As-received Ti Research Articles

Embedment of HA/Ti composite on superplastic titanium alloy (Ti–6Al–4V)

In this research, embedment of HA-2 wt.% Ti composite powder on superplastic Ti–6Al–4V was conducted through continuous pressing technique to improve the low strength of the conventional pure HA coatings. The embedment process was carried out at temperature below the allographic temperature. The bond strength evaluation of HA-2 wt.% Ti composite layer was performed using wear test method under different applied pressure. The experimental results indicated that the HA-2 wt.% Ti composite layer had uniform thickness and well bonded to the substrate. EDX and line scanning analysis revealed that HA elements were detected at the substrate indicating embedment process was successful. The wear test results proved that the strength of the embedded layer on the superplastic Ti–6Al–4V was much better than the as-received Ti–6Al–4V.

Direct laser cladding of Co on Ti–6Al–4V with a compositionally graded interface

In the present study, attempts have been made to fabricate Co layers on the surface of Ti–6Al–4V substrate with a compositionally graded interface by direct laser cladding. Laser processing is carried out by pre-placing the powder (or powder blends) on the substrate, and melting it using a high power continuous wave CO 2 laser with Ar as shrouding gas. A compositionally graded interface is developed by applying powder blends of Ti to Co at a ratio of 90:10 near to Ti–6Al–4V substrate to 10:90 prior to development of Co layer. A defect-free microstructure is developed with the presence of Ti 2Co and TiCo and Co 2Ti at the interface. The volume fraction of individual phase was found to vary with the depth from the Co-clad zone. A significant improvement in microhardness is achieved at the interfacial region. Uniform corrosion resistance increases along the graded interface, but the pitting corrosion resistance is marginally deteriorated. Direct laser clad layer possesses a better biocompatibility than that of as-received Ti–6Al–4V sample.

LASER ASSISTED SURFACE MODIFICATION OF Ti–6Al–4V FOR BIOIMPLANT APPLICATION

The present study aims at enhancing the wear resistance of Ti –6 Al –4 V by laser surface nitriding. Laser surface treatment has been carried out by melting of the sand blasted Ti –6 Al –4 V substrate using a high power continuous wave Diode laser with nitrogen as shrouding environment (at a gas flow rate of 51/min). Laser surface nitriding led to formation of dendrites of titanium nitrides. The microhardness is improved to a maximum of 900–950 VHN (Vickers hardness number) in laser surface nitriding as compared to 260 VHN of the as-received substrate. Surface nitriding increased primary potential for pit formation (Epp1) as compared to Ti –6 Al –4 V . Biocompatibility behavior showed a better cell viability due to surface nitriding as compared to the as-received Ti –6 Al –4 V .

Surface elastic properties of Ti alloys modified for medical implants: A force spectroscopy study

We report here the first nanoscale surface elasticity measurements on surface-modified titanium alloys using the force spectroscopy mode in scanning force microscopy. Samples of three vanadium-free titanium alloys, Ti–7Nb–6Al, Ti–13Nb–13Zr and Ti–15Zr–4Nb, were investigated. Surface modification of the three alloys was produced by thermal oxidation in air at 750 °C for different times, which resulted in the formation of protective oxide layers with different surface composition and morphology. The elastic properties of the surface layers were studied comparatively in the as-received Ti alloys and after the oxidation process using cantilevers with different stiffness to evaluate the influence of the indentation depth. In all cases, Young’s modulus of the sample surfaces was found to be lower than 65 GPa, and as low as 20 GPa for some of the oxidized samples. Variations observed for the three oxidized Ti alloys can be related to the different chemical composition of the outer layers generated for the different oxidation times.

Ti 및 Si 혼합 분말의 전기방전소결에 의한 Titanium Silicide의 합성 연구

The synthesis and consolidation of titanium silicide by electro-discharge-sintering has been investigated. As-received Ti powder was in flaky shape and the mean particle size was <TEX>$45.0{\mu}m$</TEX>, whereas the mean particle size of the pre-milled Si powder with angular shape was <TEX>$8.0{\mu}m$</TEX>. Single pulse of 2.5 to 5.0 kJ/0.34g-elemental Ti and pre-milled Si powder mixture with the composition of <TEX>$Ti-37.5at.\%$</TEX> Si was applied using <TEX>$300{\mu}F$</TEX> capacitor. The solid with <TEX>$Ti_5Si_3$</TEX> phase has been successfully fabricated by the discharge with the input energy more than 2.5kJ in less than <TEX>$129{\mu}sec.$</TEX> Hv values were found to be higher than <TEX>$1000kgf/mm^2$</TEX>. The formation of <TEX>$Ti_5Si_3$</TEX> occurred through a fast solid state diffusion reaction.

XPS study of porous dental implants fabricated by electro-discharge-sintering of spherical Ti–6Al–4V powders in a vacuum atmosphere

A single electro-discharge-sintering (EDS) pulse (0.7–2.0 kJ/0.7 g), from a 300 μF capacitor, was applied to atomized spherical Ti–6Al–4V powder in a vacuum to produce a porous-surfaced implant compact. A solid core surrounded by a porous layer was formed by a discharge in the middle of the compact. X-ray photoelectron spectroscopy was used to study the surface characteristics of the implant material. C, O, and Ti were the main constituents, with smaller amounts of Al, V, and N. The implant surface was lightly oxidized and was primarily in the form of TiO2 with a small amount of metallic Ti. A lightly etched EDS implant sample showed the surface form of metallic Ti, indicating that EDS breaks down the oxide film of the as-received Ti–6Al–4V powder during the discharge process. The EDS Ti–6Al–4V implant surface also contained small amounts of aluminum oxide in addition to TiO2. However, V detected in the EDS Ti–6Al–4V implant surface did not contribute to the formation of the oxide film. The small amount of N in the implant surface resulted from nitride material that was also found in the as-received Ti–6Al–4V powders.

Surface characteristics of porous titanium implants fabricated by environmental electro-discharge sintering of spherical Ti powders in a vacuum atmosphere

A single pulse of 1.5 kJ, from a 300 μF capacitor, was applied to 0.7 g of atomized spherical Ti powders to produce a porous-surfaced implant compact by environmental electro-discharge sintering (EEDS) in a low vacuum atmosphere. A solid core was formed by a discharge in the middle of the compact which is surrounded by a porous layer. Ti, C and O were the main constituents, with a smaller amount of N. The EEDS implant surface was lightly oxidized and was primarily in the form of TiO 2 . The lightly etched sample showed the surface form of metallic Ti, indicating that the EEDS breaks down the oxide film of the as-received Ti powder during the discharge process. However, a small amount of N in the form of nitride, which was also found in the as-received Ti powder, was not changed in its chemical state by EEDS.

Porous Ti-6Al-4V alloy fabricated by spark plasma sintering for biomimetic surface modification.

Porous compacts with both biological and biomechanical compatibilities and high strength were developed. Spherical powders of Ti-6Al-4V alloy, which were either as received or surface modified with the use of calcium ions by hydrothermal treatment (HTT), were fabricated by a spark plasma sintering process. The porous compacts of pure Ti were used as reference materials. Porosity was approximately 30%, and compressive strengths were 113 and 125 MPa for the as-received Ti alloy powders and those modified by the HTT process, respectively. The bending strength and elastic modulus of as-received Ti alloy powders were 128-178 MPa and 16-18 GPa, respectively. Each of the compacts was immersed in simulated body fluid (SBF). The amount of adsorption/precipitation of calcium phosphate through the compacts was measured by weight change and was observed by SEM. The compacts were covered with calcium phosphate after 2 weeks of immersion in SBF. The compacts of Ti alloy had plenty of precipitated apatite crystals, and modification by HTT accumulated more precipitation. Because calcium phosphate is a mineral component of bone, apatite, which is precipitated on the surface of the compacts, could adsorb proteins and/or drugs such as antibiotics. It is expected that a large amount of proteins and/or drugs could be impregnated when the porous compacts developed are used.

Effect of various surface conditions on fretting fatigue behavior of Ti–6Al–4V

An experimental investigation was conducted to explore the fretting fatigue behavior of Ti–6Al–4V specimens in contact with varying pad surface conditions. Four conditions were selected: bare Ti–6Al–4V with a highly polished finish, bare Ti–6Al–4V that was low-stress ground and polished to RMS #8 (designated as ‘as-received’), bare Ti–6Al–4V that was grit blasted to RMS #64 (designated as ‘roughened’) and stress relieved, and Cu–Ni plasma spray coated Ti–6Al–4V. Behavior against the Cu–Ni coated and as-received pads were characterized through determination of a fretting fatigue limit stress for a 10 7 cycle fatigue life. In addition, the behavior against all four-pad conditions was evaluated with S-N fatigue testing, and the integrity of the Cu–Ni coating over repeated testing was assessed and compared with behavior of specimens tested against the as-received and roughened pads. The coefficient of friction, μ, was evaluated to help identify possible crack nucleation mechanisms and the contact pad surfaces were characterized through hardness and surface profile measurements. An increase in fretting fatigue strength of 20–25% was observed for specimens tested against Cu–Ni coated pads as compared to those tested against as-received pads. The experimental results from the S-N tests indicate that surface roughness of the coated pad was primarily responsible for the increased fretting fatigue capability. Another factor was determined to be the coefficient of friction, μ, which was identified as ~0.3 for the Cu–Ni coated pad against an as-received specimen and ~0.7 for the bare as-received Ti–6Al–4V. Specimens tested against the polished Ti–6Al–4V pads also performed better than the specimens tested against as-received pads. Fretting wear was minimal for all cases, and the Cu–Ni coating remained intact throughout repeated tests. The rougher surfaces got smoother during cycling, while the smoother surfaces got rougher.

Structural characterisation of melt-spun Ti50Ni25Cu25 ribbons

The structure of melt-spun Ti 50 Ni 25 Cu 25 ribbons after various heat treatments has been studied by X-ray and TEM analyses. As-received amorphous Ti 50 Ni 25 Cu 25 ribbons, when annealed at 500°C for a few minutes, crystallise into the B2 structure, which fully transforms into the orthorhombic martensite upon cooling. The X-ray scans of Ti 50 Ni 25 Cu 25 ribbons annealed for 5 min. at 500°C show the well developed orthorhombic pattern, which was used for refinement of the orthorhombic martensitic structure of TiNi-Cu alloys. The refined structure of the orthorhombic martensite in TiNi-Cu alloys differs from the standard B19 type suggested previously. X-ray investigation reveals a shift of atoms in the (010) ORT layers from the centro-symmetric positions towards the [001] ORT direction. The longer annealing of Ti 50 Ni 25 Cu 25 ribbons at 500C causes TiCu precipitation and results in appearance of untransformed B2 grains at room temperature. Annealing at 700C causes Ti 3 Cu 4 precipitation with significant Cu depletion of the matrix resulting in the appearance of the mixed orthorhombic and monoclinic martensite.

Formation mechanism of titanium silicide by mechanical alloying

The syntheses of five titanium silicides (Ti3Si, TiSi2, Ti5Si4, Ti5Si3, and TiSi) by mechanical alloying (MA) have been investigated. Rapid, self-propagating high temperature synthesis (SHS) reactions were involved in producing the last three materials during room temperature high-energy ball-milling of elemental powders. Such reactions appeared to occur through ignition by mechanical impact in the fine powder mixture formed after a critical milling period. From in-situ thermal analyses, each critical milling period for the formation of Ti5Si4, Ti5Si3, and TiSi was observed to be 22, 35.5 and 53.5 minutes, respectively. However, the formation of Ti3Si and TiSi2 did not occur even after 360 minutes of milling of as-received Ti and Si powder mixture, due to the lack of homogeneity of the powder mixture. Other ball-milling procedures were employed for the syntheses of Ti3Si and TiSi2 using different sizes of Si powder and milling medium materials. Ti3Si was synthesized by milling a Ti and 60 minutes premilled Si powder mixture for 240 minutes. α-TiSi2 and TiSi2 were produced by high energy partially stabilized zirconia (PSZ) ball-milling for 360 minutes in a steel vial followed by jar-milling of a Ti and 60 min premilled Si powder mixture for 48 hr. The formation of Ti3Si and TiSi2 occurs through a slow solid state diffusion reaction, and the product(s) and reactants coexist for a certain period of time. The formation of titanium silicides by MA and the reaction rate appeared to depend on the homogeneity of the powder mixture, milling medium materials, and heat of formation of the product involved.

Effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium castings

Statement of problem. Porosity is a frequently observed casting defect in dental titanium alloys. Purpose. This study evaluated the effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium (cp Ti) castings. Material and methods. Eight groups (A-H) of 16 rectangular wax patterns each (30 mm in length, 3 mm in width, and 1 mm in depth) were prepared. The wax patterns were invested with a magnesia-based material and cast with cp Ti (grade II). Groups A, C, E, and G were cast under a pressure of 1 atm, and groups B, D, F, and H were cast under a pressure of 0.5 atm of He, Ar, Kr, and Xe, respectively. The extent of the porosity of the cast specimens was determined radiographically and quantified by image analysis. Three specimens of each group and 3 cylinders of the as-received cp Ti used as a reference were embedded in resin and studied metallographically after grinding, polishing, and chemical etching. These surfaces were used for determination of the Vickers hardness (VHN) as well. Eight specimens from each group were fractured in the tensile mode, and the 0.2% yield strength, fracture stress, and percentage elongation were calculated. Porosity was analyzed with 2-way ANOVA and the Newman-Keuls multiple range test. VHN measurements and tensile properties for specimen groups were compared with 1-way ANOVA and the Newman-Keuls multiple range test (95% significance level). Results. The porosity levels per group were (%): A = 5.50 ± 4.34, B = 0.77 ± 1.27, C = 2.44 ± 3.68, D = 0.06 ± 0.12, E-H = 0. Two-way ANOVA showed that there was no detectable interaction (P<.05) between gas type and applied pressure. Metallographic examination revealed no differences in microstructure among the groups studied. A finer grain size was observed in all cast groups compared with the original cp Ti. The VHN of the as-received cp Ti was significantly greater than all the cast groups tested. Groups cast under He showed the highest VHN, yield strength, and fracture stress. No significant differences were found in percentage elongation values among the groups. Conclusion. Porosity and mechanical properties of cp Ti castings are dependent on the gas type and pressure, whereas the microstructure remains unaffected. (J Prosthet Dent 2000;84:575-82.)

Graphite formation in PM ferrous powder with boron and self-lubrication effects : J.B.Yang, H.Nishie. (Mitsubishi Materials Co, Japan.)

Friction behavior of the network-structured CNTs coated pure Ti plate was evaluated by ball-on-disk wear test using SUS304 ball specimen under dry condition. The friction coefficient was significantly low and stable compared to the as-received Ti plate with no coating film. CNTs coating film had two important roles; self-lubrication and bearing effects to reduce the friction coefficient and carbon solid-solution hardening to improve the abrasive wear property of Ti plate. The annealing treatment at higher temperature (1123 K) was more effective to reduce the friction coefficient than that at lower temperature (973 K) because the Ti plate surface was uniformly covered with CNTs film even after sliding wear test. This is due to TiC interlayer formation via a reaction between Ti plate and carbon elements originated from CNTs during annealing. As a result, a strong interface bonding between CNTs film and Ti plate surface was obtained by higher temperature annealing treatment, and obstructed the detachment of CNTs film during wear test.

Dehydration of 2-propanol over CuTi metallic glasses: effect of pretreatments and reaction on the structure and surface properties

CuTi catalysts, prepared from metallic glass precursors, selectively dehydrate 2-propanol to propylene at 673 K, in contrast to CuZr alloys or Cu foil, with which mostly dehydrogenation to acetone occurs. The catalytic run at 673 K results in complete crystallization of the bulk of CuTi alloys. A higher activity with a slightly lower selectivity is observed when an oxygen treatment is applied prior to the reaction. The morphology of the as-received CuTi ribbons is substantially altered as a consequence of the reaction. The results of N 2O titration indicate that the Cu(0) surface area is very low either in the as-received state or after the reaction. X-ray photoelectron spectroscopy depth profile measurements demonstrate considerable Cu enrichment in the near-surface region as a result of the reaction. However, on the topmost layer, only Cu(II) species exist. This is in contrast to the case of CuZr alloys, where both Cu(0) and Cu(II) species coexist. The different reaction paths we observe might be attributed to this finding.