Papers by Keyword: Grain Size

Abstract: The combination of advection and migration of grain boundaries is analyzed on the basis of a simple mesoscale model, where parallelepipedic grains are considered under uniaxial compression straining. Strain hardening and dynamic recovery are described by the classical Yoshie-Laasraoui-Jonas equation. Grain-boundary migration is driven by the difference in dislocation densities between one representative grain and the average over the material. Finally, nucleation is assumed to occur at grain boundaries. Special attention is paid to the aspect ratio, which starts from unity (infinitely small cubic nucleus) and tends to zero when the grain disappears. In spite of the role of migration, the average shape of the grains is determined as a first approximation by their lifetimes.

Abstract: In present work, a high Zn-containing Al-Zn-Mg-Cu alloy with different grain sizes was fabricated by extrusion and related precipitation characteristics and mechanical property were investigated after uniform heat treatments. The results showed that precipitation characteristics for the three alloys were almost the same. Matrix precipitates were GPII zone and η' phase and possessed small size and dense distribution while grain boundary precipitates exhibited discontinuous distribution. The rank of strength and fracture toughness for the three alloys are SG>MG>LG. Tearing ridges had been found on all the fracture surface while only LG alloy possess obvious dimple characteristics. The a-N curve showed that crack length list is MG>LG >SG under a same cycle number. The da/dN-ΔK curve also proved that fatigue crack propagation (FCP) rate of MG alloy is slightly larger than that of LG alloy, both were apparently larger than that of SG alloy. The width of fatigue striations on FCP fracture surface also backed it. Besides, obvious transgranular cracking characteristics and apparent secondary cracks were found on the FCP fracture surface.

Abstract: This paper focuses on the mechanical property differentiation and phase content differentiation of HRB400 rebars under the direct rolling of without-heating (DROW) process. The results showed that the temperature distribution from the head region to the tail region of the billet before rolling under the DROW process was different compared to the traditional hot rolling (THR) process, which resulting in the difference of each phase volume fractions and the grain size of the rebar. Compared with the THR process, the phase distribution of the rebars under the DROW process is not uniform, showing the characteristics of low ferrite content in the head region, followed by the tail region, and the highest in the middle region. It was demonstrated that the DROW process could improve the mechanical properties of the rebar, but the difference in phase content and grain size distribution leads to a large variability in the enhancement of the mechanical properties of rebar rolled in different areas of the billet.

Abstract: The micro-nanoBaTiO₃ ceramics of different sizes have been prepared simply and controllably via a self-assembly sintering method. The effects and scopes of the application of this method in the controllable synthesis of the micro-nanoBaTiO₃ ceramics are investigated. Through the given size of BaTiO₃ powders and the combination way, the ceramics with different grain sizes, such as 400~500 nm, can be controllably synthesized. Therefore, the use of this method is conducive to the realization of the controllable synthesis of the micro-nanoBaTiO₃ ceramics.

Abstract: Alumina is the most promising ceramic armor material and SHPB testing is typically used to investigate dynamic deformation behaviour and ballistic mechanisms. In this research the effect of the incident wave shaping technique on the stress equilibrium state during testing was analysed. The compressive strength of alumina ceramic materials was evaluated under high strain rate compressive loads of 1200-1800/s. The SHPB compression strength was found to increase with decreasing grain size to a maximum of 3.80±0.25 GPa, and the ceramic materials studied exhibited high strain-rate sensitive mechanical properties due to crack tip inertia effects.

Abstract: The mechanical properties of steel often determine to a greater extent its performance characteristics, including service life of the equipment. Often, for operational control of mechanical properties, magnetic parameters are used such as, for example, the coercive force. Both mechanical and magnetic properties of steel are associated precisely with the structure of the material. The influence of the structure on these properties became known a long time ago, however, in similar works, the influences exerted by the structure with different degrees of dispersion are not considered. In this work, the goal was set to consider the effect of grain size difference on the magnetic and mechanical characteristics of steel.

Abstract: On the example of shape memory alloys in coarse-grained and ultrafine-grained states there is demonstrated an influence of pulse current on deformation behavior, microstructure and mechanical properties during cold rolling. The combination of cold rolling with the introduction of a pulsed current stimulates an increase in the deformation ability and strong structural refinement into the region of nanograins in a hard-deformed shape memory TiNi alloy. For both coarse-grained and ultrafine-grained structural states, the maximum achievable one-time and the total degree of deformation are higher in the case of using a pulsed current. Subsequent annealing improves the strength and functional properties. It has been shown that effect of pulsed current on deformability during cold rolling is higher in an alloy with a high content of impurities.

Abstract: Currently, two main methods of applying abrasive grains to the surface of a flexible backing - mechanical and electrostatic - are used for the manufacture of grinding tools. The mechanical method of abrasive applying involves pouring an abrasive onto a backing, on which an adhesive has been previously applied. In this case, grains are fixed on the surface of a backing in a non-optimal way in a chaotic manner without taking into account their geometric parameters. This subsequently leads to rather low performance of such tools, thereby not allowing the full use of their capabilities. In the electrostatic coating, abrasive grains are oriented along their major axis perpendicular to a backing. A large number of studies show that grain orientation by this method improves the cutting performance of an abrasive paper. At the same time, the mechanism of the effect of an electrostatic field on abrasives of various grain sizes, depending on the interelectrode space, has not been fully studied. Based on this, studies aimed at scientific substantiation of the process of orientation of abrasive grains on the working surface of an elastic tool in an electrostatic field are of great relevance. This work is devoted to the study of the effect of an electrostatic field on abrasive grains. The article presents some results of studies of the susceptibility of brown aluminium oxide 14A of various grain sizes to the electrostatic effect.

Abstract: Corrosion-resistant steels with a high nitrogen content are used as structural materials for high-load critical products. Their high strength and ductility, austenite stability, corrosion and wear resistance are highly relevant for parts and structures operating in marine environments. In addition to a high level of operational properties, they are subject to the requirement of manufacturability, including weldability. Welding of such steels, due to the high concentration of nitrogen, is a complex technological operation, and it is necessary to avoid the appearance of gas nitrogen pores, hot cracks, a sharp drop in mechanical properties in any zones of welded joint. In this work, we investigated the regularities of changes in microhardness in different zones of welded joints (base metal, heat-affected zone of the weld, fusion zone and weld metal) of two grades of austenitic Cr-Ni-Mn-Mo-N high-strength steels with a high equilibrium nitrogen content (up to 0.6%). They fundamentally differ in the structural state of the base metal being welded: deformed (hot-rolled sheet) and cast (metal of a heat-treated cast plate). It has been shown that despite the use of different welding methods (MIG, MMA and TIG), the options for welding fillers and the type of weld groove, there are general patterns for each of the two types of base metal. The work also evaluated the correlation between these regularities and such basic characteristics of the structure and properties of rolled and cast metal of welded joints, such as the grain size and values ​​of the yield stress.

Abstract: Present studies are based on adding ferrochrome slag as reinforcement in AA 7075 alloy manufactured via the stir casting process. Two different slag particles are chosen; they are 36μm (Micro) and 68 nm (Nano). This was added to evaluate the size effects in the given alloy matrix. The composites were tested for unique microstructural properties and mechanical properties. The results Revealed uniform particle distribution within the matrix and good bonding between the matrix and the reinforcement. Better mechanical properties are obtained for both micro and nanocomposites than base alloy. This is further enhanced by ageing treatments. nanocomposites show superior mechanical properties than either alloy or micro composite. Interestingly, nanocomposite exhibits an increase in strength with good ductility; same is confirmed with fracture studies.