Papers by Keyword: Boride

Abstract: The effect of boronizing treatment on the conductivity of a high-conductivity and heat-resistant Al-Zr alloy conductor material was studied. The results showed that the conductivity of industrial pure Al containing transition element (Ti, V, Cr, Mn)>0.01 wt % (mass fraction, the same below) was improved to a certain extent by using boronizing treatment to remove transition metal elements through the formation of borides. Using the boronizing treatment, B can react with transition elements to form blocky (Ti, V, Fe)B₂ and flocculent (Ti, V, Fe, Zr)B₂. The boronizing treatment makes Ti and V out of the solid solution state, form borides and finally deposit to the bottom of the furnace, thus significantly improving the conductivity of the ingot. In addition, Cr and Mn were not found in the borides at the bottom of the furnace. However, for the high-conductivity and heat-resisting Al-Zr alloy conductor material, B will have poison effects on Zr during boronizing treatment, thus reducing the heat-resistance of the alloy. Therefore, in the preparation process of high-conductivity and heat-resistant Al-Zr alloy conductor material, the converter process should be added after boronizing treatment to ensure that the Al-Zr alloy conductor material has good heat-resistance and conductivity at the same time.

Abstract: Our group prepared an ReB₂-based ceramic with a composition of Re-74.5at% B to investigate its microstructure, high-temperature microvickers hardness, and high-temperature tribological properties in air. The microvickers hardness of the ReB₂-based ceramic was higher than 2600 at temperatures below 1073 K. The friction coefficients of ReB₂-based ceramic/Si₃N₄ sliding pairs were stable and low (≃ 0.15) at 1073 K. We concluded that the low friction coefficients of the sliding pairs resulted from the formation of low-friction hexagonal BN and B₂O₃ films. The friction coefficients of the ReB₂-based ceramic/Si₃N₄ sliding pairs were also low at 298 K (≃ 0.3 to 0.4) and 1273 K (≃ 0.1), but were unstable and high ( 0.6) at 673 K.

Abstract: Investigation on the casting, hot-rolling and heat treatment process of a high boron-bearing advanced high strength steel was conducted. The scanning electron microscopy (SEM), electron-probe micro-analyzer (EPMA), electron backscattered diffraction (EBSD) and X-ray diffraction (XRD) were employed to analyze the evolution of microstructure which includes the phase constitution and boride morphology during hot processing. Through the control of as-casted, heat treated microstructure and using interrupted tensile tests, the strengthening mechanism was revealed. Results showed that, the strain-induced ferrite transformation of austenite and grain size were the decisive factors which control the strength and ductility, while the defects and internal stress etc. were the secondary factors.

Abstract: Sintered steels, with and without boron addition, were prepared from powder compacts of pre-alloyed Fe-1.5Mo powder mixed with varied amounts of graphite (0, 0.1, 0.2, 0.3, and 0.4 wt.%) and hexagonal boron nitride (0 and 0.5 wt.%). Sintering was performed either in hydrogen or in vacuum atmosphere at 1280 °C for 45 minutes. The post-sintering cooling was performed in a furnace that was equivalent to 0.1 °C/s. The sintered boron-free steels showed dual-phase microstructure consisting polygonal ferrite and precipitate-containing grains. Each precipitate-containing grain contained packets, each of which was characterized by lamellar structure with alternating fibrous particles and ferritic laths, when carbon contents were in the range 0.1-0.3 wt.%. All the grains containing fine needle particles decorating ferritic lath boundaries were observed in the sintered Fe-Mo-0.4C steels. Boron addition caused some effects on sintered steels. The action of boron was the formation of grain boundary boride in the vacuum-sintered steels although it was hardly observed in case of hydrogen-sintered steels. Boron also promoted precipitation inside polygonal ferrite grains and along ferritic lath boundaries. The precipitate particle shape was fine needle-like in the sintered boron-containing steels. Due to liquid phase sintering, as a result of eutectic melting, the associated grain growth was observed. Disappearance of grain boundary boride was evidenced in the hydrogen-sintered steels. Without boron addition, hardening of the sintered steels strongly depended on carbon content. With boron addition, all the sintered steels showed high tensile strength and hardness even in the case of no graphite addition. Hardening action by carbon in the sintered boron-containing steels was weaker than that in the sintered boron-free steels.

Abstract: The widespread demand for light-weight materials in various emerging industrial sectors lead to the fabrication of aluminum- boron carbide composites. In this study, the B₄C particles were coated copper and Ni-B through electroless process using formaldehyde and sodium borohydride respectively as reducing agents under optimized condition. The microstructural and hardness behavior were investigated for powder metallurgy processed 20 vol. % of B₄C and coated B₄C particles in the aluminum matrix. Microscopic observation revealed that coating improved the dispersibility of B₄C particles in the matrix. The coated particles showed an increase in hardness and particle compaction with reduced porosity.

Abstract: The present study reports the growth of layers formed in the surface of the boride steel AISI W2; by the application of the dehydrated paste-pack boriding process and using three different temperatures at 1173, 1223 and 1273 K, with 2, 4, 6 and 8 h of exposure. The substrate and the boride Fe₂B were analysed quantitatively and qualitatively. The growth of the boride layer Fe₂B was examined using optical microscopy (OM), scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD). The properties were mechanically evaluated, using a Vickers indenter with loads of 0.5 and 1 N, with a constant distance of 15 μm and 30 μm. To determine the fracture toughness (Kc) and the adherence of the boride layer Fe₂B, the Rockwell C test method (VDI 3198) was used. The morphology present in the boride Fe₂B layer showed a smooth flat, whit ranged thickness from 13.96 ± 1.61 μm to 79.86 ± 4.13 μm. The presence of boride Fe₂B layers of steel substrate was confirmed by XRD and the distribution of alloying elements by Energy Disperses for Spectroscopy (EDS). The hardness of the boride layers Fe₂B ranged from 157 9± 17 to 1875 ± 25 HV. The fracture toughness of boride Fe₂B layer observed ranged from 4.15 to 4.75 MPam^1/2. The boride layer has a scale delamination H3 to H6. The boride layers formed in the surface have the function to increase the service life of W2 steels used in the industry.

Abstract: A certain amount of Ti was added into high boron alloyed stainless steel with content 2.25%B, and then high boron alloyed stainless steel composite casting slab with three layers was fabricated , in which central layer is high boron alloyed stainless steel containing Ti and cladding is plain 304 stainless steel without Ti. The microstructure of core and interface and the mechanical property of the composite plate were studied after hot forged, hot rolled and solution treated process respectively. The results show that the boride in as-cast microstructure of core are (Fe,Cr)₂B phase with long strip and TiB₂ phase with petal shape, moreover the formation of TiB₂ phase decreases the amount of (Fe,Cr)₂B phase. Two kinds of boride are fully broken after hot rolling and distributed in the form of block uniformly in matrix, and TiB₂ phase is more fine uniform. The mechanical property especially plastic performance of high boron alloyed stainless steel composite plate containing Ti after solution treatment is improved significantly, it has reached and surpassed the United States ASTM A887-89 delivery standards.

Abstract: Hard and brittle (Fe,Cr)₂B phase caused by excess boron in high boron alloyed stainless steel has adverse effects on the hot working performance and mechanical properties of material. Adding Ti into high boron alloyed stainless steel can improve the type, morphology and distribution of boride phase. The results show that TiB₂ phase with petals or small block shape forms after adding Ti into high boron alloyed stainless steel, and as the increase of Ti content, TiB₂ phase replaces (Fe, Cr)₂B gradually. Moreover, the petal-like TiB₂ phase becomes smaller and more granular after high temperature deformation, and the segregation of matrix composition is significantly weakened by the formation of TiB₂ phase.

Abstract: The microstructure and mechanical behaviors of the Al-Mg-B ternary alloy have been investigated in order to fabricate a composite system composed of (Al,Mg)B₂ in a Al-Mg matrix. Several Al-Mg-B ternary alloy compositions were selected for identification of borides and matrix formation during solidification. The in-situ (Al,Mg)B₂ phase was developed in an eutectic matrix of Al₈Mg₅ and Al, and formed in the location of inter and intra the Al dendritic region, indicating that the formation of (Al,Mg)B₂ was developed at the initial solidification process. Dominating factors for controlling the (Al,Mg)B₂ phase and mechanical behaviors are discussed in terms of structural identifications.

Abstract: The tribological behavior of Si3N4-hBN composites sliding on Fe-B alloy without lubrication was investigated by using a pin-on-disc wear tester. The results showed that, the addition of hBN to Si3N4 could not effectively improve the tribological characteristics of Si3N4-hBN when it slid against Fe-B alloy. Without lubrication, the wear of Si3N4-hBN composites was resulted from cracking and fracture, while the hard phase Fe2B in Fe-B alloy spalled off during the friction test. So, high friction coefficients (>0.9) and high wear coefficients (>1×10-5mm3/Nm) were obtained.