抄録
Several workers(1)∼(5) have made crystallographic studies of ω phase in titanium alloys. Austin et al(1) and Frost et al(2) have reported that the ω phase is bcc with edge length three times that of the basic bcc cell. Silcock(3) and Bagaryatskii et al(4) have independently proposed a hexagonal structure oriented with respect to the β cell. An attempt was made to clarify the true ω structure. For this aim, a single crystal X-ray analysis has been carried out by using Ti-8.2%Mn and Ti-14.1%Mo alloys, and the precipitation in the Ti-Mo alloy has been observed by transmission electron microscopy. The results obtained are summarized as follows: (1) The Laue photographs obtained from aged crystals showed cubic Laue symmetry. As a result of detailed intensity measurements, it was comfirmed that the true ω structure is the hexagonal cell which has four orientations in each β cell with the relationship [111]β||[0001]ω; [1\bar10]β||[1\bar210]ω as proposed by Silcock. In this experiment, no reflection was observed from the relpoints of which calculated structure factors are equal to zero. Therefore, there is no need to consider the rampling plane proposed by Bagaryatskii et al, that is, the atomic positions may be 0 0 0; 1/3 2/3 1/2; 2/3 1/3 1/2 rather than 0 0 0; 1/3 2/3 0.48; 2/3 1/3 0.52. (3) As a result of transmission electron microscopic observation, it was found that the shape of ω particles is ellipsoidal. The major axis of the ellipsoid may be parallel to the ⟨111⟩β directions and oriented with four orientations.
