Crystallographic features of the $\alpha$-phase structure in hafnium and hafnium–titanium alloys

The structure of a hafnium crystal undergoing $\beta\to\alpha$ (bcc $\to$ hcp) polymorphic transformation upon gradual cooling and the structure of Hf$_{55}$Ti$_{45}$ and Hf$_{30}$Ti$_{70}$ alloys formed under various kinetic conditions of polymorphic transformation are studied. The structure of the $\alpha$ phase in cast hafnium is shown to consist of lath crystals grouped into packets. The misorientations between separate laths in a packet are less than 1$^{\circ}$. The Hf–Ti alloys in the cast state exhibit a mixed structure consisting of $\alpha$-phase crystals of several morphological types. A structure of packet martensite is observed in the Hf–Ti alloys after quenching. Each packet includes laths of several crystallographic orientations. There is no regular alternation of differently orientated laths in the packet. The same set of $\alpha$-phase orientations within an initial $\beta$-phase grain is observed independently of the cooling rate of the Hf–Ti alloys upon $\beta\to\alpha$ polymorphic transformation. The misorientation of substructural elements within an $\alpha$-phase crystal in the Hf–Ti alloys is $\sim$5$^{\circ}$ for the cast state and $\sim$2.2$^{\circ}$ after quenching.