Papers by Keyword: TiAl

Abstract: Titanium alloy is an attractive material for aerospace and automobile applications due to its lightweight and high strength. Titanium metal matrix composite (MMCs) is one of the promising materials which could be employed to enhance stiffness and wear resistance of titanium alloy. In this study, reinforcement of in-situ and ex-situ particulates has been investigated. The experimental results show that a dense microstructure with uniformly distributed in-situ TiB reinforcement phase in the Ti+B+Sn system could be obtained. It is present in either needle or blocky shape. This process involved warm pressing of mixed powder in semi-solid stage followed by sintering, which eliminated costly CIP and HIP processes. However, it is found that the ex-situ particulates in the titanium metal matrix are not suitable as reinforcements in Ti-Sn metal matrix as they either reacted with titanium during sintering process or generated a void at the interface between the reinforcement and the matrix.

Abstract: Materials exhibit microstructures and textures that influence their use and properties. Xray and neutron diffraction allow characterization of the bulk texture, whereas Electron Backscattered Diffraction (EBSD) permits determination of the local texture. In many cases Transmission Electron Microscopy (TEM) remains necessary to characterize the substructure and the local texture for highly deformed materials. Depending on the scale considered, all these complementary techniques permit the coupling of texture and microstructure so that it becomes possible to control microstructure and its evolution during a processing route. Some examples in titanium aluminides, (α + β) titanium alloys and an Fe-Ni alloy will illustrate this challenge.

Abstract: In order to improve the grindability of titanium alloys, the inhibition of chemical affinity between abrasives and titanium alloys and cooling enhancement in grinding zone are carried out in this paper. Slotted electroplated CBN grinding wheels with optimum topography are used, and different grinding fluid supply systems such as conventional tangential spraying coolant supply, inner chamber coolant jet impingement, radial high-pressure coolant jet impingment are employed in creep feed deep grinding experiments on titanium alloy (TC4). The experimental results show that high-pressure jet impingement has remarkable cooling effect. The temperature of the workpiece surface can be steadily kept below the critical film boiling temperature 120~130°C, while the workpiece surfaces is badly burnt with conventional coolant supply. The study will exploit an important research orientation that has great potential in high efficiency grinding. Further perfection of this study will not only enable us to increase the available material removal rate to a new level but also solve the workpiece burn problem of the difficult-to-machining materials in high efficiency grinding.In order to improve the grindability of titanium alloys, the inhibition of chemical affinity between abrasives and titanium alloys and cooling enhancement in grinding zone are carried out in this paper. Slotted electroplated CBN grinding wheels with optimum topography are used, and different grinding fluid supply systems such as conventional tangential spraying coolant supply, inner chamber coolant jet impingement, radial high-pressure coolant jet impingment are employed in creep feed deep grinding experiments on titanium alloy (TC4). The experimental results show that high-pressure jet impingement has remarkable cooling effect. The temperature of the workpiece surface can be steadily kept below the critical film boiling temperature 120~130°C, while the workpiece surfaces is badly burnt with conventional coolant supply. The study will exploit an important research orientation that has great potential in high efficiency grinding. Further perfection of this study will not only enable us to increase the available material removal rate to a new level but also solve the workpiece burn problem of the difficult-to-machining materials in high efficiency grinding.

Abstract: The affect of boron (B) on the microstructure and creep behavior of a Ti-15Al-33Nb (at%) alloy was investigated. In addition to the normal constituent phases present in the monolithic alloy, the B-modified alloy contained borides enriched in titanium and niobium. These borides were present in the form of needles/laths up to 50 μm long and 10 μm wide which took up 5-9% of the volume. Constant load, tensile-creep experiments were performed in the stress range of 150-340 MPa and the temperature range of 650-710°C, in both air and vacuum environments. An addition of 0.5 at% B did not improve the creep resistance of the monolithic alloy, while the addition of 5 at% B significantly improved the creep resistance.

Abstract: Titanium and some of its alloys are widely used as load-bearing implant materials. In particular, titanium-zirconium (Ti-Zr) alloys have a high potential for biomedical applications due to the excellent biocompatibility of both Ti and Zr. Nevertheless, the surfaces of the Ti-Zr alloys need to be modified to provide the implant material’s bioactivity. In the present study, an alkali-heat (AH) treatment process followed by the soaking in simulated body fluid (SBF) was attempted for the preparation of calcium phosphate (CaP) coatings on the surface of the TiZr alloy. Phase transformation, surface morphology, and interfacial microstructure were investigated using scanning electron microscope (SEM) with an energy-dispersive electron probe X-ray analyser (EDS). The results indicate that the AH treatment produced a nano-porous bioactive sodium titanate / zirconate hydrogel surface layer which induced the deposition of a Ca-P layer during soaking in the SBF. This Ca-P layer on the TiZr alloy surface can be expected to bond to the surrounding bones directly after implantation.

Abstract: Various types of titanium alloys with high strength and low elastic modulus and, at the same time, vanadium and aluminium free have been developed as surgical biomaterials in recent years. Moreover, porous metals are promising hard tissue implants in orthopaedic and dentistry, where they mimic the porous structure and the low elastic modulus of natural bone. In the present study, new biocompatible Ti-based alloy foams with approximate relative densities of 0.4, in which Sn and Nb were added as alloying metals, were synthesised through powder metallurgy method. The new alloys were prepared by mechanical alloying and subsequently sintered at high temperature using a vacuum furnace. The characteristics and the processability of the ball milled powders and the new porous titanium-based alloys were characterised by X-ray diffraction, optical microscopy and scanning electron microscopy .The mechanical properties of the new titanium alloys were examined by Vickers microhardness measurements and compression testing.

Abstract: Porous Ti-Nb alloys are promising candidates for biomedical applications. In the present study, alloy powders containing 60 wt-% Nb were prepared by high-energy milling of Nb, Ti, and/or TiH2 powders. The high-energy milling process was carried out in a planetary ball mill. The starting and as-milled materials were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM). Elemental (Nb, and Ti) and TiH2 powder mixtures with composition Nb-40wt%Ti were mechanically alloyed for 2 to 30 h. The formation of a BCC Nb(Ti) solid solution by high-energy milling using elemental Ti powder to produce Nb-40Ti was observed after milling for 30 h. A HCP-Ti solid solution was formed after milling for 30 h due to the partial decomposition of titanium hydride powder mixture during high-energy milling.

Abstract: With the prolonged average duration of life, there is an increase concern for repair of bone, joints and teeth which deteriorated and lose their functions. Thus, research of artificial materials for implants has assumed an important role in the implants development. The trend of the current research in orthopedic implants is based in the development of titanium alloys with low modulus of elasticity, next to the bone, and toxic elements free. In this work, results of the Ti-13Zr- 13Nb alloy sintering are presented. This alloy due its high biocompatibility and lower modulus of elasticity is a promising candidate for implants fabrication. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 800 at 1500 °C, in vacuum. Sintering behavior was studied by means of dilatometry. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Density was measured by Archimedes method. It was shown that the samples were sintered to high densities and presented homogeneous microstructure from the elements dissolution. Processing parameters were optimized in order to reduce the interstitial pick-up (O, C, N and H) and to minimize grain growth during sintering.

Abstract: A series of test for the fatigue crack growth rate da/dN and the threshold ΔKth values were performed with CT specimens on a ship-condenser material titanium alloy plate and rolled ring. Base metal, welded joint and HAZ (heat affected zone) materials were used to make different test specimens. Specimens made from the titanium plate were cut along L-T direction, those made from rolled ring were obtained along C-R and L-R direction respectively. Results show that the fatigue crack growth rate value of welded joint is much higher than those of base metal and HAZ material. The da/dN values of C-R direction specimens are much higher than those of L-R direction specimens, whereas the ΔKth values are lower. It means that welding process may lead to a great reduction in the fatigue property for titanium alloy and the effect of crack orientation on fatigue property is not negligible for titanium alloy. To select a proper orientation of titanium material is therefore very important in engineering practice. Results also indicate that a simplified method can be used to calculate the ΔKth values for titanium material, that is, ΔKth values may be calculated directly from the da/dN expression in a zone near the threshold and the laborious measurements of ΔKth may therefore be saved.

Abstract: The effective fracture toughness testing of materials intended for application in MicroElectroMechanical Systems (MEMS) devices is required in order to improve understanding of how they may be expected to perform upon the micro scale. γ-TiAl based materials are being considered for application in MEMS devices required to operate at elevated temperatures. The effect of different preparation methods upon resulting fracture toughness and development of testing methods for these devices is therefore of importance. Micro-sized cantilevers of the γ-TiAl alloy “Alloy 7” (Ti-46Al-5Nb-1W) were therefore prepared using either mechanical or chemical final stage polishing and subsequently used to evaluate fracture toughness. The effectiveness of the evaluation of micro-sized samples of γ-TiAl in this manner is considered, as well as the effects of the different processing methods and variations in properties according to lamellar orientation.