Dynamic compaction of titanium aluminides by explosively generated shock waves: Experimental and materials systems
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I.
INTRODUCTION
TITANIUM aluminides are potential materials for many of the rotating and static components in the compressor sections of gas turbine engines t~'2] in aerospace applications because of their low density and high-temperature properties, t3'al The objectives of this work were twofold: (1) to present the macrostructural features resulting from dynamic compaction of rapidly solidified titanium aluminides by explosively generated shock waves and (2) to investigate the effects of alloy composition, niobium powder additions, shock-induced chemical reaction between mechanically blended powder mixtures of titanium and aluminum, initial temperature, amount of explosive, and detonation velocity of the explosive on the cracking density of compacts. II.
EXPERIMENTAL PROCEDURE
A. Material Characterization Table I lists the characteristics (alloy type, run number, composition, pct carbon, and powder size) of the rapidly solidified powders as obtained from Pratt & Whitney, West Palm Springs, FL, and used for the compaction experiments. These powders were produced by the rapid solidification rate (RSR) process. The particle size distribution obtained by sieve analysis was performed at Pratt & Whitney. There is a considerable degree of variation in the compositions reported in Table I. The main differences are in the carbon content and in the presence of erbium for part of the powders. The highA. FERREIRA and J.R. KOUGH, Department of Metallurgical and Materials Engineering, and N.N. THADHANI are with the Center for Explosives Technology Research, New Mexico Institute of Mining and Technology, Socorro, NM 87801. M.A. MEYERS and S.N. CHANG are with the Center of Excellence for Advanced Materials, University of California, San Diego, La Jolla, CA 92093. Manuscript submitted September 5, 1989. METALLURGICAL TRANSACTIONS A
carbon powders (Ti3A1) are the top four ones in Table I and were solely used for filler material in the containers. For the central portions of the containers, which were subsequently analyzed and tested, the low-carbon powders were used. Erbium additions for a number of runs are intended to improve the high-temperature properties through the formation of erbium oxide.
B. Experimental Systems The experimental setup consisted of two coaxial tubes, the external one being accelerated inward to impact the internal tube that contains the powder. A detailed description of the system is presented elsewhere.iS1 The basic experimental system is shown in Figure 1, and this technique is called the flyer-tube or double-tube technique. The explosive charge (an ammonium nitrate-fuel oil (ANFO) mixture with 6 pct oil) is detonated at the top, and a DuPont DETA SHEET* (a 2-mm-thick PETN-based *DETA SHEET is a trademark of E.I. DuPont de Nemours & Co., Inc., Wilmington, DE.
plastic explosive) is used to create a more uniform detonation front. The explosive charge is contained in a polyvinyl chloride (PVC) plastic tube resting on a wood base and surrounds a mild steel flyer tube, in the center of which is the asse
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