Composition and structure of Ti-C/DLC graded composite films

The Ti-C→DLC gradient composite films were characterized systematically.The elemental depth profile and elemental chemical state evolution were determined by X-ray photoelectron spectroscopy (XPS).The transmission electron microscope (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to study the structure of interfacial zone between DLC film and Ti-C layers.Results show that there are composition transition zone between DLC film and either Ti-C layer or steel substrate on condition that pre-deposited Ti layers on the steel substrate then plasma based bias deposited DLC films.In Ti-C graded layer,the chemical state of titanium and carbon are changed gradually.The structures of zone in Ti-C layer near the DLC film is consisted of random oriented nanocrystallines TiC dispersed in amorphous DLC matrix.The structure of the zone between DLC film and Ti-C graded layer is gradually changed too.     

Properties and structure of RE-Ni-W-P-SiC composite coating prepared by impulse electrodeposition

The properties and structure of electrodeposited RE （CeO2）-Ni-W-P-SiC composite coating were investigated. The results show that the hardness and electrodepositing speed of composite coatings obtained at an impulse current are higher than those at a direct current. The hardness and wear resistance of the coating are obviously increased by adding RE and SiC. The hardness of the coating increases with the increase of treatment temperature and current density, and reaches the optimum value at 400 ℃ and at 10 A/dm^2, respectively. The optimum operation parameters of electrodeposition of the composite coating are as follows： pH value is 4.5, bath temperature is 65 ℃, and current density is 10 A/dm^2.     

Influence of vacuum heat treatment on structure and micro-hardness of electroless Ni-P-SiC composite coating

The electroless Ni-P-SiC composite coatings were prepared and the influence of vacuum heat treatment on its structure and properties was analyzed. The Ni-P-SiC composite coatings were characterized by morphology, structure and micro-hardness. The morphology and structure of the Ni-P-SiC composite coatings were studied by scanning electron microscopy （SEM） and X-ray diffractometry （XRD）, respectively. A great deal of particles incorporation and uniform distribution were found in Ni-P-SiC composite coatings. XRD results show a broad peak of nickel and low intensity SiC peaks present on as-deposited condition. Micro-hardness of as-deposited Ni-P-SiC composite coatings is improved greatly, and the best micro-hardness is obtained after heat treatment in a high vacuum at 400 ℃.     

Effect of substrate temperature on microstructures and dielectric properties of compositionally graded BST thin films

Compositionally graded Ba1-xSrxTiO3 （BST） （x = 0-0.3） thin films were prepared on Pt/Ti/SiO2/Si substrate at different substrate temperatures ranging from 550 ℃ to 650 ℃ by radio-frequency （rf） magnetron sputtering. The effect of substrate temperature on the preferential orientation, microstructures and dielectric properties of compositionally graded BST thin films was investigated by X-ray diffraction, scanning electron microscopy and dielectric frequency spectra, respectively. As the temperature increases, the preferential orientation evolves in the order： randomly orientation→ （111） → highly oriented （111） （α（111）= 60.2%）. The surface roughness of the graded BST thin films varies with the substrate temperatures. No visible internal interface in the compositionally graded thin films can be observed in the cross-sectional SEM images. The graded BST thin films deposited at 650 ℃ possess the highest dielectric constant and dielectric loss, which are 408 and 0.013, respectively.     

Influence of nitrogen gas on structure and properties of DLC films prepared by XeCl pulsed laser deposition

Diamond-like carbon （DLC） films were prepared by PLD process using 308 nm（XeCl） laser beam with high power （500 W） and high fi＇equency（300 Hz）. The effects of nitrogen pressure on the structure and properties of the DLC films under such extremely high power and repetition rate were studied. The results indicate that the microstructures of the films are varied fi＇om amorphous carbon to graphitized carbon in long-order with the increase of N2 pressure, and the optical properties of the films are deteriorated as compared to that of DLC films without nitrogen.     

Effect of ball milling process on the microstructure of titanium-nanohydroxyapatite composite powder

Titaninm-nanohydroxyapatite （Ti-nHA） composite powders, composed of titanium with 10 vol.% and 20 vol.% of nano-hydroxyapatite, were milled in a planetary ball mill using alcohol media to avoid excessive heat. XRD and SEM were performed for characterization of the microstructure, and the homogeneity of Ti/HA nanocomposite powder was evaluated by EPMA with prolonged ball milling time. The results show that under the condition of wet milling, the grain size of Ti-nHA composite powders is decreased with the increase in ball milling time and the amount of the addition of nHA. While for milling of 30 h, the nanocomposite powder with free structure, which consists of the nano-hydroxyapatite （nHA） particles and titanium （Ti） phase, is obtained. Three stages of milling can be observed from the dement mapping of Ti, Ca, and P by EPMA; meanwhile, it is found that the nHA would be more homogenously distributed after milling for 30 h.     

Microstrucmre and mechanical properties of Al2O3/TiAl composite

Al2O3/TiAl composites were fabricated by PAXD （pressure-assisted exothermic dispersion） method. The effects of Nb205 content on the microstructure and mechanical properties of the composites were investigated. The results show that the ultimate phases of the composite consist of TiAl, Ti3Al, Al2O3 and a small amount of NbA13. SEM reveals that a submicron γ＋（α2/γ） dual phases structure can be presented after sintered at 1 200 ℃, Furthermore, with the increase of Nb205 content, the ratio of TiAl to Ti3Al phase decreases correspondingly, the grains of the corflposites are remarkably refined, and the produced Al2O3 particles are uniformly dispersed. When 6% Nb205 is added, the composite has the best comprehensive properties. It exhibits a Vickers hardness of 4.77 GPa and a bending strength of 642 MPa. Grain-refinement and dispersion-strengthening are the main strengthening mechanisms.     

Microstructure and properties of in situ synthesized TiB2＋WC reinforced composite coatings

Nickel-based composite coatings reinforced by in situ synthesized TiB2 and WC particles were deposited on stainless steel by laser cladding,and their microstructure and mechanical properties were investigated.The results show that the coatings are mainly composed of γ-Ni cellular dendrites and dispersed spherical/strip/network shaped TiB2 and equiaxiai WC particles.The initial WC particles are dissolved to become fine and mostly dispersed within γ-Ni cellular dendrites.The coating prepared at a special laser energy of 0.225 kJ.mm-2 is uniform,continuous,and free of pores and cracks.With the decrease in special energy density,TiB2 phase changes from fine spherical particles which cluster together to strip shape with different morphologies and further crystallizes to form network structure,and the dispersion zone also gradually changes from intragranular to intergranular phase.The coating possesses a higher microhardness compared with the substrate,and it has a good metallurgical bond with the substrate and excellent cracking resistance.     

Effects of hot rolling on microstructure and properties of a 20 vol. % SiCp／Al composite

A 20 vol.% SiCp/Al composite was fabricated by squeeze casting, of which a new process for fabricating the preform was used by blending Al powder and SiC particulates with average diameters of 10 and 3.5μtm, respectively. The microstructure of the as-cast and the hot-rolled composite was investigated by using TEM, EDS, and SEM, and their tensile properties were measured at room temperature. The results show that the ultimate tensile strength and ultimate elongation of the hot-rolled composite are 80% and 140% higher than those of the as-cast one. The TEM observation result indicates that there are high density of dislocations and dislocation tangles in the hot-rolled composite. Al2O3 layers in the composite resuiting from the surface oxidation of the aluminum powders were damaged to spherical particles during hot rolling. All the results indicate that hot-rolling can improve the mechanical properties of the composite and, therefore, engineering components of the 20 vol.% SiCp/Al composite can be produced by squeeze casting followed by hot-rolling.     

Microwave permittivity of SiC-Al2O3 composite powder prepared by sol-gel and carbothermal reduction

SiC-Al2O3 composite powder was prepared by sol-gel and carbothermal reduction method. The powder synthesized was characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM） to confirm the phase formation, and the thermodynamic analysis was performed systematically. Moreover, the variation of its microwave permittivity with different atomic ratio of Al/Si was investigated in the frequency range of 8.2-12.4 GHz. The results show that, the powder obtained consists of spherical particles of 300-400 nm in diameter, which are composed of SiC and Al2O3 microcrystal with the grain size of approximately 45 nm. The results of XRD accord with those of the thermodynamic analysis. It is impossible for Al atoms to dissolve in the lattice of SiC during the carbothermal reduction process. Along with the increase of atomic ratio of Al/Si in the xerogel, the amount of Al2O3 in the powder synthesized increases, which reduces both ε＇, the real part of complex permittivity, and tg δ（ε＂/ε＇）, the dissipation factor, where ε＂ is the imaginary part of complex permittivity.     

Preparation and dielectric properties of compositionally graded （Ba, Sr）TiO3 thin film by sol-gel technique

Compositional graded BaxSr1-xTiO3 （x=0.6, 0.7, 0.8, 0.9, 1.0） （BST） thin films （less than 400 nm） were fabricated on Si and Pt/Ti/SiO2/Si substrates by sol-gel technique. A special heating treatment was employed to form the uniform composition gradients at 700 ℃. The microstructures of the films were studied by means of X-ray diffraction, atomic force microscope and field emission scanning electron microscopy. The results show that the films have uniform and crack-free surface morphology with perovskite structure phase. The small signal dielectric constant （εr） and dielectric loss （tanδ） are found to be 335 and 0.045 at room temperature and 200 kHz. The dielectric properties change significantly with applied dc bias, and the graded thin film show high tunability of 42.3% at an applied field of 250 kV/cm. All the results indicate that the graded BST thin films prepared by sol-gel technique have a promising candidate for microelectronic device.     

基材、添加元素及中间层对DLC膜结构与性能的影响

扼要地介绍了基体材料、在ＤＬＣ膜中添加元素及各种中间层对ＤＬＣ膜结构与性能影响的研究现状。     

Electronic structure and physical properties of hcp Ti3Al type alloys

According to the basic information of sequences of Ti and Al characteristic atoms in hcp Ti-Al system, the compositional variations of the electronic structure, atomic potential energies, atomic volumes, lattice constants and cohesive energies of the ordered hcp Ti3Al type alloys were calculated by the framework of systematic science of alloys（SSA）. The electronic structure of the hcp Ti3Al compound consisted of ψ4h^Ti and ψ0h^Al atoms is 0.75[Ar] （3dn）^0.573（3dc）^2.1685（4sc）^0.972（4sf）^0.3093＋0.25[Ne]（3sc）^1.32（3pc）^1.19（3sf）^0.49. The factors of controlling lattice stability are electronic structure, atomic energies and atomic concentration. The ψ4h^Ti atoms play a determinative role in forming D019 structure with a=0.287 2 nm, c=0.456 4 nm, atomic cohesive energy e=4.810 8 eV/atom and heat of formation △H=-0.332 8 eV/atom. These calculated values are in good agreement with experimental values （a=0.287 5 nm, c=0.46 0 nm, △H=-0.27, -0.29 eV/atom）. The calculated cohesive energy of the hcp Ti3Al compound is slightly bigger than that of the fcc Ti3Al.This is a good sign that makes it feasible to stabilized L 12 structure of the hcp Ti3Al compound by ternary element, The new element should have more dc-electrons than Ti-metal and occupy at the Ti-lattice points.     

Mechanical alloying and characteristics of spark plasma sintering of Ti-A1 composite powders

The mechanical alloying process of Ti-Al composite powders were carried out by use of high energy ball-milling machine. Structure variations of powder mixtures during mechanical alloying and characteristic of spark plasma sintering were investigated. The results show that during milling, TiAl, Ti3Al and Ti2Al phase intermetallic compounds are formed, simultaneously with powder refinement for the （TiH2-45Al-0.2Si-SNb） and （TiH2-45Al-0.2Si-7Nb） mixtures. The particle sizes of two powder mixtures are less than 300 nm after milling for 30 h. Sintering process of the milled powder can be completed in a short time by spark plasma sintering, and the sintering microstructure is composed of fine and homogeneous TiAl and Ti3Al phase.     

Hot deformation and processing maps of titanium matrix composite

The hot deformation characteristics of TiC particles reinforced titanium matrix composite were studied in the temperature range from 900 ℃ to 1 150℃ and in the strain rate range of 10-3-10 s i by compression tests with Gleeblel500 simulator system. The flow behavior was described by the hyperbolic sine constitutive equation, and an average activation energy of 436.72 kJ/mol was calculated. The processing maps were calculated and analyzed according to the dynamic materials model. The maps show domains in some combinations of temperatures and strain rates and these domains are correlated with specific microstructural processes occurring during hot deformation by metallographic investigations and kinetic analysis. At the low strain rate domain occurs in the temperature range of 900-960 ℃ and strain rate range of 0.001-0.03 s^-1 superplasticity and dynamic recrystallization were observed. At a high strain rate domain occurs in the temperature range of 980-1 120 ℃ and strain rate range of 0.1-10 s^-1 the ,8 phase undergoes dynamic recrystallization. Also, at a strain rate range of 0.1-10 s^-1 and the temperature range of 900-930℃, the material exhibits flow localization.     

Thermodynamic principle and properties of electroplated RE-Ni-W-P-B4C composite coatings

The φ --pH diagram of Ni-W-P-H2O system at 298.15 K, 10 1325 Pa was plotted by thermodynamic calculation software FactSageTM 5.1. The results show that tungsten and phosphorus can be co-deposited with nickel in type of NiaW, Ni3P, Ni5P2. respectively. XRD analysis shows that the main phase of RE-Ni-W-P-BaC coatings is amorphous as deposited. After heated at 673 K for 3 h, part phases change to crystalline which are Ni, Ni3P, P, W, Ni3C, Ni3B, CeO2. SEM shows the micrograph of the coatings is even and the solid particles scatter well. The thickness of the coating is 2 219 μm after electroplating for 96 h. The micro-hardness of the coatings is HV 825-HV t 097 as-deposited and increases to HV 1 236 after heat treated. The wear resistance of the coatings is good and the friction coefficient changes from 0.10 to 0.33 during the abrasion process. The resistance to oxidation of the composite coatings is better than Ni-W-P alloy coatings and worse than that of RE-Ni-W-P-SiC coatings.     

Study on interracial structure and strength of Si3N4/Ti/Cu/Ti/Si3S4 PTLP bonding

Partial transient liquid-phase bonding （PTLP bonding） of Si3N4 ceramic with Ti/Cu/Ti multi-interlayer is performed with changing the thickness of Ti foil. The influence of Ti foil thickness on interface structure and joint strength was discussed. The joint interface structures are investigated by scanning electron microscope （SEM） and energy dispersion spectroscopy（EDS）. The results show that the maximum joint strength of 210 MPa is obtained at room temperature in the experiments. When joining temperature and time are not changed and the process of isothermal solidification is sufficient , interface structure, reaction layer thickness and isothermal solidification thickness change with the thickness of Ti foil.     

Effects of ZrO2 on the structure and magnetic properties of CoPt thin films

[CoPt 1.5 ml/ZrO2 xnm]10 multilayer films were deposited on glass substrates by magnetron sputtering and then annealed in vacuum at 600℃ for 30 min. Their structures and magnetic properties were investigated as a function of ZrO2 content. The results show that the grain size and coercivity first increase and then decrease with the increase in ZrO2 content. The maximum coercivity and grain size are obtained at 37 vol.% of ZrO2. The content of ZrO2 in the film plays an important role in the separation of CoPt grains and in the reduction of intergrain exchange interaction. On the basis of the studies of angular dependent coercivity, it is found that the magnetization reversal of CoPt films with （111 ） texture is different from either the domain wall motion or the S-W type of rotation mode.     

Simulation and visualization of recrystallization microstructure after solution treatment

Simulation models for heterogeneous and simultaneous nucleation and random growth of nuclei were developed in terms of the mechanism of recrystallization and Monte Carlo stochastic simulation method. Combining deterministic simulation with stochastic simulation, the simulation and visualization of the reerystallization microstructure of Ti-15-3 alloy after hot compression deformation and solution treatment were realized. Comparison of the simulated results with the experimental ones suggests that the size and distribution of the simulated recrystallized grains agree well with the actual ones. This proves that the obtained statistic equivalent microstructure models are effective. This study is helpful for determining reasonable hot forming process and improving the forming quality.