Omega phase of zirconium: Formation under shock wave compressin and stability at atmospheric pressure

Kutsar, A. R.; Lyasotski, I. V.; Podurets, A. M.; Sanches-bolinches, A. F.

doi:10.1080/08957959008246160

Cited by 16 publications

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“…The high melting point (2128 K) of Zr often classifies it as a refractory metal. Although there are some works in the high temperature behavior of zirconium at high pressures [8][9][10][11] , its melting curve has not yet been investigated and this absence of experimental data has strongly motivated this study. On the other hand, the high pressure melting of transition metals has always been a subject of intense debate, because of the large uncertainties in the temperature measurements and the criteria used to identify the melting, so that different approaches can yield very different results.…”

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confidence: 99%

Melting curve of elemental zirconium

2019

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Melting experiments require rapid data acquisition due to instabilities of the molten sample and optical drifting due to the high required laser power. In this work, the melting curve of zirconium has been determined for the first time up to 80 GPa and 4000 K using in-situ fast x-ray diffraction (XRD) in a laser-heated diamond anvil cell (LH-DAC). The main method used for melt detection was the direct observance of liquid diffuse scattering (LDS) in the XRD patterns and it has been proven to be a reliable melting diagnostic. The effectiveness of other melting criteria such as the appearance of temperature plateaus with increasing laser power is also discussed. PACS numbers: 92.60.hv, 61.50.Ks, 74.62.Fj, 81.30.Bx Zirconium (Zr) and its alloys have a very wide range of applications, from the chemical processing (as corrosion resistant materials) to the semiconductor industry 1 . Moreover, its good strength and ductility at high temperatures and the low thermal neutron cross-section absorption make it an ideal material for use as cladding at nuclear reactors 2 . Alloys of Zr with Cu, Al, Ti and Ni have been demonstrated to exhibit extraordinary glass forming ability 3 , while metallic glass formation in singleelement zirconium has also been discovered, with a wide stability in high pressure and temperature conditions 4 .Zirconium is a d-orbital transition metal with a rich and interesting phase diagram. At ambient conditions it crystallizes to an hcp structure (α-phase), while at temperatures higher than 1136 K it transforms to a bcc (β-) phase. By increasing pressure at ambient temperature it transforms to another hexagonal, but not close-packed, called the ω-phase and then back to β-phase around 35 GPa 5-7 . Similar transitions also occur in other group IV transition metals, such as Ti and Hf, and it seems that the electronic transfer between the broad sp band and the much narrower d band is the driving force behind those structural transitions.The high melting point (2128 K) of Zr often classifies it as a refractory metal. Although there are some works in the high temperature behavior of zirconium at high pressures 8-11 , its melting curve has not yet been investigated and this absence of experimental data has strongly motivated this study. On the other hand, the high pressure melting of transition metals has always been a subject of intense debate, because of the large uncertainties in the temperature measurements and the criteria used to identify the melting, so that different approaches can yield very different results. In most cases shock wave (SW) experiments and molecular dynamics (MD) calculations provide dramatically steeper curves than those obtained with the laser speckle method in a LH-DAC, where the melting is visually detected by observing the movements on the sample surface during heating. Tantalum is a good example of such a controversy, with melt-ing temperatures that differ thousands of K at 100 GPa by applying different experimental techniques [12][13][14][15] . Another more recent example is...

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Melting curve of elemental zirconium

2019

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“…1(b). Indexing of the thin section of shocked specimen shows that the experimentally observed Silcock orientation relationship [26,27] between α and ω (rather than unrotated α and ω) is obeyed (see Supplemental Material, Fig. S3 [21]).…”

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Collective nature of plasticity in mediating phase transformation under shock compression

et al. 2014

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An open question in the behavior of metals subjected to shock is the nature of the deformation that couples to the phase transformation process. Experiments to date cannot discriminate between the role of known deformation processes such as twinning or dislocations accompanying a phase change, and modes that can become active only in extreme environments. We show that a deformation mode not present in static conditions plays a dominant role in mediating plastic behavior in hcp metals and determines the course of the transformation. Our molecular dynamics simulations for titanium demonstrate that the transformation is preceded by a 90°lattice reorientation of the parent, and the growth of the reoriented domains is accompanied by the collective action of dislocations and deformation twins. We suggest how diffraction and transmission electron microscopy experiments may validate our findings. Materials dynamics, particularly the behavior of solids under extreme compression, is a topic of broad scientific and technological interest [1][2][3][4][5]. The shock impulse provides a unique probe to excite and thereby examine the response of materials to dynamic compression. It is well known that if a material undergoes shock compression beyond the Hugoniot elastic limit, it exhibits rapid plastic flow which is expected to occur via the generation and propagation of defects (twin, dislocations, etc.) [1,[6][7][8][9][10], and possible phase transformations [11][12][13][14]. In the presence of large peak stresses, strain rates, and significant inelastic strain due to shock, these plastic deformation modes can differ from those observed under longer time scales or more quasistatic conditions [1,6], and may interact with the phase transformations [15,16]. However, when solids undergo phase transformations, a key question is how these deformation modes mediate the phase transformation process.The group-IV hexagonal-close-packed (hcp) metals Zr, Ti, and Hf, with transition temperatures and pressures that are relatively accessible, have served as an excellent test bed for studying aspects of deformation and phase transformation behavior under driven conditions. For the α (hcp) to ω (hexagonal) phase transformation, progress over the last three decades from recovery experiments and analysis of wave profiles [17][18][19] has largely focused on capturing the behavior of the equation of state, orientation relationships in microstructures, understanding the influence of impurities such as oxygen, and characterizing the deformation. A number of studies have recognized that the plastic flow behavior as a result of the transformation is accompanied by twinning and slip under different loading and temperature conditions [18][19][20]. However, recovered samples under shock have invariably been for polycrystals and the deformation modes of twinning and

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“…The results of the ω-Zr phase stability tests are difficult to compare because they were performed by various methods. For example, the dilatometer method was used to study stability [26]. A more direct method was used by Brown et al [2].…”

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Zirconium Phase Transformation under Static High Pressure and ω-Zr Phase Stability at High Temperatures

et al. 2019

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High-purity Zr has been observed to undergo a phase transformation from the α-phase to the hexagonal ω-phase under high pressure generated either statically or by shock loading. The transition pressure from α-Zr to ω-Zr at 300 K is 2.10 GPa. The main aim of this research was to determine the conditions of α-Zr in ω-Zr transformation and the state of stresses after the high-pressure pressing and sintering of zirconium powders. Commercially acquired zirconium powders of 99.9% and 98.8% purity were used in this study. Qualitative and quantitative phase analysis of the materials was carried out using X-ray diffraction. The materials were statically pressed and sintered using a Bridgman-type toroidal apparatus at under 4.0 and 7.8 GPa. After pressing, the transformation proceeded for the zirconium powder containing 98.8% purity (with hydrides admixture) but did not occur for the high-purity zirconium powders with 99.9% purity. The zirconium powders were sintered using the HPHT (High Pressure—High Temperature) method at temperatures of 1273 K and 1473 K. The transformation proceeded for both powders. The highest contribution of the ω-Zr phase was obtained in the zirconium (98.8% purity with the hydrides contents) sintered for 1 min at a temperature of 1473 K and a pressure of 7.8. The ω-phase content was 87 wt.%. The stress measurement was performed for the pressed and sintered materials using the sin2ψ X-ray diffraction method. The higher sintering temperature resulted in a decrease of the residual stresses in the ω-Zr phase for the sintered zirconium. The higher levels of stress limited the transformation of the α-Zr phase into the ω-Zr phase. Investigated materials characterized by higher compressive macrostresses were also typical of the greater stability of the ω-Zr phase at high temperatures.

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Omega phase of zirconium: Formation under shock wave compressin and stability at atmospheric pressure

Cited by 16 publications

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Melting curve of elemental zirconium

Melting curve of elemental zirconium

Collective nature of plasticity in mediating phase transformation under shock compression

Zirconium Phase Transformation under Static High Pressure and ω-Zr Phase Stability at High Temperatures

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