Deformation of rapidly solidified dispersion strengthened titanium alloys
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I.
INTRODUCTION
O X I D E dispersion strengthening (ODS) of titanium-based alloys creates the potential of a new generation of lightweight, high-performance alloys with improved strengths and creep properties at elevated temperatures. The improvements in mechanical performance have been attributed to the presence of insoluble oxide particles which act as barriers to dislocation motion and remain microstructurally stable even to high temperatures. A principal difficulty encountered in the development of ODS alloys is the need for a processing technique capable of creating a uniform distribution of finely spaced, insoluble particles. However, the recent application of rapid solidification (RS) techniques to titanium-based alloys has indicated the potential to obtain oxide particle dispersoids distributed homogeneously within the matrix. These alloys utilize rare earth elemental additions to titanium because of their ability to scavenge interstitial oxygen from titanium solid solution and form a dispersion of thermally stable rare earth oxide precipitates. Several investigators have established the potential of RS in oxide dispersion strengthened titanium alloy development through extensive evaluation of the thermal stability of candidate microstructures in the unconsolidated form of ribbon, flake, or splats.tl-H~ However, the evaluation of the thermal stability following consolidation and the resulting bulk mechanical properties has progressed to a much lesser extent. Sastry, Peng, and Beckerman have measured the tensile strengths and steadystate creep rate of extruded RS Ti, Ti-l.0Er, and Ti1.5Nd at two levels of stress at the temperatures of 482, 600, and 700 ~ ~2] These data show decreased steadystate creep rates for the dispersoid-containing alloys with the Ti-Er alloy exhibiting superior creep resistance. Gigliotti et al. have reported very recently the minimum creep rate and creep ductility at 650 ~ for several complex Ti alloys (containing varying amounts of A1, Sn,
S.L. KAMPE, formerly of Michigan Technological University, Houghton, MI, is with Martin Marietta Laboratories, Baltimore, MD 21227. D.A. KOSS, Chairman and Professor, is with the Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16803. Manuscript submitted April 13, 1988. METALLURGICAL TRANSACTIONS A
Zr, and Nb) with erbium elemental additionsJ 13,14] In contrast, they report ductility improvements in alloys containing the rare earth dispersoids but an associated loss of strength. Enhanced creep resistance with no compromise in ductility was obtained using rare earth additions to titanium matrices of higher (A1 + Sn) content. It should be noted that data reported by Sastry et al. for various RS Ti-A1 alloys with rare earth additions also have demonstrated enhanced room temperature strength and ductility over non-dispersoid containing a l l o y s . [15'16] Although based on specific testing conditions, the above developmental work demonstrates the potential of RS processing techniques as a means
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