Perturbed angular correlation studies of uniaxial compressive stressed zinc, titanium, rutile, Ti₂AlN, and Nb₂AlC

Abstract

We use the perturbed angular correlation method with (111)In-(111)Cd probe atoms to in situ study the changes in the electric field gradient at room temperature of polycrystalline Ti(2)AlN and Nb(2)AlC, titanium and zinc, and rutile samples, as a function of cyclic uniaxial compressive loads. The load dependence of the quadrupole coupling constant νQ was found to be large in titanium and zinc but small in Ti(2)AlN, Nb(2)AlC and rutile. Reversible and irreversible increases in the electric field gradient distribution widths were found under load and after releasing the load, respectively. Annihilation of dislocations, as well as elastic deformation, are considered to contribute to the reversible behavior. The irreversible response must be caused by a permanent increase in dislocation and point defect densities. The deformation induced broadening of the electric field gradient can be recovered by post-annealing of the deformed sample.

Determination of gradient elastic tensors: stress and strain dependencies of electric field gradients in cubic and hexagonal systems

“…The experimentally deduced broadening parameter has been the standard deviation of a Gaussian distribution δ around the mean EFG [16] which causes some problems in the comparison with the values calculated here. A simple Gaussian distribution cannot correctly reproduce the asymmetric PDF of V zz in a polycrystalline material under uniaxial load.…”

“…Quantities which are derived from the gradient elastic tensor, like the stress dependence of the EFG under isostatic pressure or uniaxial pressure in polycrystalline materials, have been measured with PAC in many hexagonal systems [2,[13][14][15][16] without knowledge of the corresponding gradient elastic constants. However, it is the exact knowledge of these constants which allows to explain aforementioned dependencies and, in addition to it, to gain further information about the studied materials as for instance about intrinsic strains in thin films [12] and quantum dots [17][18][19] or dislocation and point defect densities [3,20,21].…”

“…MAXphases, a class of ternary carbides or nitrides, in which a complex crystallographic structure comes along with a lack of macroscopic single crystalline samples [22]. Knowledge about their gradient elastic constants would allow to in-situ monitor dislocation densities under cyclic deformation from which the understanding of the deformation behavior could significantly be improved [16].…”

Elektrische Quadrupolwechselwirkung in defektreichen und deformierten MAX-Phasen

“…Während sich Titan ab dem Erreichen der Streckgrenze über den gesamten Messbereich plastisch verformt, verhalten sich Zink und insbesondere die MAX-Phasen nur sehr begrenzt duktil. Durch die flache Geometrie lassen sich jedoch selbst dann noch PAC-Spektren aufnehmen, wenn a Dieses Kapitel basiert im Wesentlichen auf Ergebnissen, die in Referenz [194] veröffentlicht wurden. Wirtsgitter grund der ungenügenden Dehnungsbestimmung wird auf einer Untersuchung der Dehnungsabhängigkeit der jeweiligen Parameter verzichtet.…”

“…Unter Ausnutzung der Proportionalität der Fließspannung zur Wurzel der Versetzungsdichte [67] und der eben gleichen Abhängigkeit der EFG-Verteilungsbreite (siehe Kapitel 4.2) wird eine lineare Abhängigkeit der Dämpfung mit der Spannung erwartet [91]. Dies steht im Einklang zum beobachteten irreversiblen Anstieg a Dieses Kapitel basiert im Wesentlichen auf Ergebnissen, die in Referenz [194] veröffentlicht wurden.…”