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Presents a study which reported the results of audio frequency elastic measurements in the alloy series Fe[sub80-x]Ni[subx]Cr[sub20] through its various magnetic transitions. Method used in identifying and preparing the alloy; Evidence supporting prediction based on mean-field theories for sound propagation in spin glass.

Ferromagnetic shape memory alloys (FSMAs) have been in active research nowadays for their unique properties of responses to both temperature changes and external magnetic fields. Recently, one such material, a CoNiAl based system, showed a photoinduced microactuation (PIMA) effect in which an incident spot of a tiny laser beam could induce actuation in these systems. This is unparalleled in ordinary materials, and its real cause is yet to be found. However, we tried to still use it in real world engineering applications, and for that, the limitations on its usability should be found. With this idea, we studied here in detail the effect of continuous degradation of the PIMA effect on a ribbon sample through TEM, as it was exposed to higher temperatures from room temperature. While the as-spun alloy had microstructured B2 ordered (Ni, Co)-Al micrometer sized grains embedded in a continuous L12 ordered cobalt-rich matrix channel, at 400 °C where the PIMA effect was fully destroyed, Co-rich nanosized precipitates were found to have formed inside the B2 grains, the actual FSMA component in the sample, and these are also found to have been oxidized. Concurrent oxidation studies showed the formation of an irregular shaped composite oxide layer with a thickness of about several hundred nanometers at the top surface. These are possibly the reasons behind the hindrance in the actuating motion. This was corroborated by magnetic studies also. [ABSTRACT FROM AUTHOR]

A series of Al–Mgx alloys, with x = 0.82, 2.09, 2.28, 2.49 and 4.47 wt.%, respectively were characterized by using positron annihilation lifetime studies (PAL), X-ray diffraction (XRD), and sound velocity and internal friction using a vibrating reed technique (VRT). PAL lifetime values increase linearly as the composition is varied, but texturing or preferential orientation is maximum at an intermediate value of composition (x = 2.49%). The internal friction shows a minimum at the same composition, and the sound velocity changes show the maximum value here too. This means that at this composition the sample is the most ordered and defect free. [ABSTRACT FROM AUTHOR]

Disorder-to-order reaction in stoichiometric Ni[sub 3]V and Ni[sub 75]V[sub 21.5]Nb[sub 3.5] alloys involve a cubic (fcc)-to-tetragonal (D0[sub 22] structure) transformation. The structural changes occurring during the transformation result in a lamellar morphology of D0[sub 22] domains with {110}[sub fcc]-type interfaces. The propagation of stacking faults across domain boundaries in Ni[sub 3]V and Ni[sub 75]V[sub 21.5]Nb[sub 3.5] has been studied using transmission electron microscopy. Different modes of propagation of stacking faults across these boundaries have been observed. These modes have been attributed to the generation of appropriate glide partials at the domain boundaries. The nature and the Burgers vectors of the glide partials have been identified using visibility and invisibility criteria. Computer simulation results have been used to substantiate the results of contrast experiments. Dislocation reaction mechanisms responsible for the generation of these glide partials have been identified. In the present work, special emphasis has been laid on the propagation mode by which stacking faults cross the domain boundaries in the same glide plane. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the evolution of order in stoichiometric Ni–25at.%V alloys with different thermal histories. In these alloys, the face-centred cubic structure of the disordered matrix transforms to a tetragonal (D022) structure during ordering. In such types of transformation, the process of order evolution involves a number of nucleation and growth processes, which are often competitive in nature. In the present work, evolution of the order has been studied in two sets of samples, one in which samples were subjected to order annealing treatment in the “melt-spun state” and the other in which samples were annealed in the “solid solution state”. Different sequences of the order evolution have been observed in the two sets of samples. In the first set of samples, grain boundary aided heterogeneous nucleation and growth of ordered domains dominated the order evolution process, whereas in the second set of samples the intragranular nucleation and growth of ordered domains dominated the ordering process. As a manifestation of different evolution sequences, different morphological changes occurred in the two sets of samples. The difference in the evolution sequences has been rationalized on the basis of driving forces influencing the ordering transformation in the two cases. [Copyright &y& Elsevier]