Sponsored by: SMD Titanium Committee, 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, PO Box 2128, Henderson, NV 89009; Prof. Daniel Eylon, Graduate Materials Engineering, University of Dayton, Dayton, OH 45409
Monday, PM Room: B5-6
February 5, 1996 Location: Anaheim Convention Center
Session Chairpersons: S.L. Semiatin, Wright Laboratory, Materials Directorate, WL/MLLN, Wright-Patterson Air Force Base, OH 45433-7817; I. Weiss, Mechanical and Materials Engineering Dept., Wright State University, Dayton, OH 45435
2:00 pm Invited
MEETING THE CHALLENGE OF HOT WORKING TITANIUM ALLOYS INTO COST EFFICIENT FINISHED COMPONENTS: G.W. Kuhlman, Alcoa Forged Products, 1600 Harvard Ave., Cleveland, OH 44105
Titanium alloys, especially advanced aluminides, are among the most difficult to fabricate engineering materials. Management of titanium thermomechanical processing (TMP) in hot working processes (forging, rolling, extrusion) has become a skillfully executed science, utilizing sophisticated process engineering, modeling and computer design and control technologies, rather than relying solely upon art or the experience of an operator. At the heart of overcoming the challenges of cost-efficient titanium component fabrication is the growing body of science and knowledge available on the interactions between required Ti alloy TMP for critical properties and the hot working processes. Using sophisticated deformation simulators, artificial intelligence and expert systems, FEM and other modeling technologies, and state-of-the-art computer controlled equipment, the titanium forger, roller, or extruder has unparalleled power at his disposal in terms of depth of deformation understanding, accurate process models and equipment capabilities. With these tools, fabrication of titanium alloy components is being efficiently accomplished. Reviewed in this paper is the state-of-the-art in key TMP, materials performance, deformation and commercial scale hot working processes for Ti Alloys.
THE DESIGN, PRODUCTION, AND METALLURGY OF ADVANCED, VERY LARGE, TITANIUM AEROSPACE FORGINGS: T.E. Howson, R. G. Broadwell Wyman Gordon Forgings, P.O. Box 8001, North Grafton, MA 01536-8001
This paper discusses the development of methods and dies for production of large airframe and engine forgings in several titanium alloys. Applicable modelling, metallurgical considerations, and mechanical properties are also presented.
A MECHANISTIC STUDY OF HOT WORKING OF CAST MULTI-PHASE NEAR- [[gamma]]Ti-Al ALLOYS: D.A. Hardwick, P.L. Martin, Rockwell Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360
Microstructural structural refinement and chemical homogeneity are the twin goals of primary ingot breakdown, and both are a necessary prerequisites for further deformation processing. Compression workability testing, coupled with extensive metallographic characterization (SEM backscatter and TEM), has been used to study the evolution of these characteristics in three near- TiAl alloys: Ti-46Al-0.2B, Ti-48Al-0.2B, and Ti-48Al-2Mo-0.2B. Details of the response to deformation of each phase in these multi-phase alloys, including the partitioning of deformation between the various phases, will be discussed.
MICROMECHANISMS OF SUPERPLASTIC DEFORMATION OF A GAMMA TITANIUM ALUMINIDE ALLOY: C.M. Lombard, S.L. Semiatin, WL/MLLN, Wright-Patterson AFB, OH 45433-7817; A.K. Ghosh, Dept. of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2316
A near-gamma TiAl material (Ti-45.5AI-2Cr-2Nb) was hot rolled to produce thin sheets. Samples of the sheet were tension tested at strain rates of 10-3-10-2s-1 and temperatures between 900 and 1200deg.C to establish the flow behavior and microstructural changes. Results showed that the optimum superplastic forming conditions were at 1200deg.C and an initial rate of 10-3s-1 Under these conditions, the maximum elongation (980%) and the minimum amount of cavitation were achieved. Various micromechanisms, such as dynamic/static grain growth, solute redistribution between constituent phases, and changes in the morphologies of the phases, will be discussed in relation to the observed flow and fracture behavior.
A CONSTITUTIVE EQUATION FOR THE HIGH TEMPERATURE DEFORMATION BEHAVIOR OF Ti-(40-54)Al ALLOYS: Catherine M. Sabinash, McDonnell Douglas Corporation, St. Louis, MO 63166; Shankar M. L. Sastry, Department of Mechanical Engineering, Washington University, St. Louis, MO 63130-4899
The elevated temperature deformation behavior of Ti-(40-54)Al was studied by compression testing at 1200deg.C to 1300deg.C and strain rates of 0. I to 0.001/s. Based on the operating mechanisms, a constitutive equation for the dependence of flow stress on temperature, strain rate, strain, and volume fraction of constituent phases was developed for single phase alpha and gamma alloys, two phase gamma + alpha2 titanium aluminides and Ti-Al-Cr and Ti-Al-Mn alloys. The equation, which utilizes readily available parameters eliminates the need for expensive high temperature testing. The equation predicts the values of peak and steady state flow stresses of alloys across the compositional range within a factor of two.
3:50 pm BREAK
A PM METHOD FOR MAKING GAMMA TITANIUM ALUMINIDE WIRE: C. F. Yolton, J. P. Beckman, J. H. Moil, Crucible Materials Corporation, Crucible Research, 6003 Campbells Run Road, Pittsburgh, PA 15205-1022
Gamma titanium aluminide alloys have attractive elevated temperature properties which make them a desirable material for advanced gas turbine engines and advanced airframe applications. These alloys are of interest for aircraft applications because they generally have a low density, good elevated temperature tensile and creep strength, and good oxidation resistance. Considerable progress has been made in the development of titanium aluminide alloys for aircraft applications. One fabrication method which has been very successful in making gamma titanium aluminide components is casting. Gamma titanium aluminide alloys such as Ti-48Al-2Nb-2Cr have good castability and the castings have good mechanical properties. As with all titanium castings, gamma titanium aluminide castings must be hot isostatically pressed to close internal cavities and weld repaired to fill surface dimples. Weld repair requires filler metal to fill the dimples, typically in the form of wire. Although gamma titanium aluminide casts well it is very difficult to hot work and process by other conventional methods. Production of welding wire is therefore difficult and costly. One means of minimizing the difficulties associated with the fabrication of gamma titanium aluminide welding wire is through the use of powder metallurgy. This paper will describe a powder metallurgy method for making gamma titanium aluminide wire in which wire is extruded directly to finish size from prealloyed powder.
LAMELLAR TO EQUIAXED GRAIN TRANSFORMATION BY TORSIONAL DEFORMATION PROCESSING OF ALPHA/BETA Ti ALLOY: G. Welsch, Case Western Reserve University, Cleveland, OH 44106; I. Weiss, Wright State University, Dayton, OH 45435; D. Eylon, University of Dayton, Dayton, OH 45469; F.H. Froes, University of Idaho, Moscow, ID 83843
The lamellar alpha + beta microstructure of cylindrical Ti-6Al-2Sn-4Zr-2Mo specimens was transformed to the equiaxed grain structure by torsionally induced shear deformation at elevated temperature. The effects of shear strain and time at elevated temperature on the microstructural development were analyzed by optical and electron metallography. By taking advantage of the strain dependence of the transformation and of the strain gradient in torsion, a duplex microstructure can be created of crack-initiation-resistant equiaxed grains in the surface region and crack-propagation-resistant lamellar structure in the interior.
INFLUENCE OF THERMOMECHANICAL PROCESSING CONDITIONS ON THE MATERIAL PROPERTIES OF Ti-6%Al-4%V/TiC COMPOSITES: P. Wanjara, R.A.L. Drew, S. Yue, McGill University, 3450 University Street, Department of Mining and Metallurgical Engineering, Montreal, Quebec, Canada, H3A 2A7
Titanium alloy composites containing up to 20 volume percent TiC particulates were processed by powder metallurgy processing. Investigation of the as-consolidated composites indicated that, although high temperature consolidation is beneficial in achieving near complete densification, degradation in the composite properties may result from extensive carbon loss from the TiC particulate reinforcements. Thermomechanical processing can reduce consolidation temperature and time while simultaneously improving the properties of the composite through elimination of the residual porosity and modification of the matrix microstructure. High temperature deformation processing was performed by compression testing at strain rates in the range of 3 x 10-4 to 2 s-1 at various temperatures above and below the beta transus (around 988deg.C for Ti-6%Al-4%V). Through systematic variations in these deformation processing parameters, the conditions for obtaining a fully dense material having a range of microstructures and mechanical properties have been investigated.
SOLUTE STRENGTHENING IN ß TITANIUM - HYDROGEN ALLOYS: O.N. Senkov and J.J. Jonas, Department of Metallurgical Engineering, McGill University, 3450 University Street, Montreal, Quebec, Canada H3A 2A7
Compression and torsion tests were carried out on a series of titanium-hydrogen alloys containing up to 37 atomic % of dissolved hydrogen. The tests were performed within the beta phase field. The dependence of the flow stress on temperature, strain rate and hydrogen content was studied. The addition of hydrogen to beta titanium leads to noticeable hardening, the amount of which increases with hydrogen concentration according to a quadratic law. Analysis of the activation parameters of plastic flow shows that they depend weakly on hydrogen concentration. The flow behavior is described in terms of thermally activated glide and takes into account internal stresses that depend on the hydrogen concentration according to a power law relationship.
THE EFFECT OF GRAIN SIZE ON AMBIENT TEMPERATURE CREEP BEHAVIOR OF [[alpha]]-TITANIUM ALLOYS: S. Chandu, S.Ankem, Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD 20742-2115
Recently it has been shown that grain size has a significant effect on ambient
temperature creep behavior of [[alpha]]Ti-Mn alloy when crept at 95% YS. The
creep strain was found to increase with increase in grain size and this has
been attributed to time-dependent twinning. In the present investigation, a
systematic study was undertaken to confirm the earlier results and to extend
the range of grain sizes to determine if the trends reported earlier hold good
over a broader range in [[alpha]]-Ti-V alloy. Details of the investigation
will be presented.
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