MICROMORPHOLOGY OF THE SURFACE OF RAPIDLY QUENCHED HEUSLER- ALLOYS

В работе представлены результаты исследований микро- и наноструктуры поверхности быстрозакаленных лент сплавов Гейслера (NiMnAl,NiMn AlSi, NiCoMn Al) методами сканирующей электронной и атомно-силовой микроскопии. Рассмотрено влияние химического состава на размер, геометрию границ и структуру зерен. Показано, что все исследуемые образцы обладают наноразмерным мартенситным рельефом, определены его параметры. Установлено, что поперечное сечение лент представлено кристаллическими зернами разной формы и размера, что обусловлено отличием скоростей охлаждения по краям и в центре ленты. Проведено элементное картирование поверхности поперечного сечения лент с помощью рентгеновского энергодисперсионного спектрометра, установлено равномерное распределение химических элементов в образцах. Показано, что легирование лент состава NiMnAl кобальтом вызывает изменение микроморфологии поверхности и оказывает значительное влияние на ход полевых зависимостей намагниченности и доменную структуру образцов. The paper describes the results of the scanning electronic and atomic force microscopy research of the surface structure of the NiMn Al, NiMn AlSi, NiCoMnAl rapidly quenched ribbons. The influence of the chemical composition on the size, boundary geometry and structure of the grains is considered. It is shown that all the test samples have a nano-sized martensitic relief, and its parameters are determined. It has been established that the cross section of the ribbon is represented by crystalline grains of different shapes which are due to differences in the cooling rates along the edges and in the center of the samples. Elemental mapping of the cross-sectional surface of the ribbons was carried out using an X-ray energy dispersive spectrometer, and a uniform distribution of chemical elements in the samples was established. It is shown that the cobalt doping of NiMn Al ribbon causes changes in the micromorphology of the surface and has a significant effect on the magnetic properties of rapidly quenched ribbons: field dependences of themagnetization and domain structure.

A comparative investigation between ProTaper Next, Hyflex CM, 2Shape, and TF-Adaptive file systems concerning cyclic fatigue resistance

Background. This study aimed to compare the cyclic fatigue resistance of ProTaper Next, Hyflex CM, 2Shape, and TF-Adaptive nickel-titanium endodontic file systems with various alloy properties and production methods and investigate the fractured cross-sectional surface of files due to cyclic fatigue by scanning electron microscopy (SEM). Methods. A total of 120 instruments were used (n=30). For standardization, #25/.06 apical diameter and taper angle were selected for each file system. The experiment of files was subjected to a static cyclic fatigue model. The time for files’ failure was recorded with a digital chronometer and multiplied by the rotation speed to calculate the number of cycles. Kolmogorov-Smirnov, one-way ANOVA, and post hoc Bonferroni analysis were used for statistical analysis. Statistical significance was set at P<0.05. Results. The number of cycles for the failure of files was compared between the groups, and significant differences were found (P<0.05). The number of cycles for instrument failure was recorded from the highest to the lowest as follows: Hyflex CM, TF-Adaptive, ProTaper Next, and 2Shape. Conclusion. The files were fractured at different average numbers of cycles in an artificial canal in all the groups. The Hyflex CM demonstrated better cyclic fatigue resistance than TF Adaptive, ProTaper Next, and 2Shape file systems. Factors such as production patterns, alloy properties, and the phase in which the files were produced might affect the lifespan of file systems.

Анализ разрушения перлитной рельсовой стали с внутренней макротрещиной

One of the most dangerous defects leading to transverse fractures of rails is internal transverse cracks in the rail head. In this work, a fractographic analysis of the cross-sectional surface of a rail with a transverse fatigue crack is carried out. The rail sample was taken out of work after many years of service. Microstructural analysis of the crack surface and the surrounding material shows a significant degradation of the physical and mechanical properties of the rail steel.

Структурно-фазовое состояние металла рельса с внутренней трещиной после длительной эксплуатации

During operation, under cyclic force action, various physical and mechanical processes occur over time in the rail metal: plastic deformation of the rolling surface, the formation of internal and surface cracks, a change in residual stresses, etc. As a result, the mechanical characteristics deteriorate and the performance of the rails decreases. In this work, a microstructural analysis of the cross-sectional surface of two rails with internal cracks - longitudinal and transverse. Rail samples were taken out of service after many years of service. Fractographic analysis of the crack surface and the surrounding material indicates a significant degradation of the physical and mechanical properties of rail steel.

Fabrication of bulk aluminum-graphene nanocomposite through friction stir alloying

Friction stir alloying is primarily employed for the fabrication of surface composite to improve surface properties like hardness, wear resistance, and corrosion resistance without significantly affecting the bulk properties of the alloy. The present study demonstrates the novel method for the fabrication of bulk aluminum-graphene nanoplatelets composite by using friction stir alloying. Here, the novelty is shown through the method of graphene nanoplatelets incorporation in the stir zone. For this purpose, a channel is fabricated on the cross-sectional surface of the aluminum plate and filled with graphene nanoplatelets. It is then covered by the cross-sectional surface of another aluminum plate of same dimensions and friction stir alloying is carried out. Reference material (RM) is also fabricated at the same parameters without any graphene nanoplatelet reinforcements for the performance evaluation of the nanocomposite. The microhardness of the fabricated composite increased by ∼57% as compared to the reference material. However, the tensile strength of the fabricated Al-graphene nanoplatelet composites decreased marginally as compared to reference material. The strengthening of the composite is explained systematically by various mechanisms. The results of microhardness and tensile test were corroborated with various characterization methods such as optical micrographs, scanning electron microscopy, atomic force microscope, and X-ray diffraction.