TiB2 Layer Research Articles

Effects of Manufacturing Processes on Microstructure and Properties of Al/A356–B4C Composites

Liquid and semi-solid stir casting processes were applied to fabricate B4C particles-reinforced aluminum–matrix composites. The effects of manufacturing processes on particle distribution, particle/matrix interface, and mechanical properties of the prepared composites were studied. The results show that particle distribution can be significantly improved by using K2TiF6–flux and Ti powders in the liquid stir casting process, whereas in the semi-solid stir casting process it could be improved by decreasing the temperature of the slurry. With additions of Ti, the decomposition of B4C was prevented, and the interfacial bonding strength was significantly improved due to the fact that a TiB2 layer formed at the particle/matrix interface. Compared to the matrix, the hardness and tensile strength of the Al–B4C composite fabricated by the liquid stir casting process were increased by 89.6% and 128.8%, respectively; those of the A356–B4C composite fabricated by the semi-solid stir casting process had no significant improvement due to the weak particle/matrix interface and the presence of particle porosity clusters.

Development and Kinetics of TiB2 Layers on the Surface of Titanium Alloy by Superplastic Boronizing

The aim of this work is to explore the possibility of combining boronizing and superplastic deformation on titanium alloy (Ti6Al4V) substrate. Superplastic boronizing (SPB) is carried out at three different temperatures of 1173 K, 1223 K, and 1273 K (900 °C, 950 °C, and 1000 °C), and it is held for four different boronizing times of 1, 2, 3, and 6 hours. TiB2 is the only boride compound identified after the boronizing process. Boronized layer thickness in the range of 44.9 ± 1.1 to 149 ± 1 μm is formed on the surface of Ti6Al4V and the surface hardness values increase with respect of the formation’s degree of the hard boronized layer. Diffusion coefficient values attained for all temperatures are (1.44 ± 0.8) × 10−13, (4.1 ± 1.5) × 10−13, and (8.86 ± 4.1) × 10−13 m2 s−1, respectively and the values are higher as compared to other works referred. The activation energy obtained for this process is 226.17 ± 8.3 kJ mol−1. The results obtained suggest that the SPB process provides a more competent and efficient process for the formation of a boronized layer on the alloy.

Interfacial interactions between liquid Ti–Al alloys and TiB2 ceramic

High-temperature interactions of liquid Ti and Ti74.3Al25.7, Ti49.3Al50.7, Ti26.5Al73.5 and Ti3.5Al96.5 (at.%) alloys with TiB2 ceramic are studied using the sessile drop technique. Molten Ti and Ti–Al alloys show a very good wetting of TiB2. A homogeneous TiB layer with a thickness of about 20 μm forms at the Ti/TiB2 interface. An approximately 200-μm-thick layer of densely packed TiB whiskers is observed at the interface of a Ti74.3Al25.7/TiB2 couple. The Ti49.3Al50.7 liquid penetrates the grain boundaries in the TiB2 ceramic and disconnects the grains in the near-interface region. The Ti26.5Al73.5 melt does not disconnect the TiB2 grains, but penetrates the grain boundaries over a distance of about 300 μm from the interface. Ti3.5Al96.5 just fills the pores in the ceramic up to a distance of about 120 μm from the interface.

Characteristics and growth kinetics of plasma paste borided Cp–Ti and Ti6Al4V alloy

In the present study, CpTi and Ti6Al4V alloy were successfully plasma paste borided using borax paste. The process was carried out in a dc plasma system at temperatures of 973, 1023 and 1073K for 3, 5 and 7h in a gas mixture of 70% H2–30% Ar under working pressure of 5mbar. The properties of the boride layers were evaluated by scanning electron microscopy, X-ray diffraction and the micro-Knoop hardness tester. Growth kinetics of the titanium boride layers on the Cp–Ti and Ti6Al4V alloy were obtained by analyzing the experimental results and parameters including the thickness of boride layer, correspondent diffusion temperature and holding time. The presence of both TiB2 top-layer and TiB whisker sub-layer was confirmed by the X-ray diffraction and scanning electron microscopy techniques. The formation rate of the dual titanium boride layers was found to have a parabolic character at all applied process temperatures. The surface hardness of TiB2 layer ranged between 2077 and 2373 HK0.025. The activation energies of boron in Cp–Ti and Ti6Al4V alloys were calculated as 93.61 and 99.79kJ·mol−1, respectively depending on the temperature and layer thickness.

Ti-doping effects on magnetic properties of dense MgB2 bulk superconductors

We have studied the effects of Ti doping on the magnetic properties of MgB2 superconducting bulks. The trapped field, which was obtained by field-cooled magnetization, , was about 3.6 T at 13 K at the surface of the single Ti5–20% doped MgB2 bulks, which was about 1.3 times larger than that of the non-doped bulk. The of 4.6 T was achieved at 14.1 K in the centre of the doubly stacked Ti-doped MgB2 bulks. The remanent magnetic flux density, which corresponds to the trapped field by zero-field cooled magnetization, , was comparable with the absolute value of coercive force with a very small vortex creep rate of about 2% over 40 h. These results suggested that the MgB2 bulk was an excellent ‘quasi-permanent’ magnet. The critical current density, , under magnetic field was also enhanced by Ti doping; under 3 T at 20 K, the of A cm−2 for the pristine sample was enhanced to that of 1.6–1.8 A cm−2 for the Ti-doped samples. The irreversibility field exceeded 5 T at 20 K for the Ti-doped samples. The existence of nanometric unreacted B and strongly Mg-deficient Mg-B particles and TiB2 layers at the periphery of Ti precipitates was suggested in the Ti-doped bulks by microscopic observation. The improvement of the vortex pinning properties in Ti-doped MgB2 originated from the creation of the nanometric nonsuperconducting particles and TiB2 layers acting as strong vortex pinning centres.

Corrosion behavior of titanium boride composite coating fabricated on commercially pure titanium in Ringer's solution for bioimplant applications.

The boriding of commercially pure titanium was performed at 850°C, 910°C, and 1050°C for varied soaking periods (1, 3 and 5h) to enhance the surface properties desirable for bioimplant applications. The coating developed was characterized for the evolution of phases, microstructure and morphology, microhardness, and consequent corrosion behavior in the Ringer's solution. Formation of the TiB2 layer at the outermost surface followed by the TiB whiskers across the borided CpTi is unveiled. Total thickness of the composite layer on the substrates borided at 850, 910, and 1050°C for 5h was found to be 19.1, 26.4, and 18.2μm respectively which includes <3μm thick TiB2 layer. The presence of TiB2 phase was attributed to the high hardness ~2968Hv15gf of the composite coating. The anodic polarization studies in the simulated body fluid unveiled a reduction in the pitting corrosion resistance after boriding the CpTi specimens. However, this value is >0.55VSCE (electrochemical potential in in-vivo physiological environment) and hence remains within the safe region. Both the untreated and borided CpTi specimens show two passive zones associated with different passivation current densities. Among the CpTi borided at various times and temperatures, a 3h treated shows better corrosion resistance. The corrosion of borided CpTi occurred through the dissolution of TiB2.

Investigation of the origin of compressive residual stress in CVD TiB2 hard coatings using synchrotron X-ray nanodiffraction

CVD hard coatings deposited on cemented carbide substrates typically exhibit tensile residual stresses, which are mainly due to differences in the thermal expansion coefficients of coating and substrate material. However, CVD TiB2 coatings have been reported to show considerable compressive residual stresses, with lacking information about their origin. Within this work, TiB2 coatings were deposited with and without TiN base layers on cemented carbide substrates using thermally activated CVD. The coating composition was examined using glow discharge optical emission spectroscopy yielding a slight sub-stoichiometry of the nanocrystalline TiB2 layers. Slices of the coating were prepared and synchrotron X-ray nanodiffraction experiments were performed in transmission geometry. Thus, gradients of stresses and texture could be determined as a function of the coating thickness. The TiN base layer showed tensile stresses, while the compressive stresses in the TiB2 layer even further increased with increasing layer thickness. No pronounced orientation could be determined for the early growth stage of the TiB2 layers, but with increasing thickness, a distinct (101) fiber texture develops. Pole figure measurements revealed no pronounced texture for the TiN base layer and corroborated the (101) texture for the TiB2 top layer. Using the sin2ψ method, compressive stresses of ~2.9GPa could be determined for the TiB2 layers, which significantly relaxed after annealing at 1000°C. Nanoindentation experiments revealed a hardness of ~44GPa. In conclusion, the nanocrystalline nature of the coatings seems to be the dominating origin of the compressive stresses of CVD TiB2 coatings.

Interfacial reaction studies of B4C-coated and C-coated SiC fiber reinforced Ti–43Al–9V composites

The interfacial reactions of B4C-coated and C-coated SiC fiber reinforced Ti–43Al–9V composites were investigated by scanning electron microscope and transmission electron microscope. The detailed microstructures as well as the chemical composition throughout the reaction zone were identified. For SiCf/B4C/TiAl composite, the reaction zone from B4C coating to TiAl matrix is composed of 4 layers, namely, a carbon-rich layer, a mixed layer of TiB2 + amorphous carbon, a TiC layer and a mixed layer of TiB + Ti2AlC. For SiCf/C/TiAl composite, the reaction zone from C coating to TiAl matrix is composed of 3 layers, namely, a fine-grained TiC layer, a coarse-grained TiC layer and a thick Ti2AlC layer. For both kinds of composites, the reaction mechanisms of the interfacial reactions were analyzed, and the corresponding reaction kinetics were calculated. The activation energies of interfacial reaction in SiCf/B4C/TiAl composite and SiCf/B4C/TiAl composite are 308.1 kJ/mol and 230.7 kJ/mol, respectively.

Effects of electrochemical boriding process parameters on the formation of titanium borides

In this study, the boriding of titanium via molten salt electrolysis was investigated in borax based electrolyte at various current densities (50–700 mA/cm2), temperatures (900–1200°C) and process durations (1 min-4 h). Thin film XRD results revealed that two main titanium boride phases TiB2 and TiB was formed even after 1 minute of process time. Scanning electron microscopy (SEM) images conducted on the cross-sections demonstrated a bilayer boride structure composed of a continuous uniform TiB2 phase and TiB whiskers that grew below the TiB2 layer toward the substrate. Dependence of boride layer thickness and morphology on the process parameters was evaluated. The results of the study showed that temperature of boriding was the most critical parameter both on boriding rate and morphology of the boride layer. It was possible to grow 8 μm thick TiB2 layer on titanium in 30 minutes of boriding at 1200°C.

Growth kinetics of titanium borides produced by CRTD-Bor method

In this study, a new boriding method called CRTD-Bor (Cathodic Reduction and Thermal Diffusion based boriding) was applied to titanium in a systematic manner and the effects of boriding process parameters on the morphological and chemical state of boride layers were explored. The presence of both TiB and TiB2 phases was confirmed by the X-ray diffraction technique. The cross-sectional examination of borided titanium verified the boride layers consisted of a homogeneous TiB2 phase on the top and TiB whiskers toward the substrate. Moreover, the growth kinetics of the TiB2 layers forming on titanium substrates was investigated during CRTD-bor which was performed at a constant current density of 200mA/cm2 in a borax based electrolyte at temperatures ranging from 900 to 1100°C for periods of 15 to 120min. The rate of the TiB2 layer formation was found to have a parabolic character at all applied process temperatures. The activation energy (Q) and the pre-exponential factor (Ko) of the TiB2 layer were determined as 189.9kJ/mol and 4.66×10−7m2s−1, respectively. The specific empirical equation that can be used to estimate the thickness of the TiB2 layers (dTiB2) for the conditions explored in the study is dTiB2=682.67exp−22833/Tt1173K≤T≤1373K;200mA/cm2.

Behavior of Boron in Molten Aluminum and its Grain Refinement Mechanism

The mechanism of heterogeneous grain refining of aluminum by ultrafine elemental boron particles was investigated. In order to facilitate the observation of the boron-aluminum interface, a boron filament was introduced in a melt at 1013 K (740 °C) containing different levels of Ti. The Al/B interface was studied using transmission electron microscopy and different phases were identified using the electron diffraction method. The experimental results showed that boron is dissolved in pure aluminum while its dissolution is inhibited in presence of titanium solute. A thin layer of TiB2 formed at the surface of boron thickens with residence time in the melt. The mechanisms by which aluminum is crystallized on boron are discussed.

Sol–gel derived hydroxyapatite coating on TiB2/TiB/Ti substrate

The low erosion resistance of titanium and its alloys has prevented their widespread application as joint implants. In addition, one essential requirement for the implants to bond with the living bone is the formation of a bone-like apatite on their surfaces in the host body. To enhance the erosion resistance of the surface, a diffused layer of TiB2 was formed at 1000°C on the commercial pure titanium. Hydroxyapatite was then coated on the boronised titanium by means of dip coating in a sol–gel solution. In order to confirm the biocompatibility of the specimens, they were soaked in a simulated body fluid for several days. The surface morphology of the specimens after exposure was studied by scanning electron microscopy, whereas X-ray diffraction patterns clearly revealed the growth of a calcium phosphate phase on top of the surface. Results showed that both wear resistance and biocompatibility of the hydroxyapatite coated samples on boronised films were improved.

Influence of modulation periods and modulation ratios on the structure and mechanical properties of nanoscale TiAlN/TiB2 multilayers prepared by IBAD

Alternate hard TiAlN/TiB2 multilayers with different modulation periods (Λ) ranging from 0.6 to 27 nm and modulation ratios (tTiAlN:tTiB2) ranging from 8:1 to 25:1 were prepared using an ion beam assisted deposition (IBAD) system. The effect of Λ and tTiAlN:tTiB2 on the hardness, elastic modulus, residual stress, and fracture resistance were investigated using various characterization techniques. All multilayers with clear interfaces displayed higher hardness than individual TiAlN and TiB2 layers. The maximum hardness of 35 GPa and critical load of 84 mN were obtained for the multilayer with a Λ of 2.2–8.8 nm and tTiAlN:tTiB2 of 8:1. Strong TiAlN (111) crystallographic texture as well as multilayer structure is thought to be be responsible for the increasing hardness of the TiAlN/TiB2 multilayers.

Cooperative doping effects of Ti and nano-SiC on transport critical current density and grain connectivity of in situ MgB2 tapes

By now, nano-SiC powder (20–30nm) is still the most effective additive for improving upper critical field and critical current density of MgB2-based superconducting materials. However, some decomposed carbon aggregates at grain boundaries and results in serious weak-links of MgB2 grains, and these weak-links limit the further improvement of critical current density, Jc of MgB2, especially at lower fields. Ti doping is reported to increase the compactness of MgB2, and modify its intergranular coupling by forming ultrathin TiB2 layer at grain boundaries. In this work, we studied the cooperative doping effects of Ti and nano-SiC on transport Jc and grain connectivity of MgB2 and the possibility to improve transport Jc of SiC doped MgB2 by introducing Ti additive. The results suggest the Ti addition can obviously improve Jc of MgB2 at lower fields and also enhance the Jc of SiC doped MgB2 by improving their grain connectivity which shows serious intergranular weak-links.

Wear Improvement of Pure Titanium Surface by TiB Precipitation after Plasma Alloying Process

Good mechanical properties with combination of biocompatibility and high corrosion resistance make titanium and its alloys desirable materials for medical applications. A big disadvantage of titanium connects with its poor wear characteristics, however in this work this property was modified by boride microplasma surface alloying. Plasma surface alloying gives a wide range of layer thickness, which is controlled by the amount of the placed powder and process parameters like gas flow, nozzle diameter and current. Formation of TiB phase precipitation was confirmed by XRD analysis. Additionally, the modified microstructure was observed by optical microscopy. The Vickers microhardness was significantly improved from 180HV for original titanium substrate to 900HV in obtained composite layer structure, with a smoth hardness reduction in the cross section profile. Strong heat penetration from microplasma melt-in technique, results in substrate dissolution with formation of stable composite Ti + TiB layer. The surface corrosion resistance in 0.9% NaCl solution was nearly the same as for pure titanium, showing stable behavior of created oxide layer, with no negative effect of dual phase microstructure. Wear resistance of received composite layer structures were significantly improved in comparison with initial titanium samples.

Effect of titanium on microstructure and fluidity of Al–B4C composites

The effect of Ti on the interfacial reactions, microstructural characteristics, and the related fluidity of Al–12%B4C composites has been investigated. Without Ti addition, B4C decomposed heavily during holding, and a large quantity of reaction-induced compounds, Al3BC and AlB2, was generated. When Ti was added, a TiB2 layer was built surrounding B4C particle surfaces, which acted as a diffusion barrier to separate B4C from liquid aluminum. Thus, the decomposition of B4C slowed down remarkably. The fluidity of the composite without Ti was the shortest of all composites and deteriorated quickly during the holding time. The fluidity of the composite melt was improved significantly with increased Ti levels. The optimum Ti level for the best fluidity results lied between 1.0 and 1.5%. The solid particle volume and the particle agglomeration are the two main factors influencing the fluidity.

Electrochemical Synthesis of TiB2 Layers Out of FLiNaK Electrolyte in the Presence of TaCl5 Additive

coatings on Mo substrates were electrodeposited out of a FLiNaK electrolyte in the presence of additive. The results show that a low concentration of in the melt changes significantly the chemical composition and consequently, the properties of the coatings. The energy-dispersive X-ray analysis indicates up to 10 atom % Ta in the coatings. X-ray phase analysis demonstrates the changes in the texture of in the direction. Codeposition of in a layer decreases the grain size and improves the smoothness of the layer. Addition of in the electrolyte permits to obtain layers of high quality and makes the process reproducible. In addition, the individual electrochemical behavior of the starting compounds, , , and , as well as their mixtures was investigated in the FLiNaK electrolyte by means of cyclic voltammetry.

Manufacturing of Reinforced High Precision Forging Dies

The economical production of near-net-shape forging parts with the highest accuracy requires high precision dies with the lowest wear. Compared to metals, ceramics show an outstanding high wear and corrosion resistance accompanied by high thermal durability, which favours their application to hot forging. However, ceramics can not endure tensile stresses. In order to enhance die life, small ceramic inserts can be integrated into the steel die body by brazing, placed within the wear critical areas. In addition to this, alternative methods from the field of surface coating are introduced for reinforcing dies. On the other hand, thin Ti-containing deposits from the gaseous phase, PVD- or PACVD, can increase the wear resistance when applied as a multilayer structure. An added top layer of TiBN or TiB2 finishes the described batches of TiN-TiCN-TiC layers. Results are presented incorporating the expertise of material science, metal forming and production engineering. This includes the development of reinforced forging dies, their design and manufacture by active metal brazing of ceramic inlays or coating processes as well as investigations regarding the grinding of steel-ceramic composite dies. The latter include parameter studies as well as grinding wheel development by performing thorough investigations of the wear mechanisms which lead to adapted and material-specific grinding strategies.

Electrochemical and Spectroscopic Investigations on the Synthesis of TiB2 Layers with Defined Properties out of FLINAK Electrolyte

not Available.

Study of Planar ${\rm MgB}_{2}/{\rm TiB}_{2}/{\rm MgB}_{2}$ Josephson Junctions Using the Proximity Effect SNS Model

Planar MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> junctions were fabricated by locally removing MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> within a gap of les 50 nm on a bilayer film of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> on SiC substrate using focused ion beam (FIB). Junctions with gaps of different depths were studied. We found that when the gap is too shallow the junction shows a flux-flow behavior, while a too deep gap will result in a junction with no supercurrent. Only junctions with the right gap depth exhibit good resistively-shunted-junction (RSJ) like current-voltage characteristics and excellent ac Josephson effect. The junctions' behavior can be described by the proximity effect superconductor-normal metal-superconductor (SNS) model, suggesting that the Josephson coupling is through the proximity effect in the metallic TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer.