Effect of Cu element on morphology of TiB2 particles in TiB2/Al−Cu composites

In order to explore the influence of Cu element on the morphology evolution of the in-situ TiB₂ particles, the 10 wt.% TiB₂ reinforced Al−5wt.%Cu based composite was prepared by mixed salt casting. The morphology characterization and transformation of TiB₂ reinforcements caused by Cu element were investigated by multi-scale microstructure characterization and statistics techniques. In the case of controlled casting, 5 wt.% Cu addition was found to transform the TiB₂ particle morphology from hexagonal plate with sharp edges and corners to hexagonal or tetragonal prism with chamfered edges and corners with the distinguishing growth steps both on the top surface and the side surface. The TiB₂ growth in Al−Cu matrix followed the rules: nano-scaled spherical nuclei—polyhedron grains—chamfered hexagonal particles—hexagonal plates—chamfered particles with obvious growth steps. The adsorption energy of Cu on different crystal surfaces of TiB₂ was caculated to reveal the influence mechanism and the results indicated that Cu was preferentially adsorbed on the (101(—)1)_TiB2 crystal planes, devoting to the small aspect ratio of TiB₂.     

Microstructures and mechanical properties of in-situ TiB2/Al−xSi−0.3Mg composites

In-situ 2 vol.% TiB₂ particle reinforced Al?xSi?0.3Mg (x=7, 9, 12, 15 wt.%) composites were prepared by the salt–metal reaction, and the microstructures and mechanical properties were investigated. The results show that the TiB₂ particles with a diameter of 20–80 nm and the eutectic Si with a length of 1–10 μm are the main strengthening phases in the TiB₂/Al?xSi?0.3Mg composites. The TiB₂ particles promote grain refinement and modify the eutectic Si from needle-like to short-rod shape. However, the strengthening effect of TiB₂ particles is weakened as the Si content exceeds the eutectic composition, which can be attributed to the formation of large and irregular primary Si. The axial tensile test results and fractography observations indicate that these composites show more brittle fracture characteristics than the corresponding alloy matrixes.     

Preparation of highly preferred orientation TiB2 coatings

This paper focuses on the preparation of titanium diboride （TiB2） coatings on the graphite substrate by continuous current plating （CCP） and pulse current plating （PIC） electrochemical techniques in fluoride electrolytes （LiF-NaF-KF） containing K2T1F6 and KBF4 as the electrochemically-active components at 700℃. Thick leveled and uniform coatings were obtained and were composed of relatively pure TiB2. The effect of the experimental parameters on the microstructure of the coatings was studied. The results showed the electrodeposition with PIC produced coatings with better quality, when compared with those obtained by CCP, under the conditions of the current density i = 0.6 A/cm^2, frequency = 100 Hz, and todtofr = 4/1. XRD analysis indicated that the preferred orientation of coatings is （110） plane, which is in accordance with the prediction of the two-dimensional crystal nuclei theory. The effect of a ratio of ton/toff and frequency on the crystal size, textule coefficient and microstress was also investigated.     

Combustion synthesis of FeAl−Al2O3 composites with TiB2 and TiC additions via metallothermic reduction of Fe2O3 and TiO2

Combustion synthesis involving metallothermic reduction of Fe₂O₃ and TiO₂ was conducted in the mode of self-propagating high-temperature synthesis (SHS) to fabricate FeAl-based composites with dual ceramic phases, TiB₂/Al₂O₃ and TiC/Al₂O₃. The reactant mixture included thermite reagents of 0.6Fe₂O₃+0.6TiO₂+2Al, and elemental Fe, Al, boron, and carbon powders. The formation of xFeAl−0.6TiB₂−Al₂O₃ composites with x=2.0−3.6 and yFeAl−0.6TiC−Al₂O₃ composites with y=1.8−2.75 was studied. The increase of FeAl causes a decrease in the reaction exothermicity, thus resulting in the existence of flammability limits of x=3.6 and y=2.75 for the SHS reactions. Based on combustion wave kinetics, the activation energies of E_a=97.1 and 101.1 kJ/mol are deduced for the metallothermic SHS reactions. XRD analyses confirm in situ formation of FeAl/TiB₂/Al₂O₃ and FeAl/TiC/Al₂O₃ composites. SEM micrographs exhibit that FeAl is formed with a dense polycrystalline structure, and the ceramic phases, TiB₂, TiC, and Al₂O₃, are micro-sized discrete particles. The synthesized FeAl−TiB₂−Al₂O₃ and FeAl−TiC−Al₂O₃ composites exhibit the hardness ranging from 12.8 to 16.6 GPa and fracture toughness from 7.93 to 9.84 MPa·m^1/2.     

超音速大气等离子喷涂TiB2−SiC涂层的制备与性能

将喷雾造粒制备的TiB2?SiC粉末进行真空煅烧,采用超音速大气等离子喷涂制备TiB2?SiC涂层,研究喷涂功率和喷涂距离对TiB2?SiC涂层性能的影响,并对超音速等离子喷涂制备TiB2?SiC涂层的工艺进行优化.结果表明:煅烧后的喷涂粉末粒径分布均匀,球形度良好,流动性增强.煅烧粉末制备的涂层结构致密、沉积效率高....     

Synthesis of TiB2 nanocrystalline powder by mechanical alloying

1 Introduction TiB2 has been widely used in some industrial fields owing to its high melting temperature, hardness, elastic modulus, electro-conductibility and thermal diffusivity, and excellent refractory properties and chemical inertness. Usually, TiB2…     

TiB2基硬质合金

通过测量润湿角和研究烧结活性，我们认为Ｆｅ和Ｆｅ－Ｍｏ合金可以作为ＴｉＢ２基硬质合金的粘结相。在保护气氛下执行正常的烧结工艺获得了全致密的ＴｉＢ２－Ｆｅ和ＴｉＢ２～ＦｅＭｏ合金。我们进行了结构和相分析，观察到了一种新相ＭＯ２ＦｅＢ２的存在，同时还评估了它们的机械性能，抗磨料磨损，切削磨损性和抗氧化性，ＴｉＢ２－ＦｅＭｏ硬质合金已经在耐磨损零件，切削及凿岩刀，喷嘴等方面得到了工业应用，并逐步在替代钨     

Effect of α phase morphology on fatigue crack growth behavior of Ti−5Al−5Mo−5V−1Cr−1Fe alloy

Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case, the fatigue crack growth sensitivity and fracture features with various tailored α phase morphologies were thoroughly investigated using fatigue crack growth rate (FCGR) test, optical microscopy (OM) and scanning electron microscopy (SEM). The tailored microstructures by heat treatments include the fine and coarse secondary α phase, as well as the widmanstatten and basket weave features. The sample with coarse secondary α phase exhibits better comprehensive properties of good crack propagation resistance (with long Paris regime ranging from 15 to 60 MPa·m^1/2), high yield strength (1113 MPa) and ultimate strength (1150 MPa), and good elongation (11.6%). The good crack propagation resistance can be attributed to crack deflection, long secondary crack, and tortuous crack path induced by coarse secondary α phase.     

Microstructure and properties of Cu−2Cr−1Nb alloy fabricated by spark plasma sintering

Cu?2Cr?1Nb alloy was fabricated by spark plasma sintering (SPS) using close coupled argon-atomized alloy powder as the raw material. The optimal SPS parameters obtained using the L₉(3⁴) orthogonal test were 950 °C, 50 MPa and 15 min, and the relative density of the as-sintered alloy was 99.8%. The rapid densification of SPS effectively inhibited the growth of the Cr₂Nb phase, and the atomized powder microstructure was maintained in the grains of the alloy matrix. Uniformly distributed multi-scale Cr₂Nb phases with grain sizes of 0.10?0.40 μm and 20?100 nm and fine grains of alloy matrix with an average size of 3.79 μm were obtained. After heat treatment at 500 °C for 2 h, the room temperature tensile strength, electrical conductivity, and thermal conductivity of the sintered Cu?2Cr?1Nb alloy were 332 MPa, 86.7% (IACS), and 323.1 W/(m·K), respectively, and the high temperature tensile strength (700 °C) was 76 MPa.     

TiB2和TiB弹性性质的理论计算

采用基于密度函数理论的赝势平面波方法和广义梯度近似对TiB2和TiB化合物的弹性性质和电子结构进行了理论计算,并用Voigt-Reuss-Hill方法计算得到多晶体的弹性模量和切变模量。结果表明：TiB2和TiB的弹性模量分别为599 GPa和443 GPa,切变模量分别为268.5 GPa和193.5 GPa,Pugh定律和泊松比等经验判据表明TiB2比TiB脆性更大;并从这两种化合物的电子结构对其弹性性质的差异进行了讨论。     

Preparation of TiB2 coatings by electroplating in molten salt

Titanium diboride （TIB2） coatings were prepared by electroplating in fluoride-chloride electrolytes （KF-KC1） containing K2T1F6 and KBF4 as the electrochemically-active components. An attempt was made to correlate the thermodynamic prediction and experimental observations. Thick, adherent, and uniform TtB2 coatings were obtained and the coating microhardness reaches the value of 33 GPa. The effects of the current density on the mechanical properties, structures, and morphologies of the coatings were studied. XRD analysis indicates that the preferred orientation of the coatings is （001）, which is in accordance with the prediction of the two-dimensional crystal nuclei theory. Thermodynamic prediction and experimental results show that some phases such as TixCy and BaCb are absent at the interface, which indicates the substrate and coatings bind mechanically or physically. Some cracks exist at the interface, which is attributed to the difference between the coefficients of thermal expansion of TiB2 and graphite.     

TiB2含量对TiB2/Cu复合材料性能的影响

研究了TiB2含量对原位生成TiB2／Cu复合材料性能的影响。结果表明：TiB2／Cu复合材料的硬度、强度随TiB2含量的增加有所提高，但强度在TiB2的含量超过2．0％后有所下降，导电率随TiB2含量的增加有所下降，软化温度基本保持在900℃左右。     

Shear localization behavior in hat-shaped specimen of near-α Ti−6Al−2Zr−1Mo−1V titanium alloy loaded at high strain rate

The microstructure characteristics in early stage shear localization of near-α Ti?6Al?2Zr?1Mo?1V titanium alloy were investigated by split Hopkinson pressure bar (SHPB) tests using hat-shaped specimens. The microstructural evolution and deformation mechanisms of hat-shaped specimens were revealed by electron backscattered diffraction (EBSD) method. It is found that the nucleation and expansion of adiabatic shear band (ASB) are affected by both geometric and structural factors. The increase of dislocation density, structure fragment and temperature rise in the deformation-affected regions provide basic microstructural conditions. In addition to the dislocation slips, the extension twins detected in shear region also play a critical role in microstructural fragmentation due to twin-boundaries effect. Interestingly, the sandwich structure imposes a crucial influence on ASB, which finally becomes a mature wide ASB in the dynamic deformation. However, due to much larger width, the sandwich structure in the middle of shear region is also possible to serve as favorable nucleation sites for crack initiation.     

High temperature oxidation of Ti−48%Al−2%W intermetallics

Powder metallurgically produced Ti-48% Al-2%W alloys were oxidized between 800 and 1050°C in air. The W-addition was quite effective in providing isothermal and cyclic oxidation resistance. The alloys oxidized parabolically up to 1050°C during isothermal oxidation, with small weight gains. The scales were adherent up to 900°C during cyclic oxidation. Oxide scales consisted primarily of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner (TiO₂+Al₂O₃) mixed layer. Tungsten was present below the intermediate Al₂O₃ layer. and also at the scale-matrix interface as W-enriched compounds. Below the oxide scale, a Ti₃Al zone containing some W and O existed.     

Thermodynamic properties of CexTh1−xO2 solid solution from first-principles calculations

A systematic study based on first-principles calculations along with a quasi-harmonic approximation has been conducted to calculate the thermodynamic properties of the Ce_xTh_1?xO₂ solid solution. The predicted density, thermal expansion coefficients, heat capacity and thermal conductivity for the Ce_xTh_1?xO₂ solid solution all agree well with the available experimental data. The thermal expansion coefficient for ThO₂ increases with CeO₂ substitution, and complete substitution shows the highest expansion coefficient. On the other hand, the mixed Ce_xTh_1?xO₂ (0 < x < 1) solid solution generally exhibits lower heat capacity and thermal conductivity than the ThO₂ and CeO₂ end members. Our calculations indicate a strong effect of Ce concentration on the thermodynamic properties of the Ce_xTh_1?xO₂ solid solution.     

Crystal structures of PrAlxGe2−x compounds

The PrAl_xGe_2−x cross-section of the Pr–Al–Ge system at 1073 K was studied. The homogeneity ranges of two ternary praseodymium alumogermanides, PrAl_1.55–1.48Ge_0.45–0.52 and PrAl_1.42–0.98Ge_0.58–1.02, were determined and their crystal structures refined from X-ray single-crystal diffraction data. The former has a hexagonal structure of the AlB₂ type (hP3, P6/mmm, a=4.3223(3), c=4.2585(4) Å for x=1.476(2)) and the latter a tetragonal structure of the LaPtSi type (tI12, I4₁md, a=4.2534(5), c=14.641(2) Å for x=1). For both structures, the Al–Ge interatomic distances are close to the sum of the covalent radii, whereas the Pr–Al(Ge) distances agree well with the sum of the metallic radii. The solubility of Ge in the cubic Laves phase PrAl₂ was found to be less than 2 at.%, that of Al in off-stoichiometric PrGe_2−x less than 8 at.%. Al(Ge)-centered R₆ trigonal prisms constitute a common geometrical feature of the structures of the germanides RGe_2−x and alumogermanides RAl_xGe_2−x formed by the light rare-earth elements. Substitution of Ge for Al, or replacement of a large rare-earth element by a smaller one, leads to a reduction of the prism volume.     

Microstructure and strength of brazed joints of TiB2 cermet to TiAl-based alloys

In this study, TiB2 cermet and TiAl-based alloy are vacuum brazed successfully by using Ag-Cu-Ti filler metal.The microstructural analyses indicate that two reaction products, Ti ( Cu, Al ) 2 and Ag bused solid solution ( Ag ( s. s ) ) , are present in the brazing seam, and the iuterface structure of the brazed joint is TiB2/TiB2 Ag ( s. s ) /Ag ( s. s ) Ti ( Cu,Al)2/Ti( Cu, Al)2/TiAl. The experimental results show that the shear strength of the brazed TiB2/TiAl joints decreases us thebrazing time increases at a definite brazing temperature. When the joint is brazed at 1 223 K for 5 min, a joint strength up to 173 MPa is achieved.     

Mechanical properties and microstructure of TiB2 ceramic influenced by ZrB2 additive

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TiB2/Ti-Al复合材料中棒状TiB2晶体的微观特征

用XDTM法制备了TiB2/Ti-Al复合材料并利用XRD、SEM和TEM对复合材料的相组成和微观组织进行了研究.结果表明:复合材料中棒状TiB2的{1010}面存在与[0001]晶向垂直的薄片状凸耳,其厚度一般小于0.2μm,伸出表面高度可达4μm,并且这些凸耳的晶面取向与棒状TiB2本身是相同的;棒状TiB2一般以垂直交叉的十字或数个十字构成的辐射状形式分布于α2/γ层片基体中;在较快的凝固过程中,棒状TiB2固-液界面前沿产生的富Al、Ti边界层和随着棒状TiB2晶体的长大,导致固-液界面上B原子过饱和度不均匀性增加,共同作用使固-液界面失稳,从而形成了棒状TiB2的形貌特征.     

THE REINFORCING MECHANISM OF TiB2 IN TiB2／A357 COMPOSITE

Mechanical properties were tested for in situ TiB2/A357 composite fabricated by LSM (mixed salts reaction) method. Micro structures of as cast and plastic deformed TiB2/A357 were investigated. The results show that there is a low misfit between (200) Al and (101)TiB2 with [011]//Al [101]TiB2. There is a change from fully dendritic structure of the α-Al of A357 to a rosette-type structure of TiB2/A357. Significant increases in proof stress and Young's modulus can be obtained at low TiB2 additions. There exist dislocation loops around neighboring TiB2 particles with about 0.1μm in diameter and dislocation multiplication near TiB2 particles.