Microstructure and mechanical properties of an ultrafine Ti-Si-Nb alloy

Nb-modified ultrafine Ti-Si eutectic alloy was made by cold crucible levitation melting, tested in compression at room temperature, and characterized by electron microscopy. Compression tests of (Ti86.5Si13.5)97Nb3 specimens measured an ultimate compressive strength of 1180 MPa and a compressive plastic strain of 12%, both of which are higher than in eutectic Ti86.5Si13.5 alloy. Electron microscopy showed that the Ti-Si-Nb alloy had a bimodal microstructure with micrometer-scale primary α-Ti dendrites distributed in an ultrafine eutectic (α-Ti + Ti5Si3) matrix. The enhanced ductility is attributed to the morphology of the phase constituents and to the larger lattice mismatches between α-Ti and Ti5Si3 phases caused by the Nb addition. The crystallographic orientation relationship of Ti5Si3 with α-Ti is (11¯00)[1¯1¯26]Ti5Si3‖(011¯1)[51¯4¯3¯]α−Τi.