Improvement of solidification structure and stress distribution of large section Fe-6.5% Si alloy ingot using weak cooling method

This study investigates the influence of Cu and La additions on the solidification structure and phase formation behavior of Fe-6.5wt%Si high silicon steel. The alloy's phase composition and structure were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The magnetic performance was measured using a high and low-temperature vibration magnetometer. The results revealed that the microstructure of the Fe-6.5wt.%Si alloy ingot, treated with Cu and La inhibitors, is segmented into three layers. From the bottom to the top, the phase morphology is fine crystals, columnar crystals, and isoaxial crystals. Adding Cu and La inhibitors significantly refined the Fe-6.5wt.%Si alloy; adding 0.05% Cu transformed thick columnar crystals into slender branches, while 0.03% La led to a uniform refinement of grains. Cu addition maintained the alloy saturation magnetization strength but increased coercivity. La addition decreased the alloy's saturation magnetization and increased coercivity.

The aim of this systematic review is to provide an overview of finite element analyses comparing standard and short dental implants concerning biomechanical properties and to detect the most relevant parameters affecting periimplant stress concentrations. After screening the literature and assessment of studies, 36 studies were included in this review. Eighty-three percent of the studies state that short dental implants have to bear higher stress concentrations compared with standard length implants. At the same time, 44% of articles note that implant diameter can be considered a more effective design parameter than implant length to reduce stress concentrations and to avoid an overload of periimplant bone. Regardless of implant dimension, in all studies, the highest stress concentrations are found in the cortical section around the upper part of the implant. Unaffected of bone quality, implant diameter is found to play a key role to minimize periimplant stress concentrations. Concerning stress reduction implant length gains increasing relevance with decreasing bone density. Furthermore, splinting of short implants constitute an appropriate tool to avoid crestal overloading.

A series of experiments were conducted by Al-2·0Si%Si alloy to investigate the effect of mould D/H ratio and shape on solidification structure under ultrasonic vibration (UV). Finally, the mechanism of grain refining was discussed. The results show that equiaxed grain occupancy is maximized when D/H is equal to 0·7 for ingots with mould volume of 80 and 120 cm3, however, the equiaxed grain occupancy has the maximum when D/H is equal to 2·0 for the ingot with mould volume of 200 cm3. Otherwise, the equiaxed grain occupancy has downtrend with increasing of mould volume. The columnar structure is easily formed in ultrasonic ingots with complex mould shape and more corners.

Large-scale Fe–6.5 wt.%Si ingot with excellent formability is required for a pilot line producing sheets through hot/cold rolling. The variation of the as-cast microstructure, ordered structures and the formability of the Fe–6.5 wt.%Si alloy ingots with the cooling rate during casting was investigated. Under air-cooling condition, inhomogeneous microstructures with a low proportion of equiaxed grains were formed, but the formation of ordered structures was partially inhibited, especially D03. Homogeneous microstructures with a high proportion of equiaxed grains were observed under the condition of furnace cooling, but the ordered structures were fully generated, and the degree of order is high. It is generally believed that high degree of order is the main factor of brittleness, but the homogeneous microstructure (including grain morphology and size) of the furnace-cooled sample helps to improve the formability. The influence of these two aspects on formability is contradictory. Therefore, the formability is tested through the flow stress during the compression and the microstructure after the compression. The results show that the furnace-cooled sample has better formability. For large-scale ingots, the control of as-cast microstructure becomes more significant than the control of degree of order. Slow cooling during casting is important for the large-scale ingots to have good formability meeting the requirements of direct hot rolling.

This paper looked at the (AlSi)3ScZr particles that precipitate in Al – Mg – Si alloys with excessive silicon when they are cooling down after casting. The effect of nanoparticles on strength is demonstrated in as-cast state. The effect of artificial ageing on the mechanical properties of studied alloys is also demonstrated. The paper examines six Al – Mg – Si alloys with different Mg/Si ratios and with scandium and zirconium additives or without them. Microhardness and mechanical properties were determined for all alloys in as-cast state. To look at the decomposition of supersaturated solid solution, specimens of alloys containing scandium and zirconium were annealed in the temperature range of 360 to 550 oC, with the soaking time varying between 10 and 50 hours. Using optical microscopy, the grain structure was studied for alloys with Mg/Si = 0.6. Besides, a scanning microscopy study of nanoparticles was conducted for 0.6MgSi0.3Sc0.15Zr alloy. For 0.3MgSi0.3Sc0.15Zr and 0.5MgSi0.3Sc0.15Zr alloys, the data about the grain structure and nanoparticles were taken from previous research studies. The results show that the solid solution supersaturated with scandium, zirconium, silicon and magnesium in the studied alloys has an extremely short decomposition time. It happens because of the combined effect of scandium and silicon. Because of the fast decomposition of the supersaturated solid solution, a great number of (AlSi)3ZrSc particles is formed when it is cooling down after casting. The main mechanism behind it is an intermittent decomposition of the supersaturated solid solution suggested by the presence of fan-shaped particles. Particles detected in the 0.6MgSi0.3Sc0.15Zr alloy retain the L12 structure, are partially coherent with aluminium matrix and contain silicon and scandium. Considering their morphology, sizes and chemical composition, they cannot belong to Sc2Si2Al phase. At the same time, they do impact the mechanical properties. Thus, in the 0.6MgSi0.3Sc0.15Zr alloy the yield strength rises by 43 MPa and the ultimate strength – by 61 MPa. The 0.3MgSi0.3Sc0.15Zr and 0.5MgSi0.3Sc0.15Zr alloys also gain higher strength, which is due to the fan-shaped semi-coherent and round fully coherent (AlSi)3ScZr particles detected in previous research studies in as-cast state. It was found that in the 0.3MgSi0.3Sc0.15Zr and 0.5MgSi0.3Sc0.15Zr alloys the yield strength rises by 32 and 67 MPa and the ultimate strength – by 67 and 78 MPa, respectively. During artificial ageing, microhardness can either rise or drop. The grain structure size produces the strongest effect on microhardness during artificial ageing: the larger the grain size is, the higher the microhardness is after artificial ageing of as-cast material. Support for this research was provided under Grant No. 21-19-00548 https://rscf.ru/project/21-19-00548/ by the Russian Science Foundation.

The non-oriented Fe-6.5wt.%Si alloy cast strip with a width of 100 mm and a thickness of 1.7 mm was prepared by the top side-pouring twin-roll-casting (TSTRC) process. The surface quality of the air-cooled and water-cooled cast strip was good. Compared with the Fe-6.5wt.%Si alloy ingot, the Fe-6.5wt.%Si alloy cast strip has a fine solidification structure and exhibits certain plasticity at room temperature. Microhardness, XRD, and TEM investigated the ordered structure and degree of Fe-6.5wt.%Si alloys prepared by three different cooling methods. The results show that the Fe-6.5wt.%Si alloy ingot prepared by the standard method has many B2-ordered phases and D03-ordered phases, and the order degree is high. The Fe-6.5wt.%Si alloy cast strip prepared by the TSTRC process has a low degree of order and only contains a small B2-ordered phase. The faster cooling rate effectively inhibits the formation of the D03-ordered phase and B2-ordered phase. The growth of the ordered phase also reduces the reverse domain boundary energy, reduces the motion resistance of superdislocations, and increases its mobility, thereby improving the room temperature plasticity of Fe-6.5wt.%Si alloy cast strips.

Phase separation of a microsized powder mixture of Si and SiC by Cu–Si alloying

The main purpose of this study was to explore the mechanical properties of the anterior cruciate ligament and its attachments following reconstruction with the all-inside technique after anterior cruciate ligament injury. Knee joint computed tomography data were collected from healthy volunteers, and knee joint models were created using Mimics software. A normal knee joint model, an all-inside reconstructed anterior cruciate ligament model, and a traditional reconstructed anterior cruciate ligament model were established. A tensile force of 134N and a bending moment of 5N/m were applied at the anterior aspect of the proximal tibia in these three models. The knee joint was subjected to external rotation, internal rotation, varus, valgus, flexion, and extension under this bending moment. The magnitude and distribution of stress on the ligament or graft and the magnitude and distribution of stress on the graft attachments were observed under different loading conditions. Under different external forces, the maximum stress on the ligament in the normal model fluctuated from 1.949 to 18.302MPa, with an uncertain distribution of maximum stress. The maximum stress on the graft in the all-inside reconstructed anterior cruciate ligament model fluctuated from 0.705 to 3.465MPa and was mainly distributed at the junction of the graft and the tibial footprint. In the traditional reconstructed anterior cruciate ligament model, the maximum stress on the graft fluctuated from 5.012 to 59.269MPa and was primarily distributed at the junction of the interference screw and the graft. The concentration of stress on the loop and plate in the all-inside reconstructed anterior cruciate ligament model fluctuated from 70.461 to 346.363MPa, with maximum stress distributed at the junction of the loop and the tibial surface. The maximum stress on the interference screw in the traditional reconstructed anterior cruciate ligament model fluctuated from 10.184 to 92.298MPa, with maximum stress primarily distributed at the end of the interference screw. Under different external forces, the graft used in all-inside anterior cruciate ligament reconstruction is subjected to fewer external forces than that used in traditional anterior cruciate ligament reconstruction, which may indicate a relatively stable mechanical environment. The strength of the loop and plate can theoretically tolerate daily knee joint movements of patients without injury.

Most of tubular joints in offshore structures have quite a number of braces and may be loaded in various ways. It is of great significance to find out the maximum stresses in the multi-brace non-coplanar tubular joints under complex load condition. Based on the results obtained from stress analysis of a set of tubular joints, the leading feature of stress distribution in the multi-brace non-coplanar tubular joints is discussed and a method for calculating the maximum stress is proposed. Furthermore, the calculating formulae are derived. INTRODUCTION Stress concentration factors of some simple tubular joints under typical load condition have been studied conscientiously. There are several empirical formulae available for the SCFs of T-, Y-, X-, K-and KT-joint under axial forces, in-plane moments and out-of-plane moments (1-4). But the actual situation of tubular joints in offshore structures is far more complex. Firstly, it depends on the load condition at which point the maximum stress occurs. In T-joints, for example, the maximum stress usually occurs near the crowns under in-plane moments or at the saddles under axial forces and out-of-plane moments. Fig. 1 shows the movement of the maximum stress point as the moment changes in deriction. Obviously, when the maximum stress occurs at saddles, the stresses at orowns are not equal to zero and vice versa. The empirical formulae available are only for the value of the SCFs, they can not be used to specify the exact locations of the maximum stress and to describe the stress distribution near intersections of the chord and braces. In practice, a real load can barely be just an axial force, an in-plane moment or an out-of- plane moment. The maximum stress can occur at nearly any point along intersections. stresses at different points can not be superimposed at all. Therefore, non of the formulae available is applicable in general1 load condition. Secondly, the SCF is the non-dimensional magnitude of the maximum principal stress and the principal axes of stress in different stress state do not coincide with each other. Fig. 1 shows that if deriction of the moment change from ?= .0° to ?= 90°, the principal axes of stress at the saddles rotate through an angle of 45°. Thus even the maximum stress point is predicated, its value can not be obtained by superimposing the principal stresses in different load condition either. Finally, the stress distribution will differ greatly from each other when many of the braces of a tubular joint are loaded in different ways. Reference (5) has pointed out that for the tubular joint shown in Fig. 2, the SCF in Case I is 2.4 times as big as that in Case III, but the magnitude of the forces exerted on the braces remains unchanged. In order to evaluate correctly the working life, the research work on calculation of the maximum stress in multi-brace non-coplanar tubular joints is necessary. Because of complexity of the geometrical configuration and load condition, the stress analysis of multi-brace tubular joints is difficult and costly. In our study, a computer program system, named 'FEAPS-TJ', has been developed for the mesh generation and finite element analysis.

Comparison of microstructures and mechanical properties of as-cast and directionally solidified Ti-47Al-1W-0.5Si alloy

Although rupture of an atherosclerotic plaque is considered to be the cause of most acute coronary syndromes, the mechanism of plaque rupture is controversial. To test the hypothesis that plaque rupture occurs at sites of high circumferential stress in the diseased vessel, the distribution of stress was analyzed in 24 coronary artery lesions. Histological specimens from 12 coronary artery lesions that caused lethal myocardial infarction were compared with those from 12 stable control lesions. A finite element model was used to calculate the stress distributions at a mean intraluminal pressure of 110 mm Hg. The maximum circumferential stress in plaques that ruptured was significantly higher than maximum stress in stable specimens (4,091 +/- 1,199 versus 1,444 +/- 485 mm Hg, p < 0.0001). Twelve of 12 ruptured lesions had a total of 31 regions of stress concentration of more than 2,250 mm Hg (mean, 2.6 +/- 1.4 high stress regions per lesion); only one of 12 control lesions had a single stress concentration region of more than 2,250 mm Hg. In seven of 12 lethal lesions (58%), rupture occurred in the region of maximum circumferential stress; in 10 of the 12 lethal lesions (83%), rupture occurred in a region where computed stress was more than 2,250 mm Hg. These data suggest that concentrations of circumferential tensile stress in the atherosclerotic plaque may play an important role in plaque rupture and myocardial infarction. However, plaque rupture may not always occur at the region of highest stress, suggesting that local variations in plaque material properties contribute to plaque rupture.

Experimental research and numerical analysis of welding residual stress of butt welded joint of thick steel plate

The effects of ultrasonic stirring treatment on grain refining and improving the mechanical properties of Al-7wt%Si cast aluminium alloy were systematically investigated in this study. The microstructures and hardness features of the cast ingot specimens were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive spectrometer (EDS), digital hardness tester, respectively. The investigation was found that the grains of the alloy were obviously refined after ultrasonic treatment. The average grain diameter of Al-7wt%Si alloy ingot was reduced from 395μm to 206μm resulted from the ultrasonic stirring and master alloy elements addition. In contrast, the hardness of the ingot specimen increased from 27HB to 37HB due to the ultrasonic stirring treatment. In fact, the tensile strength of the alloy was also increased because of the grain refinement and the degassing function of the ultrasonic stirring. The observation also revealed that some dispersed gas cavity was agglomerated in the upper part of the alloy ingot.

Porous Si/C anode materials by Al–Si dealloying method with PEA surfactant assisted cross-linked carbon coating for lithium-ion battery applications

The influence of high-intensity ultrasound on the microstructure and the distribution of solute elements Si in α (Al) of Φ10mm Al-1% Si alloy bonding wire produced by horizontal continuous casting have been investigated. Experimental results show that under high-intensity ultrasonication the microstructure is refined, the solid solubility and the uniformity of the distribution of Si in α (Al) are improved and the solute segregation is suppressed. The effect of high-intensity ultrasonic vibration on restraining solute segregation in Al-1% Si alloy ingot in horizontal continuous casting is explained from such factors as the diffusion of solute, solidification interval, solidifying front shape, temperature field, flow pattern and microstructure.