Property-Control of Titanium Alloys by Spark Sintering

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The relationship between the number of pulses and the specific resistivity of titanium alloy compacts has been investigated to reveal the phenomena which are caused between powders in the early stage of the spark sintering process. The specific resistivity of the compacts decreased with the number of pulses. The reasons for the decrease of these values during pulse discharge are considered as follows : (1) The metallic contact area is created due to the dielectric breakdown of an oxide film on the powder surface. (2) The heat is generated due to a high current density in the metallic contact area which was already created between powder particles by initial compaction or the prior pulse discharges, and the metallic contact area is spread. It is suggested that the in situ sbility of dielectric breakdown between powder particles and the heat generation in the metallic contact area during pulse discharge process leads to improved particle sinterability.The investigations for property-control have been performed on titanium alloys such as Ti, Ti-6Al-4V,TiAl, Ti_3Al produced by spark sintering technique. Fine grained compacts are obtained by controlling of resistance sintering temperature, pressure and time. The mechanical properties such as tensile, impact and fracture toughness properties are revealed on the compacts with fine grains. Furthermore, specimens with high densities and approaching the equilibrium state can be obtained in a shorter time by spark sintering than conventional sintering. Such shorter high temperature exposure is important to prevent grain growth.