Porous Ti6Al4V alloys with high strength-to-modulus ratio fabricated by unidirectional freeze casting of SiC fiber-containing slurry

Abstract

Porous titanium alloys with high strength-to-modulus ratio are one of the promising materials for bone implants. In the present work, porous Ti6Al4V alloys with SiC fiber bridges and fiber reinforced wall structure were obtained by unidirectional freeze casting of SiC fiber-containing slurry. The effect of SiC fiber content on the pore structure, microstructure, interface and compressive properties was systematically investigated. The formations of fiber bridges and fiber reinforced wall structure were elaborated through analyzing the interaction between fibers and ice front. Addition of SiC fibers has significant effects on the porosity, structural wavelength, and pore morphology of porous alloys. Porosity increases with the increase in fiber content, and pore morphology changes from lamellar to dendritic. Porous Ti6Al4V alloys mainly contain equiaxed α and β phase. Crystalline phases of Ti5Si3 and TiC are present at the interface. Micropores are also observed on the fiber side close to the interface due to the Kirkendall effect. Both Young's modulus and yield stress increase with the increase in SiC fiber content, while they dramatically decrease at higher fiber content of 10 vol%. SiC fiber bridges and fiber reinforced wall structure have synergetic strengthening effects for suppressing buckling deformation of lamellar walls and thus for improving the strength of porous titanium alloys. Porous Ti6Al4V alloys fabricated by 2 vol% SiC fibers possess high porosity of 67% and high strength-to-modulus ratio of 0.027.