Papers by Keyword: Ti₆Al₄V

Abstract: The microstructures of Ti6Al4V alloy after hydrogenation have been investigated and analysed by optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the influence of hydrogenation on the hardness of α and β phases has been analysed by microhardness testing. The microstructure observation revealed that δ hydride (fcc structure) precipitated in the specimens with 0.278 wt.% and 0.514 wt.% hydrogen, and a lot of dislocations and twins have been found simultaneously. The diffraction peaks moved to the lower angles because of the lattice expansion of β phase with the solution of hydrogen atoms. The result of microhardness testing shows that the hardness of α and β phases increases synchronously with increasing of hydrogen and the increment of β is larger than that of α. It is considered that the formation of δ hydrides, lattice defects and alloying element diffusion are the major factors leading to the microhardness change.

Abstract: The importance of determining and understanding the very high cycle fatigue behaviors of materials has gained strength in recent years. Ti-alloys, in view of their high strength-to-weight ratio, have a range of structural applications. Of these, Ti-6Al-4V, belonging to the alpha-beta type is the most widely used. The present paper deals with investigations on the fatigue behavior of TC4, the Chinese equivalent to Ti-6Al-4V, up to very high cycles. Fatigue testing was carried out on a piezoelectric ultrasonic fatigue machine operating at 20 kHz frequency. Hourglass shaped resonant specimens were tested in ambient air at room temperature under completely reversed loading conditions (R = -1). Failure in the alloy was seen to occur right up to the gigacycle regime, with the fractures being found to initiate from the surface unlike in steels. The fracture surfaces exhibit brittle characteristics containing river patterns and cleavage facets, as well as striations.

Abstract: Laser shock processing (LSP) employs high-energy laser pulses from a solid-state laser system to create intense shock waves into a material, which can induce compressive residual stresses in the target surface and improve its mechanical property efficiency. Residual stress of Ti6Al4V alloy both before and after LSP with multishocks was analysised. The depth of compressive residual stress was found to have a dependence on the number of shocking layers and a slight dependence on the level of irradiance. Surface stress improvements of more than 50% increases are possible after laser shock processing with either large spot or small spot patterns. The large spot gave a surface stress of 432MPa and a depth of over 1mm. The low intensity small spot gave a surface stress of 285MPa with a depth comparable to the large spot. Laser shock processing induces a compressive residual stress field, which increases fatigue crack initiation life and reduces fatigue crack growth rate.

Abstract: Hydroxyapatite (HA) was widely used as coating on metals and alloys to enhance the interconnection between metal implants and bone. To improve the bonding strength and bioactivity, in this work, bioactive glass (G) was added and HA-G composite coating was prepared on Ti-6Al-4V at low temperature. The scanning electronic microscope (SEM) graphs showed that the surface of the coating was composed with needle-like crystals, and the X-ray diffractometer (XRD) and Fourier transform infra-red spectrometry (FTIR) results proved that the crystals was carbonate hydroxyapatite (CHA), no other crystal phase was detected. The SEM micrographs of the cross section showed that the coating was porous and bonded closely with the surface of the alloy. The energy diffraction spectra (EDS) result show that a Si-Ti-Al-V-O layer was formed at the interface and enhance the interconnection between the coating and alloy. The bonding strength of the coating was 34.8±6.8MPa, which was much higher than that of the pure HA coating on Ti-6Al-4V prepared by plasma spraying method. The HA-G composite coating on Ti-6Al-4V showed high bonding strength, porous structure, and bone like CHA composition, which has good potential to be used as bone substitutes.