Papers by Keyword: Metallic Alloys

Abstract: The manner of studying of the fracture modes could be done through fractography. Fractography is the study of fracture surface morphologies and it gives an insight into damage and failure mechanisms, underpinning the development of physically-based failure criteria. In composites research it provides a crucial link between predictive models and experimental observations. Fractographic methods are routinely used to determine the cause of failure in all engineering structures, especially in product failure and the practice of forensic engineering or failure analysis. In material science research, fractography is used to develop and evaluate theoretical models of crack growth behavior. One of the aims of fractographic examination is to determine the cause of failure by studying the characteristics of a fracture surface. Different types of crack growth produce characteristic features on the surface, which can be used to help identify the failure mode. The overall pattern of cracking can be more important than a single crack, however, especially in the case of brittle behavior materials. Initial fractographic examination is commonly carried out on a macro scale utilizing low power optical microscopy and oblique lighting techniques to identify the extent of cracking, possible modes and likely origins. When it is needed to identify the nature of failure, an analysis at high magnification is required and scanning electron microscopy (SEM) seems to be the best choice. The problem of fracture behavior of biometallic materials is a real one, being well and repeatedly presented in literature. Variations in alloy compositions can lead to subtle differences in mechanical, physical, or electrochemical properties. However, these differences are minor compared with the potential variability caused by differences in fabrication methodology, heat treatment, cold working, and surface finishing, where surface treatments are particularly important for corrosion and wear properties. The aim of this paper, therefore, is to summarize the different types of metals and alloys used as biomaterials, the corrosion of metals in the human body, and different failure damages of metallic implants.

Abstract: The present manuscript is designed to investigate the possibility of manufacturing iron-metal alloys (Fe-M) via thermal techniques. These techniques are mainly depends on simultaneous reduction-sintering reactions of metal oxides. The reduction of metal oxides is an important property in metallurgical processes. It can be applied to M-Fe-O systems and also is used to develop inter-metallic alloys with specific properties. The produced metallic materials have wide range of applications and are characterized by unique physical and mechanical properties. The composition of the produced alloys is often a key element in optimizing their properties. Iron oxide doped another metal oxide such as nickel oxide is used as starting materials to produce metallic materials containing iron contaminated with nickel metal using thermal techniques. The sintering-reduction reactions of the composite oxide materials are investigated under different operation conditions. The experimental results show that the reduction-sintering thermal techniques are economic and promising routes for the production of different Fe-M alloys. The different factors affecting the rate of reduction such as temperature and ratio of doping materials are investigated. The results obtained are used to demonstrate the kinetics and mechanisms of reduction of metal oxides.

Abstract: During the past two decades, processing of ultrafine grained materials using severe plastic deformation techniques has attracted great interest in the scientific community. Although the up-scaling of processes and the lack of ductility of ultrafine grained alloys are still some important challenges, these techniques look promising because they produce bulk materials free of porosities. More recently, some strategies to combine precipitation hardening and ultrafine grained structures have been proposed. It has also been shown that nanoscaled composite materials could be successfully processed. This experimental work rose however some very fundamental scientific questions about the influence of severe plastic deformation on the precipitation mechanisms or on the formation of supersaturated solid solution through mechanical mixing. The driving force and the thermodynamics of these phase transformations are of course affected by the high amount of energy stored in severely deformed alloys, especially as interfacial energy. But grain boundaries, with the help of dislocations and point defects, also play an important role in the kinetics. In this paper, it is proposed to shortly review these phenomena and the underlying mechanisms with a special emphasis on the contribution of grain boundaries.

Abstract: Nanostructured materials have attracted considerable attention in recent years because of their unique and amazing properties. With a high surface activity due to their small particle size, enormous surface area and specific mechanical properties, it has been used for various engineering purposes including chemical, mechanical and civil engineering applications. The rapid development of nanostructured materials and nanotechnology will change the traditional processes of fabrication and applications of construction materials. nanosized materials can be used in construction industry to produce lighter and stronger structural composites such as modified steel. The present work introduces a novel idea for the production of metallic alloys from nanosized nickel ferrites using powder technique routes. nanosized nickel ferrite (50 nm) is being used as starting material for the production of metallic alloy containing iron and nickel. The prepared alloys were characterized physically and chemically through X-ray diffraction and optical microscope. The composition of these alloys is often a key factor to control the mechanical, chemical and physical properties of the synthesized alloys. The reduction processes take place in a stepwise manner via the formation of a series of intermediate oxides. The microstructures of the produced alloy together with the kinetics data obtained from reduction process were used to elucidate the reduction mechanism under isothermal conditions.

Abstract: Plastic flow localization behaviour has been investigated in commercial Zr alloys used in the nuclear power industry. The type of deformation localization pictures corresponding with the stage preceding material fracture is described. Proposed is a method for assessing the reserve ductility of the metal subjected to deformation in rolling of thin-wall Zr alloy tubes by examining the local strain patterns.

Abstract: The information in the basic references about the relation between elastic constants and particularly Young’s modulus (E) behavior and plastic deformation indicates that this parameter is constant or almost constant. At the beginning of the XX century several authors indicated that E of some metals decreased when cold deformation increased and detected reductions up to 15% in steels, aluminum, copper, brass... In the last years this behavior is taking into account during the finite-element analysis of sheet metal stamping or other plastic deformation processes. This work includes an extensive review of papers of our research team and of other authors related with the behavior of Young’s modulus during plastic deformation of some metallic alloys. This parameter can diminish up to 10% by plastic deformation (tension test) in iron, aluminum, and stainless steel (UNS S 30403) but remains practically unaltered in aluminum alloys deformed before or after aging. Results of Young’s modulus in nanostructured copper and copper alloys determined by ultrasonic technique are also presented. Additional results of Young’s modulus of UNS G10180 and UNS G10430 steels measured during loading and unloading steps in tension test are also included. High differences in the E values were detected between both steps.

Abstract: Multicomponent bioactive nanostructured films (MuBiNaFs) with an excellent combination of chemical, mechanical, tribological, and biological properties were developed and deposited by sputtering of composite targets produced via the self-propagating high-temperature synthesis method. Reviewed substrate materials included Ti-, Ni-, and Co-based alloys, insoluble polymers, and deimmunized donors bones. Our results showed that the MuBiNaF deposition can be effectively combined with either a bulk material modification to improve its mechanical properties, or a surface modification to control surface roughness and blind porosity. Among other promising applications, the fabrication of hybrid materials incorporated with stem cells or medicine is mentioned.

Abstract: This paper has examined some recent findings concerning the processing of fully dense hetero-nanostructured materials (i.e. consisting of nano, ultrafine and micrometric grains) which can be produced by using the interplay between heavy deformation and recrystallization. By plastic deformation of bulk materials, an improved strength/ductility balance can be obtained directly by imparting high strain deformation (by ECAE) until the occurrence of recrystallization. Using a powder metallurgy route, the strong potential of electric field assisted sintering (ECAS) for producing multi-scale microstructures when a milled powder is used is also demonstrated. In this case, in addition to modify the classic processing parameters (time/temperature of ECAS), altering the nature of the milled powder - by Y2O3 addition during the milling stage - is also a good way to delay the onset of recrystallization and, thereby, increase the fraction of ultrafine grains.

Abstract: Fe60Co40 and Fe72Al28 nano-alloys were synthesized from elemental powders via highenergy mechanical alloying. The prepared samples were characterized using X-ray diffraction, scanning electron microscopy and X-band waveguide to measure the reflection loss in a frequency range of 9-10 GHz. The XRD patterns show that disordered Fe60Co40 solid solution with a bodycentred cubic structure is formed for milling times longer than 12 h, and after 4h milling, the solid solution Fe72Al28 has been largely formed. Morphological studies indicate an average grain size of 10 to 15 nm. The microwave- absorbing characteristic reveal good performance for Fe60Co40 compared to Fe72Al28, the maximum reflection loss is about -12 dB for the absorber.

Abstract: The solid microstructure built in the solid governs the properties of materials elaborated from the melt. In order to clarify the dynamical mechanisms controlling solidification processing, we use in situ and real-time synchrotron X-ray radiography at ESRF (European Synchrotron Radiation Facility) to analyze microstructure formation in thin aluminum alloys solidified in the Bridgman facility installed at the ID19 beamline. During directional solidification of Al - 3.5 wt% Ni alloys, global mechanical constraints induced by the shape are found to act on the solid microstructure. In particular, radiography videos of dendritic growth show disorientations of sidebranches induced by mechanical stresses. In the solidification of AlPdMn quasicrystals, live imaging reveals that facetted growth proceeds by the lateral motion of ledges at the solid-melt interface. When the solidification rate is increased, the kinetic undercooling becomes sufficient for grain nucleation and growth in the liquid. These grains develop specific features that can be attributed to grain competition and concomitant poisoning of growth caused by the rejection of aluminum in the melt.