Papers by Keyword: β Grains

Abstract: The Ti-6Al-4V alloy were solution heat-treated at 960°C for 1 hour and then cooling by water-quenching immediately and 2 bar argon atmosphere, respectively. After being aged at 550°C for 5 hours, the tensile and Charpy impact test were performed. Based on the results, it is found that the quantity of primary α grains will increasing with decreasing the cooling rate following the solution heat treatment, and which will result in the tensile strength and toughness decreasing. Moreover, the optical and SEM micrographs indicated that the cracks propagated with traversing the prior β grains and propagating along the primary α grain boundaries in both of the tensile and impact fractured specimens. This implies that the strength of α grain boundary is less than that of α grain, which will play an important role on the mechanical properties of tensile strength and toughness.

Abstract: In titanium alloys it is known that in bulk sections the solidification conditions in ALM commonly lead to undesirable, coarse, columnar β grain structures. Here, we have investigated the effect of build geometry on the grain structure and associated texture in Ti-6Al-4V ALM components produced by Selective Electron Beam Melting (SEBM). Through reconstruction of the primary β-phase, it has been confirmed that in thick sections large columnar β grains grow with a strong <001>_β fibre texture, although there is a significant skin effect. In contrast, in thin walls nucleation off the surrounding powder and growth inwards dominates. Local heterogeneities are also observed within section transitions. It is shown that the weaker α transformation texture arises from a random distribution across the possible habit variants.