Microstructures and mechanical properties of explosively consolidated Ti powder with a pressure medium
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I.
INTRODUCTION
S H O C K consolidation has been highlighted as a consolidation technique for advanced materials powders such as rapidly solidified alloys tl-6] and amorphous [71 and ceramic powdersJ s,9,wl In particular, cylindrical axisymmetric explosive consolidation is known to be a suitable technique for producing a high density compact because of the simplicity and economy of the required assembly among the various shock consolidation techniques. Moreover, with this technique, processing time is short, and a high pressure is easily obtained. Good recovery of the compact is also advantageous, t~'~ Nevertheless, there have been some fundamental problems to overcome. They are the difficulty in producing a net-shaped compact and the formation of cracks and a central melt hole in the resulting compact.tl,6'~'12] These problems are mainly associated with the inhomogeneous transfer of shock waves resulting from their mutual interference and with the occurrence of "Mach stem" generated by the extremely high pressure due to the superposition of the shock waves at the center, tl,lll According to Wilkins, tt21 when the strength of "Mach stem" is too large, a central hole is drilled along the axis of the compact, as demonstrated by the melting of the material. Therefore, the required shock pressure for axisymmetric explosive consolidation is considered to be high enough to produce perfect compaction but not to generate the "Mach s t e m . "[l'll'12l M. NISHIDA, Associate Professor, A. CHIBA, Professor, and K. IMAMURA, Technician, are with the Department of Materials Science and Resource Engineering, Faculty of Engineering, Kumamoto University, Kumamoto 860, Japan. T. YAMAGUCHI and H. MINATO, formerly Graduate Students, Kumamoto University, are with Nippon Steel Corporation, Nagoya 476, and Kitakyushu 805, respectively, Japan. Manuscript submitted December 6, 1988. METALLURGICAL TRANSACTIONS A
In the present study, commercially available Ti powder was selected as consolidated material for a basic research of the explosive consolidation of Ti alloy powders. Explosive consolidation with a pressure medium was applied to the production of net-shaped compacts and to the prevention of cracking and "Mach stem" formation. The microstructural and mechanical characteristics of the resulting compacts were determined by density measurement, optical and transmission electron microscopy (TEM) observations, and tensile testing. II.
EXPERIMENTAL PROCEDURE
Irregular hydride-dehydride (HDH) titanium powders (TSP-350, produced by Osaka Titanium Co., Ltd., Amagasaki, Hyouyo 660, Japan) were used in this study. The powders were of a commercially pure grade, as indicated in Table I. Figure 1 shows scanning electron and optical micrographs of the titanium powders. The powders have angular or irregular shapes and contain a few grains. The large grains are about 2 5 / x m and the small ones about 10/zm. The quality of the compact is defined by the size, size distribution, and surface condition of the powders, t6'Hj However, from the practica
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