Papers by Keyword: Borides

Abstract: The surface layer of steel was reinforced by electron-beam cladding at air atmosphere. Two types of powder mixtures were used to receive coatings: (1) titanium and graphite, (2) titanium and boron carbide. The formation of heterogeneous structure was observed in specimens after the electron-beam treatment by the methods of optical microscopy and scanning electron microscopy. The X-ray diffraction analysis was used to analyze the phase composition of the coatings. The wear resistance level of the coatings was estimated by friction test against loosely fixed abrasive particles. It was found that surface alloying of steel with carbon containing components led to the formation of material with an enhanced wear resistance level.

Abstract: A new type of gradient boron alloyed composite material, containing boron alloyed core layers and stainless steel coatings around the core, were designed and prepared by composite casting and hot rolling. The evolution of microstructures, phases and precipitations, as well as their influence on hot rolling process and performance are investigated. A mixture of austenitic matrix and uniformly distributed borides are obtained in the hot rolled stainless steel with 2-2.5 % boron, while massive borides are in the length of 80-120 μm together with micro gaps at the interface between the borides, and the matrix is remained after hot rolling for the core layers with higher boron contents. Hot deformation would be hindered since more precipitations of these orthorhombic or tetragonal phases occur with an increase of the boron concentration in the core layers.

Abstract: This paper presented the application of microwave-discharge plasma apparatus which was used to evaluate the catalytic properties of ZrB₂-based ultra-high temperature ceramics in the simulated real service environment by the wall temperature response method based on the heat balance principle. The results showed that the material composition had a significant influence on the catalytic properties of ZrB₂-based ultra-high temperature ceramics, and the catalytic activity of ZrB₂-SiC composites with Cr addition had been increased significantly. The relationship between catalytic properties of ZrB₂-based ultra-high temperature ceramics and surface composition was discussed in detail. The composition optimization was considered to be a very effective way to inhibit the recombination reactions of dissociated atoms on the surface of ultra-high temperature ceramics.

Abstract: ZrB₂-based ceramic composites were prepared through hot-pressing at a temperature of 1880°C. An intragranular microstructure was achieved because of the existence of nanoSiC. In this paper, the mechanical properties of ceramic materials of ZrB₂-SiC-G were studied, and the influence of intragranular microstructure on the mechanical properties was analyzed. The values of flexural strength and fracture toughness of ZrB₂-20vol%SiCnp-15vol%G reached 551.9MPa and 5.25MPa·m^1/2, respectively. Compared to ZrB₂-20vol%SiC-15vol%G with micro-SiC, the fracture toughness was improved.

Abstract: Engineering materials with better high temperature oxidation properties are needed to increase the thermodynamic efficiencies of the energy production and transportation systems. Because of their high melting temperatures, refractory metals like Nb or Mo are brought together with intermetallic compounds as two components of a new class of composite materials. To acquire a balanced high temperature mechanical and oxidation properties, these materials generally have multiphase and multicomponent structures. Borides of some transition elements are also being considered as high temperature structural materials for new aerospace vehicles. These materials are also required to have sufficient high temperature oxidation resistance in order to provide reliable and long service lives.

Abstract: This study focuses on tribological performance of as-received and borided Ti6Al4V alloys against ceramic counterfaces (Al2O3 and Si3N4 balls) in water. The wear mode of the alloy changed from ploughing to polishing by achieving a remarkable reduction in wear loss upon boriding. On the borided surface, the destructive action of the Si3N4 ball was very limited, when compared to that of the Al2O3 ball.

Abstract: The mechanical engineering industry is always in the search of new hardfacing alloys which nowadays make it possible to solve considerable delicate problems of abrasive wear and corrosion. These alloys are heterogeneous materials and are generally composed of a ductile matrix and a significant proportion in hard phases (carbides, borides or silicides), which give a good wear resistance and corrosion. The following studies made on alloys containing Ni, rich in Silicon and tungsten. We noted that addition of these elements (Si and W) got interesting mechanical properties. The alloys that we chose for this study contain the elements C, B, Si, Cr and W with additions in Ti and Mo. The aim of this work is the characterisation of the various phases formed during solidification, to study chemical affinities in this system poly-constitutes and to make a correlation between the chemical composition, the conditions of development and the microstructures obtained.

Abstract: The microstructures of B-bearing cast steel containing 0.8-1.2 wt.%B, 0.8-1.2 wt.%Cr, 1.0-1.5 wt.%Mn, 0.6-1.0 wt.%Si and 0.10-0.25 wt.%C have been characterized by means of optical OM, SEM, EPMA and XRD. The solidification structure of B-steel consists of pearlite, ferrite, martensite and boride (Fe2B), while the hardness is 1430-1480 HV. Borides distribute along the grain boundary in the form of eutectic. Fine lath martensite and eutectic Fe2B can be obtained by water quenching at 1223 K-1273 K. The hardness and impact toughness of the B-steel exceed 55 HRC and 150 kJ/m2, respectively. The abrasion resistance determined using a pin abrasion tester is obviously higher than that of the martensitic cast steel and nears to the high chromium white cast iron.

Abstract: a kind of as-cast nickel-base single crystal superalloy was TLP bonded using Ni-Cr-B amorphous foil at different temperatures. Special attention is paid to the formation of boride in diffusion zone of TLP joints at different conditions. The chemical composition and microstructure of borides were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At different bonding temperature, M3B2 precipitates appear distinct morphologies. At 1200°C, both blocky and plate-like borides formed owing to the diffusion of boron atoms into base metal and precipitation during the cooling process. At 1230°C or above, due to the diffusion of boron atoms the constitutional liquation of original γ/γ′ eutectics in the base metal occurs and borides formed when the system was cooled to room temperature. The analysis of TEM results reveals that M3B2 has a tetragonal structure and is rich in Mo, W, and Cr elements.