Does Bulk Metallic Glass of Elemental Zr and Ti Exist?

To verify the high-pressure formation of the bulk metallic glass in elemental Zr and Ti, which Zhang and Zhao [Nature (London) 430, 332 (2004)] and Y. Wang et al. [Phys. Rev. Lett. 95, 155501 (2005)] recently reported, the high-pressure states were investigated by our newly developed in situ angle-dispersive x-ray diffraction using a two-dimensional detector and x-ray transparent anvils. Despite the disappearance of all the Bragg peaks in the one-dimensional energy-dispersive data, two-dimensional angle-dispersive data showed several intense Bragg spots even at the conditions where the amorphization was reported. This finding suggests that Zr and Ti do not transform into an amorphous state, but that their grain size becomes large, which causes the missing Bragg peaks in energy-dispersive data.

Figure 1

Schematic view of the experimental setup in the angle- and energy-dispersive x-ray diffraction methods.

Figure 2

X-ray diffraction profiles of Zr at high pressures and high temperatures obtained in an energy-dispersive mode. Starting material ($\alpha$ phase) transformed into the $\omega$ phase near 4 GPa. Then all the Bragg peaks disappeared at 7.7 GPa and $650°\mathrm{C}$ as if it had transformed into an amorphous state. The profiles were collected for an exposure time of 100 sec. It is noteworthy that the intensity of the baseline is maintained while heating from $600°\mathrm{C}$ to $700°\mathrm{C}$.

Figure 3

X-ray diffraction images of Zr and Ti at high pressures and high temperatures obtained in an angle-dispersive mode. (a) Complete Debye rings from the $\omega$-Zr at 8.3 GPa and $500°\mathrm{C}$. (b) Phase transition to the $\beta$-Zr begins at 8.3 GPa and $650°\mathrm{C}$. (c) Bragg spots from the $\beta$-Zr at 8.1 GPa and $700°\mathrm{C}$. Debye rings are from boron and hexagonal boron nitride. The strip along the vertical axis represents the region where the diffraction data is obtained in the energy-dispersive measurement. (d) X-ray diffraction image of Ti at 10.7 GPa and $1050°\mathrm{C}$. Debye rings are from boron and hexagonal boron nitride.

Figure 4

Diffuse scattering intensity of bcc Zr at 7.5 GPa and $1000°\mathrm{C}$ and that of bcc Ti at 10.4 GPa and $1000°\mathrm{C}$. Arrows on the abscissa show $Q$ positions that correspond to $\frac{2}{3}\sqrt{3}|a^{*}|\times n$ ($n$ is an integer).