Local microstructural modification in dynamically consolidated metal powders
- PDF / 5,134,597 Bytes
- 12 Pages / 594 x 774 pts Page_size
- 75 Downloads / 194 Views
I.
INTRODUCTION
D Y N A M I C consolidation is currently of considerable interest as a means of forming monolithic bodies from rapidly solidified or metastable powders. ~ ~0The technique, in which shock waves are used to mechanically drive the powder to high density, is unique in that energy is deposited primarily at particle interfaces. 1~ This can restrict accompanying microstructural changes in powder particles to the near-surface region, producing localized melting and phase transformation ~-7 without substantial alteration of the interior. In this paper, the microstructures of dynamically compacted 4330V steel, aluminum-6 pct silicon, and copper powders, formed under well-characterized conditions, are presented and discussed in terms of an energy flux model of energy deposition during consolidation. H'~2 The experiments explore a range of relevant compaction conditions and material and powder properties. The material characteristics and experimental details are first briefly considered, followed by a presentation of the microstructural observations. These observations are analyzed in terms of both the known shock history of the specimens and the energy deposited in the powder. The implications of the observations and analysis are then discussed, with particular regard to the influence of powder characteristics on the final microstructure.
II.
EXPERIMENTAL
A. Starting Materials Three powders were studied: inert gas atomized 4330 vanadium-modified steel (4330V), ultrasonically atomized aluminum-6 pct silicon alloy, and irregular copper. These were chosen to represent a range of material and powder characteristics, summarized in Tables I and II, respectively.
W.H. GOURDIN is a Physicist with Lawrence Livermore National Laboratory, Livermore, CA 94550. Manuscript submitted October 31, 1983. METALLURGICAL TRANSACTIONS A
Dynamic consolidation of a spherical copper powder is considered elsewhere. H,~3 1. 4330V The optical microstructure of the as-received 4330V powder is shown in Figure 1 and consists of fine laths of martensite similar to those observed in oil-quenched 4340 steels.~4 X-ray diffraction analysis shows a small amount of retained austenite as well. Scanning electron micrographs reveal a generally spherical particle shape, with small (5 to 20/zm) spherical nodules on the surface of many powder particles (Figure 1). These nodules apparently separate individual particles, an effect which, together with a limited size distribution, reduces the packing density to only 50 pct of the solid density (Table II). 2. Aluminum-6 pct silicon The structure of the aluminum-6 pct silicon alloy powder is shown in Figure 2. Surface nodules are present, as in the steel, but the large fraction of fine particles yields a higher packing density (Table II). The optical microstructure consists of a distinctive pattern of silicon precipitates surrounding aluminum cells. X-ray diffraction analysis indicates that the amount of silicon in solid solution in these cells does not exceed the maximum equilibrium solid solubility,
Data Loading...
