In-situ determination of the HfO2 -Ta2O5 -temperature phase diagram up to 3000°C
The previously unknown experimental HfO2–Ta2O5‐temperature phase diagram has been elucidated up to 3000°C using a quadrupole lamp furnace and conical nozzle levitator system equipped with a CO2 laser, in conjunction with synchrotron X‐ray diffraction. These in‐situ techniques allowed the determination of the following: (a) liquidus, solidus, and invariant transformation temperatures as a function of composition from thermal arrest experiments, (b) determination of equilibrium phases through testing of reversibility via in‐situ X‐ray diffraction, and (c) molar volume measurements as a function of temperature for equilibrium phases. From these, an experimental HfO2–Ta2O5‐temperature phase diagram has been constructed which is consistent with the Gibbs Phase Rule.
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Publication Date:
NSF-PAR ID:
10084215
Journal Name:
Journal of the American Ceramic Society
ISSN:
1551-2916
5. The first in situ quantitative synchrotron X-ray diffraction (XRD) study of plastic strain-induced phase transformation (PT) has been performed on $\alpha-\omega$ PT in ultra-pure, strongly plastically predeformed Zr as an example, under different compression-shear pathways in rotational diamond anvil cell (RDAC). Radial distributions of pressure in each phase and in the mixture, and concentration of $\omega$-Zr, all averaged over the sample thickness, as well as thickness profile were measured. The minimum pressure for the strain-induced $\alpha-\omega$ PT, $p^d_{\varepsilon}$=1.2 GPa, is smaller than under hydrostatic loading by a factor of 4.5 and smaller than the phase equilibrium pressure by a factor of 3; it is independent of the compression-shear straining path. The theoretically predicted plastic strain-controlled kinetic equation was verified and quantified; it is independent of the pressure-plastic strain loading path and plastic deformation at pressures below $p^d_{\varepsilon}$. Thus, strain-induced PTs under compression in DAC and torsion in RDAC do not fundamentally differ. The yield strength of both phases is estimated using hardness and x-ray peak broadening; the yield strength in shear is not reached by the contact friction stress and cannot be evaluated using the pressure gradient. Obtained results open a new opportunity for quantitative study of strain-induced PTs andmore »