Synthesis of TiC–TiB–TiB2 composite powders by solid reaction of powders

In the present work, TiC–TiB–TiB₂ diffusion-layer-coated B₄C composite powders were synthesised via a powder immersion method using Ti and B₄C powders as reactants. The phase compositions and microstructure of the treated powders were characterised by employing X-ray diffraction and scanning electron microscopy. No significant reaction between B₄C and Ti could be detected at 800°C. After treatment at 900°C, the products generated were composed of TiC and TiB. After treatment at 1000°C, the products generated were primarily composed of TiC and TiB, with a small amount of TiB₂. The composition and proportions of the produced phases varied with process temperatures and the composition of the initial powders used. Powder mixtures with a Ti/B₄C molar ratio of 3.5:1 and treated at 1000°C for 14?h were more suitable for synthesis of TiC–TiB–TiB₂-coated B₄C composite powders.     

On sintering of Ti–Ni (–TiB2) alloys to near full density

Abstract

Using a combination of mixed elemental powders and TiB₂, a series of Ti–Ni and Ti–Ni–B alloys were optimised for sintering by varying the nickel and boron contents, the particle size of the elemental powders and the compaction pressure. The sintering temperature was maintained at 1200°C to limit the costs of a potential commercial sintering operation. For Ti–Ni alloys, a density of 99% was attained in Ti–7Ni made using fine Ti and Ni powders sintered in the solid state, and from liquid phase sintering of Ti–8Ni made using coarser powders. Porosity was almost eliminated from Ti–7Ni–xB alloys made by adding 1–3%TiB₂ to the coarser Ti and Ni powders. The action of TiB₂ as a sintering aid is possibly owing to a combination of the formation of a small amount of liquid at the sintering temperature and the restriction of grain growth owing to the presence of TiB particles.     

Fabrication of in situ TiB2–TiC reinforced steel matrix composites by spark plasma sintering

Abstract

In situ TiB₂ and TiC particulates reinforced steel matrix composites have been fabricated using cheap ferrotitanium and boron carbide powders by spark plasma sintering (SPS) technique. The sintering behaviour and the formation mechanism of the composite were studied. The results show that when the composite was sintered at 1050°C for 5 min, the maximum relative density and hardness of the composite are 99·2% and 83·8 HRA respectively. The phase evolution of the composite during sintering indicates that the TiB₂ and TiC reinforcements were formed in situ as follows: first, the solid/solid interface reaction between Fe₂Ti and B₄C, resulting in the formation of a small amount of TiB₂ and TiC below 950°C; second, the solid–liquid solution precipitation reaction in the Fe–Ti–B–C system, resulting in the formation of the main TiB₂ and TiC reinforcements at ～1000°C.     

Investigation of the Structure and Properties of Materials in the SiC ― TiB2 System

The structure and properties of sintered and hot-pressed materials of the SiC TiB₂ system were investigated. The optimal conditions for obtaining dense ceramics with minimum grain size of the phase components was determined. It was established that composites containing from 25 to 50 vol.@percnt; TiB₂ have a bend strength equal to 450 MPa at 20°C; this increases to 500 MPa at 1600°C for ceramics with a pseudoeutectic structure. The material is highly heat resistant in the temperature range 900-1200°C.     

Kinetics of Na2O evaporation from CaO–Al2O3–SiO2–MgO–TiO2–Na2O slags

The present work is carried out to study the evaporation of Na₂O from CaO–Al₂O₃–SiO₂–TiO₂–MgO–Na₂O slags with high basicity and high alumina in the temperature range of 1500–1560°C. The ratio of evaporation was determined by monitoring the Na₂O content change of the slag melt under isothermal reduction conditions. The results show that the evaporation ratio increases with increasing the temperature. Higher basicity and increasing concentrations of Na₂O, Al₂O₃ are also found to increase the evaporation ratio of Na₂O, while MgO addition only slightly enhances the evaporation ratio. With TiO₂ content increasing, the evaporation ratio first increases and then decreases. The evaporation rate of Na₂O appears to be controlled by chemical reaction at the slag/gas interface in the beginning, followed by a mixed reaction-mass transfer regime, and finally a liquid-phase mass transport step. The apparent activation energy is 134.74?kJ?mol^?1 for the chemical reaction regime and 268.53?kJ?mol^?1 for the liquid-phase mass diffusion step.     

Effect of Heat Treatment on the Physicochemical Properties of Ultrafine ZrO2–Y2O3–CeO2–Al2O3–CoO Powders

Powder Metallurgy and Metal Ceramics - Variations in the phase composition, specific surface area, and morphology of structural components in the ultrafine powder of composition (wt.%) 70 (90 ZrO2...     

自蔓延高温合成TiB2粉末

通过对稀释剂加入量、压制压力等反应条件对燃烧波蔓延速率的影响，研究了带还原阶段的ＳＨＳ反应。掌握了用此工艺制备ＴｉＢ＿２粉末。     

自蔓延高温合成制备TiB2

采用Ｔｉ和Ｂ粉压坯，用电焊机作燃烧合成时的点火装置，利用燃烧合成方法制备ＴｉＢ２。用ＸＲＤ、ＳＥＭ技术对合成产物进行结构、组织分析。结果表明，用燃烧合成法在４５７．０℃～８５６．１℃之间可制备得到ＴｉＢ２。用自蔓延高温合成（ＳＨＳ）制备ＴｉＢ２粉末，其粒度可达１～５μｍ。     

Solid-State Reactions of SiC–TiO2–MgO System and Phase Relations in SiC–SiO2–TiC–TiO2–MgO System

Powder Metallurgy and Metal Ceramics - Preliminary experiments revealed solid-state reactions in the SiC–TiO2–MgO system that resulted in forming TiC compound, providing, thus, a new...     

Effect of Na2O on Viscosity,Structure and Crystallization of CaF2–CaO–Al2O3–MgO–TiO2 Slag in Electroslag Remelting

Russian Journal of Non-Ferrous Metals - The effect of Na2O on the viscosity, structure, and crystallization behavior of CaF2–CaO–Al2O3–MgO–TiO2 slag was studied using the...     

Fabrication of Al2O3/(ZrB2 + TiB2) Composite Using MACS and Microwaves

Because of the excellent thermal and mechanical properties of engineering ceramics, they have been used as structural materials or composite matrixes and reinforcements in recent years. Alumina, titanium diboride, and zirconium diboride have found important uses in the past two decades. In this study, Al₂O₃/(ZrB₂ + TiB₂) ceramic composite powders were fabricated in situ and mechanical activation by milling was used to assist combustion synthesis (CS). A mixture of Al, ZrO₂, TiO₂, and B₂O₃ powders were used as raw materials. Mechanical activation was done using ball milling of different durations. Afterward, combustion was initiated using microwaves on the activated mixtures. X-ray diffraction (XRD) and scanning electron microscopy were used to investigate the purity and microstructure of the products. XRD analysis of the samples in the final stages of the process revealed that Al₂O₃/(ZrB₂ + TiB₂) composite powder was successfully fabricated using mechanical activation and CS, but that the CS reaction did not occur in unmilled samples. It was shown that increasing milling time from 3 to 10 hours increased purity and homogeneity of the products to the point that no noticeable impurity existed in the samples milled for 10 hours.     

Effect of TiO2 on the crystallisation behaviour of CaF2–CaO–Al2O3–MgO slag for electroslag remelting of Ti-containing tool steel

The crystallisation characteristics of CaF₂–CaO–Al₂O₃–MgO slags with various TiO₂ contents from 0 to 9.73 mass% were studied using a single hot thermocouple technique, SEM-EDS and X-ray diffraction. The crystallisation mechanism of TiO₂-bearing slag was identified based on kinetic analysis. It was found that increasing TiO₂ from 0 to 6.43 mass% inhibited the crystallisation ability of electroslag remelting-type CaF₂–CaO–Al₂O₃–MgO slag, whereas further increasing TiO₂ content up to 9.73 mass% enhanced the slag crystallisation signally. When increasing TiO₂ content to 6.43 mass%, the crystalline phase shift from CaO to Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ at high temperatures. At lower temperatures, the crystalline phase change from polygonal Ca₁₂Al₁₄O₃₂F₂ to need-like CaTiO₃. Further increasing TiO₂ content to 9.73 mass%, the crystalline phase are Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ in the range of 1473–1613?K. The crystallisation of crystalline phase in the isothermal crystallisation is surface nucleation and controlled by interface reaction when TiO₂ content is lower than 6.43 mass% in the slag. It is bulk nucleation and diffusion-controlled one-dimensional growth in slag with 9.73 mass% TiO₂.     

Viscosity of CaO–MgO–Al2O3–SiO2 melts containing SiC particles

The influence of SiC particle on viscosity of CaO–MgO–Al₂O₃–SiO₂ melts was investigated by the rotating-cylinder method. It was found that temperature dependence of viscosity could be described by the Arrhenius law for systems with or without SiC particle addition. The activation energies of liquid–solid mixtures were mainly determined by liquid phase. Temperature had little influence on the relative viscosity (defined as the viscosity ratio of solid–liquid mixture to pure liquid). Viscosity and relative viscosity increased as decreasing rotation speed and increasing volume fraction of SiC solid particle. For the same volume fraction of SiC particle, relative viscosity was affected by the liquid slag compositions. The relative viscosity was smaller when composition of liquid slag had a larger CaO/SiO₂ ratio or MgO/Al₂O₃ ratio. Meanwhile, it was found that the smaller SiC particle will lead to a larger relative viscosity.     

Effects of super-gravity field on precipitation and growth kinetics of perovskite crystals in CaO–TiO2–SiO2–Al2O3–MgO melt

The precipitation and growth behaviours of perovskite crystals from CaO–TiO₂–SiO₂–Al₂O₃–MgO melt in a super-gravity field with different gravity coefficients at different cooling rates were investigated in this study. In a super-gravity field, the first precipitated perovskite crystals migrated quickly along the super-gravity direction, and gradually concentrated and grown into larger crystals in the bottom area, while the new perovskite crystals keep precipitating and concentrating towards the bottom area simultaneously. Furthermore, by simplifying the layered samples obtained by super-gravity into three areas along super-gravity direction: slag-rich area, interface area and perovskite-rich area, the variations in volume fractions and equivalent diameters of perovskite crystals against gravity coefficients and cooling rates were obtained by weighting the values of the three areas. And the results indicated that increasing gravity coefficient was not only beneficial for the precipitation but also for the growth of perovskite crystals in the slag melt. Afterwards, the effects of super-gravity field on the precipitation and growth kinetics of perovskite crystals were further discussed.     

Viscosity of low silica CaO–5MgO–Al2O3–SiO2 slags

Abstract

The viscosity of CaO–5MgO–Al₂O₃–SiO₂ slag with low silica was measured by rotating cylinder method up to 1823 K. Slag compositions were chosen based on five different levels of SiO₂ content between 0 and 11·80%. The MgO content was 5·0%. The mass ratio of CaO/Al₂O₃ was varied from 0·66 to 1·95. It was shown that viscosity decreased with increasing temperature and decreased with increasing the mass ratio of CaO/Al₂O₃, following by an increase with further increasing the mass ratio of CaO/Al₂O₃. The viscosity decreased with the NBO/T ratio increasing, and the trend that flow activation energy changes with the NBO/T ratio of slag was the same as the trend that viscosity changes with the NBO/T ratio. Based on the experimental data as the boundary of the homogenous phase region, the mass triangle model was used to calculate the viscosity of low silica region.     

The Influence of the ZrO2 Solid Solution Amount on the Physicochemical Properties of Al2O3–ZrO2–Y2O3–CeO2 Powders

Powder Metallurgy and Metal Ceramics - Alumina-based nanocrystalline powders with different ZrO2 amounts were produced for the first time by hydrothermal synthesis in an alkaline environment for...     

Effect of Al2O3–SiO2–MnO inclusions on precipitation of MnS in Si–Mn-killed 304 stainless steels

Laboratory experiments and thermodynamic calculation were conducted to investigate the precipitation of MnS inclusions in Si–Mn-killed 304 stainless steels with various Al and S concentrations. Three types of MnS-contained inclusions were detected: MnS phase dissolved in the MnO–SiO₂ inclusion, the Al₂O₃-rich core phase surrounded by a MnS out layer, and the individual MnS. In steel with less than 0.001% Al, the liquid SiO₂–MnO-rich inclusions can hardly influence the precipitation of MnS inclusions during the cooling process of 304 stainless steels. With the increase of Al in steel, more solid Al₂O₃-rich inclusions are formed, which can act as nucleation agents for MnS inclusions and dramatically promote the precipitation of MnS inclusions during the cooling process of Si–Mn-killed 304 stainless steels.     

Effects of basicity,MgO and MnO on mineralogical phases of CaO–FeOx–SiO2–P2O5 slag

The selective separation phosphorous rich phase from steel slag could be an effective way to utilise the steel slag. The mineralogical phase after cooling of steel slag is essential to selective separation of steel slag. In the present work, the mineralogical phases of CaO–FeO_x–SiO₂–P₂O₅ slag after controlled cooling were investigated by X-ray diffraction and scanning electronic microscopy and energy dispersed spectroscopy technique. It was found that the heat treatment at 1573?K would lead to the precipitation of Ca₂SiO₄–Ca₃P₂O₈ (C2S-C3P) solid solution for all samples. The heat treatment at 1273?K would lead to the precipitation of C2S-C3P, CaSiO₃ and Fe₂O₃. The increase of basicity would promote the crystallisation of CaO–FeO_x–SiO₂–P₂O₅ slag. The Effects of additions of MgO and MnO on phase formations of CaO–FeO_x–SiO₂–P₂O₅ slag were also studied. Fe₂O₃ gradually transformed into MgFe₂O₄ and MnFe₂O₄ in slag after crystallisation with addition of MgO and MnO, respectively. The sizes of MgFe₂O₄ and MnFe₂O₄ crystals increased with increases of MgO and MnO content. The increase of MgO and MnO content would promote the precipitation of MgFe₂O₄ phase and MnFe₂O_4, respectively. The precipitation of crystals from slag during cooling was interpreted by the kinetic and thermodynamic factors. It was proposed that addition of MgO and MnO in slag would be beneficial to magnetic separation of steel slag.