Addition Of Si Powder Research Articles

Fabrication of broadband wave-transparent porous Si3N4 ceramics by powder hybrid mechanism combined with binder jetting 3D technology

Binder jetting 3D printing is a novel methodology for fabricating broadband wave-transparent porous Si3N4 ceramics, but it faces challenges in low bending strength post-sintering, which impedes its broader application. This study proposed a hybrid mechanism by mixing Si and Si3N4 powders to surmount this challenge, and systematically scrutinized the mechanical and dielectric performance evolution of sintered samples at 1700–1800 °C after investigating nitride rules. Adding Si powder notably improved the bending strength, while retaining superior wave-transparent performance. When Si: Si3N4 was 50:50, at 1750 °C and 1800 °C, the bending strength was enhanced by 2.9 and 2.5 times compared to no Si powder addition. The real permittivity was consistently below 3.3. This work presented an effective methodology for modulating the overall performance of porous Si3N4 ceramics.

Effects of the volume fraction on the microstructural and mechanical properties of TiCp/high-manganese steel composites

To improve the adaptability to complex shaped products, TiC particulates (TiCp) reinforced high-manganese steel matrix (TiCp/HMS) composites were prepared by the squeeze casting infiltration method, and the microstructure and the mechanical properties of the composites were investigated, with different TiCp volume fractions (35%, 50%, 65%). Water glass was applied as binder in the TiCp preforms, in which iron powder was added to adjust the TiCp fractions, and Si powder to activate the bonding of TiCp/steel interface. The results showed that with the increase of the volume fraction, the hardness of the composites increases gradually, with the highest reaching 60.7 HRC at 65 % TiCp, which is 2.7 times that of the matrix. However, the bending strength decreases gradually, with the maximum 439.0 MPa obtained at 35% TiCp. The impact toughness of the composites changes slightly. Due to the use of water glass, brittle glass phase is formed at the TiCp/steel interface, which reduces the mechanical properties of the composites. The addition of Si powder can improve the comprehensive mechanical properties of the composites.

Effects of in situ Mg-Sialon and β-Sialon on the microstructure and properties of MgAl2O4-SiC composites

MgAl2O4-SiC composites were prepared under flowing nitrogen at 1500 °C by using MgAl2O4 powder, SiC powder, Al powder and Si powder as raw materials. Through microstructural observation and analysis, the effects of in situ Mg-Sialon and β-Sialon with different amounts of Si powder addition were investigated in this paper. The results show that the samples without Si addition main contained MgAl2O4, SiC and well development plate structure Mg-Sialon phase. After addition of Si powder, not only the above three phases appeared, but also β-Sialon phase appeared. Meanwhile, with increasing Si contents, the content of β-Sialon phase increased and samples were more dense, limiting the development of the plate structure Mg-Sialon phase. With increasing Si content from 0 wt% to 20 wt%, the apparent porosity shows decreased trend, while the bulk density and cold module of rupture show increased. The samples with 20 wt% Si addition can get the minimum apparent porosity (33.5 %), maximum bulk density (2.13 g•cm−3) and cold module of rupture (87.0 MPa). Besides, the formation mechanism of Mg-Sialon and β-Sialon was discussed in detail and the role of Si was elucidated.

Sustaining strength-ductility synergy of SLM Fe50Mn30Co10Cr10 metastable high-entropy alloy by Si addition

Metastable high entropy alloys possesses excellent ductility and toughness, but its low strength hinders its engineering applications. Therefore, many studies have been carried out to improve the strength of metastable high entropy alloys while maintaining high ductility. In this paper, a new high entropy alloy is fabricated by selective laser melting (SLM) with the addition of Si powder into Fe50Mn30Co10Cr10 metastable high entropy alloy powders, with compositions (Fe50Mn30Co10Cr10)100-xSix (x = 0, 1, 3, 5). The results show that the yield strength and ultimate tensile strength of Si-containing metastable high-entropy alloys gradually increase with the increase of Si elements, and the performance is far better than that of without Si addition. The Si element increases the metastability of the γ(FCC) phase in the high-entropy alloy, and promotes the phase transformation-induced plasticity by adjusting the twinning strain during the deformation process; so that the total elongation of the material prepared by SLM can reach 30% and above. The combined effect of multiple strengthening mechanisms such as dislocation, deformation twinning, and phase transformation has greatly increased the strength of high-entropy alloys. In addition, the excellent strength-ductility combination of the alloy containing Si element indicates that the composition has good printability for laser additive manufacturing, which can provide a reference for expanding the diversification of high-entropy alloys in the additive manufacturing process.

Novel synthesis of ZrO2-SiCw-C insert ring materials for slide plates

To reduce the cost and firing temperature of traditional ZrO2 insert rings, the new ZrO2-SiCw-C (w-whisker) insert ring materials were successfully synthesized using ZrO2, Si, graphite powders as starting materials, and phenolic resin as binder. The effects of amount of Si powder addition (5, 8 and 11 wt%) and firing temperatures (1100 °C, 1200 °C and 1400 °C) on the phase composition, microstructure and properties of as-obtained products have been investigated. The results show that Si reacts with C or CO at high temperature to form SiCw, which intersperses in the ZrO2 material to develop an interlocking network structure, resulting in strengthening effect and leading to an increase in the strength of the composites. The composites have good oxidation resistance due to the formation of some glass film on the sample surface. The optimum firing temperature is 1200 °C, which is much lower than that of pure ZrO2 material (>1700 °C). The as-prepared ZrO2-SiCw-C materials possess good properties, making good prospects for fabricating insert rings of slide plates.

Effect of firing atmosphere on the microstructure and properties of Al2O3–SiC–C castables

Al2O3–SiC–C (ASC) castables were performed using brown fused alumina as aggregates, silicon carbide, white fused alumina, ultrafine α-Al2O3, microsilica, calcium aluminate cement, silicon powder and ball pitch as matrixes. Microstructural observations and analysis of the effects of firing atmosphere and Si powder addition were investigated in this paper. The results show that the strength and strain tolerance of ASC castables with Si powder addition were significantly improved, but their thermal shock resistance was slightly degraded. Compared with the samples after firing in air atmosphere, cold strength and thermal shock resistance of samples after firing in reducing atmosphere were improved, and hot strength of samples tested in reducing atmosphere was little affected by the pretreatment conditions. The difference in properties was closely related to the phase composition and microstructure of ASC castables fired in air atmosphere and reducing atmosphere. The growth process of SiC whiskers was also discussed in detail.

A novel approach to lightweight alumina‐carbon refractories for flow control of molten steel

ABSTRACTFunctional refractory materials for flow control devices of molten steel in continuous casting used to be prepared from Al2O3–C refractories containing dense corundum aggregates. According to the traditional concept, the denser the refractories, the higher the strength of refractories. However, we prepared a new lightweight Al2O3–C refractory material using microporous corundum aggregates instead of dense corundum aggregates, which were reinforced by in situ formed SiC whiskers. A comparative analysis of microstructures and properties was carried out for conventional and lightweight Al2O3–C refractories with and without Si powder addition. We showed that microporous aggregates formed a better aggregate/matrix interface bonding and an improved distribution of SiC whiskers. The SiC whiskers formed not only in the matrix, but also inside of the microporous aggregates and at the aggregate/matrix interface by a vapor‐solid reaction mechanism. Due to the formation of a microporous aggregate/matrix interface reinforced by SiC whiskers, the crack propagation along the aggregate/matrix interface was suppressed, whereas the percentage of cracks propagating within the aggregates was enhanced. Thus, the synergy between in situ formed SiC whiskers and microporous aggregates resulted in a significant higher strength of lightweight Al2O3–C refractories compared to conventional ones. The results therefore provide an original strategy to strengthen Al2O3–C refractories.

Synthesis of Si-Y Coatings on Nb in Fluoride-Chloride Molten Salts

The preparation of multicomponent coatings based on silicon and yttrium on the niobium substrate was investigated. Y-Si/NbSi2 coatings on the Nb substrate by currentless deposition in molten salts were produced. The preparation of NbSi2 layers is carried out in NaF-NaCl-Na2SiF6 melts with the addition of Si powder. The preparation of Y-Si layers is carried out in NaCl-KCl-YF3 melts containing Y powder. Coating samples are studied using SEM. It is established that sequentially synthesized coatings are characterized by a two-layer structure. Using the EDS method, the chemical composition of the obtained layers is established: Y – 26.68; Nb – 62.55; Si – 10.76 wt. %. The oxidation test of the obtained coatings Y-Si/NbSi2 on Nb samples is performed. It is found that testing at 1200 ˚C for 2 hours leads to a mass loss of 62 mg/cm2·h.

Effect of Si content on impact-abrasive wear resistance of Al2O3p/steel composites prepared by squeeze casting

The 40Cr steel matrix composites were reinforced with Al2O3 particulates (Al2O3p) through Si adding to improve the impact-abrasive wear resistance, in which Si powder ranging up to 25% of the Al2O3p weight was added into the Al2O3p preforms; then, the composites were fabricated by squeeze casting. For all composites, alumina particles are evenly distributed, and Si powder is dissolved in the matrix. Without Si powder addition, the 40Cr steel matrix contains only pearlite; however, ferrite appears and increases with Si powder addition. In the impact-abrasive wear tests, the impact frequency is 80 min–1 and the impacting energy is 2 J. With increasing Si powder, the wear of the composites first decreases obviously, reaches the minimum at 10% and then increases. The effect of Si addition on the wear resistance can be attributed to two reasons: one is increasing the hardness of the matrix, and the other is improving the interfacial bonding between Al2O3p and steel. The wear mechanism of the composites is abrasive wear when the Si powder is < 10 wt%. Otherwise, it is a mixed mode of abrasive and delamination wear.

Microstructure and Mechanical Properties of Deep Penetration Laser Welding Joints in Steel/Aluminum with Si Powder Addition

Microstructure and Mechanical Properties of Deep Penetration Laser Welding Joints in Steel/Aluminum with Si Powder Addition

Effect of Si addition on the mechanical and thermal properties of sintered reaction bonded silicon nitride

Advanced silicon nitride (Si3N4) ceramics were fabricated using a mixture of Si3N4 and silicon (Si) powders via conventional processing and sintering method. These Si3N4 ceramics with sintering additives of ZrO2+Gd2O3+MgO were sintered at 1800°C and 0.1MPa in N2 atmosphere for 2h. The effects of added Si content on density, phases, microstructure, flexural strength, and thermal conductivity of the sintered Si3N4 samples were investigated in this study. The results showed that with the increase of Si content added, the density of the samples decreased from 3.39g/cm3 to 2.92g/cm3 except for the sample without initial Si3N4 powder addition, while the thermal diffusivity of the samples decreased slightly. This study suggested that addition of Si powder, which varied from 0 to 100%, in the starting materials might provide a promising route to fabricate cost-effective Si3N4 ceramics with a good combination of mechanical and thermal properties.

Foaming inhibition of SiC-containing porcelain ceramics by using Si powders during sintering

Porcelain green bodies were prepared using porcelain stoneware tile powder as the major raw material, with silicon carbide (SiC) and Si powders as additives. These were fired at 1000–1200°C. The effects of Si powder addition on the microstructure, crystalline phases, and relative density of SiC-containing porcelain bodies were systematically investigated, and the related mechanism was also discussed in detail. The results show that even with the addition of a small amount of Si powder, the foaming degree of the porcelain bodies containing SiC with particle size and content in a wide range can be effectively inhibited. In particular, this effect becomes more pronounced as the Si powder particle size is reduced. It is believed that this work will have important scientific value for the oxidation protection of SiC and the foaming inhibition during the direct recycling of large amounts of polishing porcelain tile residues in the world.

Oxidation protection of SiC in porcelain tile ceramics by adding Si powder

Polishing porcelain tile residues (PPR) have accumulated to millions of tons and increases every year. It has become important to recycle the PPR due to the economic gains and environmental sustainability of doing so. However, its direct recycling in the production of porcelain tile has been limited by the fact that SiC particles oxidise during sintering which prevents the processing of dense ceramics. In this study, Si powder was introduced into the porcelain ceramics matrix containing SiC. The effect of Si powder additive on inhibiting the oxidation of SiC was evaluated using the relative density and the microstructure of the sintered samples. Results showed that the porcelain body containing SiC could be fully densitified when the suitable content of Si powder addition is introduced. These results indicate that it is a promising method to effectively protect the oxidation of SiC particles in the porcelain ceramics matrix during sintering.

Enhanced Sintering of Boron Carbide-Silicon Composites by Silicon

Boron carbide (B4C)-silicon (Si) composites have been prepared by aqueous tape casting, laminating, and spark plasma sintering (SPS). The influences of silicon (Si) content on the phases, microstructure, sintering properties, and mechanical properties of the obtained B4C-Si composites are studied. The results indicate that the addition of Si powder can act as a sintering aid and contribute to the sintering densification. The addition of Si powder can also act as a second phase and contribute to the toughening for composites. The relative density of B4C-Si composites samples with adding 10 wt.% Si powder prepared by SPS at 1600 °C and 50 MPa for 8 min is up to 98.3%. The bending strength, fracture toughness, and Vickers hardness of the sintered samples are 518.5 MPa, 5.87 MPa m1/2, and 38.9 GPa, respectively. The testing temperature-dependent high-temperature bending strength and fracture toughness can reach a maximum value at 1350 °C. The B4C-Si composites prepared at 1600, 1650, and 1700 °C have good high-temperature mechanical properties. This paper provides a facile low-temperature sintering route for B4C ceramics with improved properties.

Application of Metal Injection Molding to Al Powder

Metal injection molding (MIM) was applied to Al powders. Sintered Al compacts were prepared by MIM in this study. At first, sintered pure-Al compacts were prepared under various process conditions. The relative densities of the compacts debound in Ar gas and sintered at 650 °C for 2 hr in vacuum of 10−3 Pa order were 86 %, 90 % and 96 % when the average particle size were 20 μm, 10 μm and 3 μm, respectively. The 3 μm powder compact had the excellent tensile strength of 120 MPa and elongation at fracture of 19 % at room temperature. Next, the addition of Si powder to Al powder was examined to improve sinterability of Al powder. Regardless of Al powder size, the addition of Si powder widely enhanced densification of sintered Al compacts. Using Al powder of 35 μm, the relative density of the sintered pure-Al compact was only 66 %, while that of the sintered Al-1 mass%Si compacts went up to 89 %. When Al powder of 11 μm was used, the sintered Al-1Si compacts had the relative density of 97 % and the tensile properties close to annealed wrought pure-Al.

Effects of Sodium Salt on Hot Mechanical Properties and Microstructure of MgO-Al-C Bricks

The effects of addition of silicon powder (1 wt. %) and Na2CO3 (converting to additional 0.5%, 1% Na2O) on the hot modulus of rupture (HMOR) of MgO-Al-C bricks were investigated. MgO-Al-C refractories were prepared by using fused magnesia and graphite flake as main starting materials, and Si, Na2CO3 or both as additives. Its phase composition and microstructure were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and EDS. The results showed that the HMOR of MgO-Al-C bricks increased slightly with addition of Si powder. However, the HMOR decreased when adding Na2CO3 and Si powder together. Moreover, the HMOR deduced with the increase of Na2CO3 content. The mechanism is that Al powder reacted to form fibrous Al4C3 and AlN, which could improve the HMOR. When silicon was added, β-SiC and M2S were formed, which could fill the passages and pores. So the densification and strength were improved. The addition of Na2CO3 could promote the oxidation of Al powder to form Al2O3, and inhibit the formation of Al4C3 and AlN. Hence the strength of MgO-Al-C deduced.

Rapid Crystallization Process of Amorphous Silicon Nitride

The crystallization of nanosized amorphous silicon nitride powder is one of the methods to produce sub‐micrometer/nanosized α‐Si3N4 powder. The application of this method is still limited by the long crystallization time, low output, and high cost. This article invents a new crystallization method of amorphous silicon nitride involving the addition of Si powder. The new process reduces the complete crystallization time from more than 6 h to 30 min, thus allowing efficient production of sub‐micrometer/nanosized α‐Si3N4 powder. Effects of factors such as additive, temperature, and duration on the crystallization process are investigated using XRD and FTIR. The experimental results showed that the added Si powder accelerates the crystallization process effectively. The final product is a mixture of α‐Si3N4 and Si2N2O. In this article, amorphous silicon nitride powder with added Si is annealed at 1450°C. Powder of nearly 100% crystalline phase content is produced either by adding 10% Si and annealing for 15 min or by adding 5% Si and annealing for 30 min.

Effect of Si addition on hot-pressed ZrB 2–SiC composite with polycarbosilane as a precursor

We have previously reported the preparation of ZrB 2–SiC composite from the pyrolyzed mixtures of polycarbosilane-coated ZrB 2 powders via hot pressing at 2073 K for 60 min under a pressure of 20 MPa in an argon atmosphere. In the present paper, Si additive was introduced into the ZrB 2–SiC composite fabricated with the same processing conditions, in an attempt to convert carbon impurities introduced by the pyrolysis of polycarbosilane into SiC. The phase composition, microstructure and mechanical properties were characterized for the composite. Analysis showed that the Si additive could react with carbon to produce the SiC. In comparison with our previously published results, the addition of Si powder enhanced the micro-hardness of the composite, and did not have significant effect on fracture toughness.

Synthesis of Thermoelectric Fe&lt;SUB&gt;0.98&lt;/SUB&gt;Co&lt;SUB&gt;0.02&lt;/SUB&gt;Si&lt;SUB&gt;2&lt;/SUB&gt; with Fine Ag Dispersion by Mechanical Milling with AgO Powder

Synthesis of n-type Fe0:98Co0:02Si2 thermoelectric materials with dispersion of fine Ag particles was tried by mechanical milling of Fe-Si powder with AgO powder and subsequent hot pressing. The AgO phase was reduced by Si, resulting in precipitation of Ag particles, SiO2 phase and -FeSi phase. Most of the Ag particles were quite small; less than 100 nm in size. The precipitation of Ag and phase significantly decreased both the Seebeck coefficient and the electrical resistivity of Fe0:98Co0:02Si2, in spite of the SiO2 formation. On the other hand, the dispersion of fine Ag particles effectively enhanced phonon scattering, resulting in the reduction in the thermal conductivity in spite of the precipitation of metallic phases. However, the dimensionless figure of merit could not be improved by AgO addition because of the significant deterioration of the Seebeck coefficient. The Si powder addition with AgO powder was found to be effective on recovering the reduction in the Seebeck coefficient. [doi:10.2320/matertrans.E-MRA2008808]

Laser brazing of aluminium

Aluminium brazing is a method used for joining Al-parts by applying liquid alloys which have lower melting points than aluminium. The main task during Al brazing is the successful elimination of the oxide layer which forms on the free Al surfaces even at low oxygen partial pressures. This layer is continuous resulting in a poor wetting ability of the surfaces to be joined. Hence, the elimination of this oxide layer is inevitable for successful brazing. This can be realised by the application of suitable flux material dissolving the oxide layer, simultaneously ensuring temporal protection against the reconstruction of oxide layer during the heating period. In this paper, the CO 2 laser beam is applied as an energy source which yields rapid local surface melting. However, the absorption ability of Al is very low around the characteristic wavelength of this energy beam. In order to improve the absorption ability, the composition of NOCOLOK ® flux was properly modified by Si powder addition. The absorption ability of the flux-covered surfaces was determined indirectly by measuring the emission coefficient at the wavelength of CO 2 laser (10.6 μm). On the basis of surface emission measurements, the flux-composition can be successfully tailored according to the technical requirement dictated by the joining of tubes or sheets with different diameter and wall-thickness.