Tial Based Alloys Manufactured By Powder Metallurgy And Study Of Their Internal Friction

TiAl alloys are widely studied because their excellent properties of the alloy such as low density and resistance to high temperature oxidation, and have been potentially developed for use in light quality high-temperature material. However, the application of TiAl alloys is often restricted by the properties of their poor room-temperature ductility and strong resistance to deformation at high temperature. Powder metallurgy method can achieve fine and homogeneous grains and expected to solve the poor ductility at room-temperature and difficult processing problems. The method which composed the high-energy ball milling, cold compression, low-temperature presintering degassing and high-temperature reactive sintering, has been investigated to prepare Ti48Al(0-12)Nb alloys. Study focused on internal friction characteristics and its influencing factors of the non-pressure vacuum sintering Ti-Al based alloy.At first, The influences of the milling time on the particle size of milled composite powder and the density of the powder billets have been investigated to determine the optimum milling time for40h. At this point the powder particle size is about4μm, the relative density of the compacts up to85.65%by the pressure get to1200MPa. The result investigated the composition of milled powder show that Ti, Al particles are merely bonded into composite particles, TiAl-based intermetallic compounds was not found. At the same time, the densification behavior in the process of pressureless sintering was also investigated, and the result show that the smaller of the milled powder particles, the greater of the pressure the cold compacts, the higher of the sintering temperature, the more dense sintered body.Dynamic Mechanical Analysis (DMA) was used to investigate the internal friction of TiAl alloys. The influences of the milling process, the sintering process and the content of Nb on internal friction of the alloys were investigated, the studies of the friction-temperature curve show that the internal friction mechanism is dislocation type internal friction mechanism and the dislocation internal friction peak and grain boundary internal friction peak were found near178℃and248℃respectively within friction-temperature curve. The internal friction (including the peak location and peak value) was affected by the powder particle size, the density of powder billets and the sintering temperature, the aging, the Nb dosage and other factors.