We have reported that isothermal aging of Ni-rich Ti-Zr-Ni alloys leads to a development of diffuse scatterings in electron diffraction patterns (SADP) followed by fine precipitation. Present research focuses on the precipitates structure and chemical composition.
A Ti-6.0mol%Zr-52mol%Ni ingot was prepared by tri-arc melting method and homogenized for 7 days at 1073 K. Isothermal aging was carried out for temperatures ranging from 673 to 823 K with maintaining times between 3.6 and 360 ks. HRTEM and chemical composition investigations were done using JEOL JEM-2010F equipped with energy dispersive X-ray system and Hitachi H-1500 operated at 800 kV.
The samples aged at 673 K up to 216 ks revealed diffuse scattering rings surrounding the matrix B2 spots in the SADP. However, fine spherical nano-size precipitates (~ 5 nm) were seen in the samples treated for 360 ks at 673 K. Lenticular precipitates with a diameter of ~ 35 nm and approximate 7 nm thick were observed for aging at 773 K for 144 ks. The <001>B2 SADP exhibits sharp satellite reflections at 1/3<110>B2 and diffuse satellites at 1/4<210>B2 elongated in <100>B2 directions. HRTEM investigations revealed the sharp satellite spots are given by the precipitates with the habit plane normal to the electron beam. Additional analysis of <011>B2 and <111>B2 SAD patterns indicate that additional reflections originate from 3 variants of the precipitates. Their Zr content is 16 ± 1.5 mol%, while Ti content stands at 31 ± 1.2 mol%. Ni concentration was slightly higher than that of the matrix.