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About the 1996 TMS Annual Meeting: Monday Morning Sessions (February 5)

February 4-8 · 1996 TMS ANNUAL MEETING ·  Anaheim, California


Proceedings Info

Sponsored by: SMD Titanium Committee and MDMD Shaping and Forming Committee

Program Organizers: Prof. Isaac Weiss and 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

Monday, AM Room: B5-6

February 5, 1996 Location: Anaheim Convention Center

Session Chairpersons: G. W. Kuhlman, Alcoa Forged Products, 1600 Harvard Ave., Cleveland, OH 44105, and R. Srinivasan, Mechanical and Materials Engineering Dept., Wright State University, Dayton, OH 45435

8:30 am Invited

HOT-WORKING OF TITANIUM ALLOYS - AN OVERVIEW: S.L. Semiatin, Wright Laboratory, Materials Directorate, WL/MLLN, Wright-Patterson Air Force Base, OH 45433-7817

The thermomechanical processing of ingot metallurgy titanium alloys will be discussed with special emphasis on microstructure evolution and workability considerations for alpha-beta, alpha- two titanium aluminide, and gamma titanium aluminide alloys. The conversion of ingot structure to fine equiaxed wrought structure will be addressed. In this regard, the breakdown of lamellar microstructures, the occurrence of cavitation/wedge cracking ('strain induced porosity'), and the development of crystallographic texture will be described. Special methods to breakdown the difficult-to-work titanium aluminide alloys will also be summarized. These methods include canned hot extrusion and canned conventional forging. Secondary processes such as bare and pack sheet rolling, superplastic forming of sheet, and closed-die forging will be reviewed. The emergence of non-standard methods for microstructure control, e.g., forging of metastable microstructures, will also be summarized.

9:00 am


Methods for control and manipulation of titanium alloy microstructures have been developed for many years by iterative trials. Variations in titanium heating, deformation and cooling practice result in greatly varied microstructural morphology and volume fraction for the various alloy phases. Efforts are being undertaken to develop an analytical tool to predict the development of titanium alloy microstructures under heating, hot working, and cooling conditions. Results of this tool have been successfully correlated to the actual forge shop applications. Further utilization of this technology will allow more rapid process development for forged titanium components with greater robustness with respect to resultant microstructure.

9:20 am


Very large closed-die titanium alloy forgings have presented a significant challenge to forgers, due to the material's very high unit pressures when sub-transus forged, difficulty in deformation processing for required TMP and pressure constraints on available heavy presses, even at 50,000 tons. Until recently, the Boeing 747 Ti-6-4 Main Landing Gear Beam (4,000 PVA) and the McDonnell-Douglas F-15 Ti-6-4 Lower Bulkheads (3,200 PVA) represented the state-of-the-art in closed-die forging size producible, particularly for the alpha-beta alloy Ti-6-4. Recently however driven by the development of the new McAir/Northrop F-18E/F fighter, the state-of-the-art in Plan View Area of large closed-die Ti forgings has been extended by nearly 25%. The F-18E/F aircraft included a series of three very large (PVA of 4,800 to 5,000 single piece Ti-6-4 bulkheads manufactured with incremental forging techniques. Fabrication of these parts as single forgings eliminated joints and reduced part fabrication costs and flow time. Presented is a summary of the fabrication approaches and mechanical properties achieved.

9:40 am

RESEARCH ISSUES IN THE HOT EXTRUSION OF TITANIUM ALLOYS: Rajiv Shivpuri, Dinesh Damodaran, The Ohio State University, Columbus, OH 43210; Tony Esposito, Plymouth Tube Co.

Hot extrusion is a basic metal working process, but for materials like titanium alloys where experience with extrusion is insufficient, many tryouts are required to determine the operating conditions due to the complex relationships among the process variables. The flow stresses of titanium alloys are higher than those of steel and hence these alloys are difficult to extrude. In comparison with steel, the high temperature flow stress of titanium alloys increases very rapidly with increasing strain rate. Besides this, the behavior of the glass lubricant used in hot extrusion is very sensitive to the surface temperature and the contact time between the hot billet and the tooling. Information about the interactions between the process variables is necessary to optimize the process, but it is difficult to obtain by experiment only. In this study the entire hot extrusion process is mathematically modeled including the induction heating, billet transfer, glass lubrication and metal flow. The objective of the study is to investigate the interactions between the major process variables involved in hot extrusion of the titanium alloy Ti-6Al-4V. The effects of ram speed, and billet initial temperature on the extrusion pressure and lubricant behavior are presented. The theoretical results are compared with experimental observations of titanium alloy extrusions done at an extrusion plant.

10:00 am

INFLUENCE OF STARTING MICROSTRUCTURE ON THE HIGH TEMPERATURE PROCESSING OF CP TITANIUM ALLOY: S. Guillard, M. Thirukkonda, P.K. Chaudhury, Concurrent Technologies Corporation, 1450 Scalp Ave., Johnstown, PA 15904

Commercially pure (CP) titanium grades 2 and 3 have been tested in compression at temperatures and strain rates corresponding to those encountered in industrial hot working operations, i.e., temperatures from 500deg. to 725deg.C, and strain rates from 0.001 to 20 s-1. Most deformation conditions led to either inhomogeneous flow, shear banding, or cracking of the grade 2 material, whereas the grade 3 material deformed homogeneously under most conditions. In addition, the flow stresses of the grade 2 material were higher than those of the grade 3 material by approximately 200 to 700%, although grades 2 and 3 materials had very similar chemical compositions. These differences were traced to the difference in starting microstructures, grade 2 exhibiting a Widmanstätten structure in contrast to grade 3 exhibiting slightly elongated grains. Samples of the grade 3 material were heat treated to duplicate the microstructure of the grade 2 material, and mechanically tested under the same processing conditions. The results, including the localization characteristics and flow stresses, are compared to study the influence of starting microstructure on hot forming of CP titanium. It is suggested that to insure successful manufacturing of CP titanium alloys, formation of the Widmanstätten structure should be prevented during prior processing.

10:20 am

BRINGING TITANIUM INTO A COMMERCIALLY ACCEPTABLE REALM FOR GENERAL USE: M. Miller, Stealth Engineering and Technologies, Inc., 1489 Cedar St, Holt, MI 48842

Issues relating to bringing titanium alloys into a commercially acceptable realm will be discussed. The topics will include (1) Bringing raw material costs to a representative comparison with other currently used materials; (2) Maintaining proper structural morphology in forging; (3) Product opportunities in areas other than aerospace, such as medical, automotive high performance, and original equipment automotive equipment; and (4) General description of those operations involved in near net-shape forging.

10:40 am BREAK

10:50 am

ELEVATED TEMPERATURE DEFORMATION BEHAVIOR OF Ti-6.8Mo-4.5Fe-1.5Al: I. Philippart, H. J. Rack, Materials Science and Engineering Program, Clemson University, Clemson, SC 29634-0921

The high temperature deformation behavior of TIMET LCB(Ti-6.8Mo-4.5Fe-1.5Al) has been investigated as a function of temperature, strain rate and strain. Stable and unstable flow regimes were established by Dynamic Materials Modeling and correlated with microstructural restoration processes. Unstable flow was observed at low strain rates (<10-2 s-1) independent of temperature, and was found to be related to grain boundary failure phenomena. Stable flow was observed at high strain rates being associated with dynamic recovery at low temperature and dynamic recystallization at higher temperatures. The observed flow behavior will be discussed considering the effect of deformation temperature, strain rate and strain on grain boundary sliding and dislocation processes.

11:10 am

SUBMICRON STRUCTURED TITANIUM ALLOYS PREPARED USING MULTISTEP ROLLING + ANNEALING TECHNIQUE: P.E. Markovsky, Institute for Metal Physics, National Academy of Sciences of the Ukraine, 36 Vernadsky str., 252142, Kiev, Ukraine

The method of obtaining ultra-fine structural (UFS) state (with grain size less than 0.5um) in two-phase titanium alloys from massive starting material (without stage of powder preparation) is discussed. This method is based on the results of investigation of "undeveloped" recrystallization. The tensile testing of these UFS materials was carried out in the temperature range form 1060deg.C to 550deg.C. It was found that UFS materials have a specific deformation behavior and significantly improved mechanical properties (at low and room temperatures) and a superplastic-like behavior at elevated temperatures.

11:30 am

MICROSTRUCTURAL EVOLUTION IN Ti-6Al-4V DURING HOT DEFORMATION: M.B. Gartside, IRC in Materials for High Performance Applications, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom

Evolution of microstructure and its effect on mechanical behavior has been investigated in Ti-6Al-4V for different initial [[alpha]] and ß morphologies. Hot tensile tests were performed in the temperature range 720-920deg.C and at strain rates of 10-4 to 10-2 s-1. The stress-strain behavior exhibited a maximum stress followed by a decrease in flow stress which was most pronounced at low temperatures, high strain rates and for the transformed ß microstructures. Optical microscopy of the transformed ß microstructures showed shearing and fragmentation of the [[alpha]] needles, particularly at high temperatures, leading to a softer microstructure of spherical [[alpha]] particles. In the as-received microstructure some rearrangement of the [[alpha]] and ß grains was observed. Tests with large rapid changes in strain rate showed that strain rate has an effect on the evolution of microstructure. These results indicate that rearrangement of the microstructure is responsible, to some extent, for the development in flow stress seen at this alloy in high temperatures.

11:50 am

SOLUTE SOFTENING OF [[alpha]] TITANIUM - HYDROGEN ALLOYS: O.N. Senkov, J.J. Jonas, Department of Metallurgical Engineering, McGill University, 3450 University Street, Montreal, Quebec, Canada H3A 2A7

Compression tests were carried out on a series of titanium - hydrogen alloys within the alpha phase field. The dependence of the flow stress, rate of work hardening and mechanical anisotropy on temperature, strain rate and hydrogen content were determined. Anomalies in the rate and temperature dependencies of the flow stress and work hardening rate were detected in the unalloyed specimens, which indicated that dynamic strain aging was occurring. Hydrogen in solid solution shifts the ranges of the anomalies towards lower temperatures; it also decreases the work hardening rate, produces marked flow softening, and decreases the mechanical anisotropy of alpha titanium. The relative values of the hydrogen - induced softening are shown to depend on strain rate and temperature.

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