In situ synthesis of Al3Niw/Al composites under high pressure

Abstracts are not published in this journal     

In situ synthesis and properties of Zr2Al3C4/ZrB2 composites

The Zr₂Al₃C₄/ZrB₂ composites are in situ synthesized by spark plasma sintering using Zr, Al, graphite, and B₄C powders as the initial materials. The introduction of ZrB₂ can not only evidently hinder the coarsening of Zr₂Al₃C₄ grains, but also benefit the densification and improve the hardness and Young’s modulus of the Zr₂Al₃C₄/ZrB₂ composites. When the ZrB₂ content is 20 vol.%, the composite shows an optimum fracture toughness value of 4.37 MPa m^1/2, about 20% higher than that of the monolithic Zr₂Al₃C₄. The unique mechanical properties can be mainly ascribed to the contribution of ZrB₂ as the reinforcing phase hindering the crack propagating. Compared with Zr₂Al₃C₄, the Zr₂Al₃C₄/20 vol.%ZrB₂ composite also exhibits a relatively higher thermal conductivity and better oxidation resistance.     

Fabrication and characterization of Ti3SiC2-SiC nanocomposite by in situ reaction synthesis of TiC/Si/Al powders

The microstructure and mechanical properties of Ti₃SiC₂-SiC nanocomposite fabricated by in situ hot pressing (HP) synthesis process were studied. The results show that dense Ti₃SiC₂-SiC composite contained minor TiSi₂ obtained by hot sintering at 1350°C for 1 h. The average grain size of Ti₃SiC₂ was 4 μm in length, and the size of SiC grains is about 100 nm. With its fine microstructure, the Ti₃SiC₂-SiC nanocomposite shows good mechanical properties.     

Pressureless sintering of Al2O3-SiC whisker composites

High-density compacts, up to 88% theoretical density, of Al₂O₃-SiC whiskers were prepared by a pressure casting and impregnation technique. Starting with these green bodies, composites of Al₂O₃–20 vol% SiC whiskers were pressureless sintered to higher than 95% theoretical density. They were further densified by hot isostatic pressing up to 99% theoretical density, resulting in a rupture strength of 680 MPa and a fracture toughness of 4.70 Mpa m^1/2.     

Microstructure,hardness and indentation toughness of high-temperature C40 Mo(Si,Al)2/SiC composites prepared by SPS of MA powders

The C40 Mo(Si_0.75Al_0.25)₂ and Mo(Si_0.75Al_0.25)₂/SiC materials containing micro-, nano-scale structure and Mo/Mo₅Si₃ phases have been prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. Sintered composites have hardness around 14 GPa. The 1.84 MPa m^1/2 toughness of C40 Mo(Si,Al)₂ can be 30% improved by addition of 20 vol.% SiC.     

In situ synthesis of hybrid-reinforced titanium matrix composites

Novel hybrid-reinforced (TiB + La₂O₃)/Ti composites were in situ synthesized utilizing the reaction between Ti, LaB₆ and B₂O₃ through homogeneous melting in a non-consumable vacuum arc remelting furnace. The thermodynamics of in situ synthesis reaction were analyzed. The phases in the composites were identified by X-ray diffraction (XRD) and the microstructures of the composites were examined by optical microscope (OM), backscattered scanning electron microscope (SEM) and field-emission SEM. Three kinds of reinforcements were found in the composites: La₂O₃ particles (diameter: ∼ 2 μm), TiB whiskers (width: ∼ 3 μm) and TiB plates (thickness: ∼ 1.5 μm). The reinforcements' sizes were fine and they were homogeneously distributed in the matrix.     

Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites

The C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composites were prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. The Mo(Si_0.75Al_0.25)₂/0–20 vol.% Al₂O₃ materials, showing micron and submicron composite structure, possess a hardness of 13.9–14.6 GPa but a poor toughness of 1.78–1.80 MPa m^1/2. The addition of 30 vol.% Al₂O₃ leads to the formation of the micron C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composite with an intergranular distribution of Al₂O₃, that results in a drop of the hardness to 10.2 GPa and an improvement of the toughness to 3.67 MPa m^1/2. The transition of the cleavage facets to the intergranular fracture with the addition of Al₂O₃ is assumed as the main toughening mechanism.     

In situ synthesis of Al2O3 particulate-reinforced Al matrix composite by low temperature sintering

The powder mixture of Al-10 wt.% SiO₂ was selected as a research system. Compared with an as-mixed powder, the phase structure and microstructure of an as-milled powder was investigated, and the temperature of the displacement reaction in the two kinds of powder was determined by thermal analysis. The preforms of the two kinds of powder were sintered based on the result of thermal analysis. The results indicate that the particle size of the Al-SiO₂ powder was refined greatly after 4 h of high energy ball milling, and diffusion couples were formed due to SiO₂ particles embedded in the Al matrix. The displacement reaction did not occur between Al and SiO₂ for the as-mixed powder, while it occurred in the range of 560–680°C for the as-milled powder. For the as-milled powder, an aluminum matrix composite reinforced with Al₂O₃ particles, which were homogeneously distributed in the Al matrix, can be fabricated by sintering at 640°C for 2 h.     

The effect of the interlayer element on the exfoliation of layered Mo2AC (A = Al,Si, P,Ga, Ge,As or In) MAX phases into two-dimensional Mo2C nanosheets

The experimental exfoliation of layered, ternary transition-metal carbide and nitride compounds, known as MAX phases, into two-dimensional (2D) nanosheets, is a great development in the synthesis of novel low-dimensional inorganic systems. Among the MAX phases, Mo-containing ones might be considered as the source for obtaining Mo₂C nanosheets with potentially unique properties, if they could be exfoliated. Here, by using a set of first-principles calculations, we discuss the effect of the interlayer ‘A’ element on the exfoliation of Mo₂AC (A = Al, Si, P, Ga, Ge, As or In) MAX phases into the 2D Mo₂C nanosheets. Based on the calculated exfoliation energies and the elastic constants, we propose that Mo₂InC with the lowest exfoliation energy and the highest elastic constant anisotropy between C₁₁ and C₃₃ might be a suitable compound for exfoliation into 2D Mo₂C nanosheets.     

In situ synthesis of Al–TiC in aluminum melt

In situ technology for the preparation of Al–TiC composite by self-propagating high-temperature synthesis is considered in this paper. It involves the synthesis of the reinforcement phase TiC from elemental powders directly in aluminum melt. Based on thermodynamic calculations, the composition and molar ratio of powders were chosen for the experiments. The effects of initial melt temperature and fluxes on the character of SHS reaction and TiC recovery were studied. The synthesis was shown to result in the formation of Al and TiC phases. The composites Al–TiC with the uncontaminated macrofracture, with the best TiC recovery and with the smallest TiC particles, can be produced at 1000 °C with fluxes.     

In situ synthesis of titanium diboride composites through volume combustion

Abstract

Hard in situ synthesis of TiB₂–Fe₂B metal matrix composite (MMC) has been synthesised by volume combustion synthesis (VCS) reactions of Fe–FeTi–FeB system. VCS samples were characterised by SEM, EDX, XRD and DTA. Results show that it is possible to synthesise in situ structured MMC samples (with TiB₂ and Fe₂B phases) by VCS. Metallographic investigations show that Fe₂B and TiB₂ are found dispersed throughout the metal matrix, and other borides are present in microlevel patches dispersed in a eutectic matrix. The Fe–TiB₂ composites sintered at temperature of 1200°C consist of three different regions, i.e. α-Fe, TiB₂ and Fe₂B regions. The increase in sintering temperature to 1400°C leads to a hypereutectic microstructure of the Fe–B binary system having TiB₂ grains uniformly distributed throughout the matrix. A semiliquid phase sintering occurred by increasing eutectic phase transformation temperatures to 1400°C, which increased the efficiency of VCS. On the other hand, increasing sintering time from 1 to 3 h decreased the volume fraction of α-Fe and increased the volume fraction TiB₂ phase.     

In situ synthesis of polymer-modified mesoporous carbon CMK-3 composites for CO2 sequestration

Here we report carbon-based composites polyethylenimine-mesocarbon (PEI-CMK-3) and polyvinylamine-mesocarbon (PVA-CMK-3) that can be used to capture and rapidly release CO(2). CO(2) uptake by the synthesized composites was determined using a gravimetric method at 30 °C and 1 atm; the 39% PEI-CMK-3 composite had ~12 wt % CO(2) uptake capacity and the 37% PVA-CMK-3 composite had ~13 wt % CO(2) uptake capacity. A desorption temperature of 75 °C was sufficient for regeneration. The CO(2) uptake was the same when using 10% CO(2) in a 90% CH(4), C(2)H(6), and C(3)H(8) mixture, underscoring this composite's efficacy for CO(2) sequestration from natural gas.     

原位聚合羟基磷灰石/聚醚醚酮复合材料

通过原位聚合法制备HA/PEEK复合材料,利用X射线衍射仪、红外光谱仪、差示扫描量热仪、扫描电镜对PEEK、HA/PEEK复合材料进行表征。研究表明,基体PEEK的聚合过程受到一定的影响;HA颗粒在基体之中有着优异的分散性。将PEEK、HA/PEEK复合材料压模成型,通过拉伸试验和硬度测量检测材料的力学性能,结果表明,HA的加入对复合材料的力学性能产生较大的影响。     

Synthesis of Mo(Si,Al)2 alloy by reactive hot pressing at low temperatures for a short time

Mo(Si,Al)2 alloy was prepared by reactive hot pressing at low temperatures for a short time under 20MPa in a vacuum using MoSi2, Mo and Al as starting powders. At 1160 °C, 5 min of soaking time was enough to obtain a high density alloy. At 1060 °C, however, 10min was needed. The formation of Mo(Si,Al)2 was accompanied by the melting of aluminum and controlled by the dissolution of molybdenum into the aluminum melt. It was proposed that the oxygen present in MoSi2 raw powder would react with aluminum and form Al2O3 in an amorphous or poor crystallization state. The mechanical properties of the alloy were a little stronger than those of monolithic MoSi2 alloy. The formed Al2O3 particles acted as crack-pinning elements, but a large toughening effect could not be obtained by this crack-pinning because of the strong interface bonding and the similar thermal expansion coefficients of Mo(Si,Al)2 and Al2O3.     

Preparation of Si3N4-SiC composites by microwave route

Si₃N₄-SiC composites have been microwave sintered using β-Si₃N₄ and β-SiC as starting materials. Si₃N₄ rich compositions (95 and 90 vol.% Si₃N₄) have been sintered above 96% of theoretical density without using any sintering additives in 40 min. A monotonic decrease in relative density is observed with increase in SiC proportion in the composite. Decrease in relative density has manifested in the reduction of fracture toughness and microhardness values of the composite with increase in SiC content although the good sintering of matrix Si₃N₄ limits the decrease of fracture toughness. Highest value of fracture toughness of 6.1 MPa m^1/2 is observed in 10 vol.% SiC composite. Crack propagation appears to be transgranular in the Si₃N₄ matrix and the toughening of the composites is through crack deflection around hard SiC particles in addition to its debonding from the matrix.