Papers by Keyword: TiB₂

Abstract: Electroless deposition technique was used to coat Ni-P on TiB₂ particles by activating the TiB₂ powder in a furnace at 400 ^◦C for 1 h. Scanning electron microscopy images and EDS spectra before and after electroless nickel plating confirm that nickel is deposited on the surface of TiB₂ particles. With the increase of heat treatment temperature, coating weight is increased firstly and then decreased, and reached the maximum value at 400 ^◦C. XRD results show that the Ni-P deposit was predominantly amorphous. However, after heat treatment, the metallic deposits can easily transform into crystalline Ni and Ni₃P phases, as confirmed by DSC and XRD analyses.

Abstract: Composites of TiC and TiB₂ (TiC-TiB₂) were prepared by self-propagating high-temperature synthesis (SHS), using compacted reactant different combinations of Ti, C, and B powders. It is very difficult to densify these materials using conventional sintering techniques. It was found that the chemical reaction between the starting Titanium, boron and carbon particles could be completed at 1200°C producing a pure TiB₂+TiC ceramic composite. Various carbon content causes the microstructure of the final products was different.

Abstract: This research employs pressureless sintering process to study the impact of different amount of titanium diboride on the performance of silicon carbide-titanium diboride composite. Results show that: no new phase was produced, and the whole process is a solid-phases sintering process. In this experiment, it has the smallest relative density and loss on ignition and porosity, and highest degree of densification of the silicon carbide-titanium diboride composite ceramics sintered body when the titanium diboride content is 50g, and the quality of SiC and TiB2 ratio is 1:1.

Abstract: In-situ micro/nanosized TiB₂ and Al₂(Y, Gd) particles reinforced magnesium matrix composite was successfully fabricated by addition of Al-Ti-B preform into Mg-Gd-Y-Zn matrix alloy, its microstructures and properties were investigated. The results show that the introduction of Al-Ti-B preform causes the precipitation of Al₂(Y, Gd) particles and the SHS synthesis of TiB₂ particles which significantly refine solidification structure. The reinforced Al₂(Y, Gd) particles with average sizes of 5-8 μm are uniformly distributed throughout the magnesium matrix, and have a good bond to the matrix. Tensile tests indicate that, compared with the former matrix alloy, mechanical properties of the multiple in-situ particles reinforced composite are improved all-roundly.

Abstract: This study explored the preparation technology of the use of compound materials as aluminum alloy spot welding electrode surface coating, in order to improve the electrode surface temperature strength and reduce electrode wear. The test results show that compound electrode coating of Cu-Ti-B is synthesized in situ at the Zr-Cr-Cu electrode surface by the resistance heat and pressure while spot welding. Structure and component analysis shows that it contains TiB2 strips and grains with good heat resistance, which can intensify the strength of coating base and reduce the plastic deformation generated in part of the electrode surface by blasting right after the electrification. So it is feasible to prolong the electrode life of aluminum alloy spot welding.

Abstract: In this paper, metal reduction preparation of TiB2 powder via magnesium reduction and aluminothermic reduction were studied. The carbon rod arc heating generated from the spread of the reaction of TiB2，and then the examinations were performed after pickling, crushing and grinding such as SEM and XRD. The results showed that the aluminothermic reduction occurred into the powder impurity phase less, but the need for better technology separation of Al2O3. Magnesium reduction reaction products with more impurities, pickling process removes only the reactants of MgO and other impurities not removed in the air and impurities were analyzed and compared.

Abstract: TiB₂ is a superhard, high-temperature and high corrosion resistant material and it is under consideration for tungsten-free cutting tools and high temperature structural applications. Although such a covalent compound requires significantly elevated temperature for the consolidation, great exothermicity of TiB₂ synthesis by means of SHS (Self-propagating High-temperature Synthesis) can be “ïn situ” utilized. In this study, TiB₂-based composites are fabricated from titanium, boron and binder metal. In order to optimize consolidation process and improve fracture toughness of the products, three types of binder, based on cobalt, nickel or copper were investigated. In respect to hardness, limited amount of binder, 5, 10 or 15 vol.% respectively, were applied; each time 5 vol.% of Ti addition for reaction with boron completeness was used. The TiB₂ based composites were fabricated from elements in one process by means of the SHS process combined with p-HIP (pseudo-hot isostatic pressing) method. The raw elemental powders were homogenized by wet mixing using ball milling technique. Dried mixtures were pressed into a compact, coiled by heating element and then exposed to the SHS-p-HIP process. After SHS initiation, the compact was pressed pseudo-isostatically under pressure of 190MPa for 5 min. The sintering additives and their concentrations significantly affected the consolidation process as well as the properties of composites. The highest hardness was obtained for samples sintered with cobalt, containing intermetallic binder. However, elemental metal binder was detected as a main component for samples sintered with copper. The relative density, SEM microstructure, phase composition and hardness are compared in this study.

Abstract: In this paper, two types of Zn-Al-Ti-B-C master alloys were produced by a two-step method and were found to have good refinement effect for Zn-50Al alloy. SEM results show that TiC and TiB2 particles act as the nucleating center of α-Al grains in Zn-50Al alloy. The presence of TiAl3-xZnx phase in the matrix of Zn-Al-Ti-B-C master alloy was found to further enhance the refinement effect. The melt thermal-rate treatment process present good grain refinement effect for Zn-50Al alloy and it was further promoted by the addition of Zn-Al-Ti-B-C master alloy into Zn-Al matrix.

Abstract: This paper presents results of experiments on pressureless sintering of boron carbide (B₄C) with addition of titânia (TiO₂) and titanium diboride (TiB₂). The TiB₂ powder was added as a second phase and the TiO₂ powder for reactive sintering and in-situ formation of TiB₂. The final concentrations of TiB₂ in the composites were 0 to 10 vol%. Sintering was performed at 2050 °C/30min in argon atmosphere. TiO₂ was completely transformed into TiB₂ with fine equiaxed grains distributed homogeneously. Composites obtained by in-situ reaction showed a densification increase with the concentration increase, while the composites with TiB₂ powder mixture showed low densification in all compositions. Relative Density of the composite with 10 vol% of TiB₂ obtained in-situ was 91% (TD) compared to 86 % for B₄C only. Vickers hardness was about 29 GPa.

Abstract: The titanium diboride reinforced titanium nitride-based ceramic cutting tool composite materials were fabricated by a new technology namely in situ synthesis followed by hot-pressed sintering. The experimental results showed that the highest density and the best mechanical properties of the composite material were obtained when the content of Ni was 5wt%. X-ray diffraction (XRD) was used to identify the phases of the composite. Microstructures of the composite were observed by means of scanning electron microscope (SEM). It is concluded that the sintered material was pure, no harmful reaction products was found; with the increase of Ni content, the proportion of short rod-like TiB₂ increased, fracture toughness of the composite materials were improved because lots of TiB₂ were pulled out; bridging phenomenon of short rod-like particles and metal particles were observed in the crack propagating process. The main toughening mechanisms of the composites were deflection and bridging of the crack as well as grains pulling out.