Microstructural stability, phase evolution and mechanical properties of a forged W-modified high-Mn β-γ-TiAl alloy

Abstract

The effects of W on the microstructure and tensile properties of two high Mn-containing β-γ TiAl alloys (nominal composition is Ti–42Al–5Mn and Ti–42Al–5Mn-0.8 W (at.%)) prepared by vacuum induction melting and conventional forging process were systematically investigated. The results showed that there were coarse columnar lamellar colonies in the as-cast W-free alloy, but in the W-added alloy, the microstructure was relatively uniform without the presence of coarse columnar lamellar colony. After forging, the two alloys were all nearly lamellar structure. With W addition, the lamellae size was reduced and the volume fraction of lamellar colonies was slightly decreased whereas the contents of βo and γ phases around the lamellar colony were increased. The partitioning behavior of W has also been investigated which was in the order of βo>α2>γ in Ti–42Al–5Mn-0.8 W. The research results also proved that W addition had little effect on the distribution behavior of Ti and Al in γ and α2, whereas it has pronounced impact on that of Mn, Ti and Al in βo. Under 800 °C ageing conditions, a large amount of granular Laves (Ti(Al,Mn)2) phase precipitated from βo phase in the as-forged W-free alloy, which resulted in the brittle fracture at room temperature. On the contrary, the microstructure and tensile properties of the W-added alloy remain relatively stable with only a small amount of Laves phase observed, most of the βo phase remained unchanged in the ageing samples. The Laves phase suppressed in W contained alloy are mainly due to the influences of W on the distribution of Mn in the βo, and the diffusion and enrichment behavior of Mn during ageing.