Ordered Omega Derivatives in (Zr3Al)-Nb Alloys

1997 ◽  
Vol 481 ◽  
Author(s):  
R. Tewari ◽  
G. K. Dey ◽  
P. Mukhopadhyay ◽  
S. Banerjee ◽  
L. A. Bendersky
Keyword(s):  
Phase Separation ◽  
Isothermal Aging ◽  
Chemical Ordering ◽  
Vacancy Ordering ◽  
Structure Phase ◽  
Lattice Correspondence ◽  
Omega Transformation ◽  
Rapidly Solidified ◽  
Bcc Phase ◽  
Periodic Arrangement

ABSTRACTVarious kinds of phase transformations, viz., spinodal decomposition, omega transformation, precipitation reactions and martensitic transformation can be induced in ternary (Zr3Al) -Nb alloys in conditions far removed from equilibrium. Transformation sequences in alloys containing 3% niobium are described and rationalized in terms of some basic tendencies such as phase separation and chemical ordering in the β (bcc) phase and displacive omega and β to α (hcp) transformations. Microstructures of rapidly solidified alloy showed a distribution of cuboidal (D88 phase) particles in the β matrix. The periodic arrangement of these particles along the <100>β directions was indicative of a spinodal transformation which preceded their formation. The β → D88 transformation could be accomplished by the superimposition of three processes, namely, chemical ordering, lattice collapse akin to ω transformation and vacancy ordering. During isothermal aging the D88 phase transformed into the B82 phase. The observed lattice correspondence and transformation morphology suggested that the D88 to B82 structural change involved the replacement of structural vacancies in the former by zirconium atoms without any reconstitution of the lattice. The evolution of the equilibrium Zr3Al (L12 structure) phase during prolonged aging were also studied.

Microstructures in Rapidly Solidified Ll2-TYPE Ni-Al-Cr Alloys

1984 ◽  
Vol 39 ◽  
Author(s):  
S. C. Huang ◽  
K. M. Chang ◽  
E. L. Hall ◽  
R. F. Laforce
Keyword(s):  
Phase Separation ◽  
Cooling Rate ◽  
Phase Reaction ◽  
Microstructural Study ◽  
Melt Spun ◽  
Rapidly Solidified

ABSTRACTA microstructural study of the melt spun alloys Ni75 Al25. Ni72.5 Al22.5Cr5. and Ni67.5A120Cr12.5 was carried out. Variations in grain morpfology; phase separation and ordering structure were observed. The results are discussed in terms of alloy stoichiometry, Cr effect on phase reaction, microsegregation of Al and the cooling rate.

Influence of Ga Substitution on the Nature of Glasses in Zr69.5Al7.5-xGaxCu12Ni11 and Ce75Al25-xGax Metallic Glass Compositions

2015 ◽  
Vol 1757 ◽  
Author(s):  
R.K. Mandal ◽  
R.S. Tiwari ◽  
Devinder Singh ◽  
Dharmendra Singh
Keyword(s):  
Phase Separation ◽  
Metallic Glass ◽  
Enthalpy Of Mixing ◽  
Chemical Pressure ◽  
Valence States ◽  
Trivalent State ◽  
Rapidly Solidified ◽  
Ga Substitution ◽  
Glass Compositions

ABSTRACTIn this presentation, results of our recent investigations on the role of Ga on Al site in Zr69.5Al7.5-xGaxCu12Ni11 and Ce75Al25-xGax metallic glass compositions will be discussed. Ga like Al is normally expected to be in trivalent state. However, it may go in monovalent state depending on other alloying elements. The rapidly solidified melt spun ribbons of above two alloys gave rise to two important conclusions. The Zr69.5Al7.5-xGaxCu12Ni11 system displayed metallic glass formation in the range of x=0 to 7.5. In this process, we have come out with a new composition of glass without Al corresponding to x=7.5. In contrast to the above, for Ce-Al(Ga) system, we have observed phase separation in glass after dilute substitution of Ga. It seems that such a phase separation in this system cannot be understood in terms of summation of enthalpy of mixing of the various possible binaries in this system. The substitution of Ga in different valence states might have created chemical pressure leading to creation of two types of distinct major clusters. The phase separation may be due to this. This has also given rise to excursion of Ce 4f-states of the alloy. This and aforesaid ‘chemical pressure’ will be corroborated based on results of binary Ce-Al system under pressure by other investigators.

scholarly journals Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7 and RE2Th2O7 (RE=Ho, Y, Gd, Nd, La)

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Jonathan M. Solomon ◽  
Jacob Shamblin ◽  
Maik Lang ◽  
Alexandra Navrotsky ◽  
Mark Asta
Keyword(s):  
Dft Calculations ◽  
Density Functional ◽  
Waste Containment ◽  
Chemical Ordering ◽  
Oxygen Coordination ◽  
Vacancy Ordering ◽  
Trivalent Cations ◽  
Yield Values ◽  
Scattering Study ◽  
The Stability

Abstract Fluorite-structured oxides find widespread use for applications spanning nuclear energy and waste containment, energy conversion, and sensing. In such applications the host tetravalent cation is often partially substituted by trivalent cations, with an associated formation of charge-compensating oxygen vacancies. The stability and properties of such materials are known to be influenced strongly by chemical ordering of the cations and vacancies, and the nature of such ordering and associated energetics are thus of considerable interest. Here we employ density-functional theory (DFT) calculations to study the structure and energetics of cation and oxygen-vacancy ordering in Ho2Zr2O7. In a recent neutron total scattering study, solid solutions in this system were reported to feature local chemical ordering based on the fluorite-derivative weberite structure. The calculations show a preferred chemical ordering qualitatively consistent with these findings, and yield values for the ordering energy of 9.5 kJ/mol-cation. Similar DFT calculations are applied to additional RE2Th2O7 fluorite compounds, spanning a range of values for the ratio of the tetravalent and trivalent (RE) cation radii. The results demonstrate that weberite-type order becomes destabilized with increasing values of this size ratio, consistent with an increasing energetic preference for the tetravalent cations to have higher oxygen coordination.

Microstructure Formation and Nanoindentation Behavior of Rapidly Solidified Cu-Fe-Zr Immiscible Alloys

2020 ◽  
Vol 993 ◽  
pp. 39-44
Author(s):  
Xiao Jun Sun ◽  
Jie He ◽  
Jiu Zhou Zhao
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Secondary Phase ◽  
Atomic Ratio ◽  
Liquid Phase Separation ◽  
Miscibility Gap ◽  
Rapidly Solidified ◽  
Liquid Liquid Phase Separation ◽  
Zr Alloy ◽  
Liquid Miscibility Gap

The binary Cu-Fe system is characterized by a metastable liquid miscibility gap. WhenZr is added into the Cu-Fe alloy, the miscibility gap can be extended into Cu-Fe-Zr ternary system. In the present study Cu-Fe-Zr alloys were prepared by single-roller melting-spinning method, and the samples were characterized by the SEM, EDS, HRTEM and nanoidentation. The results show that liquid-liquid phase separation into CuZr-rich and FeZr-rich liquids takes place during rapid cooling the Cu-Fe-Zr alloy, and the mechanism depends on the atomic ratio of Cu to Fe. With increasing Zr content, the size of secondary phase formed by the liquid-liquid phase separation reduces to nanoscale. The structure with amorphous Cu-rich nanoparticles embedded in the amorphous Fe-rich matrix was obtained in the as-quenched Cu20Fe20Zr60 alloy. For its structure particularity of the Cu20Fe20Zr60 sample, mechanical evaluation was carried out by using nanoindentation.

Crystal structure phase separation in anion-deficient La0.70Sr0.30MnO3 − δ manganite system

2007 ◽  
Vol 1 (6) ◽  
pp. 705-710 ◽  
Author(s):  
S. V. Trukhanov ◽  
I. O. Troyanchuk ◽  
I. A. Bobrikov ◽  
V. G. Simkin ◽  
A. M. Balagurov
Keyword(s):  
Crystal Structure ◽  
Phase Separation ◽  
Structure Phase

scholarly journals Vacancy-mediated fcc/bcc phase separation inFe1−xNixultrathin films

2016 ◽  
Vol 94 (8) ◽  
Author(s):  
T. O. Menteş ◽  
N. Stojić ◽  
E. Vescovo ◽  
J. M. Ablett ◽  
M. A. Niño ◽  
...  
Keyword(s):  
Phase Separation ◽  
Bcc Phase
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