The Ordering of Ni₃V

Abstract

Stoichiometric Ni3V undergoes a cubic + tetragonal ordering transition (A1 + D O , ) by means of nucleation and growth. Electron diffraction microscopy and other experimental techniques reveal that the reaction is continuous, proceedind in three stages: I. Nucleation of coherent particles of the ordered phase in clusters of common orientation; 11. Growth of these clustered nuclei to impingement forming isolated cells of unique orientationeach cell is subdivided into anti-phase domains; 111. Growth of the celle to consume the remaining disordered phase, producing a mosaic substructure of mutually orthogonal cells, or "transformation twins". Severe internal strains develop during the sequence, and secondary structural changes, such as twinning and recrystallization, effect their relief.Stoichiometrisches Ni3V macht einen ttbergang (A1 + DO,,) von der kubischen zur tetragonalen Ordnung mittels Keimbildung und Wachstum durch. Elektronenbeugungsmikroskopie und andere experimentelle Methoden zeigen, daB dieser ProzeB in drei Stufen vor sich geht. I. Keimbildung kohiirent,er Partikel der geordneten Phase in Kluster mit gemeinsamer Orientierung. 11. Zusammenwachsen dieser Keime zu isolierten Zellen einheitlicher Orientierungjede Zelle ist unterteilt in Antiphasen-Domiinen. 111. Wachstum dieser Zellen bis zum Verschwinden der restlichen fehlgeordneten Phase, wobei eine Mosaik-Substruktur zueinander senkrechter Zellen oder ,,Transformations-Zwillinge" gebildet wird. Verschiedene innere Spannungen entwickeln sich wiihrend dieses Prozesses ; sekundiire Strukturveriinderungen wie Zwillingsbildung und Rekristallisation beeinflussen deren Relief.

High resolution study of ordering reactions in gold-chromium alloys

“…8c) shows the {100} and {110} superlattice reflections which do not exist after quenching. The diffraction pattern is similar to (12 spots are significantly weaker than {100} and {110} superlattice spots, which suggests that they originate from a different type of superlattice.…”

Vibrational entropy and microstructural effects on the thermodynamics of partially disordered and orderedNi3V

“…This is consistent with previous results of transmission electron microscopy studies that showed a ''tweed'' microstructure of quenched Ni 3 V. The tweed microstructure has a fine-scale distribution of internal strains, but no regions that are distinctly tetragonal. 17,21,22 Since the quenched sample had a high degree of the chemical order of the D0 22 structure, but none of the long-range tetragonality, we call it partially disordered.…”

“…The domains are mutually arranged in a microtwin-type microstructure to minimize the elastic energy. 17,18,21,22 Such a microstructure can be optimized to minimize elastic energy at only one temperature, however. With changes in temperature, the ordered domains expand or contract anisotropically, generating internal elastic energy owing to geometrical mismatch between the lenticular packets.…”

“…Tanner showed that the tetragonality of ordered Ni 3 V can vary from about 1 to 2 %, depending on the thermal processing. 17 ͑Our ordered alloy had a tetragonality of 1.7%.͒ Nonequilibrium tetragonalities require the presence of internal stresses. In Tanner's work, significant strain contrast was found in transmission electron micrographs of ordered Ni 3 V at room temperature, and others have reported large strain effects around Ni 3 V precipitates in Ni-V alloys.…”

“…In the present work we used differential scanning calorimetry to measure ⌬C p (T) for two states of the metallic alloy Ni 3 V. The material was quenched from high temperature to provide a state of partial disorder, which we confirmed to have strong chemical order, but none of the tetragonality of the equilibrium D0 22 structure. 17,18 The second state of the material was the D0 22 equilibrium structure, obtained by annealing the alloy.…”