Phase transformation and mechanical properties of as-cast Ti41.5Zr41.5Ni17 quasicrystalline composites

Abstract

Phase transformation behavior of the quasicrystalline icosahedral phase (I-phase) and mechanical properties in a Ti41.5Zr41.5Ni17 alloy have been investigated using suction-casted bulk samples with various sample sizes (ϕ = 2, 3 and 5 mm). For 2 and 3 mm diameter rod samples, micrometer size dendritic β-(Ti,Zr) phases are precipitated in the matrix and continuously I-phases are developed in the vicinity of the primary β-(Ti,Zr) phases. With further increase of the sample size (i.e. decrease of cooling rate; ϕ = 5 mm), the length scale and volume fraction of primary β-(Ti,Zr) dendritic phase are continuously increased and the constitution of matrix phase is changed from I-phase to eutectic lamella composed of bcc β-(Ti,Zr) and hcp C14 Laves phases. The characterization of mechanical properties was carried out by compression and microhardness tests at room temperature. Depending on the selection, size and volume fraction of constituent phases, the values of hardness and compressive fracture strength are varied. The fracture surface morphologies of failed samples exhibit cleavage and quasi-cleavage patterns revealing the typical brittle failure characteristics.