Property-Control of Titanium Alloys by Spark Sintering

研究了脉冲次数与钛合金压坯比电阻率之间的关系，揭示了电火花烧结早期粉末之间的现象。压坯的比电阻率随脉冲次数的增加而减小。脉冲放电过程中这些值减小的原因如下：(1)由于粉末表面氧化膜的介质击穿而产生了金属接触区。(2)由于初始压实或之前的脉冲放电在粉末颗粒之间已经产生的金属接触区中的高电流密度产生了热，并且金属接触区被扩散。研究表明，脉冲放电过程中粉末颗粒间介电击穿的原位稳定性和金属接触区的生热作用可以改善颗粒的烧结性。对采用电火花烧结技术制备的钛合金进行了性能控制研究。通过控制电阻烧结温度、压力和时间，可以得到细晶的压坯。研究了细晶压坯的拉伸、冲击和断裂韧性等力学性能。此外，与常规烧结相比，火花烧结可以在更短的时间内获得密度较高的接近平衡状态的样品。这种较短的高温暴露对于防止晶粒长大很重要。

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.