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A concise review of the applications of NiTi shape-memory alloys in composite materials Composite materials have increasingly been used in construction and in the aerospace and automotive industries because they are lightweight, strong and corrosion resistant, and because their anisotropic properties can be controlled; maintenance costs are also low. However, there is a growing demand for improved composite materials which have 'smart' capabilities, that is, they are able to sense, actuate and respond to the surrounding environment. Shape-memory alloys (SMAs) possess sensing and actuating functions. Embedding SMAs into composite materials can create smart or intelligent composites. Amongst the commercially available SMAs, NiTi alloys-in the form of wires, ribbons or particles-are the most widely used because of their excellent mechanical properties and shape-memory performance. These materials have found application in broad fields of engineering and science as a result of their superior thermomechanical properties. Here we review the use of NiTi SMAs in applications such as vibration control, shape control, position control and adaptive stiffening. General properties of NiTi shape-memory alloys NiTi SMAs can exist in two crystal phases: (1) the stronger austenite (or parent) phase which is stable at high temperatures and (2) the softer martensite (product) phase which is stable at low temperatures. 7 The NiTi SMA in its martensitic phase can be easily deformed because of its relative softness. The austenite phase has a well-ordered body-centred cubic structure that presents only one variant. The martensite phase has a lower symmetry and may exist in multiple variants depending on the type of phase transformation. Therefore, although there are several ways by which martensite can be formed out of austenite, there is only one route by which the martensite formed will revert to austenite. The understanding of the characteristics of NiTi SMAs such as SME and pseudoelasticity, is important in the design and implementation of NiTi-based devices.

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In this study the friction-stir processing (FSP) technique was applied for the development of surface composites of aluminium alloy (AA 1050) reinforced with titanium carbide (TiC) powder of particle size range below 60 μm compressed into the groove. Rotational speeds of 1200 min -1 and 1600 min -1 and the travel rates of (100, 200 and 300) mm/min were used for the process. This study investigates the effect of processing parameters on the wear-resistance behavior of friction-stir processed Al-TiC composites. This was achieved through microstructural characterization using optical and scanning electron (SEM) microscopes equipped with Oxford energy-dispersion spectrometry (EDS) (Tescan), microhardness profiling and wear resistance tests. From the results, it was found that the processing parameters influenced the distribution of the TiC particles. The microhardness profiling of the processed samples revealed an increase in the hardness value compared to the parent material. The wear-resistance test results confirmed the FSP technique enhanced properties in surface engineering. Keywords: aluminium alloy, friction-stir processing, microhardness, microstructure, surface composite, TiC V {tudiji je bila uporabljena tehnika me{anja s trenjem (angl. FSP) za razvoj povr{inskih kompozitov iz aluminijeve zlitine (AA 1050), oja~anih s titanovim karbidom (TiC) v prahu, z velikostjo delcev v obmo~ju pod 60 μm, stisnjenih v utor. Pri tem postopku so bile uporabljene hitrosti vrtenja 1200 min -1 in 1600 min -1 in hitrosti pomikanja (100, 200 in 300) mm/min. [tudija raziskuje vpliv procesnih parametrov na odpornost kompozitov Al-TiCi proti obrabi s trenjem. Izvedena je bila mikrostrukturna karakterizacija z uporabo svetlobnega in vrsti~nega elektronskega mikroskopa (SEM), opremljenega z Oxford energijsko disperzijsko spektrometrijo (EDS) (Tescan), profiliranja mikrotrdote in preizkusa obrabe. Iz rezultatov je bilo ugotovljeno, da so parametri obdelave vplivali na distribucijo TiC delcev. Profiliranje mikrotrdote na vzorcih je pokazalo, da je vrednost trdote pove~ana v primerjavi z osnovnim materialom. Rezultati testa odpornosti obrabe so potrdili, da FSP-tehnika izbolj{a lastnosti povr{ine.

Equal channel angular pressing is one of the techniques in metal forming processes in which an ultra-large plastic strain is imposed on a bulk material in order to make ultra-fine grained and nanocrystalline metals and alloys. The technique is a viable forming procedure to extrude materials by use of specially designed channel dies without substantially changing the geometry by imposing severe plastic deformation. This technique has the potential for high strain rate superplasticity by effective grain refinement to the level of the submicronscale or nanoscale. We review recent work on new trends in equal channel angular pressing techniques and the manufacturing of die-sets used for the processing of metals and alloys. We also experimented on a copper alloy using the equal channel angular pressing technique to examine the microstructural, mechanical and hardness properties of the ultra-fine grained and nanocrystalline materials produced. After deformation, all samples were subjected to a hardness test and the results showed improved mechanical behaviour of the ultra-fine grained copper alloy that was developed. This research provides an opportunity to examine the significance of the equal channel angular pressing process for metals and alloys. That is, these ultra-fine grained materials can be used in the manufacturing of semi-finished products used in the power, aerospace, medical and automotive industries.

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Purpose The nuclear battery technology depends on the spontaneous decay of the atomic nuclei of radioactive isotopes to generate electricity. One of the merits of a nuclear battery is its high-energy density, which can be around ten times higher than that of hydrogen fuel cells and a thousand times more than that of an electrochemical battery. A nuclear battery has an extremely long life and low maintenance and running costs coupled with applications in remote and hostile environmental environments. The rise of silicon technology has intensified research activities in the area of nuclear batteries. The paper aims to present a general overview of a nuclear battery. Design/methodology/approach This paper presents a general overview of a nuclear battery and will significantly reduce reliance on non-renewable energy source. The requirement for long-lived power supplies have necessitated the pragmatic shift toward the realization of cleaner, safer and renewable energy sources. Findings Nuclear battery is a safe enabling technology for many applications including military and commercial applications. They have very long operating life under harsh environmental conditions. These cells demonstrate high potential for use in low power applications under a broad range of temperatures. Originality/value The nuclear battery technology has been receiving considerable in-depth research for applications that require long-life power sources.

PurposeSevere plastic deformation (SPD) has provided new opportunities in investigations of enhanced mechanical properties like high strength and ductility by permitting grain refinement to a nanometer level, especially ultra‐fine grained and nanocrystalline metals and alloys. These materials have been attracting more and more research interest during the past few decades due to scientific curiosity and their engineering potentials with a significant advancement in their understanding. The purpose of this paper is to find the relationship between processing, structures and properties of these novel materials with the ultimate goal of producing a model to account for the grain size changes at the nano‐scale.Design/methodology/approachIn this paper, specimens with various grain sizes from 23 to 80 μm are obtained via processing by SPD, using equal channel angular press (ECAP) technique. The effect of grain size on the hardness properties of nanostructured copper alloy has been investigated using micro‐hardness testing of the samples to test the mechanical properties of this material.FindingsThe results reveal that the copper alloys processed by SPD using ECAP technique after various passes differ in the grain size and mechanical properties. The hardness test exhibits grained size dependence according to Hall‐Petch relationship from room temperature. The increase in the hardness with number of passages suggest increasing in strain during deformation, as the passes increase the smaller grain size can be produced.Originality/valueThe paper usefully shows how nanostructured materials by SPD technique will offer a possible solution to the problem of using light metals for certain applications by increasing the strength of materials which could be used in structures where previously strength requirement in various industries, including such as, for example, transportation, medical devices and electronics. Understanding the relationship between processing, structures and properties will enhance the performance of metals and alloys in a target application which is important in improving the mechanical properties of engineering materials that are necessary fundamental for applications of lightweight materials and structures. The influences of structural parameters, such as grain size, grain shape on plastic deformation which is important parameters in study the mechanical properties of nanostructured materials.