Stability, phase transformation and deformation behavior of Ti-base metallic glass and composites

Melt-spun ribbons and copper-mold cast cylinders of (Ti0.5Cu0.23Ni0.2Sn0.07)(100-x)Mo-x bulk glass-forming alloys are prepared. Both Ti50Cu23N20Sn7 and (Ti0.5Cu0.23Ni0.2Sn0.07)(95)Mo-5 melt-spun glassy ribbons exhibit large supercooled liquid regions, high reduced glass transition temperatures, and good thermal stabilities. During continuous heating of the melt-spun ribbons, both alloys present a two-stage crystallization behavior. Mo slightly lowers the glass-forming ability but significantly decreases the temperature of the second stage crystallization. For both alloys, the stable phases after heating are Ti2Ni, TiCu, Ti3Sn and beta-(Cu,Sn). As-cast Ti50Cu23Ni20Sn7 cylinders contain dendritic hcp-Ti solid solution precipitates, as well as interdendritic glassy and Sn-rich crystalline phases. The ultimate compression stress reaches 2114 MPa with 5.5% plastic strain for 2-mm diameter cylinders. Yielding occurs at 1300 MPa, and Young's modulus is 85.3 GPa. Mo improves and stabilizes the precipitation of a beta-Ti solid solution but prevents glass formation in as-cast (Ti0.5Cu0.23Ni0.2Sn0.07)(95)Mo-5 bulk alloys. The bulk samples contain dendritic beta-Ti solid solution precipitates, Ti2Ni particles and Sn-rich phases. The ultimate compression stress is 2246 MPa with about 1% plastic strain for a 3-mm diameter cylinder. sigma(0.2) is about 1920 MPa and Young's modulus is 104 GPa. The high strength is attributed to both Mo solution strengthening and Ti2Ni particle strengthening. The limited ductility is induced by the precipitation of brittle Ti2Ni particles. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.