Control of Amount of α-Al Phase Particles in near Eutectic Al-Si Alloy by Electromagnetic Stirring

Al-Si alloy is widely used as a casting alloy. The α-Al phase in the semi-solid state has low Si content in the Al-Si alloy. Then by separation of these α-Al phases from semi-solid Al-Si alloy, refining of aluminum can be possible. But, in near eutectic Al-Si alloy, few primary α-Al phases can be crystallized. If the fraction ratio of the α-Al phase can be increased, near eutectic Al-Si alloy can refine, and this method can be used for recycling. In this study, the effect of electromagnetic stirring (EMS) on the microstructure, especially the amount of the α-Al phase particles was investigated. A rotational magnetic field was applied to JIS ADC12 alloy which has near eutectic content during slow cooling from the liquid state to the solid-state, by using a three-phase AC coil. By applying EMS at solidification, the shape of the α-Al phase became particle shape from dendrite shape, and the amount of α-Al phase particles was increased. Moreover, by applying unidirectional intermittent EMS, the volume fraction of α-Al phase particles was decreased with increasing intermittent applying time. In ADC12 alloy, the primary α-Al phases can be crystallized only 10% generally, but it could be obtained over 40% by applying EMS. This means that the semi-solid slurry of near eutectic alloy with over 40% of fraction solid can be obtained by applying EMS.

A И-Shaped Curve of Hot Tearing Susceptibility in Magsimal®-59-Based Alloys

The hot tearing susceptibility of Al-6Mg-xSi (x = 0-6.0 wt.%) alloys was studied using constrained rod casting. Addition of Si content resulted in double ternary eutectic reactions and then changed the freezing range and eutectic liquid fraction greatly, which made the hot tearing susceptibility show a И-curve with the increasing of Si content. The И-curve was obviously different from the λ-curve that supported by most researchers.

Kinetic study on the reaction between Incoloy 825 alloy and low-fluoride slag for electroslag remelting

A kinetic model for the reactions between the low-fluoride slag CaF2–CaO–Al2O3–MgO–Li2O–TiO2 and Incoloy 825 alloy was proposed based on the two-film theory. The applicability of the model was verified to predict the variation of components in the slag–metal reaction process. The results show that the controlling step of the reaction 4[Al] + 3(TiO2) = 3[Ti] + 2(Al2O3) is the mass transfer of Al and Ti in the liquid alloy and the controlling step of the reactions 4[Al] + 3(SiO2) = 3[Si] + 2(Al2O3) and [Si] + (TiO2) = [Ti] + (SiO2) is the mass transfer of SiO2 in the molten slag. With increasing TiO2 content in the slag from 3.57% to 11.27%, the Al content in the alloy decreased whereas the Ti content increased gradually. The Si content continued to decrease during the slag–metal reaction. Soluble oxygen in the alloy reacts with Al, Ti, and Si, resulting in a decrease of the oxygen content in the alloy. The variations of TiO2 content were in good agreement with the calculated results by the kinetic model whereas the measured results of Al2O3 and SiO2 in the slag were lower than the calculated results, which is mainly due to the volatilization of fluoride.

Salt-Induced Damage Alleviation in Tanacetum Balsamita L. by Foliar Application of Dobogen Biofertilizer, Glucose and KNO3

The effects of NaCl salinity stress and foliar application of KNO3, glucose and Dobogen were tested on Tanacetum balsamita. The results showed the significant interaction effects of salinity and foliar sprays on chlorophyll a, K+, Na+, Mg2+, Fe2+, Zn2+, Mn2+ and Si content, K/Na ratio and total phenolic and flavonoid contents. The highest phenolic content was acquired with 100 mM salinity and foliar spray of Dobogen and glucose, 50 mM NaCl × KNO3 application and 50 mM salinity× nonfoliar application. The highest K/Na ratio was observed in control plants and controls × KNO3 and/or Dobogen application. The greatest Si content was recorded with controls × Dobogen and KNO3 applications and no saline × no foliar control plants. Malondialdehyde, flavonoid and proline contents as well as catalase activity were influenced by the independent effects of treatments. Chlorophyll b and superoxide dismutase were affected by salinity. Total soluble solids and Ca2+ were influenced by foliar applications. Malondialdehyde and proline were the highest at 150 mM salinity. Salinity adversely affected the physiological responses of costmary. However, foliar treatments partially ameliorated the salinity effect, and the results would be advisable to the extension section and pioneer farmers.

Molecular Indicators of Biomaterials Osteoinductivity - Cell Migration, BMP Production and Signalling Turns a Key

In this work we dissected the osteoinductive properties of selected, PLGA-based scaffolds enriched with gel-derived bioactive glasses (SBGs) of either binary SiO2-CaO or ternary SiO2-CaO-P2O5 system, differing in CaO/SiO2 ratio (i.e. high -or low-calcium SBGs). To assess the inherent ability of the scaffolds to induce osteogenesis of human bone marrow stromal cells (BMSC), the study was designed to avoid any osteogenic stimuli beyond the putative osteogenic SBG component of the studied scaffolds. The bioactivity and porosity of scaffolds were confirmed by SBF test and porosimetry. Condition media (CM) from BMSC-loaded scaffolds exhibited increased Ca and decreased P content corresponding to SBGs CaO/SiO2 ratio, whereas Si content was relatively stable and overall lower in CM from scaffolds containing binary SBGs. CM from cell-loaded scaffolds containing high-calcium, binary SBGs promoted migration of BMSC and BMP-response in reporter osteoblast cell line. BMSC culture on these scaffolds or the ones containing ternary, low-calcium SBGs resulted in the activation of BMP-related signaling and expression of several osteogenic markers. Ectopic bone formation was induced by scaffolds containing binary SBGs, but high-calcium ones produced significantly more osteoid. Scaffolds containing ternary SBGs negatively influenced the expression of osteogenic transcription factors and Cx43, involved in cell-cell interactions. High-calcium scaffolds stimulated overall higher Cx43 expression. We believe the initial cell-cell communication may be crucial to induce and maintain osteogenesis and high BMP signaling on the studied scaffolds. The presented scaffolds’ biological properties may also constitute new helpful markers to predict osteoinductive potential of other bioactive implant materials. Graphical Abstract

Sustainable and Clean Utilization of Coal Gangue: Activation and Preparation of Citrate-Soluble Silicon Fertilizer

Silicon (Si) fertilizer is of great significance to modern agricultural production; the citrate-soluble silicon fertilizer based on coal gangue is one way to protect the environment and meet the agricultural needs of China. In this study, we produced high-efficiency coal-gangue based silicon fertilizer by calcining a mixture of coal gangue, calcium carbonate (CaCO3) and corn stalk powder at high-temperature (i.e., high-temperature activation technology); the effect of temperature and mixing ratio on the available-Si content of activated coal gangue was studied, followed by an analysis of the mechanism of available- Si formation. The results showed that the layered structure of coal gangue was severely damaged above 600 ℃, and the kaolin began to transform into metakaolin and other substances, where the available-Si content was not high (less than 10%). When CaCO3 alone was added, the peak intensity of quartz and muscovite in coal gangue decreased significantly with the increase of CaCO3. However, CaCO3 mainly played a catalytic role in the entire calcination and activation process, forming only a small amount of calcium silicate on the contact surface with coal gangue; however, the available-Si content was still below 12.60%. When corn stalk powder alone was added, the oxides of the corn stalk ash participated in the chemical reaction involving coal gangue, forming nepheline (K(Na, K)3Al4Si4O16) and other silicates, and the available-Si content was significantly higher than that with CaCO3. When coal gangue, CaCO3, and corn stalk powder were mixed and calcined, the available-Si content was as high as 22.97% under the synergistic effect of CaCO3 and corn stalk powder; the concentration of harmful heavy metals was below 0.025 mg/L. The above is in line with the requirements of silicon fertilizer for use in agriculture, thus confirming the preparation of coal gangue-based silicon fertilizer in an efficient manner.

Effect of Si Content on the Properties of A356 Aluminum Alloy

The effects of different Si contents on the microstructure and mechanical properties of A356 aluminum alloy were studied by metallographic microscope analysis and tensile property test. The results show that when the silicon content is between 7% and 11 %, with the increase of silicon content, the eutectic silicon in the matrix increases, and the tensile strength and elongation decrease. When the silicon content increased to 13%, the primary silicon structure appeared in A356 aluminum alloy, and its mechanical properties increased.

Ultrasonic-Assisted Brazing of Titanium Joints Using Al-Si Based Fillers: Numerical and Experimental Process Design

The ultrasonic-assisted brazing process was studied both numerically and experimentally. The ultrasonic brazing system was modeled by considering the actual brazing conditions. The numerical model showed the distribution of acoustic pressure within the filler and its variations according to the gap distance at different brazing temperatures. In the experimental part, brazing joints were studied and evaluated under multiple conditions and parameters. Although either the initial compression load or the ultrasonic vibration (USV) can initiate the interaction at the interface, the combined effect of both helped to produce joints of a higher quality with a relatively short brazing time, which can be further optimized in terms of their mechanical strength. The effect of the Si content on the joint interface, and the effect of the brazing conditions on the microstructures were studied and discussed.

Analysis of the Degradation in the Creep Strength of High-Cr Martensitic Steels

To investigate the formation process of the Z-phase, which lowers the long-term rupture strength of high-Cr martensitic steel, the creep curves of Grades T91, T92, and P92 were analyzed along with the experimental steels of 9Cr-1W and 9Cr-4W by applying an exponential law to the temperature, stress, and time parameters. The activation energy (Q ), activation volume (V ), and Larson-Miller constant (C ) were obtained as functions of creep strain. At the beginning of creep, sub-grain boundary strengthening occurs due to dislocations that are swept out of the sub-grains, which is followed by strengthening due to the rearrangement of M23C6 and the precipitation of the Laves phase. After Q  reaches a peak, heterogeneous recovery and subsequent heterogeneous deformation begin at an early stage of transient creep in the vicinity of several of the weakest boundaries due to coarsening of the precipitates. This activity triggers an unexpected degradation in strength due to the accelerated formation of the Z-phase. Stabilization of M23C6 and the Laves phase is important for mitigating the degradation of the long-term rupture strength of high-strength martensitic steel. The stabilization of the Laves phase is especially important for the Cr-Mo systems because Fe2Mo is easily coarsened at ~600 °C as compared to Fe2W. Lowering the hardness and Si content also prevents excess hardening due to the Laves phase, which also mitigates the degradation. The online monitoring of creep curves and the QVC  analysis render it possible to detect signs of long-term degradation under targeted conditions within a relatively short period.

Interplay between eutectic and dendritic growths dominated by Si content for Nb-Si-Ti alloys via rapid solidification

Rapid solidification techniques such as electron beam additive manufacturing are considered as promising pathways for manufacturing Nb-Si based alloys for ultra-high-temperature applications. Here we investigate the microstructure diversity of a series of Nb-Si-Ti alloys via electron beam surface melting (EBSM) to reveal their rapid solidification behaviors. Results show that the microstructural transition from coupled to divorced Nbss/Nb3Si eutectics can be triggered by increasing Si content. The formation of fully lamellar eutectics, evidenced by scanning transmission electron microscopy and atom probe tomography (APT), is achieved in the EBSM-processed Nb18Si20Ti alloy (at%), in contrast to the hypereutectic microstructures in arc-melted counterparts. The dendritic microstructures containing divorced eutectics are generated with a higher content of Si during rapid solidification. The transition from faceted to non-faceted growth of intermetallic Nb3Si occurs with the formation of primary Nb3Si dendrites. The interplay between eutectic and dendritic growths of silicides is discussed to provide insights for future alloy design and manufacture.