Papers by Keyword: Boron Carbide

Abstract: The outstanding performance of many aluminum matrix composites (AMCs) regarding specific stiffness makes AMCs attractive materials for lightweight construction. Low density boride compounds promise both an increase in stiffness and decrease in composite density. Therefore for this study AlB₂, B and B₄C were chosen for composite manufacturing. The composites were fabricated with the stir casting process. To avoid gas entrapment during mixing and ensure nonporous composites, partial vacuum was adapted during particle feeding and stirring. Poor wettability of used particle material in contact with liquid aluminum hindered particle incorporation, but alloying elements such as titanium were shown to affect wettability and particle incorporation for B₄C. Zn had no influence on wettability or reactivity and did not improve particle incorporation. In contrast to Zn, Ti improved adhesion and wettability, but particle incorporation was improved exclusively for B₄C. Besides alloying Ti, the use of high-shear force mixers improved particle incorporation enabling uniform particle distribution. AMCs with up to 12 vol.% of B₄C particles were produced via stir casting without alloying Ti.

Abstract: In this work, the “4M-System” (Machine for Multi-Material-Manufacturing) has been developed by RHP Technology for the manufacturing of Titanium Metal Matrix Composites. This equipment allows the Additive Layer Manufacturing (ALM) of large structures and uses a Plasma Transferred Arc (PTA) as a heat source for depositing feedstocks (powder/wire) layer by layer onto a substrate. Test coupons, made of Titanium powders and having different concentrations of B₄C particles, were deposited to form Metal Matrix Composites. Various processing parameters such as deposition rate, travel speed of the torch as well as plasma parameters (power/current/gas flow) were assessed for getting pore- and crack-free samples. After deposition, the specimens were cut and the cross-sections were analysed by optical- and scanning electron microscopy. Furthermore, the hardness, Young’s Modulus, and tensile strength were measured. Ti-Metal Matrix Composite materials resulted in higher strength and Young´s Modulus in comparison to the pure Ti-metal matrix. Using the 4M-System, B₄C particle reinforced Ti-MMC’s were successfully manufactured. Thus the 4M-System proved the capability of joining multi-material concepts, which also promises to create graded concentrations of reinforcement in the material.

Abstract: In the present work, in situ reinforced titanium composites (TMCs) synthesized using inductive hot pressing (iHP) are studied. The effects of B₄C phases and applied processing conditions, on the microstructure and properties of TMCs, are investigated. With the addition of B₄C particles, the microstructure of TMCs is refined and the strength is improved.Products of reactions which occur during the manufacturing process are analysed in detail. Microstructure observation illustrates, that B₄C survives - depending on the processing conditions. The reinforcing phases are homogeneously distributed in Ti matrix. Moreover, results of densification, mechanical properties and hardness measurements help to identify the most suitable processing conditions to produce this kind of TMCs.

Abstract: Polycarborane, as a kind of boron carbide polymeric precursor, was synthesized by hydroboration reaction with styrene, divinylbenzene as the carbon resource and borane as the boron resource in this work. The polymer precursor which had good solubility and film-forming ability was soluble in most organic solvents. Furthermore, polycarborane was used to fabricate hollow polymer microspheres by emulsion technique. The compact boron carbide ceramic hollow microspheres were prepared by ceramization of the polymer microspheres. Ceramic microspheres with diameters ranging from 1 to 1.5 mm and shell thicknesses from 15 to 30 μm were easily prepared by changing emulsion composition and curing conditions. Micrographs of SEM showed that the hollow microspheres had smooth surface and good sphericity. These boron carbide ceramic hollow microspheres are of significant importance for application in the field of neutron moderator in nuclear reactors, power generation in deep space flight, etc.

Abstract: Present investigation focusses on combined effect of B₄C and SiC on the improvement in hardness with an average size of 35-40μm on Al6061 hybrid composite. Composites are produced by stir casting process. The effect of artificial aging treatment with different aging temperatures of 100, 150 and 200OC on the improvement in hardness is also investigated. Optical micrographs and Brinell hardness number have been discussed. An attempt is made to find out the intermetallic phase responsible for strengthening by Transmission Electron Microscopy. Due to positive response to age hardening treatment there is an improvement in the mechanical properties of Al6061 alloy & its hybrid composite. The aging kinetics is more accelerated in case of hybrid composites as compared to unreinforced Al6061 alloy because of presence of reinforcement particulate, which act as nucleation site for precipitation. Artificially aged at 100OC shows improvement in hardness by 120-220% due to the precipitation of secondary solute rich phase of alloying elements as compared Al6061 alloy.

Abstract: Protective coatings able to provide improved tribological behavior and corrosion resistance are demanded in many industrial applications. Although hard chrome is a very effective solution and is widely used, environmental issues related to hexavalent chromium push to develop alternative treatments. Within the framework of the HardAlt European Project, electrodeposited composite coatings have been developed and main results of this investigation are reported in this work. Boron carbide micro-particles were dispersed in a Ni-P matrix under different operating conditions, in order to produce coatings with different composition and particle content. Structural and morphological characterization was performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical properties were evaluated by micro-indentation and the tribological performance was assessed by block-on-ring tests. Electrochemical experiments were carried out to examine the corrosion behavior of the composite coatings. Interesting results were obtained for composite coatings as regards hardness values, tribological behavior and corrosion resistance, even though some improvements can be realized. However, the results presented in this work show that composite coatings may represent a promising alternative to hard chrome for selected applications and also suggestions for further investigation are gained.

Abstract: Non-traditional machining process had made possible the machining of hard to cut materials. Among several non-traditional processes electrochemical machining has been given attention since there occurs no burrs or tool wear. Composites with nano reinforcements had outclassed their counterparts in terms of the properties shown by the nano composites. In the present work aluminium matrix has been reinforced with boron carbide and nano graphite which is added as a solid lubricant to improve tribological properties. The composite is subjected to electrochemical machining with a view of optimizing the process parameters. The process involves introducing abrasive particles while machining which aids in machining. Optimization of process parameters was based on the response surface methodology techniques with four independent input parameters such as voltage, current, electrolytic concentration and feed rate and ECM process performance in terms of material removal rate and overcut.

Abstract: Nowadays, the demands for materials with high strength based on a titanium matrix are increasing. The manufacturing of titanium composites through low cost and near-net-shape techniques is a challenge for the industry. There are different processing routes to meet these requirements of the market. As it is well known fast powder metallurgical densification techniques could satisfy these needs. In the present work, several titanium metal matrix composites (TiMMCs) have been fabricated by using a fast hot consolidation technique, namely direct hot pressing (dHP) in order to reduce the manufacturing time. Through a pressure assisted sintering with direct heating of a pressing die the consolidated composites can be formed directly from powders in a short period of time (15 min). The matrix materials were selected from two titanium grade 1 powders and as reinforcement materials boron carbide and boron amorphous particles were employed. Varying the reinforcement’s content in addition to their particle size, their influence on the composites behaviour was expected. Furthermore in this research work, the mechanical and microstructural characterisation of the specimens was carried out in order to identify the best combination of process parameters, material reinforcement and matrix powders.Nowadays, the demands for materials with high strength based on a titanium matrix are increasing. The manufacturing of titanium composites through low cost and near-net-shape techniques is a challenge for the industry. There are different processing routes to meet these requirements of the market. As it is well known fast powder metallurgical densification techniques could satisfy these needs. In the present work, several titanium metal matrix composites (TiMMCs) have been fabricated by using a fast hot consolidation technique, namely direct hot pressing (dHP) in order to reduce the manufacturing time. Through a pressure assisted sintering with direct heating of a pressing die the consolidated composites can be formed directly from powders in a short period of time (15 min). The matrix materials were selected from two titanium grade 1 powders and as reinforcement materials boron carbide and boron amorphous particles were employed. Varying the reinforcement’s content in addition to their particle size, their influence on the composites behaviour was expected. Furthermore in this research work, the mechanical and microstructural characterisation of the specimens was carried out in order to identify the best combination of process parameters, material reinforcement and matrix powders.

Abstract: Amorphous silicon carbide (a-SiC) and boron carbide (a-B₄C) thin films were deposited using reactive magnetron sputtering of SiC and B₄C target, respectively. Nanoindentation tests performed up to 450 °C in air were performed to explore and compare their hardness and elastic modulus.Hardness of a-B₄C film decreases at smaller rate in comparison to a-SiC film up to 450 °C. Similarly, elastic modulus value of B₄C is more stable with temperature than that of a-SiC.

Abstract: The ZrB₂ powders with different morphology were prepared by pressureless reactions, using ZrO₂, B₂O₃, B₄C, and graphite as raw materials. Three kinds of chemical reaction system were employed. The ratio of raw materials and reaction temperature were adjusted to prepare ZrB₂ powders of different morphology and particle size. The phase composition and purity of the as-prepared powders were analyzed by XRD, while the morphology and particle size were analyzed by SEM. The ZrB₂ powders were purified by removing impurities at 600 °C in a muffle furnace in air atmosphere. The results showed that in the reaction systems of ZrO₂-B₂O₃-C and ZrO₂-B₄C-C, the ZrB₂ could be generated at 1500 °C. The morphology of the as-prepared ZrB₂ powders were particles, rod-like or near spherical for ZrO₂-B₂O₃-C system and particles for ZrO₂-B₄C-C system. In the reaction system of ZrO₂, B₂O₃, B₄C, and C with a mole ratio of 3:2:1:8, the ZrB₂ powders with high purity could be produced at 1700 °C. The ZrB₂ powder was near spherical. After heat treatment, the particle size and morphology changed to some extent.