Electrophoretic deposition of nanocrystalline hydroxyapatite on Ti6Al4V/TiO2 substrate

Hydroxyapatite is a bioactive material that is the main inorganic constituent of human hard tissue (Ca/P ratio of 1.67) whose coatings provide requisite surface bioactivity to the bone implants. In the current work, the characteristics of nanocrystalline hydroxyapatite (HA) coatings, electrophoretically deposited on Ti6Al4V substrate, have been investigated. To enhance the coating’s compatibility, a 0.75 μm thick TiO₂ layer was thermally grown as a diffusion barrier prior to electrophoretic deposition of HA. Subsequently, HA was electrophoretically deposited (EPD) at different deposition voltages (100–250 V) while keeping the deposition time as 10 s. Both anodic oxidation during EPD for 10 s and thermal oxidation during sintering at 1000°C for 2 h resulted in the growth of a TiO₂ layer thickness of more than 25 μm. Enhancement of voltage also has shown significant influence on the mechanism of the evolution of biphasic microstructures, attributed to the simultaneous growth of TiO₂ and HA phases. Optimized distribution of HA and TiO₂ phases was evidenced at 200 V, with explicit HA retention as observed via transmission electron microscopy. An empirical relationship is developed to relate the voltage with the suppression of cracking in the deposited coatings.     

Potential dependent selective dissolution of Ti–6Al–4V and laser treated Ti–6Al–4V in acid/chloride media

The corrosion properties of Ti–6Al–4V and laser surface melted (LSM) Ti–6Al–4V samples were investigated in 0.05 M H₂SO₄/0.05 M NaCl solution. Laser surface treatment was found to increase the corrosion potential and decrease the corrosion rates of the alloy. The current–potential profile of the LSM was found to be generally noisy below 0.5 V, indicating an unstable surface, which undergoes continuous dissolution and repassivation. However, above 0.5 V the LSM specimen exhibited higher corrosion current compared to the untreated alloy. Inductively coupled plasma (ICP) analysis of metals in solution was carried out after controlled potential electrolysis. Generally, the aluminium percentage was found to be the highest in solution compared to titanium and vanadium. The aluminium percentage in solution reached 94% compared to titanium and vanadium upon polarization in the passive region at 1.01 V. SEM showed that some local and shallow pitting to occur in both the untreated and LSM alloy. EDS results showed that aluminium composition of the electrolysed alloy surface is lower than the original material composition, and decreased from 6% in the original alloy to 0.18% after two hours of electrolysis of the LSM specimen.     

Microstructure and shear strength of ZrB2SiC/Ti6Al4V joint by TiCuZrNi with Cu foam

In this paper, brazing behaviors between ZrB₂SiC and Ti6Al4V by Cu foam interlayer were studied. The microstructure, formation mechanism, mechanical property and fracture surface of the joints were systematically studied. The results showed that the phases in the joints were α+β-Ti, TiCu, Ti₂Cu, Cu(s, s), TiC, TiB₂ and Ti₃SiC₂. An optimum shear strength reached up to 435??MPa?at a brazing temperature of 910?°C and holding time of 20?min. Such a shear strength was 90?MPa higher than the one without the Cu foam. The obtained high shear strength of joint was discussed from microstructure and residual stress. With the increase of brazing time, Cu(s,s) gradually disappeared and the content of Ti₂Cu intermetallic compound increased, which was harmful for the joint. Furthermore, the residual stress of joint with Cu foam was calculated to be 324?MPa, lower than the one without Cu foam interlayer.     

Effect of microstructure on the adhesion strength of TiBx coating on Ti6Al4V substrate

TiB_x coatings were deposited on Ti6Al4V and Si (100) wafer substrates by D.C. magnetron sputtering with various target-to-substrate distances (T.S. distances) from 50 mm to 200 mm. The influence of T.S. distance on the microstructure, hardness and adhesion strength of TiB_x coatings and Ti6Al4V substrate system was investigated. Results showed that the microstructure of TiB_x coatings transformed from dense to fibre columnar grain with the increase in T.S. distance, whilst the hardness decreased from 20.9 GPa to 9.4 GPa. The Rockwell-C indentation adhesion strength grade was also improved from HF6 to HF1. An adhesion evaluation factor G, which is related to the mechanical properties and the microstructure of TiB_x coating, is proposed based on the test results. The adhesion strength increased with G, which corresponded well with the results of indentation test. The high-speed rubbing test with a sliding speed of 300 m/s was performed to check the Al-adhesion resistance of the TiB_x coating against Al–hBN seal coating.     

Microwave hydrothermal synthesis and photocatalytic properties of TiO2/BiVO4 composite photocatalysts

TiO₂/BiVO₄ composite photocatalysts with heterojunction structures were synthesized by the one-step microwave hydrothermal method. The physical and photophysical properties of the as-prepared photocatalysts were fully characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), UV–vis diffuse reflectance spectra, photoluminescence (PL) and BET surface area analysis. The photocatalytic activities were evaluated by the decolorization of rhodamine B under UV and simulated sun-light irradiation. The results reveal that the as-prepared TiO₂/BiVO₄ composites exhibit higher photocatalytic activities than pure BiVO₄. The 20% TiO₂/BiVO₄ sample shows the best photocatalytic activity. The enhancement of photocatalytic activity is mainly attributed to the increasing separation rate of photogenerated charge carriers. The possible photocatalytic mechanism is discussed on the basis of the calculated energy band positions.     

Microstructure and mechanical properties of functionally graded TiCp/Ti6Al4V composite fabricated by laser melting deposition

Crack-free functionally graded TiC particle (TiC_p) reinforced Ti6Al4V (TiC_p/Ti6Al4V) composite was manufactured by laser melting deposition (LMD) technology with TiC volume fraction changing gradually from 0% to 50%. This research focuses on the relationship between the microstructure and mechanical properties (microhardness and tensile properties) of TiC_p/Ti6Al4V composites under different TiC volume fractions. Besides the unmelted TiC particles, the granular and chain shaped eutectic TiC phases are observed in the composite with 5 vol% TiC due to the melting and dissolution of TiC particles into matrix. The granular and dendritic primary TiC phases are obtained in the composite with 10 vol% TiC, while the chain shaped eutectic TiC phases can scarcely be seen. The main reinforcement phases are primary TiC phases when the TiC volume fraction exceeds 15%. (i) The quantity of unmelted TiC particles, (ii) the quantity and size of primary TiC phases and (iii) the porosity of composite increase gradually when the TiC volume fraction increases. The interfaces exhibit good bonding between consecutive layers. The microhardness of the functionally graded TiC_p/Ti6Al4V composite increases gradually with TiC volume fraction increasing. It is attributed to the C element in solid solution and the appearance of eutectic and primary TiC phases. The microhardness at the top layer with 50 vol% TiC is improved by nearly 94% compared with that at the Ti6Al4V side. The tensile strength of TiC_p/Ti6Al4V composite with 5 vol% TiC is enhanced by nearly 12.3% compared with that of the Ti6Al4V matrix alloy. However, both the tensile strength and elongation of composite decrease gradually when the TiC volume fraction exceeds 5%. The reason is that the quantity of brittle unmelted TiC particles and the quantity and size of dendritic TiC phases increase with TiC volume fraction increasing. The fracture mechanism of the TiC_p/Ti6Al4V composite is quasi-cleavage fracture.     

Non-isothermal nitridation kinetics of Ti6Al4V in Al2O3-based refractories

To establish a kinetic model of nitridation of Ti6Al4V in Al₂O₃-based refractories, the non-isothermal nitridation of Ti6Al4V–Al₂O₃ composite refractories at various heating rates was investigated using a thermogravimetric (TG) analyzer for large samples. The activation energy (E) and kinetic model (G(α)) for the nitridation of Ti6Al4V were determined using the isoconversional and master plots methods, respectively. The nucleation and growth of nitriding products of the TiN solid solution was the controlling step in the nitridation of Ti6Al4V in Al₂O₃-based refractories. The Avrami-Erofeev kinetic model, depicted by the G(α) = [-ln (1-α)]⁴ equation, is the most rational kinetic model. The values of E and A for the nitridation of Ti6Al4V were calculated to be 214.99 kJ/mol and 1.46 × 10⁷ (S^?1), respectively.     

Fabrication of CdS and CuWO4 modified TiO2 nanoparticles and its photocatalytic activity under visible light irradiation

CdS and CuWO₄ modified TiO₂ nanoparticles (CdS–CuWO₄-TiO₂) were prepared by the chemical impregnation method. The as-prepared nanoparticles were characterized using UV–visible-diffuse reflectance spectroscopy (UV–vis-DRS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and B.E.T. surface area analysis techniques. The photocatalytic activity was evaluated based on the degradation of a dye (eosin-Y) and inactivation of a bacterium (Pseudomonas aeruginosa). The results revealed that CdS–CuWO₄-TiO₂ showed high photocatalytic activity over CdS-TiO₂, CuWO₄-TiO₂ and TiO₂. Moreover the reusability and stability of the photocatalyst for the degradation of eosin-Y was also studied.     

Al-TiO2-C体系热力学分析及Al2O3-TiC复相陶瓷的燃烧合成

对Al-TiO2-C燃烧合成体系进行了热力学计算,并利用Al-O-N、Ti-O-N、C-O-N三个体系的叠加优势区相图分析了该燃烧合成体系的平衡产物相.结果表明,Al-TiO2-C燃烧合成体系的绝热燃烧温度为2398 K,燃烧合成平衡相为Al2O3和TiC.XRD检测结果与热力学分析结果相吻合,说明该燃烧合成反应进行得较为彻底,证实热力学分析结果可信.原位生成的Al2O3和TiC两相分布较均匀,燃烧合成产物疏松多孔,易于通过球磨方式达到破碎、磨细的目的.     

Characterization of carbon/carbon composite/Ti6Al4V joints brazed with graphene nanosheets strengthened AgCuTi filler

Carbon/carbon (C/C) composite and Ti6Al4V alloy (wt%) were successfully brazed with graphene nanosheets strengthened AgCuTi filler (AgCuTiG). Graphene nanosheets (GNSs) with low CTE and high strength were dispersed into AgCuTi filler by ball milling. The interfacial microstructure was systematically characterized by varieties of analytical means including transmission electron microscopy (TEM). Results show that typical interfacial microstructure of the joint brazed at 880 °C for 10 min is a layer structure consisting of (Ti6Al4V/diffusion layer/Ti2Cu + TiCu + Ti3Cu4 + TiCu4/GNSs + TiCu + TiC + Ag(s,s) + Cu(s,s)/TiC/C/C composite). The interfacial microstructure and mechanical properties of brazed joints changed significantly as temperature increased. High temperature promoted the growth of TiCu and TiC phases, which were attached to GNSs. Meanwhile, the diffusion layer and primary reaction layers thickened as temperature increased, while the thickness of brazing seam decreased. The maximum shear strength of 30.2 MPa was obtained for the joint brazed at 900 °C for 10 min. GNSs decreased the thickness of brittle reaction layers and promoted the formation of TiCu and TiC phases in brazing seam, which caused the strengthening effect and decreased the CTE mismatch of brazed joints. The fracture modes are also discussed in this paper.     

Influence of annealing temperature on microstructure evolution of TiAlSiN coating and its tribological behavior against Ti6Al4V alloys

TiAlSiN multicomponent coating, owing to its high hardness and excellent high temperature resistance, was widely used in the cutting field of difficult-to-cut materials such as titanium alloys. For machining titanium alloys, high temperature is easy to gather on the tool chips and deteriorate the cutting tools. Moreover, high temperature will also promote the microstructure evolution and make the wear mechanism more complex. In this paper, TiAlSiN coatings were deposited on cemented carbides and annealed at 400 °C, 600 °C and 800 °C respectively for 60 min in air, followed by reciprocating friction tests against Ti6Al4V counterparts. AFM, SEM, EDS and XPS were applied to investigate the microstructure evolution and tribological behavior of TiAlSiN coating after high temperature annealing. The results demonstrated that the oxidation resistance of TiN phase in TiAlSiN coating was worse than Si₃N₄ and AlN phases. These nitrides can be oxidized to TiO₂, SiO_x and AlO_x under 600 °C, and the depth of oxide layer was increased with the rising annealing temperature, resulting in the coarsened microstructure. The wear mechanisms of as-deposited TiAlSiN coating were oxidation wear and adhesion wear. With the rising annealing temperature, abrasive wear was gradually enhanced. For the TiAlSiN coating annealed at 800 °C, abrasive wear became the dominant wear mechanism.     

Investigation of Ti3AlC2 formation mechanism through diffusional reaction between carbon and Mo-modified Ti6Al4V

Carbon and Mo-coated Ti6Al4V alloy diffusion couple was used to investigate Mo-modified diffusion reaction between carbon and Ti6Al4V. Randomly dispersed carbide particles were observed in Ti6Al4V alloy after 900℃ exposure. Carbide particles were found evolving from defective TiC_x (x<1) to mixture of TiC_x and defective Ti₃AlC₂. Although Mo atoms were hardly detected in particles, their dilution effect along Ti alloy grain boundary (GB) is beneficial to carbon diffusion and carbide formation along GB. Based on high-resolution TEM (HRTEM) imaging, high density stacking faults (SFs) and nanotwins were observed in TiC_x particles which explain Raman activation of defects in TiC. Formation of SFs and nanotwins in TiC_x is attributed to carbon vacancies, which inversely promotes incoherent twin boundary (ITB) formation. Transformation from TiC_x to Ti₃AlC₂ is considered driven by Al indiffusion along ITBs. Intergrowth of TiC_x in defective Ti₃AlC₂ is the compromise to low Al concentration in Ti6Al4V.     

Preparation,scratch adhesion and anti-corrosion performance of TiO2-MgO-BHA coating on Ti6Al4V implant by plasma electrolytic oxidation technique

Bovine hydroxyapatite (BHA) (from cortical bone), was selected as the main electrolyte for plasma electrolytic oxidation (PEO) on Ti6Al4V implant. The prepared PEO coatings were examined by X-ray diffraction, field emission scanning electron microscope and energy-dispersive X-ray spectroscopy. The surface roughness, adhesion strength, wettability, surface energy and corrosion behaviour of the film were also investigated. The results show that the oxide layer (26 μm) formation on the Ti6Al4V was rough and porous. The micro-pores were filled with anatase TiO₂, cubic MgO and hexagonal BHA particles. The porous structures and the compound particles were mainly composed of Mg, O, Ca, P, Ti, Na and Al. Unlike previous coatings produced from calcium and phosphorus inorganic solutions, the coating formation from a newly developed bovine bone-derived HA electrolyte revealed an additional MgO phase in the coating layer. Moreover, higher amount of single phase hexagonal crystalline BHA phase with a Ca/P ratio of 1.1 was achieved with a single PEO process. A film-to-substrate adhesion strength of 1862.24 mN and scratch hardness of about 4.1 GPa was achieved from this method. The TiO₂/MgO/BHA film exhibited better wettability, higher surface energy and superior corrosion resistance compared to the bare Ti6Al4V substrate.     

Facile synthesis of TiO2-supported Al2O3 ceramic hollow fiber substrates with extremely high photocatalytic activity and reusability

TiO₂ oxide was deposited on a microstructured α-Al₂O₃ ceramic hollow fiber substrate by a simple one-step solution-immersion process with tetraethyl orthosilicate (TEOS) as a binder. The effects of the starting coating solution's composition on the photocatalytic properties of TiO₂ powders deposited on a substrate was determined by using TiO₂-supported Al₂O₃ ceramic hollow fiber substrates fabricated from coating solutions with different compositions and examining the substrates' effect on the methylene blue (MetB) degradation reaction under ultraviolet light. A strong correlation was observed between the initial coating solution compositions and the final photocatalytic characteristics of the TiO₂-supported Al₂O₃ ceramic hollow fiber substrates. Under optimal conditions, the MetB removal efficiency reached about 91% in a few minutes. To the best of our knowledge, this is the highest and most rapidly attained MetB removal efficiency reported for TiO₂-supported Al₂O₃ ceramic hollow fiber substrates. Furthermore, apart from attaining an extremely high photocatalytic activity within minutes, the fabricated TiO₂-supported Al₂O₃ ceramic hollow fiber substrates exhibited high photocatalytic stability even after several cycles.     

Effect of carburizing treatment on microstructural,mechanical and tribological performances of Cr doped DLC coating deposited on Ti6Al4V alloy

Cr doped diamond-like carbon (DLC) coating was deposited on the carburized Ti6Al4V alloy (TA) by magnetron sputtering (MS). The physical and chemical characteristics of Cr doped DLC coating were obtained using scanning electron microscope, energy dispersive spectroscope, Raman spectrometer, X-ray photoelectron spectroscopy and Fourier transform infrared, and the mechanical property and adhesion force were analyzed by nanoindenter and scratch tester. The effects of carburizing treatment on the coefficient of friction (COF) and wear mechanism of Cr doped DLC coatings were investigated on a ball-on-disk tribometer. The results show that the adhesion force and mechanical property of Cr doped DLC coating deposited on the carburized TA are higher than those deposited on the original TA. The average coefficients of friction (COFs) of Cr doped DLC coatings deposited on the original and carburized TAs under the dry-friction condition are 0.157 and 0.143, respectively, showing that the carburizing treatment has the obvious effect of friction reduction for the Cr doped DLC coating. The wear mechanism of Cr doped DLC coating deposited on the carburized TA is combined action of abrasive wear and adhesive wear, which are contributed to the enhancement of mechanical property of Cr doped DLC coating by carburization treatment. Furthermore, the average COFs of Cr doped DLC coatings deposited on the original and carburized TAs under the oil-lubrication condition are 0.152 and 0.131, respectively, which are superior to those under the dry-fiction condition. The carburizing treatment promotes the formation of self-repairing carbonyl of Cr doped DLC coating, and the oil-wet characteristic of Cr doped DLC coating with the aromatic aldehyde of CO as the functional group plays the main role of friction reduction.     

Investigation of the adsorption of tropocollagen type I on titanium and Ti6Al4V

The adsorption of tropocollagen type I on titanium and Ti6Al4V has been investigated using physicochemical (zeta potential measurements), biochemical (ELISA), and imaging methods (SEM, AFM). Zeta potential measurements on both materials showed isolectric points in the pH_iep range 4.3-4.8 if the metal surfaces were covered with amorphous oxide layers. Adsorption of both collagen molecules and fibrillar collagen led to a shift of about 0.5 pH units towards the alkaline region. From ELISA-based results it can be concluded that in the investigated concentration range of 0.01-0.5 mg/ml, the adsorption of collagen molecules leads to the formation of a rather uniform covering. The influence of pH and ionic strength on the adsorption behavior has been investigated. A model of the competitive adsorption of both tropocollagen molecules and in vitro reconstituted fibrils is presented. Based on this model, two methods are proposed for the improved adsorption of collagen fibrils: (i) adsorption from solutions that are essentially free from tropocollagen and oligomeric species; and (ii) use of already adsorbed tropocollagen as nucleation sites for further fibrillar growth.     

Voltammetric stability of anodic films on the Ti6Al4V alloy in chloride medium

The biocompatibility and mechanical integrity of Ti and Ti6Al4V alloy can be affected by corrosion processes. This paper presents studies on the stability of anodic oxide films on Ti6Al4V and Ti in chloride medium. The oxides were grown potentiodynamically up to 8.0 V in the phosphate buffer saline (PBS) solution (pH 6.8) at 25 and 37 °C. The morphology of the obtained anodic oxides and the type of corrosion that occurred were analyzed by SEM–EDS. The Ti6Al4V alloy presented less corrosion resistance than pure Ti. Elemental analyses showed that the decrease of the alloy corrosion resistance is due mainly to the corrosion of Al.     

Effect of TiO2 on the Sinterability and Microstructure of Mullite Sythesized from Al（OH）3 and SiO2

1IntroductionAs an ideal raw material for refractories produc-tion,mullite has been widely used in refractories in-dustry.But little amount of natural mullite has beenfound so that almost all of the mullite used now has tobe synthesized from natural miner…     

Manifestation of enhanced and durable photocatalytic H2 production using hierarchically structured Pt@Co3O4/TiO2 ternary nanocomposite

A hierarchical structure composed of Pt@Co₃O₄/TiO₂ (CTP) ternary nanocomposite was synthesized and demonstrated for its enhanced and durable production of hydrogen from glycerol under simulated solar light irradiation. The rate of hydrogen production over the optimized composition was found to be 19.2 mmol h^?1 g^?1_cat. The obtained XRD and XPS results revealed the facile formation of the composite. The heterojunction formed in the ternary system remarkably enhanced the visible light absorption properties and charge separation in CTP as evidenced from their UV–visible absorption and PL spectra, respectively. The optimized union of the materials with specific properties and their intimate physical contacts might be the origin for the manifested, improved and durable photocatalytic efficiency towards hydrogen production.     

Influence of the morphology and microstructure on the photocatalytic properties of titanium oxide films obtained by sparking anodization in H3PO4

The aim of this paper is to investigate changes in morphology and microstructure of TiO₂ films, prepared by sparking anodization of Ti in a H₃PO₄ solution, by applying different formation charges. We show that although films obtained by this technique are rarely used in photocatalytic applications, the morphological and microstructural changes during sparking anodization produce TiO₂ films that can be used as photocatalysts. In contrast to qualitative analysis commonly found in the literature, we used quantitative methods of analysis to quantify average pore diameter and pore density from the morphology and structural parameters from X-ray diffraction (XRD) patterns using the Rietveld refinement. The results indicated that changes in both the morphology and crystalline structure have a strong influence on the photoactivity of the films. From this investigation, we concluded that, for films prepared in early stages of anodization, the morphology had the biggest influence on photoactivity, and after applying 72C of charge, crystalline properties dominated the photocatalytic characteristics of the films.