Synthesis and properties of an ultrafine grained Ti-45Al-2Cr-2Nb-1B-0.5Ta alloy prepared by double mechanical milling and spark plasma sintering

Ti-45Al-2Cr-2Nb-1B-0.5Ta (at.%) bulk alloys with dense and ultrafine grains were fabricated by Double Mechanical Milling (mechanical milling + heat treatment + mechanical milling) and spark plasma sintering method. The phase composition and microstructure Of the milled powder and bulk alloy sintered by SPS at different temperature (900 degrees C, 1000 degrees C and 1100 degrees C), and the relationship between microstructure and properties of bulk alloys were investigated. The results demonstrate that high-quality composite powders (low contaminant, size uniform distribution and elements homogeous dispersion) call be obtained by double mechanical milling. The composite powders prepared by primary mechanical milling were uniform and partially solid Solution. Ti3Al, Ti, Al3Ti and TiAl phases were found after heat treatment while Al phase disappeared. The filled grain size and particle size were achieved by subsequent mechanical milling, The whole mechanical milling leads to alloying and the refined grain and particle, which also Cause lattice distortion and powders system energy increased. SPS results showed that the densified and ultrafine grained Ti-45Al-2Cr-2Nb-1B-0.5Ta alloy is mainly consisted of TiAl, Ti3Al phase and a small quantity of TiB2 phase. With the increasing of sintering temperature, grain size of TiAl based alloy increase. The mechanical properties depend on microstructure and grain size. The relationship between compression properties, bending properties and microstructure was discussed.