinforced by [[alpha]]2 - phase precipitates. For example, Ti-6Al-4V alloy with average grain size 1-2 um after this treatment has UTS > 1300 MPa, A5 > 9% and creep resistance characteristics at 500deg.C better than special high temperature titanium alloy Ti6242 in bimodal state tested at the same conditions.
HEAT TREATMENT OF LARGE-SCALE SEMIPRODUCTS FROM TITANIUM ALLOYS: A.A. Ilyin, M. Yu. Kollerov, A.A. Krastilevsky, Moscow State University of Aviation Technology, Metals Science Dep., Petrovka St. 27, Moscow, K-31, Russia, 103767
Specific strength is among the first ordered requirements for the materials utilized in commercial industry (especially in aerospace). Thus on each stage of semiproducts and products manufacture they need various types of strengthening, including heat treatment. Strengthening heat treatment has not found wide application towards the large-scale semiproducts due to temperature distribution inhomogenity through the cross-section of semiproduct. It causes the irregular phase composition and structure through the semiproduct reansverse, as well as causes the high level of temporary residual micro and macro-stresses. The new type of diagrams are suggested to predict a titanium alloy phase composition formed during the ß-phase decomposition at continuous cooling. There was found some regular trends of cooling rates from various temperatures and future ageing influence on mechanical properties of Ti alloys of diverse classes. It is shown that the maximum level of strength and ductility is observed after cooling from ß-area with the rate near as called third critical rate (Vc3). The formation of residual and temporary microstresses appeared as a result of inhomogenity of temperature field and the phase transformation taking place during heating and cooling through the cross-section of plates and bars from Ti-6Al-4V; Ti-6Al-2Mo-4V-1Cr-1Fe; Ti-5Al-4Mo-4V-1Cr-1Fe. The critical size of semiproducts, which could be heated and cooled in various natures without residual microstresses, was received. On the base of formed microstructure, phase composition, properties and microstresses level through the cross-sections of large-scale semiproducts (bars and plates) from investigated alloys, the new types heat treatment, that leads to the maximum strength properties with simultaneous ductility and minimum level of microstresses, as well as minimum irregularity of mechanical properties along the cross-section of semiproducts, were learned out.
TITANIUM AND ITS ALLOYS-AN OVERVIEW: S.C. Sharma, B.M. Girish, Rathnakar Kamath, Centre for Manufacturing Research and Technology Utilisation R.V. College of Engineering, Banglore - 560 059, India
In the recent years, titanium has found wide applications as a structural
material, mainly due to its high mechanical properties, low specific weight and
outstanding corrosion resistance. It can be satisfactorily worked, both hot and
cold and has good weldability. Formation of a stable oxide film on its surface
helps provide high corrosion resistance. Titanium which has a melting point of
1725deg.C, has two allotropic forms namely [[alpha]]-titanium and
ß-Titanium. The titanium alloys are of special intrest since they have
better mechanical properties than pure titanium. One important factor about the
titanium alloys is that they have the highest specific strength among all of
the structural materials. The present paper reviews the status of titanium and
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