The Effect of the Oriented Structure on Mechanical Properties of Titanium Aluminide Fabricated by Electron Beam Melting

Abstract

This study was conducted to reveal the relationship between the oriented microstructure and mechanical properties of Ti-48Al-2Cr-2Nb fabricated by electron beam melting (EBM). The microstructure observation in EBM sample showed that duplex structure/γ band layers fabricated by EBM process.

Tensile and creep tests were conducted for two kinds of samples fabricated by EBM. One was a sample in which loading direction was parallel to the building direction (vertical sample) and another was sample in which the loading direction was normal (horizontal sample). The tensile test showed anisotropic tensile properties at room temperature, 650℃ and 750℃. The tensile strengths of the vertical samples were inferior to the horizontal samples due to the oriented duplex structure with γ band layers. The creep lives were 206 h tested at 650℃/450 MPa and 298 h tested at 750℃/200 MPa in the vertical sample, whereas they were 332 h tested at 650℃/450 MPa and 326 h tested at 750℃/200 MPa in the horizontal sample; i.e., the creep test also showed the anisotropy of creep rupture life due to the oriented microstructure.

As-built sample fabricated by electron beam melting (EBM) showed the anisotropy in tensile and creep properties of Ti-48Al-2Cr-2Nb alloy. Fig. (a) and Fig. (b) show the tensile properties of vertical and horizontal samples tested at room temperature, 650℃ and 750℃, and the creep curves tested at 650℃/450 MPa, respectively. The creep-ruptured surface showed the fine facets in the vertical sample (Fig. (c)) and the dimples in the horizontal sample (Fig. (d)).