Characterization and mechanical properties of in situ synthesized Ti5Si3/TiAl composites

A series of composites of Ti₅Si₃/TiAl were synthesized by combination of mechanical alloying (MA) and hot isostatic pressing (HIPing). 20 h-milled powders of 65Ti-17Al-18Si (at.%) and 58Ti-21Al-21Si (at.%) were used as precursors incorporated into elemental 50Ti-50Al (at.%) powder matrices, followed by HIPing at 1100 °C and 150 MPa. Analyses by X-ray diffraction (XRD) as well as energy dispersive spectrometer (EDS) revealed the presence of three phases, namely, TiAl, Ti₃Al and Ti₅Si₃. Observations by optical microscopy (OM) and scanning electron microscopy (SEM) showed features of equiaxed grain matrix (TiAl) with a number of distributed large clusters and small particles of Ti₅Si₃. The size of scattered distributed particles was estimated to be less than 1 μm while the large clusters and matrix grains are in the range of 10-50 μm. The mechanical properties of composites were evaluated by micro- and nano-hardness measurements and compression tests at ambient temperature. The alloys exhibited significant compressive deformability (10-20%) and pronounced strain hardening. While the matrices exhibited hardness of 4-7 GPa, the distributed Ti₅Si₃ particles indicated hardness of 10-12 GPa. © 2003 Elsevier Science B.V. All rights reserved.