The aluminothermic reduction of boric acid

The effect of metallic aluminium powder on the production of boron carbide–alumina composite was studied. Boric acid, carbon and aluminium powders were mixed in stoichiometric ratio, ball milled and heat treated at temperatures between 1300 and 1650 °C for 1–5 h in the presence of argon flow. Depending on the ratio of boron oxide to carbon, the formation of boron carbide by the carbothermal reduction, was possible at a temperature of around 1500 °C, but with the addition of metallic aluminium to the mixture of boric acid and carbon, the carbide formation temperature was reduced at least 300 °C. At 1300 °C, B₄C was the major phase with alumina in the reaction products. The liquid–solid reaction mechanism, which occurred during the aluminothermic process, had a specific influence on the formation of boron carbide.     

Nano silicon top-layer for composite-induced multiphasic enhancement of thermal stability of hardness of diamond-like carbon nanofilm at 900 °C

The effect of 25-nm silicon top-layer on the hardness and thermal stability of 100-nm diamond-like carbon (DLC) film annealed at 750–900 °C has been investigated. The evolution of surface morphology, microstructure and reaction between C and Si was examined by high resolution scanning/transmission electron microscope, Raman and FTIR spectroscopy. The hardness of films was investigated using nano-indentation. After 750–900 °C annealing, the hardness of single carbon layer greatly decreased at 750 °C and then slightly increased at 900 °C due to the formation of SiC at the interface between the single C film and the Si substrate. In contrast, no significant variation occurred on the hardness of two-layer Si/C film under RTA at 750–900 °C. Although the higher annealing temperature resulted in higher sp²/sp³ bonding ratio as well as more sp² bonding formation in the carbon layer to soften the structure, the added Si top-layer can protect DLC from reaction with environmental oxygen and sustain the hardness of the composite film because of the multiphasic formation with extra SiC on the surface and at the interface between the C layer and Si substrate through great interdiffusion between Si and C for extending DLC high-temperature application.     

Infiltration mechanism and factors influencing carbon/carbon–Zr–Ti–C composites prepared by liquid metal infiltration

The effects of fibre architecture, reaction temperature and holding time on the infiltration performance of carbon/carbon (C/C)–Zr–Ti–C composites prepared by liquid metal infiltration were investigated. The results indicated that samples with a chopped-web needled preform and low initial density had a high final density. Increasing the reaction temperatures resulted in a decrease of the final density of samples. Additionally, increasing the initial holding time appeared to obviously result in a high final density, but its effectiveness was not obvious in later observations. An analysis of the infiltration kinetics and mechanisms indicated that the diffusivity of carbon in the carbide, the open-pore sizes and their distribution in C/C composites were the essential characteristics that controlled the height of infiltrating melts.     

Grinding of silicon wafers using an ultrafine diamond wheel of a hybrid bond material

An ultrafine diamond wheel of a mesh size of 12,000 was fabricated by using a hybrid bond material, which consists of silicon carbide, silica and alumina. The employment of the newly developed wheel enabled excellent performance during grinding of silicon wafers. An extremely smooth surface of an average roughness of 0.6 nm was achieved. TEM examinations showed that the total thickness of the defected layer was less than 60 nm.     

High-energy heavy ion beam annealing effect on ion beam synthesis of silicon carbide

Silicon carbide (SiC) is a superior material potentially replacing conventional silicon for high-power and high-frequency microelectronic applications. Ion beam synthesis (IBS) is a novel technique to produce large-area, high-quality and ready-to-use SiC crystals. The technique uses high-fluence carbon ion implantation in silicon wafers at elevated temperatures, followed by high-energy heavy ion beam annealing. This work focuses on studying effects from the ion beam annealing on crystallization of SiC from implanted carbon and matrix silicon. In the ion beam annealing experiments, heavy ion beams of iodine and xenon, the neighbors in the periodic table, with different energies to different fluences, I ions at 10, 20, and 30 MeV with 1-5 × 10¹² ions/cm², while Xe ions at 4 MeV with 5 × 10¹³ and 1 × 10¹⁴ ions/cm², bombarded C-ion in implanted Si at elevated temperatures. X-ray diffraction, Raman scattering, infrared spectroscopy were used to characterize the formation of SiC. Non-Rutherford backscattering and Rutherford backscattering spectrometry were used to analyze changes in the carbon depth profiles. The results from this study were compared with those previously reported in similar studies. The comparison showed that ion beam annealing could indeed induce crystallization of SiC, mainly depending on the single ion energy but not on the deposited areal density of the ion beam energy (the product of the ion energy and the fluence). The results demonstrate from an aspect that the electronic stopping plays the key role in the annealing.     

Friction and wear behavior of laser-sintered iron–silicon carbide composites

Laser sintering is currently one of the most popular techniques to develop innovative materials for many of the high tech industrial applications owing to its ability to build complex parts in a short time. As such, material researchers are focusing on developing advanced metal matrix composites through selective laser sintering method to develop an intricate component eliminating delay in production time. In the light of the above, the present work focuses on developing iron–silicon carbide (nickel coated) composites using direct metal laser sintering technology. A laser speed of 50, 75, 100 and 125 mm/s were adopted. Metallographic studies, friction and wear test using pin-on-disc have been carried out on both the matrix metal and its composites. Load was varied from 10 to 80 N while sliding velocity was varied from 0.42 to 3.36 m/s for a duration of 30 min. A maximum of 7 wt.% of silicon carbide has been successfully dispersed in iron matrix by laser sintering. Increased content of SiC in iron matrix has resulted in significant improvement of both hardness and wear resistance. Lower the sintering speed, higher is the hardness and wear resistance of both the matrix metal and its composites. However, coefficient of friction of composites increased with increased SiC under identical test conditions. SEM observations of the worn surfaces have revealed extensive damage to the iron pins, when compared with that of the composites.     

Liquid forging of thin Al–Si structures

Liquid forging is a pressurized solidification process, wherein finished components can be produced in a single process from molten metal to solid, utilizing re-useable die tools. In conventional die casting (gravity and pressure), components with a minimum wall thickness of about 0.6 mm can be fabricated. However, parts with section thickness as thin as 0.2 mm can be liquid forged using near eutectic Al–Si or Al–Si–Cu alloys. Water based lubricant containing micrographite is effective in releasing the component during ejection. In addition, it aids in shaping the component to required dimensional accuracy. These liquid forged parts are pore free. Thermal analysis of liquid forged 0.8 mm plate revealed rapid freezing at the rate of about 700 °C/s. During the process, die and punch were maintained at 200–250 °C. X-ray residual stress analysis on the surface of the liquid forged plate showed high intensity values for 0.1 mm plate. Distribution of eutectic silicon at inter dendritic region is extremely fine to nanoscale level.     

硅及硅合金对反应烧结SiC耐磨材料性能与结构的影响

本文首先分析了熔渗材料硅及硅合金的润湿性、流动性、烧失率的变化.结果表明:熔渗材料硅在1 430℃,硅铁合金在1 470℃时润湿角小(分别为0°和6°)、流动性大(分别为267%和198%)、烧失率小(均小于15%).同时分析了反应烧结SiC耐磨材料性能,并采用扫描电子显微镜、X射线衍射仪、EDS分别对其显微结构、主晶...     

Microstructure and mechanical properties of WC Ni–Si based cemented carbides developed by powder metallurgy

In this paper the influence of the Ni binder metal and silicon as an additional alloying element on the microstructure and mechanical properties of WC-based cemented carbides processed by conventional powder metallurgy was studied. Microstructural examinations of specimens indicated the presence of a very low and even distributed porosity and the presence of islands of metal binder in the microstructure of the cemented carbides. Furthermore, despite the addition of silicon and carbon in the cemented carbides, it was not observed the presence of small fractions of undissolved SiC and free graphite nodules in their microstructure. Vickers hardness and Flexural strength tests indicated that the cemented carbide WC–Ni–Si with 10 wt.% of binder presented bulk hardness similar to the conventional WC–Co cemented carbides and superior flexure strength and fracture toughness.     

Modification of thermally sprayed cemented carbide layer by friction stir processing

The modification of a thermally sprayed cemented carbide (WC-CrC-Ni) layer by friction stir processing (FSP) was studied. The cemented carbide layer was successfully modified using a sintered cemented carbide (WC-Co) tool. The defects in the cemented carbide layer disappeared and the hardness of the cemented carbide layer increased to ∼ 2000 HV, which was about 1.5 times higher than that of the as-sprayed cemented carbide layer. Additionally, the cemented carbide layer was bonded to the SKD61 (Nominal composition: 0.35-0.42 mass% C, 0.8-1.2 mass% Si, 0.25-0.5 mass% Mn, 4.8-5.5 mass% Cr, 1.0-1.5 mass% Mo, 0.8-1.2 mass% V, balance Fe) substrate by diffusion of the metallic elements and the distortion of the coating-substrate interface producing a mechanical interlocking effect.     

Segregation of silicon in silumin-carbon fiber composites

Conclusion At the surface of carbon fibers in alloy AL2-carbon tape composites obtained by the liquid phase method, apart from Al₄C₃ phase, silicon carbide crystals and primary silicon crystals are observed, as a result of which the overall concentration of aluminum carbide in the composite is reduced.A. A. Baikov Institute of Metallurgy, Moscow. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 24–26, August, 1984.     

Spray forming of hypereutectic Al–Si alloys

To develop advanced aluminum alloys with high silicon content, hypereutectic aluminum silicon alloys AlSix (x = 18, 25, and 35 wt.%) in the form of cylindrical billet have been spray formed under different thermal conditions. To help in spray forming parameter selection and interpretation of experimental results, phase diagram of the alloys and their thermochemical data such as liquid fractions and enthalpies in function of temperature have been calculated. The spray formed hypereutectic Al–Si alloys are typically composed of refined and uniformly distributed primary silicon and modified eutectic. Thermal conditions and silicon content of the deposited materials have significant influence on the metallurgical quality of the spray formed Al–Si alloys. Strong cooling condition is required for spray forming Al–Si alloys with high silicon content.     

Characterization of expanded austenite developed on AISI 316L stainless steel by plasma carburization

Expanded austenite generation through ion carburizing of AISI 316L using two different reactive gas mixtures (Ar 50%, H₂ 45%, CH₄ 5% and Ar 80%, H₂ 15%, CH₄ 5%) has been studied. It was found that an ∼ 14 µm surface layer of expanded austenite was developed with 30 min processing for both gas mixtures. Nevertheless, AES analyses have shown that on the ∼ 150 nm surface layer carbon in a concentration of ∼ 12% was diffused and located as carbide. For longer periods of processing, while for the gas mixture with 50% of Ar no significant modifications within those 150 nm surface layer were produced, for the gas mixture with 80% of Ar a gradual increase in the carbon concentration with time was found, with the extra carbon remaining as free carbon. The difference between both situations can be attributed to the different resulting current densities that have been of 7.0 mA cm^− 2 and 8.1 mA cm^− 2 for 50% and 80% of Ar respectively. Higher current densities result in higher carbon and Ar ions fluxes inducing, from one side surface element concentration modification through sputtering, and from the other the enhancement of carbon diffusion on the first hundred nanometers of the surface layers. This free carbon on top of the surface layers can act as solid lubricant reducing wear rate. Nevertheless, and in spite of the fact that expanded austenite was proved to be corrosion resistant, a reduction against NaCl solution corrosion in relation to the base material was observed. This lost to corrosion resistance can be attributed to carbide development on the layers closer to the surface that can work as a trigger for localized corrosion.     

Effect of carbon content on the microstructure and properties of (Ti0.7W0.3)C-Ni cermet

(Ti_0.7W_0.3)C solid solution powder was synthesized by high-energy ball milling. We investigated the effect of excess carbon in this system on the microstructure, pore level, and mechanical properties of (Ti_0.7W_0.3)C?-20 wt.% Ni cermet. We also report the variations in the carbon stoichiometry of the (Ti_0.7W_0.3)C_x phase in the powder and in the (Ti_0.7W_0.3)C_x?-20 wt.% Ni cermet after carbothermal reduction and liquid phase sintering, respectively. The particle size of the solid-solution carbide decreased with increasing carbon content in the (Ti_0.7W_0.3)C-?20 wt.% Ni cermets. This occurred because the dissolution of the solid solution (Ti,W)C is hindered by the high activity of carbon. However, an increase in the carbon content generated pores and carbon segregation, resulting in poor mechanical properties, as also observed in other carbide cermets.     

Deposition and super liquid repellency of fluorinated ZnO nanoparticles on carbon fabrics

The liquid-repellent behavior of fluorinated zinc oxide (ZnO) nanoparticles deposited onto carbon fabric (CF) by a pulse microwave-assisted (MA) method followed by surface fluorination treatment was investigated. The MA process is performed at 80 °C within 10 min with different pH values of 5.5, 8 and 12. The hexagonal ZnO nanoparticles with an average size of 100 nm exhibit a well-defined wurtzite crystal structure without any heat treatment. The ZnO nanoparticles produced by MA synthesis at pH = 8 display the maximal density over CF substrate. The fluorination coating effectively imparts super water and oil repellencies on the ZnO–CF surface; i.e., the contact angles are 163° (water) and 153° (ethylene glycol, EG). The liquid repellencies toward water and EG droplets show an increasing function of surface density of ZnO nanoparticles. This result can be attributed to the fact that an air layer is confined in the nanoparticles, thereby inducing a rougher gas–vapor–solid contact line, referred to as the Cassie state. Based on the Young–Duprè equation incorporated with the Cassie parameter, the lowest work of adhesion (W_ad) values of the ZnO–CF surface for water and EG repellencies are estimated to be 3.16 and 4.93 mJ/m², respectively. Accordingly, this work sheds some light on the creation of a two-tier texture by an efficient MA route and on how the surface density of ZnO nanoparticles strongly affects the repellent behavior of the resultant ZnO–CF composites.     

Room temperature process for chemical vapor deposition of amorphous silicon carbide thin film using monomethylsilane gas

The silicon carbide thin film formation process, which was completely performed at room temperature, was developed by employing a reactive silicon surface preparation using argon plasma and a chemical vapor deposition using monomethylsilane gas. Time-of-flight secondary ion mass spectrometry showed that silicon-carbon bonds existed in the obtained film, the surface of which could remain specular after exposure to hydrogen chloride gas at 800 °C. The silicon dangling bonds formed at the silicon surface by the argon plasma are considered to easily accept the monomethylsilane molecules at room temperature to produce the amorphous silicon carbide film thicker than monolayer. Thus, the entire silicon carbide thin film formation process at room temperature is possible.     

Laser cladding of SiC/Si composite coating on Si-SiC ceramic substrates

Pieces of silicon infiltrated silicon carbide (Si-SiC) were coated with a SiC particles reinforced Si matrix composite (SiC/Si) obtained from mixtures of SiC + SiO₂ and SiC + Si by laser cladding. A Nd:YAG pulsed laser delivering an average power of 920 W was used to apply such coatings using the powder blowing technique. The results demonstrate that the use of the SiC + SiO₂ powder mixture produces a severe damage on the base material, whereas the use of the SiC + Si mixture leads to the formation of sound coatings without substrate damage. XRD and nanoindentation measurements corroborate the production of silicon carbides surrounded by a metallic silicon matrix. This method could be used for repairing surface defects of silicon infiltrated silicon carbide ceramics (Si-SiC).     

Process optimization of Ti–Nb alloy coatings on a Ti–6Al–4V plate using a fiber laser and blended elemental powders

A fiber laser was used to modify the surface composition of a Ti–6Al–4V plate through deposition of the blown powder mixture of Ti–45 wt.%Nb. Scanning electron microscopy and energy dispersive spectroscopy (EDS) were employed to examine the clad sections microstructure and chemical composition. The optimized set of laser processing parameters, including the laser power of 1100 W, the laser scan speed of 350 mm/min (or ∼5.83 mm/s), the laser spot diameter of 2 mm and the powder feed rate of 0.1 g/s was found with the identification of combined parameters, the laser specific energy, the powder density and the newly defined laser supplied energy (i.e. representing the amount of energy given to the unit mass of the blown powder). It is shown that, with these parameters, continuous beads can be formed with pore-free sections and a homogeneous composition corresponding to that of β (Ti, Nb) solid solution phase. Furthermore, Al and V elements are thoroughly replaced with a more biocompatible element, Nb, in the second layer of a Ti–Nb cladding build-up on the surface of the Ti–6Al–4V plate (i.e. after ∼1 mm in clad thickness from the clad/substrate interface).     

Shape adaptive grinding of CVD silicon carbide

Because of the direct relationship between removal rate and surface roughness in conventional grinding, ultra-precision finishing of hard coatings produced by chemical vapour deposition (CVD) usually involves several process steps with fixed and loose abrasives. In this paper, an innovative shape adaptive grinding (SAG) tool is introduced that allows finishing of CVD silicon carbide with roughness below 0.4 nm Ra and high removal rates up-to 100 mm³/min. The SAG tool elastically complies with freeform surfaces, while rigidity at small scales allows grinding to occur. Since material removal is time dependent, this process can improve form error iteratively through feed moderation.     

Effect of infiltration parameters on composition of W-ZrC composites produced by displacive compensation of porosity (DCP) method

In this study, the effect of infiltration parameters on composition of W-ZrC composites produced by displacive compensation of porosity (DCP) method was investigated. For this purpose, a porous tungsten carbide preform was prepared by cold isostatic pressing (CIP) of tungsten carbide powder and polyvinyl alcohol (PVA). The porous preform was debinded for 4 h at 400 °C and sintered for 4 h at 1400 °C. The sintered preform was then infiltrated by molten Zr₂Cu at 1300 °C and 1200 °C for 1, 3, 5 and 7 h. Scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS) and X-ray diffraction (XRD) were used to study the cross section of infiltrated specimens. The results indicated that the amount of tungsten and zirconium carbide phases increased by increasing the infiltration temperature, whereas the effect of infiltration time on composition of W-ZrC composite was negligible.