In situ synchrotron X-ray diffraction study of reaction routes in Ti-Al3Ti-based composites: The effect of transition metals on L12 structure stabilization

Abstract

In the last few decades, Ti-Al3Ti composites have attracted great attention due to their outstanding mechanical characteristics, such as low density, high specific strength and stiffness, and ballistic properties. However, their application is still limited due to the low ductility and fracture toughness of the Al3Ti phase. A promising way to improve the composite’s properties is to transform the Al3Ti crystal structure from the tetragonal D022 type to the cubic L12 type. In this study, the stabilization of the L12 structure of titanium trialuminide during the fabrication of the Ti-Al3Ti composite is discussed. For this reason, the method of in situ synchrotron X-ray diffraction analysis was used to observe the reactions in the ternary Ti-Al-M systems (where M is Zn, Au, Ag, Ni, Pd, Pt, Mn, Fe, Co or Cr) during heating from room temperature to 830 °С. Zn and Ag were found to be the most efficient stabilizers of the L12 structure. In composites alloyed with Fe, Co, and Cr, the L12 structure of Al3Ti was not stabilized. Formation of L12-structured titanium trialuminide in the remaining systems was accompanied by the formation of a large number of co-products. To select the elements stabilizing L12 structure in the composite with an excess amount of Ti, the following principle was formulated: the preferable stabilizers are the elements with FCC and HCP structures and a melting temperature below 1100 °С, and which do not form refractory Al-rich binary compounds with a melting point above 1000 °С.