Factors affecting pressure infiltration of packed SiC particulates by liquid aluminum

Pressure infiltration is being currently used to evaluate the wettability of ceramic particles and fibers by liquid metals. The objective of this work is to investigate the effect of type and surface condition of the particulates and infiltration atmosphere on pressure infiltration of packed SiC particulates by pure liquid aluminum. Fourteen SiC particulates from five different suppliers, of green (high purity) and black (low purity) types, were used. Two of the particulates were subjected to either low- or high-temperature heat treatments in order to either burn organic residues or promote oxidation. Infiltrations were carried out in air, argon, argon/hydrogen, and nitrogen/hydrogen atmospheres. The results indicate that the threshold pressure does not depend appreciably on the type of particulate. A heat treatment at 600 ‡C improves the infiltration performance of particulates having a large amount of organic residues, whereas oxidation at 1000 ‡C decreases the threshold pressure. The results also illustrate the effects of the infiltration atmosphere; in particular, it is shown that inert or reducing atmospheres improve wettability. Formerly Research Associate with Industrial Espaˉnola del Aluminio, Centro de Investigación y Desarrollo     

Wetting of ceramic particulates with liquid aluminum alloys: Part II. Study of wettability

Wetting phenomena in ceramic particulate/liquid Al-alloy systems were investigated experimentally using a new pressure infiltration technique developed by the authors. Studies were performed on two different ceramic particulates, SiC and B₄C, with four different liquid aluminum alloy matrices, pure Al, Al-Cu, Al-Si, and Al-Mg. Five major variables tested to study wetting phenomena in ceramic/Al-alloy systems were holding time, melt temperature, alloying element, gas atmosphere, and particulate. Metal: ceramic interfaces were investigated with optical microscopy, SEM, EPMA, and Auger Electron Spectroscopy (AES) in order to understand better the wetting process. The threshold infiltration pressure decreased with, temperature as well as with pressurization time for all the ceramic/metal systems. A strong correlation was found between the alloying effect on the threshold pressure and the free energy of formation of oxide phase of the alloying element. More reactive alloying elements were more effective in improving wettability. In air atmospheres, the threshold pressure usually increased markedly as a result of a thick oxide layer formation on the liquid front. Compacts of B₄C particulates showed lower threshold pressures than those of SiC, particulates. Fracture occurred in a generally brittle manner in infiltrated SiC, specimens. AES element profiles on the fracture surfaces showed fast diffusion of Si, and pile-up of C at the metal∶SiC boundaries which promoted fracture through the carbon-rich layer. The fracture surfaces of infiltrated B₄C specimens indicated plastic deformation, hence a more ductile failure mode.     

Fabrication of Al-3 Wt pct Mg matrix composites reinforced with Al2O3 and SiC particulates by the pressureless infiltration technique

In Al-3 wt pct Mg/Al₂O_3p (or SiC _p ) composites fabricated by the pressureless infiltration method, the infiltration behavior of molten metal, the mechanical properties, and the interfacial reactions were investigated. The spontaneous infiltration of the molten Al-3 wt pct Mg alloy into the powder bed occurred at a relatively low temperature (700 °C for 1 hour under a nitrogen atmosphere). Spontaneous infiltration of the molten metal is related to the formation of Mg₃N₂ by the reaction of Mg and nitrogen. The tensile strength and 0.2 pct offset yield strength and elongation tend to decrease with increasing infiltration temperature and time, because of an increased interfacial reaction. In Al-3Mg/Al₂O₃ composites, MgAl₂O₄ was observed at interfaces between Al₂O₃ and the matrix, as well as at oxide films of the Al powder surface. In addition, MgO was observed at interfaces between Al₂O₃ and the matrix. On the other hand, Al₄C₃ was formed at interfaces between SiC and the matrix in Al-3Mg/SiC composites. In addition, MgAl₂O₄ was observed as a reaction product at the interfaces between oxide films of SiC and the matrix, as well as at oxide films of the Al powder surface. Since the Si released as a result of the interfacial reaction is combined with Mg, age hardening can occur by the precipitation of Mg₂Si via T6 treatment.     

Wetting of ceramic particulates with liquid aluminum alloys: Part I. Experimental techniques

An experimental technique for evaluation of wettability of solid particulates with liquid metal was developed. Uniformly packed powder specimens were prepared with a tamping device specially made for the present experiment, and wetting tests were conducted by pressure infiltration of liquid Al-alloys into the powder specimens. The threshold pressure for infiltration was used as a measure of wettability. With this technique, wettabilities were measured for 10 μm diameter SiC and B₄C particulates by several Al-based alloys. Threshold pressures obtained from this technique showed reproducibility to approximately ±7 kPa. Microstructures of infiltrated powder specimens indicated planar front infiltration with no disruption of powder compact during infiltration test and virtually no porosity.     

In Situ ceramic particle-reinforced aluminum matrix composites fabricated by reaction pressing in the TiO2 (Ti)-Al-B (B2O3) systems

Particulate TiB₂ reinforced aluminum-based metal matrix composites (MMCs) were successfully fabricated by means of the reaction processing method. TiB₂ particulates were formed in situ through the reaction of Ti and B in Ti-Al-B, TiO₂ and B in TiO₂-Al-B, and TiO₂ and B₂O₃ in TiO₂-Al-B₂O₃ systems. The results showed that in situ TiB₂ particulates formed in the Ti-Al-B system had a size of 5 μm and they exhibited block and rodlike structures. Moreover, coarse Al₃Ti blocks several tens of micrometers in size were also formed simultaneously. On the other hand, equiaxed Al₂O₃ and TiB₂ particulates with a size of less than 2 μm were formed in situ in the TiO₂-Al-B and TiO₂-Al-B₂O₃ systems. The Al₃Ti phase was completely eliminated in the TiO₂-Al-B system with increasing B content. Tensile tests revealed that the Al₂O₃ · TiB₂/Al composite fabricated from the TiO₂-Al-B system exhibits excellent mechanical properties. The yield strength of the Al₂O₃ · TiB₂/Al composite appeared to increase with increasing TiB₂ content. The yield strength of the Al₂O₃ · TiB₂/Al composite could be further increased by introducing CuO into the TiO₂-Al-B system. Such an increment in mechanical strength arose from the strengthening effect caused by the Al₂Cu precipitates. The incorporation of CuO had no effect on the in situ reaction process of the TiO₂-Al-B system. Finally, the effect of SiC addition on the microstructure and mechanical properties of the composites fabricated from the TiO₂-Al-B and TiO₂-Al-B-CuO systems was also investigated.     

Microstructure of AI2O3 fiber-reinforced superalloy (INCONEL 718) composites

Composites of INCONEL 718 alloy reinforced with either single-crystal (SAPHIKON) or polycrys-talline (Du Pont's FP) A1₂O₃ fiber were fabricated by pressure casting. Optical and transmission electron microscopy were used to characterize the microstructure of the composites and to determine the nature of the fiber/matrix reaction. The widely dispersed fibers in the SAPHIKON-fiber-reinforced composite had no influence on the solidification of the matrix. Six phases, γ-Ni₃Al, γ'-Ni₃Nb, δ-Ni₃Nb, TiC, NbC, and Laves, were present in the matrix of the composite. The last three phases were formed during solidification and the others precipitated during subsequent cooling. The high density of fibers in the FP-fiber-reinforced composite led to a more uniform microstructure within the matrix. Only three phases,γ″-Ni₃Nb, NbC, and Laves, were identified. Diffusion of Ti into the A1₂O₃ fiber resulted in preferential grain growth in the FP fiber in areas adjacent to the fiber/matrix interface. The fiber/matrix bond strength in shear in the SAPHIKON-fiber-reinforced composite was in excess of 150 MPa.     

Al2O3+TiC混合陶瓷刀具加工高铬铸铁辊的实践

介绍了高铬铸铁主要性能，特点和加工难度，对比分析了Al2O3 TiC混合陶瓷刀具材料成分，温度，硬度和耐用度的关系；优化选择了该刀具加工高铬铸铁的切削参数。     

Influence of additives of Al2O3 on properties of aluminum nitride-based ceramic

The properties of AlN-based materials with additives of 5–50 mass% Al₂O₃ are investigated. It is established that addition of Al₂O₃ to AlN increases the oxidation resistance of the materials as well as their mechanical strength and thermal resistance while preserving their electroinsulating properties and corrosion resistance to molten metals. AlN-Al₂O₃ composites may be used in high-temperature technology as refractory materials, electrical insulators, as well as radio-transparent materials.     

Wettability of silicon carbide ceramic by Al2O3/Dy2O3 and Al2O3/Yb2O3 systems

Wettability is an important phenomenon in the liquid phase sintering of silicon carbide (SiC) ceramics. This work involved a study of the wetting of SiC ceramics by two oxide systems, Al₂O₃ /Dy₂O₃ and Al₂O₃ /Yb₂O₃, which have so far not been studied for application in the sintering of SiC ceramics. Five mixtures of each system were prepared, with different compositions close to their respective eutectic ones. Samples of the mixtures were pressed into cylindrical specimens, which were placed on a SiC plate and subjected to temperatures above their melting points using a graphite resistance furnace. The behavior of the melted mixtures on the SiC plate was observed by means of an imaging system using a CCD camera and the sessile drop method was employed to determine the contact angle, the parameter that measures the degree of wettability. The results of variation in the contact angle as a function of temperature were plotted in graphic form which showed that the curves displayed a fast decline and good spreading. All the samples of the two systems presented final contact angles of 40° to 10° indicating their good wetting on SiC in the argon atmosphere. The melted/solidified area and interface between SiC and melted/solidified phase were evaluated by scanning electron microscopy (SEM) and their crystalline phases were identified by X-ray diffraction (DRX). The DRX analysis showed that Al₂O₃ and RE₂O₃ reacted and formed the Dy₃Al₅O₁₂ (DyAg) and Yb₃Al₅O₁₂ (YbAg) phases. The results indicated that the two systems had a promising potential as additives for the sintering of SiC ceramics.     

新型陶瓷材料Ti3SiC2制备技术的研究进展

Ti3SiC2兼有金属和陶瓷的许多优异性能。因此，Ti3SiC2在作为高温结构材料、自润滑材料以及电极材料等方面具有十分广阔的应用前景。本文重点介绍了Ti3SiC2的各种制备技术，并指出了各自的应用特点和存在的主要问题以及未来的研究方向。     

Reaction-Inhibition During Sintering of SiC with Al2O3 Additions

Abstract

The mechanisms and products of the reactions which occur during the sintering of SiC with Al₂O₃ as a sintering aid were analysed. The effects of two sintering atmospheres, namely pressurised CO and Ar gases, on the reaction thermodynamics and reaction products were investigated. Thermodynamically predicted reaction products were correlated with experimentally determined reaction products. The observed weight losses and the final sintered densities are explained on the basis of the proposed reaction mechanisms. The major finding of the present analysis is that a pressurised CO gas atmosphere greatly enhances the densification characteristics of SiC ceramics.

Résumé

Nous avons analysé les mécanismes et les produits des réactions qui se produisent lors du frittage du SiC avec du Al₂O₃ comme aide de frittage. Nous avons étudié les effets de deux atmospheres de frittage: du CO gazeux pressurisé et du Ar gazeux pressurisé, sur la thermodynamique des réactions et les produits de ces réactions. Les produits des réactions prédits par la thermodynamique ont été mis en corrélation avec les analyses expérimentales de ces produits. Sur les bases des mécanismes de réactions proposées, nous avons expliqué les pertes de poids observées et les densités de frittage finales. La découverte la plus importante de la présente analyse est qu'une atmosphère de CO gazeux pressurisé ameliore beaucoup les caractéristiques de densification des céramiques SiC.     

反向共沉淀法制备Y2O3-ZrO2陶瓷粉末

鉴于在ZrO2中加入Y2O3做稳定剂可有效提高ZrO2陶瓷的高温相稳定性,以ZrOCl2.8H2O和YCl3为原料,聚乙二醇(PEG)为分散剂,采用反向共沉淀法制备出Y2O3-ZrO2陶瓷粉末.利用XRD、SEM、DSC-TG、BET和激光粒度衍射对Y2O3-ZrO2粉末进行性能表征.结果表明:Y2O3-ZrO2粉末在800 ℃煅烧后的平均晶粒尺寸为25.2 nm,采用喷雾干燥得到的粉末球形度好,粒度分布窄;加入适量分散剂能较好地抑制颗粒团聚.     

Composites with a functional gradient in the systems Si3N4−Al2O3−Y2O3−TiC

Composites with a functional gradient in the system Si₃N₄−Al₂O₃−Y₂O₃−TiC were made by laminating and sintering ceramic films obtained by tape casting. The films had high contents of TiC and Al₂O₃ and were of different thicknesses. Materials with a high density and high fracture toughness (K_1c≈9.3 MPa·m^1/2) were obtained. Warsaw Polytechnic Institute. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 1–7, July–August, 1999.     

The interaction of hydrogen with the interface of AI2O3 particles in iron

A mathematical model to calculate the trap binding energy and trap density is suggested considering the theories of hydrogen trapping and hydrogen retrapping. When iron containing 2.0 wt pct Al₂O₃ is heated with a uniform heating rate of 3 K-min^-1, a hydrogen peak is observed at 853 K in the evolution ratevs temperature plot. This is due to hydrogen evolution from the Al₂O₃/lattice interface. The trap activation energy and trap binding energy of hydrogen at the Al₂O₃/lattice interface are estimated as 79 kJ ⋅ mol^-1 and 71.4 kJ ⋅ mol^-1, respectively, fitting experimental data to the model. This indicates that the Al₂O₃/lattice interface acts as an irreversible trapping site for hydrogen. By combining the trap binding energy and trap activation energy, the energy level of hydrogen around the Al₂O₃/lattice interface is suggested. The saddle point energy of hydrogen at Al₂O₃/lattice interface, 7.56 kJ ⋅ mol^-1 is nearly equivalent to the activation energy for hydrogen diffusion through a normal lattice, 6.9 kJ ⋅ mol^-1. Formerly Graduate Student, Korea Advanced Institute of Science and Technology.     

The effect of consolidation temperature on microstructure and mechanical properties in powder metallurgy-processed 2XXX aluminum alloy composites reinforced with SiC particulates

The effects of consolidation temperature on the development of microstructure and resulting mechanical properties of 2XXX aluminum composites were studied in an effort to fabricate composites with enhanced properties. Type 2009 and 2124 aluminum composites reinforced with 15 pct SiC particulates were produced at four different consolidation temperatures, i.e., 560 °C, 580 °C, 600 °C, and 620 °C, followed by extrusion at 450 °C. The 2124 Al-SiC _p composites consolidated at 560 °C showed the most homogeneous and the finest microstructures with the best mechanical properties, which were even better than the whisker-reinforced counterparts. All the results of the tensile tests, hardness tests, in situ scanning electron microscope (SEM) observations of the fracture process, and the apparent fracture toughness indicated that the prominent mechanical property improvement observed in the 2124 Al-SiC _p was associated largely with the reduction of volume fraction of the detrimental coarse and brittle manganese-containing particles, as well as grain refinement. The detrimental manganese-containing particles that were routinely observed in the 2124 Al-SiC composites were very effectively refined by the reduction of consolidation temperature, and they rather contributed to the overall mechanical properties of the composites through Orowan-type strengthening and grain growth inhibition.     

Influence of Li2O on the carbonate capacity of CaO- CaFv2- AI2O3 Melts

The influence of Li₂O on the carbonate capacity of CaO-CaF₂-Al₂O₃-based fluxes is examined by a thermogravimetric technique over the temperature range 1250 °C to 1350 °C. The values of the carbonate capacities (Cc = wt pct CO₂/P_CO2) were calculated by the solubility and the partial pressure of carbon dioxide. The replacement of CaO by Li₂O resulted in a decrease of the carbonate capacity. The addition of Li₂O, from 0.4 to 2.0 pct, to the CaO-CaF₂-Al₂O₃ increases the carbonate capacity at 1300 °C by 50 pct. At 0.4 pct Li₂O,Cc is 1.2, and at 2.1 pct Li₂O,Cc is 2.1. The replacement of CaF₂ by Al₂O₃ was found to have no significant influence on the carbonate capacity of the investigated ternary system. SIMEON SIMEONOV, formerly Visiting Research Fellow, Institute of Industrial Science, University of Tokyo. KOJI FUKTTA, formerly with the Institute of Industrial Science, University of Tokyo.     

La2O3对激光熔覆TiC/Ni基复合涂层的影响

利用CO2横流激光器在低碳钢基体表面熔覆含稀土氧化物La2O3的镍基TiC金属陶瓷复合层,研究了不同含量的La2O3对激光熔覆镍基金属陶瓷复合层组织及性能的影响。结果表明,加入适量的稀土氧化物La2O3可有效改善激光熔覆复合层的显微组织,减少复合层中的裂纹、孔洞、夹杂;加速复合层中TiC颗粒的溶解和改善TiC颗粒的形状变化,同时,熔覆复合层的耐磨性和耐蚀性明显提高。     

Interfacial tensions of liquid Fe-Ni alloys and stainless steels in contact with CaO-SiO2″AI2O3-based slags at 1550 °C

In the present work, the interfacial tensions of Fe-Ni alloys in contact with slags of the CaO-Al2O3-SiO2 system were measured at 1550 °C. Nickel additions to the alloy were found to decrease interfacial tension. The effects of alumina and titania additions to the slag on the interfacial tension of the Fe-20 wt pct Ni alloy were determined: alumina was found to increase the interfacial tension by a small amount, while titania was found to decrease it drastically. Using the present interfacial tension data for the CaO-Al2O3-SiO2 system and the ones measured by Jimbo and Cramb, Girifalco and Good’s interaction coefficient (ϕ) was determined as a function of the slag composition using regression analysis and was found to be a useful means of correlating interfacial tension data. The interfacial tension of an Fe-20 wt pct Ni-2.39 wt pct Al alloy in contact with a CaO-Al2O3-SiO2 slag was found to decrease drastically in the first 60 to 75 minutes of the experiment due to the dynamic effects of mass transfer. Slight lowering of interfacial tensions of industrial stainless steels due to sulfur transfer from liquid metal to slag was also observed. The equilibrium interfacial tensions of type 304 stainless steels were found to be more dependent on the slag chemistry than on the nickel and chromium content of the alloy. Formerly Graduate Student, Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA