Dynamic compaction of titanium aluminides by explosively generated shock waves: Microstructure and mechanical properties
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I.
INTRODUCTION
T H E 1980s witnessed a great interest in intermetallic compounds, particularly in nickel and titanium aluminides. The increased interest is due to the desire to reduce the weight and improve the performance of aircraft turbine engines. The alloys based on titanium aluminides are emerging as attractive candidates because of their interesting properties: good strength at ambient temperature and good strength and high stiffness retention at high temperatures. More specifically, TiAl has a higher modulus at 1000 ~ and Ti3A1 has a higher modulus at 815 ~ than Ti at room temperature, tl'2] and the strength of TiAl does not drop with temperature until approximately 600 ~ t31 Titanium aluminides also present good oxidation resistance because of the protective oxide coating provided by aluminum. However, a generic problem with titanium aluminides is their low ductility and poor fracture toughness at room temperature, t2-6~ making them difficult to fabricate. The most successful method of improving the ductility of TiaAl has been the addition of fl-stabilizing elements, tTJ such as Nb. Niobium additions increase the nonbasal slip activity12'7'8~ and also result in microstructural refinement,t7'81 which has the effect of reducing the slip length. Furthermore, if enough Nb is added, a two-phase microstructure is retained (a2 + /3),t6~ in which the presence of a more ductile body-centered cubic (bcc) phase (fl) helps to increase the ductility. Another method for increasing the ductility is to introduce a second phase, by rapid solidification, in order to homogenize the planar slip. t9A~ However, the rapidly solidified A. FERREIRA, Professor and Lieutenant Colonel, is with the Military Institute of Engineering, Urca, Rio de Janeiro, RJ 22093, Brazil. M.A. MEYERS, Professor, is with the Department of Applied Mechanics and Engineering Sciences, University of California-San Diego, La Jolla, CA 92093-0411. N.N. THADHANI, Associate Research Professor, is with the Center for Explosives Technology Research, New Mexico Institute of Mining and Technology, Socorro, NM 87801. Manuscript submitted September 5, 1989. METALLURGICAL TRANSACTIONS A
particles must be consolidated by a convenient process so that the properties acquired by rapid solidification are not lost due to the long thermal excursions in conventional powder processing techniques. Shock compaction is an attractive process for these materials, because the surfaces of the particles melt and rapidly resolidify while the particle interiors undergo only moderate heating. The objectives of this article are to present the microstructural features and mechanical properties resulting from dynamic compaction of rapidly solidified titanium aluminides by explosively generated shock waves.
II.
EXPERIMENTAL PROCEDURE
The shock consolidation of the rapid solidification processed (RSP) Ti-aluminide powders were conducted using double-cylinder tube implosion geometry. 1t2~ The detailed description of the experimental setup, as-received powder characteristics, and the ma
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