Effects of Al addition on the microstructure and properties of Nb/Nb5Si3 in situ composites fabricated via spark plasma sintering

Dense Nb/Nb5Si3 composites were fabricated via spark plasma sintering technology using Nb, Si, and Al elemental powders as raw materials. The microstructttres of the synthesised composites were analyzed through scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. The results show that the composites consisted of residual Nb particle phase and Nb5Si3 phase. The microstructure of the Nb/ Nb5Si3 in situ composites was evidently affected by Al addition, which prompted the formation of the Al3Nb10Si3 phase. In addition, the Rockwell hardness of the composites decreased with the increase in AI additions. The Rockwell hardness of Nb-20Si is 60HRC, which decreased to approximately 52.7 HRC when the Al content increased to 15 at%. The oxidation resistance of the Nb/NbsSi3 in situ composites significantly improved with the increase in Al addition.     

Thermodynamic analysis of the formation of <Emphasis Type="Italic">In-situ</Emphasis> reinforced phases in cast Al-4.5Cu alloy

The thermodynamic analysis of the formation of in-situ reinforced phases in （TiB2＋Al3Ti）/Al-4.5Cu composites prepared by mixed salts reaction was conducted, and heat changes of mixed salts system were analyzed by differential thermal analysis（DTA）.The results show that although TiB2 possesses the strongest formation ability in Al-Ti-B ternary system, [Ti] is relatively excessive in the in-situ reaction and it combines with Al to form AlaTi phase. The reinforced phases are TiB2 and AlaTi in the produced composites due to the reaction taking place to form reinforced phase with the addition of mixed salts into Al-4.5Cu melt between 900 ℃ and 1 032 ℃.     

Microstructure and mechanical properties of an in situ synthesized TiB and TiC reinforced titanium matrix composite coating

A titanium-based composite coating reinforced by in situ synthesized TiB and TiC particles was fabricated on Ti6Al4V by laser cladding. The microstructure and mechanical properties were investigated. The coating was mainly composed of β-Ti cellular dendrites and an eutectic in which a large number of rod/needle-shaped TiB and a few equiaxial TiC particles were homogeneously embedded. The microstructural evolution could be divided into four stages: precipitation and growth of primary β-Ti phase, formation of the binary eutectic β-Ti+TiB, formation of the ternary eutectic β-Ti+TiB+TiC, and solid transformation from β-Ti to β-Ti. Microhardness of the coating showed a gradient variation from the surface (about HV0.2 876) to the bottom (about HV0.2 660) and was prominently improved in comparison with that of the substrate. Fracture toughness of the coating also exhibited a gradient variation from the surface (6.3 MPa·m1/2) to the interface (11.9 MPa·m1/2). Wear resistance of the coating was significantly superior to that of Ti6Al4V.     

Effects of Si and Ce on the microstructure and hydrogen storage property of Ti<Subscript>26.5</Subscript>Cr<Subscript>20</Subscript>V<Subscript>45</Subscript>Fe<Subscript>8.5</Subscript>Ce<Subscript>0.5</Subscript> alloy

In this paper, the effects of Si and Ce on the microstructure and hydrogen storage property of Ti_26.5Cr₂₀V₄₅Fe_8.5Ce_0.5 alloy were studied, respectively. First of all, effects of Si on the microstructure and hydrogen storage properties of Ti_26.5Cr₂₀(V₄₅Fe_8.5)_1−x Si _x Ce_0.5 (x = 0, 0.5, 1.0, 1.5 and 2.0 at%) alloys were studied by X-ray diffraction, scanning electron microscopy and P-C isotherm measurements. As the Si addition increases, the hydrogen absorption capacities of alloys decrease but the equilibrium pressure increases, due to the formation of Laves phase. Secondly, the effect of Ce on Ti_26.5Cr₂₀ (V₄₅Fe_8.5)_0.98Si₂ alloy was studied. It was found that Ce addition is an effective way to eliminate the effect of Si on the hydrogen storage properties of the alloy. Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA05Z144)     

Preparation of TiAl/Ti2AlC Composites with Ti/Al/C Powders by In-situ Hot Pressing

TiAl/Ti2AlC composites were prepared by in-situ hot pressing of TilAl/C powders mixtures and sintered at different temperatures were investigated by X- ray diffraction （ XRD ） of samples. The reaction procedure of Ti-Al-C system could be divided into three stnges. Below 900℃ , Ti reacts with Al to form TiAl intermetallics ; above 900 ℃ , C reacts with remain Ti to form TiC triggered by the exothermal reaction of Ti and Al ; TiAl reacts with TiC to produce dense TiAl/Ti2AlC compasites.In the holding stage, ternary Ti2AlC develops to layered polycrystal and composites pyknosis in the meanwhile. The mechanism of synthesis and microstructure was especially discussed.     

Fabrication and magnetic properties of Sm3(Fe,Ti)29Nx/α-Fe dual-phase nanocomposite permanent magnetic material

Sm3(Fe,Ti)29Nx/α-Fe dual-phase nanometer magnetic material was fabricated through rapid solidification, crystallization and nitridation of Sm-Fe (Ti) alloy. The effect of combination of rapid solidification and Ti alloy addition on the phase formation and microstructure of the Sm-Fe alloy is investigated in this paper. The microstructure of amorphous phase and dual-phase nano-grain crystals before and after crystallization annealing were observed using a high-resolution transmission electron microscope (HREM). The dual-phase nano-grains after annealing were compacted together with a clear interface with the direct exchange-coupling mechanism. Different annealing processes were used to examine the melt-spun alloy. Comparison of the images of SEM showed that annealing at 750℃ for 10 min was most suitable to get homogeneous and nano-grains. No obvious kink was detected in the second quadrant of the hysteresis loop like a single hard magnet, and strong exchange coupling was found between hard magnets and soft magnets.     

THE PROCESS AND MECHANISM OF TiAl－BASED ALLOY SYNTHESIZED FROM Ti AND AlP OWDERS

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Mechanism and kinetic model of <Emphasis Type="Italic">in-situ</Emphasis> TiB<Subscript>2</Subscript>/7055Al nanocomposites synthesized under high intensity ultrasonic field

In-situ TiB2/7055Al nanocomposites are fabricated by in situ melt chemical reaction from 7055Al-K2TiF6-KBF4 system under high intensity ultrasonic field,and the mechanism and kinetic model of in-situ melt chemical reaction are investigated.X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicate that the sizes of in-situ TiB2 nanoparticles are in the range of 80-120 nm.The results of ice-water quenched samples show that the whole process contains four stages,and the overall in-situ reaction time is 10 minutes.The in situ synthesis process is controlled mainly by chemical reaction in earlier stage (former 3 minutes),and by the particulate diffusing in later stage.The mechanism of key reaction between Al3Ti and AlB2 under high intensity ultrasonic in the 7055Al-K2TiF6-KBF4 system is the reaction-diffusion-crack-rediffusion.Furthermore,the reactive kinetic models in 7055Al-K2TiF6-KBF4 system are established.     

Synthesis of Ti3SiC2/TiB2 Composite by In-situ Hot Pressing （HP） Method

Ti3SiC2/TiB2 composite was successfully obtained by hot pressing Ti/TiC/Si/B4C power mixtures.Volume fraction of TiB2 in Ti3SiC2/TiB2 composite can not exceed 10%.Incorporation of excessive TiB2 will affect the reactions process.TiC and Ti5Si3 were two important intermediate phases during the whole reactions.The microstructure characteristics of the Ti3SiC2/TiB2 composites were analyzed using scanning electron microscopy （SEM） and transmission electron microscopy （TEM）.The experimental results show that the grains of Ti3SiC2/TiB2 composite are structured in a layered form,and the formation of TiB2 particles as reinforcements with elongated or equiaxed shape distributes in Ti3SiC2 matrix.     

Effect of β-TCP Ceramic on the Total Protein of Osteoblasts

The osteoblast with the β-TCP ceramic was co-cultured. Scanning electron microscopy shows the cells adhered onto β-TCP ceramic surface and grew better, proving the β-TCP ceramic has a biocompatible property. The Coomassie brilliant blue G-250 stain shows that the total protein in the experimental groups was highly increased compared with the control group （p〈0.05）. Flow-cytometric analysis shows that β-TCP ceramic could promote the osteoblast transform from the G0/G1 phase to S phase. Those all demonstrate the product of the degradation of the β-TCP ceramic may take part in the protein metabolism of osteoblast.     

Bulk metallic glasses formed by alloying the Cu6Zr5 cluster

The bulk metallic glass formation in the Cu-Zr-M ternary systems by alloying of a binary basic Cu₆Zr₅ cluster was investigated, where M stands for Sn, Mo, Ta, Nb, Ag, Al and Ti. The Cu₆Zr₅ cluster is a capped Archimedean antiprism that characterizes the local structure of the Cu₁₀Zr₇ crystalline phase. This cluster composition almost superposes with Cu-Zr eutectic Cu_0.56Zr_0.44. A series of alloys along the cluster line (Cu₆Zr₅)_1-xM_x were examined for their glass forming abilities. Alloy rods with a diameter of 3 mm were prepared by copper mould suction casting method and analyzed by XRD and thermal analysis. The Cu-Zr based bulk metallic glasses were discovered with minor Nb, Sn, Mo, Ta additions (≤2at%) and Al, Ti, Ag (8at%≤concentration≤9at%). The alloying mechanism was discussed in the light of atomic size, cluster-linking structure and electron concentration factors.     

Straight SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanorod Y junctions

Novel straight silicon oxide [SiO _x (1<x<2)] nanorod Y junctions have been synthesized on Si plate by thermal evaporation of mixed powders of silica and carbon nanofibers at 1300°C and condensation on a Si substrate without assistance of any catalyst. The synthesized samples were characterized by means of scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy. The results suggested that the straight nanorod Y junctions are amorphous and consist only of elements Si and O, and these rods with diameters about 50–200 nm have a neat smooth surface. The growth of such silicon oxide nanorods may be a result of the second nucleation on the surface of rods causing a change in the growth direction of silicon oxide nanorods developed. Supported by the Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing, and the Program of Science & Technology Activity for Chinese Homecoming Fellow Abroad and Research Program of Beijing Key Laboratory for Sensor (Grant No. KM200810772009)     

Theoretical calculation of the impact work in the alloying non-quenched and tempered steel

Liu et al.[1―5]1) have calculated the finishing rolling tensile strength σb, yield strength σs, elongation δ of the alloying non-quenched and tempered steel with the covalent elec-1) Liu Z L, Lin C, Guo Y C. Theoretical calculation of the finishing rolling elongation in alloying non-quenched and tempered steel. Progress in Natural Science, in presstron number nA of the strongest bond in alloying phases and the smallest electron density difference ?ρ of phase interfaces. It is calculat…     

Statistical values of valence electron structure parameters applied to research on phase transition temperature and eutectoid reaction of titanium alloy

Based on the empirical electron theory of solids and molecules (EET), the statistical values of valence electron structure parameters Sn _A and SE _A which can characterize the properties of alloy phases are calculated, and influences of alloying elements (e.g., V, Nb, Mo, Hf, Zr, Fe, Mn, Co, Cr, Si, and so on) on the phase transition temperature and eutectoid reaction of titanium alloy are discussed with the statistical values of valence electron structure parameters. The research results agree well with real situations. Supported by the National Natural Science Foundation of China (Grant No. 50471022, 50741004) and National Key Basic Research Program of China (“973”) (Grant No. 2007CB613807)     

Regularities of formation of ternary intermetallic compounds between two transition elements and one non-transition element

The pattern recognition methods and a four-parameter model, based on extended Miede-ma's cellular model of alloy phases, are used to study the regularities of formation of ternary compounds between two transition elements (T,T ') and one non-transition element (N) (T-T '-N system) . The criterion of formation can be expressed as some functions of φ (electronegativity), n1/3ws (valence electron density in Wagner-Seitz cell), R (Pauling's metallic radii) and Z (number of valence electrons in atom).     

Fabrication of in situ Ti2AlN/TiAl composites by reaction hot pressing and their properties

Ti2AIN/TiAI composites with different volume fractions of reinforcement were successfully fabricated by hot-pressing sintering method （reaction hot pressing） using Ti, Al and TiN powders as starting materials. The synthesis process includes four stages： first, the reactions between Al and Ti powers and between Al and TiN powders respectively occur and result in TiAl3 phase; secondly, AI powders in the sample are exhausted; the remaining Ti cores react with TiAl3 layer to form Ti-Al intermetallics; moreover, a few Ti2AlN particles precipitate from the TiAl3 phase; thirdly, Ti-Al intermetallics react with the remaining Ti cores to form Ti3Al and TiAl phases. TiAl phase and original TiN powers are in direct contact each other; finally, the residual TiN powers react with TiAl phase and result in a plenty of TizAIN phase. Compared with TiAl matrix, the hardness, elastic modulus and high-temperature compressive strength of Ti2AlN/TiAl composite are improved obviously and they are all enhanced with increasing the volume fraction of Ti2AlN phase.     

Friction and wear performances of cathodic arc ion plated TiAlSiN coating under oil lubricated condition

TiAlSiN coating was deposited on H13 hot work mould steel using cathodic arc ion plating (CAIP). The surface-interface morphologies and phases of the obtained coating were analyzed using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), respectively, and the morphologies, distributions of chemical elements and profiles of worn tracks were also researched using scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), and optical microscope (OM), respectively. The friction-wear performances of TiAlSiN coating under oil lubricated and dry fiction conditions were investigated, and the wear mechanisms of TiAlSiN coating were discussed. The experimental results show that the coating is primarily composed of (Ti, Al)N, AlTiN, and TiN hard phases, Si₃N₄ exists between the (Ti, Al)N crystal grains, increasing the coating microhardness to 3200HV. The TiAlSiN coating has excellent performances of reducing friction and wear resistance, the average coefficient of friction (COF) of TiAlSiN coating under oil lubricated condition is only 0.05, lowered than the average COF of 0.211 under dry friction condition, the wear rate decreases by about 81.2% compared with that under dry friction condition. The wear mechanism of TiAlSiN coating under oil lubricated and dry friction conditions is composed of abrasive wear, fatigue wear, and abrasive wear, respectively. The internal friction of oil lubrication is a main factor of decreasing fatigue wear.     

Eleetronie Structures and Bonding Properties of Ti2AlC and Ti3AlC2

The relation among electronic structure, chemical bond and property of Ti2AlC, Ti3AlC2 and doping Si into Ti2AlC was studied by density function and the discrete variation （DFT-DVM） method. After adding Si into Ti2AlC, the interaction between Si and Ti is weaker than that between Al and Ti, and the strengths of ionic and covalent bonds decrease both. The ionic and covalent bonds in Ti3AlC2, especially in Ti-Al, are stronger than those in Ti2AlC. Therefore, in synthesis of Ti2AlC, the addition of Si enhances the Ti3AlC2 content instead of Ti2AlC. The density of state （DOS） shows that there is mixed conductor characteristic in Ti2AlC and Ti3AlC2. The DOS of Ti3AlC2 is much like that of Ti2AlC. Ti2SiAl1-xC has more obvious tendency to form a semiconductor than Ti2AlC, which is seen from the obvious difference of partial DOS between Si and Al 3/7.     

Microstructures and Properties of SiC／Al2O3 ／Al- Si Composites Prepared by Reactive Penetration

The composition, microstructures and properties of SiC/Al2O3/Al-Si composites formed by reactive penetration of the molten aluminum into the preforms of SiO2 and SiC were investigated. The composition of the composites was measured by X-ray diffraction ( XRD ). The microstructures of the composites were also measured by scanning electron microscopy (SEM) and optical microscopy. In addition, the factors affecting the properties of the composites were discussed. The experiments show that the mechanical properties of the composites depend on their relative densities and the sizes of the fillers“ SiC gains“. The denser the SiC/Al2O3/Al-Si composites, the higher their bending strength. As the filler “SiC gains“ become fine, the bending strength of the composites increases.     

Thermodynamic Analysis of the Formation of In-situ Reinforced Phases In Cast AI-4.5Cu Alloy

The thermodynamic analysis of the formation of in-situ reinforced phases in (TiB2 Al3Ti)/Al-4.5Cu composites prepared by mixed salts reaction was conducted, and heat changes of mixed salts system were analyzed by differential thermal analysis (DTA). The results show that although TiB2 possesses the strongest formation ability in Al-Ti-B ternary system, [Ti] is relatively excessive in the in-situ reaction and it combines with Al to form Al3Ti phase. The reinforced phases are TiB2 and Al3Ti in the produced composites due to the reaction taking place to form reinforced phase with the addition of mixed salts into Al-4.5Cu melt between 900℃ and 1032℃.