The Effect of Heat Treatment on the Structure and Mechanical Properties of Nanocrystalline Cu–14Al–3Ni Alloy Subjected to High-Pressure Torsion

The effect of heat treatment on the microstructure, phase composition, mechanical properties, and microhardness of the shape-memory Сu–14 wt % Al–3 wt % Ni alloy prepared in the nanocrystalline state, which results from the severe plastic high-pressure torsion (HPT), is studied. Electron microscopy and X-ray diffraction analysis are used in combination with electrical resistivity measurements in order to obtain data on the peculiarities of thermoelastic martensitic transformations and decomposition in the HPT-processed alloy subjected to thermal actions.

A Reconfigurable Perovskite/Polymer Composite Film for Real-Time Detection of Agricultural Spraying

Responsive composites that can display sophisticated responses under environmental stimuli are of paramount importance for developing smart materials and systems. However, the hierarchical design of their multiscale constituents to achieve such response remains a challenge. Here, we report a responsive polymer composite obtained by integrating hierarchical interactions between the polymer network meshes, perovskite nanoinclusion, and a microstructured layout. More specific, a layered composite film has been made with perovskite nanoparticles embedded in a hydratable polymer network as the top layer. The perovskites inclusions can undergo a reversible transformation between a nanocrystalline state and a dissociated ion state, triggered by spraying aqueous solutions on the polymer top layer, resulting in an on/off switch of fluorescence at 510 nm. Meanwhile, the surface layer experiences a reconfigurable micro-wrinkling that can gradually change the film transmittance between 90% and 10%. The two orthogonal responses show a good reversibility for at least 15 cycles. They can be manipulated independently as they respond differently to the amount of water applied. We demonstrate the use of such film by real-time, quantitative, and repeatable detection of spraying and subsequent droplet distribution. Such a sensing capability is urgently needed in precision agriculture for fast assessing the deposition quality of pesticides and fertilizers, yet still not available. Our findings enable the design of perovskite-based responsive composites with multiple functions as well as novel device applications in sensors, actuators, and optoelectronics.

Structural and Phase Transformations and Physical and Mechanical Properties of Cu-Al-Ni Shape Memory Alloys Subjected to Severe Plastic Deformation and Annealing

Using the methods of electron microscopy and X-ray analysis in combination with measurements of the electrical resistance and magnetic susceptibility, the authors have obtained data on the peculiar features of pre-martensitic states and martensitic transformations, as well as subsequent decomposition, in the alloys with shape memory effect of Cu–14wt%Al–3wt%Ni and Cu–13.5wt%Al–3.5wt%Ni. For the first time, we established the microstructure, phase composition, mechanical properties, and microhardness of the alloys obtained in the nanocrystalline state as a result of severe plastic deformation under high pressure torsion and subsequent annealing. A crystallographic model of the martensite nucleation and the rearrangements β1→β1' and β1→γ1ꞌ are proposed based on the analysis of the observed tweed contrast and diffuse scattering in the austenite and the internal defects in the substructure of the martensite.

Microstructure, Grain Growth and Hardness of Nanostructured Ferritic ODS Steel Powder during Annealing

Nanocrystalline oxide-dispersion strengthened ferritic alloy formation and its annealing behavior were examined through modern X-ray diffraction pattern analysis and supplemented by microhardness and microscopic measurements. The basic microstructure features, with particular emphasis on evolution of domain size distribution and defect content during mechanical and thermal treatment, were quantified via the whole powder pattern modeling approach. The microstructure of the powdered alloy, formed during mechanical alloying, evolved toward nanocrystalline state consisting of narrow dispersion of very fine crystallites with substantial dislocation density, which exhibited relatively high stability against elevated temperature. It was shown that crystallite size is seriously sustained by the grain-boundary strain, therefore coarsening of grains begins only after the density of dislocations drops below certain level. Obtaining correct results for the annealing-related data at specific temperature range required the incorporation of the “double-phase” model, indicating possible bimodal domain size distribution. The dislocation density and grain size were found not to be remarkably affected after consolidation by hot isostatic pressing.

Magnetic Properties of Nanocrystalline (Nd,R)-(Fe,Co)-B (R = Pr, Ho) Alloys after Melt Spinning, Severe Plastic Deformation and Heat Treatment

Magnetic force microscopy (MFM) and magnetometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to study the magnetic and structural properties of the (Nd,Pr)-Fe–B and (Nd,Ho)-(Fe,Co)-B alloys. The alloys are synthesized using an arc or induction furnaces. The nanocrystalline state of the (Nd,Ho)-(Fe,Co)-B alloys is reached by two techniques, namely, melt spinning (MS) and severe plastic deformation (SPD). Hydrogenation and multistage treatment of (Nd,Ho)-(Fe,Co)-B alloys, which includes severe plastic deformation of melt-quenched ribbons and subsequent heat treatment, is also used. The surface morphology and domain structure of samples are studied. These pictures are used to interpret the observed magnetic hysteresis loops of the samples. It was found that multistage treatment allows one to obtain samples with higher values of coercivity due to the formation of a special microstructure with oval grain (the aspect ratio equal to ∼ 3).

Structural Changes of Co Caused a Change of the Solution pH During Chemical Deposition

The phase transformations of the Co lattice are discussed, which determine the anomalous changes in the magnetic properties of chemically deposited Co-P films obtained at various pH values. The coercivity of the Hc films obtained at low pH values exceeds 1 kOe and decreases to several units Oe in the films obtained at high pH values. It is shown that the observed changes in the magnetic properties of Co-P films are caused by the transition of the cobalt crystal lattice to the nanocrystalline state

Структурные особенности наноструктурного эквиатомного сплава TiNi при многократных мартенситных превращениях

The paper describes in detail a study dealing with the influence of multiple martensite transformations on the equiatomic alloy of the TiNi system microstructure. Thermocyclic treatment of the equiatomic alloy in the nanocrystalline state obtained by the intensive torsional plastic deformation method was carried out.

Possibilities of the Quantitative Comparison of Catalytic Capacity in Autocatalytic Processes of Palladium-Containing Nanocatalysts

When studying the nanocrystalline state, in some cases, an increase in functional activity is observed with an increase in the size of nanoparticles. In this case, the most active atoms are situated on the faces and have a higher coordination in comparison with the atoms on the tops and the edges. One of the explanations for this phenomenon is the formation of hypercycles due to the occurrence of autocatalytic processes. For oscillatory processes inherent in autocatalysis, when the parameters of a nonequilibrium process change over time, it is difficult to apply traditional methods of processing the results of analytical studies. In this regard, it is necessary to develop a methodology for a comparative study of short-term parameters of processes on the same scale, highlighting the main ones and eliminating insignificant and random ones, such as the phase shift at the beginning of self-oscillations or time-localized deviations from activity. This paper presents the results of such a study on the example of palladium-containing nanosystems in the reaction of low-temperature oxidation of CO. It is shown that the study of the behavior of nanocatalysts during the formation of hypercycles is informative using the calculated generalized parameters of the process

Wear and friction dependence on grain size

The tribological characteristics of pure metals and ceramics with graphene obtained by electrochemical, deformation and powder metallurgical methods are compared for a coarse-grained and nanocrystalline state. Reducing the grain size to the nanoscale region in the structure helps to reduce wear and friction coefficient compared to conventional analogues. The possibilities of modelling the contact of solids with the atomic structure of the surface are considered.